Add UDP socket client/server multiplayer protocol

Implements the multiplayer transport layer from ROADMAP.md: UUID-based
client identity, a reliable-packet channel over UDP, handshake/ack/
ping/disconnect/player-joined/player-left/player-state packet types,
and split online (networked) vs offline (in-process singleplayer)
server modes wired into the engine's update/dispose loop.

ROADMAP.md

@@ -33,8 +33,9 @@ for a memory/CPU optimization survey specifically targeting the PSP build
 9. Build the socket server and client implementation, including
    handlers for the different packet types.
 10. Add a dedicated multiplayer entity type, `clientplayer`, alongside
-    the existing `npc` and `player` types. Limit to 8 (defined
+    the existing `npc` and `player` types. Limit to 16 (defined
-    constant) for now.
+    constant, see SERVER_CLIENT_COUNT_MAX/CLIENT_COUNT_MAX in
+    src/dusk/network/socket/) for now.
 11. Send and receive `clientplayer` position over the network.
 12. Create a UI menu for creating a server and joining a server. For
     now, join IPs are hard-coded (testing against a fixed IP of

src/dusk/engine/engine.c

@@ -18,6 +18,9 @@
 #include "ui/ui.h"
 #include "assert/assert.h"
 #include "network/network.h"
+#include "network/socket/client/client.h"
+#include "network/socket/client/clientroster.h"
+#include "network/socket/server/serveronline.h"
 #include "game/game.h"
 #include "system/system.h"
 #include "console/console.h"
@@ -67,6 +70,8 @@ errorret_t engineInit(const int32_t argc, const char_t **argv) {
 errorret_t engineUpdate(void) {
   // Order here is important.
   errorChain(networkUpdate());
+  errorChain(clientUpdate());
+  errorChain(serverOnlineUpdate());
   timeUpdate();
 
   const systemdialogtype_t dialogType = systemGetActiveDialogType();
@@ -99,6 +104,11 @@ void engineExit(void) {
 errorret_t engineDispose(void) {
   errorChain(gameDispose());
   errorChain(sceneDispose());
+
+  errorChain(serverOnlineStop());
+  client_t *localClient = clientRosterFindLocal();
+  if(localClient) localClientDisconnect(&localClient->local);
+
   errorChain(networkDispose());
   localeManagerDispose();
   errorChain(uiDispose());

src/dusk/network/CMakeLists.txt

@@ -7,7 +7,9 @@ target_sources(${DUSK_LIBRARY_TARGET_NAME}
   PUBLIC
     network.c
     networkinfo.c
+    networkaddr.c
 )
 
 # Subdirs
 add_subdirectory(http)
+add_subdirectory(socket)

src/dusk/network/networkaddr.c

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "networkaddr.h"
+#include "util/memory.h"
+
+bool_t networkAddrEquals(const networkaddr_t *a, const networkaddr_t *b) {
+  if(a->port != b->port) return false;
+  return memoryCompare(
+    a->ip.ip, b->ip.ip, NETWORK_INFO_IPV4_OCTET_COUNT
+  ) == 0;
+}

src/dusk/network/networkaddr.h

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/networkinfo.h"
+
+typedef struct {
+  networkinfoipv4_t ip;
+  uint16_t port;
+} networkaddr_t;
+
+/**
+ * Compares two network addresses for equality.
+ *
+ * @param a The first address.
+ * @param b The second address.
+ * @return true if the IP and port both match, false otherwise.
+ */
+bool_t networkAddrEquals(const networkaddr_t *a, const networkaddr_t *b);

src/dusk/network/socket/CMakeLists.txt

@@ -0,0 +1,16 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+target_sources(${DUSK_LIBRARY_TARGET_NAME}
+  PUBLIC
+    packet.c
+    packetregistry.c
+    packetreliable.c
+    packetinbox.c
+)
+
+# Subdirs
+add_subdirectory(client)
+add_subdirectory(server)

src/dusk/network/socket/client/CMakeLists.txt

@@ -0,0 +1,15 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+target_sources(${DUSK_LIBRARY_TARGET_NAME}
+  PUBLIC
+    client.c
+    clientroster.c
+    localclient.c
+    clientthread.c
+)
+
+# Subdirs
+add_subdirectory(handler)

src/dusk/network/socket/client/client.c

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "client.h"
+#include "clientroster.h"
+
+errorret_t clientUpdate(void) {
+  client_t *local = clientRosterFindLocal();
+  if(!local) errorOk();
+
+  return localClientUpdate(&local->local);
+}

src/dusk/network/socket/client/client.h

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "localclient.h"
+#include "remoteclient.h"
+
+typedef enum {
+  CLIENT_TYPE_NULL,
+  CLIENT_TYPE_LOCAL,
+  CLIENT_TYPE_REMOTE,
+} clienttype_t;
+
+typedef struct {
+  clienttype_t type;
+  union {
+    localclient_t local;
+    remoteclient_t remote;
+  };
+} client_t;
+
+/**
+ * Drains and updates the roster's local client slot, if any is
+ * connected/connecting. A no-op if this process isn't a client of any
+ * server. Called once per frame.
+ *
+ * @return An error if a fatal error occurred while processing.
+ */
+errorret_t clientUpdate(void);

src/dusk/network/socket/client/clientroster.c

@@ -0,0 +1,51 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientroster.h"
+#include "util/memory.h"
+
+client_t CLIENT_ROSTER[CLIENT_COUNT_MAX];
+
+void clientRosterInit(void) {
+  memoryZero(CLIENT_ROSTER, sizeof(CLIENT_ROSTER));
+}
+
+client_t * clientRosterFindLocal(void) {
+  for(uint32_t i = 0; i < CLIENT_COUNT_MAX; i++) {
+    if(CLIENT_ROSTER[i].type == CLIENT_TYPE_LOCAL) return &CLIENT_ROSTER[i];
+  }
+
+  return NULL;
+}
+
+client_t * clientRosterFindById(const uuid_t *id) {
+  for(uint32_t i = 0; i < CLIENT_COUNT_MAX; i++) {
+    client_t *client = &CLIENT_ROSTER[i];
+    if(client->type != CLIENT_TYPE_REMOTE) continue;
+    if(uuidEquals(&client->remote.id, id)) return client;
+  }
+
+  return NULL;
+}
+
+client_t * clientRosterClaim(const clienttype_t type) {
+  for(uint32_t i = 0; i < CLIENT_COUNT_MAX; i++) {
+    client_t *client = &CLIENT_ROSTER[i];
+    if(client->type != CLIENT_TYPE_NULL) continue;
+
+    memoryZero(client, sizeof(client_t));
+    client->type = type;
+    return client;
+  }
+
+  return NULL;
+}
+
+void clientRosterRemove(client_t *client) {
+  memoryZero(client, sizeof(client_t));
+  client->type = CLIENT_TYPE_NULL;
+}

src/dusk/network/socket/client/clientroster.h

@@ -0,0 +1,50 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+#include "network/socket/client/client.h"
+
+#define CLIENT_COUNT_MAX 16
+
+extern client_t CLIENT_ROSTER[CLIENT_COUNT_MAX];
+
+/**
+ * Resets every roster slot back to CLIENT_TYPE_NULL.
+ */
+void clientRosterInit(void);
+
+/**
+ * Finds the one CLIENT_TYPE_LOCAL slot in the roster, if any.
+ *
+ * @return The local client slot, or NULL if not connected/hosting.
+ */
+client_t * clientRosterFindLocal(void);
+
+/**
+ * Finds a CLIENT_TYPE_REMOTE slot by its assigned id.
+ *
+ * @param id The remote client's id to search for.
+ * @return The matching slot, or NULL if not found.
+ */
+client_t * clientRosterFindById(const uuid_t *id);
+
+/**
+ * Claims the first CLIENT_TYPE_NULL slot in the roster and assigns it
+ * the given type. The rest of the slot's data is zeroed.
+ *
+ * @param type The type to assign to the claimed slot.
+ * @return The claimed slot, or NULL if the roster is full.
+ */
+client_t * clientRosterClaim(const clienttype_t type);
+
+/**
+ * Returns a slot to CLIENT_TYPE_NULL, clearing its data.
+ *
+ * @param client The slot to free.
+ */
+void clientRosterRemove(client_t *client);

src/dusk/network/socket/client/clientthread.c

@@ -0,0 +1,43 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientthread.h"
+#include "assert/assert.h"
+
+void clientThreadRun(thread_t *thread) {
+  assertNotMainThread("clientThreadRun must not run on the main thread.");
+  localclient_t *self = (localclient_t *)thread->data;
+
+  uint8_t buffer[PACKET_WIRE_SIZE_MAX];
+
+  while(!threadShouldStop(thread)) {
+    size_t received = 0;
+    errorret_t ret = networkDgramSocketPlatformReceive(
+      &self->socket, buffer, sizeof(buffer), &received
+    );
+
+    if(errorIsNotOk(ret)) {
+      errorCatch(errorPrint(ret));
+      continue;
+    }
+
+    if(received == 0) continue;
+
+    packet_t packet;
+    errorret_t decodeRet = packetWireDecode(buffer, received, &packet);
+    if(errorIsNotOk(decodeRet)) {
+      errorCatch(errorPrint(decodeRet));
+      continue;
+    }
+
+    clientThreadEnqueue(self, &packet);
+  }
+}
+
+void clientThreadEnqueue(localclient_t *self, const packet_t *packet) {
+  packetInboxPush(&self->inbox, packet);
+}

src/dusk/network/socket/client/clientthread.h

@@ -0,0 +1,29 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "thread/thread.h"
+#include "network/socket/packet.h"
+#include "network/socket/client/localclient.h"
+
+/**
+ * Background reader thread body: blocks on the socket's receive with a
+ * short timeout, decoding and enqueueing each valid datagram into
+ * self's inbox. thread->data must be the localclient_t to read for.
+ *
+ * @param thread The thread this is running on.
+ */
+void clientThreadRun(thread_t *thread);
+
+/**
+ * Pushes a decoded packet into self's inbox for the main thread to
+ * drain. Silently drops the packet if the inbox is full.
+ *
+ * @param self The local client whose inbox to push into.
+ * @param packet The packet to enqueue.
+ */
+void clientThreadEnqueue(localclient_t *self, const packet_t *packet);

src/dusk/network/socket/client/handler/CMakeLists.txt

@@ -0,0 +1,17 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+target_sources(${DUSK_LIBRARY_TARGET_NAME}
+  PUBLIC
+    clientpackethandlerlist.c
+    clientpackethandlerhandshakeaccept.c
+    clientpackethandlerhandshakereject.c
+    clientpackethandlerdisconnect.c
+    clientpackethandlerack.c
+    clientpackethandlerping.c
+    clientpackethandlerplayerstate.c
+    clientpackethandlerplayerjoined.c
+    clientpackethandlerplayerleft.c
+)

src/dusk/network/socket/client/handler/clientpackethandlerack.c

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerack.h"
+#include "network/socket/payload/packetack.h"
+
+errorret_t clientPacketHandlerAck(
+  localclient_t *self,
+  const packet_t *packet
+) {
+  packetack_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  packetReliableChannelAck(&self->reliable, payload.sequence);
+
+  errorOk();
+}

src/dusk/network/socket/client/handler/clientpackethandlerack.h

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/client/handler/clientpackethandlerlist.h"
+
+/**
+ * Handles an ACK: marks the matching reliable-pending send as
+ * delivered.
+ *
+ * @param self The local client the packet arrived on.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t clientPacketHandlerAck(
+  localclient_t *self,
+  const packet_t *packet
+);

src/dusk/network/socket/client/handler/clientpackethandlerdisconnect.c

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerdisconnect.h"
+#include "network/socket/payload/packetdisconnect.h"
+
+errorret_t clientPacketHandlerDisconnect(
+  localclient_t *self,
+  const packet_t *packet
+) {
+  packetdisconnect_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  errorret_t ret = errorThrowImpl(
+    &ERROR_STATE, ERROR_NOT_OK, __FILE__, __func__, __LINE__,
+    "Disconnected by server"
+  );
+  if(self->onDisconnected) self->onDisconnected(ret, self->user);
+
+  localClientTeardown(self);
+
+  errorOk();
+}

src/dusk/network/socket/client/handler/clientpackethandlerdisconnect.h

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/client/handler/clientpackethandlerlist.h"
+
+/**
+ * Handles a server-initiated DISCONNECT (kick): fires onDisconnected
+ * and tears down.
+ *
+ * @param self The local client the packet arrived on.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t clientPacketHandlerDisconnect(
+  localclient_t *self,
+  const packet_t *packet
+);

src/dusk/network/socket/client/handler/clientpackethandlerhandshakeaccept.c

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerhandshakeaccept.h"
+#include "network/socket/payload/packethandshakeaccept.h"
+
+errorret_t clientPacketHandlerHandshakeAccept(
+  localclient_t *self,
+  const packet_t *packet
+) {
+  packethandshakeaccept_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  self->id = payload.id;
+  self->state = LOCAL_CLIENT_STATE_CONNECTED;
+  packetReliableChannelAckType(&self->reliable, PACKET_TYPE_HANDSHAKE);
+
+  if(self->onConnected) self->onConnected(self->user);
+
+  errorOk();
+}

src/dusk/network/socket/client/handler/clientpackethandlerhandshakeaccept.h

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/client/handler/clientpackethandlerlist.h"
+
+/**
+ * Handles a HANDSHAKE_ACCEPT: records the assigned id, moves to
+ * CONNECTED, and fires onConnected.
+ *
+ * @param self The local client the packet arrived on.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t clientPacketHandlerHandshakeAccept(
+  localclient_t *self,
+  const packet_t *packet
+);

src/dusk/network/socket/client/handler/clientpackethandlerhandshakereject.c

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerhandshakereject.h"
+#include "network/socket/payload/packethandshakereject.h"
+
+errorret_t clientPacketHandlerHandshakeReject(
+  localclient_t *self,
+  const packet_t *packet
+) {
+  packethandshakereject_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  packetReliableChannelAckType(&self->reliable, PACKET_TYPE_HANDSHAKE);
+
+  if(self->onRejected) self->onRejected(payload.reason, self->user);
+
+  localClientTeardown(self);
+
+  errorOk();
+}

src/dusk/network/socket/client/handler/clientpackethandlerhandshakereject.h

@@ -0,0 +1,21 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/client/handler/clientpackethandlerlist.h"
+
+/**
+ * Handles a HANDSHAKE_REJECT: fires onRejected and tears down.
+ *
+ * @param self The local client the packet arrived on.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t clientPacketHandlerHandshakeReject(
+  localclient_t *self,
+  const packet_t *packet
+);

src/dusk/network/socket/client/handler/clientpackethandlerlist.c

@@ -0,0 +1,28 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerlist.h"
+#include "clientpackethandlerhandshakeaccept.h"
+#include "clientpackethandlerhandshakereject.h"
+#include "clientpackethandlerdisconnect.h"
+#include "clientpackethandlerack.h"
+#include "clientpackethandlerping.h"
+#include "clientpackethandlerplayerstate.h"
+#include "clientpackethandlerplayerjoined.h"
+#include "clientpackethandlerplayerleft.h"
+
+clientpackethandlercallback_t *
+CLIENT_PACKET_HANDLERS[PACKET_TYPE_COUNT] = {
+  [PACKET_TYPE_HANDSHAKE_ACCEPT] = clientPacketHandlerHandshakeAccept,
+  [PACKET_TYPE_HANDSHAKE_REJECT] = clientPacketHandlerHandshakeReject,
+  [PACKET_TYPE_DISCONNECT] = clientPacketHandlerDisconnect,
+  [PACKET_TYPE_ACK] = clientPacketHandlerAck,
+  [PACKET_TYPE_PING] = clientPacketHandlerPing,
+  [PACKET_TYPE_PLAYER_STATE] = clientPacketHandlerPlayerState,
+  [PACKET_TYPE_PLAYER_JOINED] = clientPacketHandlerPlayerJoined,
+  [PACKET_TYPE_PLAYER_LEFT] = clientPacketHandlerPlayerLeft,
+};

src/dusk/network/socket/client/handler/clientpackethandlerlist.h

@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "network/socket/packet.h"
+#include "network/socket/client/localclient.h"
+
+typedef errorret_t (clientpackethandlercallback_t)(
+  localclient_t *self,
+  const packet_t *packet
+);
+
+extern clientpackethandlercallback_t *
+  CLIENT_PACKET_HANDLERS[PACKET_TYPE_COUNT];

src/dusk/network/socket/client/handler/clientpackethandlerping.c

@@ -0,0 +1,18 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerping.h"
+
+errorret_t clientPacketHandlerPing(
+  localclient_t *self,
+  const packet_t *packet
+) {
+  (void)self;
+  (void)packet;
+
+  errorOk();
+}

src/dusk/network/socket/client/handler/clientpackethandlerping.h

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/client/handler/clientpackethandlerlist.h"
+
+/**
+ * Handles a PING: a no-op, since receiving any packet already refreshes
+ * self->lastReceivedAt in the drain loop before dispatch.
+ *
+ * @param self The local client the packet arrived on.
+ * @param packet The received packet.
+ * @return Always ok.
+ */
+errorret_t clientPacketHandlerPing(
+  localclient_t *self,
+  const packet_t *packet
+);

src/dusk/network/socket/client/handler/clientpackethandlerplayerjoined.c

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerplayerjoined.h"
+#include "network/socket/payload/packetplayerjoined.h"
+#include "network/socket/client/clientroster.h"
+#include "util/string.h"
+
+errorret_t clientPacketHandlerPlayerJoined(
+  localclient_t *self,
+  const packet_t *packet
+) {
+  (void)self;
+
+  packetplayerjoined_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  client_t *slot = clientRosterFindById(&payload.id);
+  if(!slot) slot = clientRosterClaim(CLIENT_TYPE_REMOTE);
+  if(!slot) errorThrow("No free roster slots for joining player");
+
+  slot->remote.id = payload.id;
+  stringCopy(
+    slot->remote.username, payload.username, PACKET_HANDSHAKE_USERNAME_MAX - 1
+  );
+
+  errorOk();
+}

src/dusk/network/socket/client/handler/clientpackethandlerplayerjoined.h

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/client/handler/clientpackethandlerlist.h"
+
+/**
+ * Handles a PLAYER_JOINED broadcast: claims (or reuses) a roster slot
+ * for the newly joined remote player.
+ *
+ * @param self The local client the packet arrived on.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode or the roster is
+ *         full.
+ */
+errorret_t clientPacketHandlerPlayerJoined(
+  localclient_t *self,
+  const packet_t *packet
+);

src/dusk/network/socket/client/handler/clientpackethandlerplayerleft.c

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerplayerleft.h"
+#include "network/socket/payload/packetplayerleft.h"
+#include "network/socket/client/clientroster.h"
+
+errorret_t clientPacketHandlerPlayerLeft(
+  localclient_t *self,
+  const packet_t *packet
+) {
+  (void)self;
+
+  packetplayerleft_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  client_t *slot = clientRosterFindById(&payload.id);
+  if(slot) clientRosterRemove(slot);
+
+  errorOk();
+}

src/dusk/network/socket/client/handler/clientpackethandlerplayerleft.h

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/client/handler/clientpackethandlerlist.h"
+
+/**
+ * Handles a PLAYER_LEFT broadcast: removes the matching roster slot, if
+ * any.
+ *
+ * @param self The local client the packet arrived on.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t clientPacketHandlerPlayerLeft(
+  localclient_t *self,
+  const packet_t *packet
+);

src/dusk/network/socket/client/handler/clientpackethandlerplayerstate.c

@@ -0,0 +1,36 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "clientpackethandlerplayerstate.h"
+#include "network/socket/payload/packetplayerstate.h"
+#include "network/socket/client/clientroster.h"
+#include <cglm/vec3.h>
+
+errorret_t clientPacketHandlerPlayerState(
+  localclient_t *self,
+  const packet_t *packet
+) {
+  (void)self;
+
+  packetplayerstate_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  client_t *slot = clientRosterFindById(&payload.id);
+  if(!slot) errorOk();
+
+  if(slot->remote.hasState &&
+     packet->sequence <= slot->remote.lastStateSequence) {
+    errorOk();
+  }
+
+  slot->remote.hasState = true;
+  slot->remote.lastStateSequence = packet->sequence;
+  glm_vec3_copy(payload.position, slot->remote.lastPosition);
+  glm_vec3_copy(payload.rotation, slot->remote.lastRotation);
+
+  errorOk();
+}

src/dusk/network/socket/client/handler/clientpackethandlerplayerstate.h

@@ -0,0 +1,23 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/client/handler/clientpackethandlerlist.h"
+
+/**
+ * Handles a PLAYER_STATE broadcast: applies the reported position and
+ * rotation to the matching roster slot, if any, and if not stale
+ * (superseded by a sequence number already applied).
+ *
+ * @param self The local client the packet arrived on.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t clientPacketHandlerPlayerState(
+  localclient_t *self,
+  const packet_t *packet
+);

src/dusk/network/socket/client/localclient.c

@@ -0,0 +1,263 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "localclient.h"
+#include "clientthread.h"
+#include "handler/clientpackethandlerlist.h"
+#include "network/socket/packetregistry.h"
+#include "network/socket/payload/packetping.h"
+#include "network/socket/payload/packetdisconnect.h"
+#include "network/socket/payload/packetack.h"
+#include "network/socket/server/serveroffline.h"
+#include "util/memory.h"
+#include "util/string.h"
+#include "assert/assert.h"
+#include "time/time.h"
+
+errorret_t localClientResendCallback(
+  const packet_t *packet,
+  const networkaddr_t *destAddr,
+  void *user
+) {
+  localclient_t *self = (localclient_t *)user;
+  (void)destAddr;
+
+  if(self->offline) return serverOfflineReceiveFromClient(packet);
+
+  uint8_t buffer[PACKET_WIRE_SIZE_MAX];
+  size_t length = 0;
+  errorChain(packetWireEncode(packet, buffer, sizeof(buffer), &length));
+
+  size_t sent = 0;
+  return networkDgramSocketPlatformSend(&self->socket, buffer, length, &sent);
+}
+
+errorret_t localClientConnect(
+  localclient_t *self,
+  const char_t *host,
+  const uint16_t port,
+  const char_t *username,
+  void (*onConnected)(void *user),
+  void (*onRejected)(
+    const packethandshakerejectreason_t reason, void *user
+  ),
+  void (*onDisconnected)(errorret_t error, void *user),
+  void *user
+) {
+  assertNotNull(self, "self must not be NULL");
+  assertNotNull(host, "host must not be NULL");
+  assertNotNull(username, "username must not be NULL");
+  assertNotNull(onConnected, "onConnected must not be NULL");
+  assertNotNull(onRejected, "onRejected must not be NULL");
+  assertNotNull(onDisconnected, "onDisconnected must not be NULL");
+
+  memoryZero(self, sizeof(localclient_t));
+
+  stringCopy(self->username, username, PACKET_HANDSHAKE_USERNAME_MAX - 1);
+  self->onConnected = onConnected;
+  self->onRejected = onRejected;
+  self->onDisconnected = onDisconnected;
+  self->user = user;
+
+  packetReliableChannelInit(&self->reliable);
+  packetInboxInit(&self->inbox);
+
+  errorChain(networkDgramSocketPlatformOpen(&self->socket));
+  errorChain(networkDgramSocketPlatformConnect(&self->socket, host, port));
+
+  self->state = LOCAL_CLIENT_STATE_HANDSHAKING;
+  self->lastReceivedAt = TIME.time;
+  self->lastSentAt = TIME.time;
+
+  threadInit(&self->readerThread, clientThreadRun);
+  self->readerThread.data = self;
+  threadStart(&self->readerThread);
+
+  packethandshake_t handshake;
+  handshake.protocolVersion = NETWORK_PROTOCOL_VERSION;
+  stringCopy(
+    handshake.username, self->username, PACKET_HANDSHAKE_USERNAME_MAX - 1
+  );
+
+  errorChain(localClientSend(self, PACKET_TYPE_HANDSHAKE, &handshake, true));
+
+  errorOk();
+}
+
+errorret_t localClientConnectOffline(
+  localclient_t *self,
+  const char_t *username,
+  void (*onConnected)(void *user),
+  void (*onRejected)(
+    const packethandshakerejectreason_t reason, void *user
+  ),
+  void (*onDisconnected)(errorret_t error, void *user),
+  void *user
+) {
+  assertNotNull(self, "self must not be NULL");
+  assertNotNull(username, "username must not be NULL");
+  assertNotNull(onConnected, "onConnected must not be NULL");
+  assertNotNull(onRejected, "onRejected must not be NULL");
+  assertNotNull(onDisconnected, "onDisconnected must not be NULL");
+
+  memoryZero(self, sizeof(localclient_t));
+  self->offline = true;
+
+  stringCopy(self->username, username, PACKET_HANDSHAKE_USERNAME_MAX - 1);
+  self->onConnected = onConnected;
+  self->onRejected = onRejected;
+  self->onDisconnected = onDisconnected;
+  self->user = user;
+
+  packetReliableChannelInit(&self->reliable);
+  packetInboxInit(&self->inbox);
+
+  errorChain(serverOfflineRegisterClient(&self->inbox));
+
+  self->state = LOCAL_CLIENT_STATE_HANDSHAKING;
+  self->lastReceivedAt = TIME.time;
+  self->lastSentAt = TIME.time;
+
+  packethandshake_t handshake;
+  handshake.protocolVersion = NETWORK_PROTOCOL_VERSION;
+  stringCopy(
+    handshake.username, self->username, PACKET_HANDSHAKE_USERNAME_MAX - 1
+  );
+
+  errorChain(localClientSend(self, PACKET_TYPE_HANDSHAKE, &handshake, true));
+
+  errorOk();
+}
+
+errorret_t localClientUpdate(localclient_t *self) {
+  assertNotNull(self, "self must not be NULL");
+  if(self->state == LOCAL_CLIENT_STATE_DISCONNECTED) errorOk();
+
+  packet_t drained[PACKET_INBOX_SIZE];
+  const uint32_t drainedCount =
+    packetInboxDrain(&self->inbox, drained, PACKET_INBOX_SIZE);
+
+  for(uint32_t i = 0; i < drainedCount; i++) {
+    self->lastReceivedAt = TIME.time;
+
+    const packettype_t type = drained[i].type;
+
+    if(PACKET_TYPE_INFO[type].reliable) {
+      packetack_t ack = { .sequence = drained[i].sequence };
+      errorret_t ackRet = localClientSend(self, PACKET_TYPE_ACK, &ack, false);
+      if(errorIsNotOk(ackRet)) errorCatch(errorPrint(ackRet));
+    }
+
+    if(CLIENT_PACKET_HANDLERS[type]) {
+      errorret_t ret = CLIENT_PACKET_HANDLERS[type](self, &drained[i]);
+      if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+    }
+
+    if(self->state == LOCAL_CLIENT_STATE_DISCONNECTED) errorOk();
+  }
+
+  bool_t expired = false;
+  packetReliableChannelTick(
+    &self->reliable, localClientResendCallback, self, &expired
+  );
+
+  if(expired) {
+    errorret_t ret = errorThrowImpl(
+      &ERROR_STATE, ERROR_NOT_OK, __FILE__, __func__, __LINE__,
+      "Connection timed out (reliable retries exhausted)"
+    );
+    if(self->onDisconnected) self->onDisconnected(ret, self->user);
+    localClientTeardown(self);
+    errorOk();
+  }
+
+  if(TIME.time - self->lastReceivedAt > LOCAL_CLIENT_TIMEOUT_SECONDS) {
+    errorret_t ret = errorThrowImpl(
+      &ERROR_STATE, ERROR_NOT_OK, __FILE__, __func__, __LINE__,
+      "Connection timed out (no packets received)"
+    );
+    if(self->onDisconnected) self->onDisconnected(ret, self->user);
+    localClientTeardown(self);
+    errorOk();
+  }
+
+  if(
+    self->state == LOCAL_CLIENT_STATE_CONNECTED &&
+    TIME.time - self->lastSentAt > LOCAL_CLIENT_PING_INTERVAL_SECONDS
+  ) {
+    packetping_t ping = { .unused = 0 };
+    errorChain(localClientSend(self, PACKET_TYPE_PING, &ping, false));
+  }
+
+  errorOk();
+}
+
+errorret_t localClientSend(
+  localclient_t *self,
+  const packettype_t type,
+  const void *payload,
+  const bool_t reliable
+) {
+  assertNotNull(self, "self must not be NULL");
+
+  const uint32_t sequence =
+    packetReliableChannelNextSequence(&self->reliable);
+
+  packet_t packet;
+  errorChain(packetEncode(&packet, type, sequence, payload));
+
+  if(self->offline) {
+    errorChain(serverOfflineReceiveFromClient(&packet));
+  } else {
+    uint8_t buffer[PACKET_WIRE_SIZE_MAX];
+    size_t length = 0;
+    errorChain(packetWireEncode(&packet, buffer, sizeof(buffer), &length));
+
+    size_t sent = 0;
+    errorChain(
+      networkDgramSocketPlatformSend(&self->socket, buffer, length, &sent)
+    );
+  }
+
+  self->lastSentAt = TIME.time;
+
+  if(reliable) {
+    errorChain(packetReliableChannelTrack(&self->reliable, &packet, NULL));
+  }
+
+  errorOk();
+}
+
+void localClientDisconnect(localclient_t *self) {
+  assertNotNull(self, "self must not be NULL");
+  if(self->state != LOCAL_CLIENT_STATE_CONNECTED) return;
+
+  packetdisconnect_t disconnect = { .id = self->id };
+  errorret_t ret = localClientSend(
+    self, PACKET_TYPE_DISCONNECT, &disconnect, false
+  );
+  if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+
+  localClientTeardown(self);
+}
+
+void localClientTeardown(localclient_t *self) {
+  assertNotNull(self, "self must not be NULL");
+  if(self->state == LOCAL_CLIENT_STATE_DISCONNECTED) return;
+
+  if(self->offline) {
+    serverOfflineUnregisterClient(&self->inbox);
+  } else {
+    threadStop(&self->readerThread);
+    networkDgramSocketPlatformClose(&self->socket);
+  }
+
+  packetReliableChannelDispose(&self->reliable);
+  packetInboxDispose(&self->inbox);
+
+  self->state = LOCAL_CLIENT_STATE_DISCONNECTED;
+}

src/dusk/network/socket/client/localclient.h

@@ -0,0 +1,169 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "thread/thread.h"
+#include "util/uuid.h"
+#include "network/networkdgramsocketplatform.h"
+#include "network/socket/packet.h"
+#include "network/socket/packetinbox.h"
+#include "network/socket/packetreliable.h"
+#include "network/socket/payload/packethandshake.h"
+#include "network/socket/payload/packethandshakereject.h"
+
+#define LOCAL_CLIENT_TIMEOUT_SECONDS 10.0f
+#define LOCAL_CLIENT_PING_INTERVAL_SECONDS 2.0f
+
+typedef enum {
+  LOCAL_CLIENT_STATE_DISCONNECTED,
+  LOCAL_CLIENT_STATE_HANDSHAKING,
+  LOCAL_CLIENT_STATE_CONNECTED,
+  LOCAL_CLIENT_STATE_DISCONNECTING,
+} localclientstate_t;
+
+typedef struct {
+  bool_t offline;
+  networkdgramsocketplatform_t socket;
+  localclientstate_t state;
+  uuid_t id;
+  char_t username[PACKET_HANDSHAKE_USERNAME_MAX];
+  packetreliablechannel_t reliable;
+  float_t lastReceivedAt;
+  float_t lastSentAt;
+
+  thread_t readerThread;
+  packetinbox_t inbox;
+
+  void (*onConnected)(void *user);
+  void (*onRejected)(
+    const packethandshakerejectreason_t reason, void *user
+  );
+  void (*onDisconnected)(errorret_t error, void *user);
+  void *user;
+} localclient_t;
+
+/**
+ * packetReliableChannelTick resend callback: re-sends packet to the
+ * server via self's connected socket. destAddr is unused (the client's
+ * socket already has a fixed peer).
+ *
+ * @param packet The packet to resend.
+ * @param destAddr Unused.
+ * @param user The localclient_t to resend on.
+ * @return An error if the send failed.
+ */
+errorret_t localClientResendCallback(
+  const packet_t *packet,
+  const networkaddr_t *destAddr,
+  void *user
+);
+
+/**
+ * Connects to a server: opens the UDP socket, starts the background
+ * reader thread, and sends a handshake. onConnected/onRejected fire
+ * once the server responds; onDisconnected fires later if the
+ * connection is lost or the server disconnects us.
+ *
+ * @param self The local client slot to connect.
+ * @param host The server's hostname or IP address.
+ * @param port The server's port.
+ * @param username This client's username, truncated to
+ *        PACKET_HANDSHAKE_USERNAME_MAX - 1 characters.
+ * @param onConnected Called once the server accepts the handshake.
+ * @param onRejected Called if the server rejects the handshake.
+ * @param onDisconnected Called if the connection is lost or dropped
+ *        after having connected.
+ * @param user Passed through to all three callbacks.
+ * @return An error if the socket could not be opened/connected.
+ */
+errorret_t localClientConnect(
+  localclient_t *self,
+  const char_t *host,
+  const uint16_t port,
+  const char_t *username,
+  void (*onConnected)(void *user),
+  void (*onRejected)(
+    const packethandshakerejectreason_t reason, void *user
+  ),
+  void (*onDisconnected)(errorret_t error, void *user),
+  void *user
+);
+
+/**
+ * Connects to the offline (in-process, non-networked) server: no
+ * socket, no reader thread. Registers self's inbox with SERVER_OFFLINE
+ * and sends a handshake through the same queued, drained-on-update path
+ * as an online connection, so the two behave identically from here on.
+ *
+ * @param self The local client slot to connect.
+ * @param username This client's username, truncated to
+ *        PACKET_HANDSHAKE_USERNAME_MAX - 1 characters.
+ * @param onConnected Called once the offline server accepts.
+ * @param onRejected Called if the offline server rejects (in practice
+ *        this can't currently happen -- kept for API parity).
+ * @param onDisconnected Called if the offline session ends unexpectedly.
+ * @param user Passed through to all three callbacks.
+ * @return An error if the offline server isn't running
+ *         (serverOfflineHost must be called first).
+ */
+errorret_t localClientConnectOffline(
+  localclient_t *self,
+  const char_t *username,
+  void (*onConnected)(void *user),
+  void (*onRejected)(
+    const packethandshakerejectreason_t reason, void *user
+  ),
+  void (*onDisconnected)(errorret_t error, void *user),
+  void *user
+);
+
+/**
+ * Drains received packets, ticks the reliability channel, and checks
+ * for a connection timeout. Called once per frame.
+ *
+ * @param self The local client to update.
+ * @return An error if a fatal error occurred while processing.
+ */
+errorret_t localClientUpdate(localclient_t *self);
+
+/**
+ * Sends a packet to the server.
+ *
+ * @param self The local client sending the packet.
+ * @param type The packet type to send.
+ * @param payload The payload struct matching type's registered size.
+ * @param reliable If true, tracks the packet for ack + retry.
+ * @return An error if the payload doesn't match type's registered size,
+ *         or the send failed.
+ */
+errorret_t localClientSend(
+  localclient_t *self,
+  const packettype_t type,
+  const void *payload,
+  const bool_t reliable
+);
+
+/**
+ * Disconnects from the server, if connected: sends a best-effort
+ * disconnect notice, then immediately tears down. A dropped notice is
+ * not retried -- the server's own receive-timeout will eventually
+ * clean up the slot regardless, so this is a courtesy, not a
+ * requirement for correctness.
+ *
+ * @param self The local client to disconnect.
+ */
+void localClientDisconnect(localclient_t *self);
+
+/**
+ * Stops the reader thread, closes the socket, and disposes of the
+ * reliability channel and inbox mutex. Leaves self in
+ * LOCAL_CLIENT_STATE_DISCONNECTED.
+ *
+ * @param self The local client to tear down.
+ */
+void localClientTeardown(localclient_t *self);

src/dusk/network/socket/client/remoteclient.h

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+#include "network/socket/payload/packethandshake.h"
+#include <cglm/types.h>
+
+typedef struct {
+  uuid_t id;
+  char_t username[PACKET_HANDSHAKE_USERNAME_MAX];
+  vec3 lastPosition;
+  vec3 lastRotation;
+  bool_t hasState;
+  uint32_t lastStateSequence;
+} remoteclient_t;

src/dusk/network/socket/packet.c

@@ -0,0 +1,139 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "packet.h"
+#include "network/socket/packetregistry.h"
+#include "util/memory.h"
+#include "util/endian.h"
+#include "assert/assert.h"
+
+errorret_t packetEncode(
+  packet_t *out,
+  const packettype_t type,
+  const uint32_t sequence,
+  const void *payload
+) {
+  assertNotNull(out, "out must not be NULL");
+  assertTrue(type < PACKET_TYPE_COUNT, "type out of range");
+
+  const size_t size = PACKET_TYPE_INFO[type].size;
+  if(size > PACKET_DATA_SIZE_MAX) {
+    errorThrow("Packet type %d payload size %zu exceeds max %d",
+      type, size, PACKET_DATA_SIZE_MAX);
+  }
+
+  out->type = type;
+  out->sequence = sequence;
+  out->length = (uint32_t)size;
+
+  if(size > 0) memoryCopy(out->data, payload, size);
+
+  errorOk();
+}
+
+errorret_t packetDecode(const packet_t *in, void *outPayload) {
+  assertNotNull(in, "in must not be NULL");
+  assertNotNull(outPayload, "outPayload must not be NULL");
+  assertTrue(in->type < PACKET_TYPE_COUNT, "in->type out of range");
+
+  const size_t expectedSize = PACKET_TYPE_INFO[in->type].size;
+  if(in->length != expectedSize) {
+    errorThrow(
+      "Packet type %d has length %u, expected %zu",
+      in->type, in->length, expectedSize
+    );
+  }
+
+  if(expectedSize > 0) memoryCopy(outPayload, in->data, expectedSize);
+
+  errorOk();
+}
+
+errorret_t packetWireEncode(
+  const packet_t *packet,
+  uint8_t *outBuffer,
+  const size_t bufferSize,
+  size_t *outLength
+) {
+  assertNotNull(packet, "packet must not be NULL");
+  assertNotNull(outBuffer, "outBuffer must not be NULL");
+  assertNotNull(outLength, "outLength must not be NULL");
+
+  const size_t totalLength = PACKET_WIRE_HEADER_SIZE + packet->length;
+  if(totalLength > bufferSize) {
+    errorThrow("Packet wire size %zu exceeds buffer size %zu",
+      totalLength, bufferSize);
+  }
+
+  const uint32_t type = endianLittleToHost32((uint32_t)packet->type);
+  const uint32_t sequence = endianLittleToHost32(packet->sequence);
+  const uint32_t length = endianLittleToHost32(packet->length);
+
+  memoryCopy(outBuffer, &type, sizeof(uint32_t));
+  memoryCopy(outBuffer + sizeof(uint32_t), &sequence, sizeof(uint32_t));
+  memoryCopy(outBuffer + sizeof(uint32_t) * 2, &length, sizeof(uint32_t));
+
+  if(packet->length > 0) {
+    memoryCopy(
+      outBuffer + PACKET_WIRE_HEADER_SIZE, packet->data, packet->length
+    );
+  }
+
+  *outLength = totalLength;
+  errorOk();
+}
+
+errorret_t packetWireDecode(
+  const uint8_t *buffer,
+  const size_t bufferLength,
+  packet_t *outPacket
+) {
+  assertNotNull(buffer, "buffer must not be NULL");
+  assertNotNull(outPacket, "outPacket must not be NULL");
+
+  if(bufferLength < PACKET_WIRE_HEADER_SIZE) {
+    errorThrow("Packet too small for header: %zu bytes", bufferLength);
+  }
+
+  uint32_t type, sequence, length;
+  memoryCopy(&type, buffer, sizeof(uint32_t));
+  memoryCopy(&sequence, buffer + sizeof(uint32_t), sizeof(uint32_t));
+  memoryCopy(&length, buffer + sizeof(uint32_t) * 2, sizeof(uint32_t));
+
+  type = endianLittleToHost32(type);
+  sequence = endianLittleToHost32(sequence);
+  length = endianLittleToHost32(length);
+
+  if(type >= PACKET_TYPE_COUNT) {
+    errorThrow("Packet has unknown type %u", type);
+  }
+
+  if(length > PACKET_DATA_SIZE_MAX) {
+    errorThrow("Packet length %u exceeds max %d", length,
+      PACKET_DATA_SIZE_MAX);
+  }
+
+  if(bufferLength < PACKET_WIRE_HEADER_SIZE + length) {
+    errorThrow("Packet buffer too small: expected %zu, got %zu",
+      PACKET_WIRE_HEADER_SIZE + length, bufferLength);
+  }
+
+  if(length != PACKET_TYPE_INFO[type].size) {
+    errorThrow("Packet type %u length %u does not match expected %zu",
+      type, length, PACKET_TYPE_INFO[type].size);
+  }
+
+  outPacket->type = (packettype_t)type;
+  outPacket->sequence = sequence;
+  outPacket->length = length;
+
+  if(length > 0) {
+    memoryCopy(outPacket->data, buffer + PACKET_WIRE_HEADER_SIZE, length);
+  }
+
+  errorOk();
+}

src/dusk/network/socket/packet.h

@@ -0,0 +1,89 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "dusk.h"
+#include "error/error.h"
+#include "network/socket/packettype.h"
+
+#define PACKET_DATA_SIZE_MAX 512
+
+typedef struct {
+  packettype_t type;
+  uint32_t sequence;
+  uint32_t length;
+  uint8_t data[PACKET_DATA_SIZE_MAX];
+} packet_t;
+
+/**
+ * Encodes a payload struct into a packet envelope, validating its size
+ * against the registered size for type.
+ *
+ * @param out The packet to fill in.
+ * @param type The packet type being encoded.
+ * @param sequence The sequence number to stamp the packet with.
+ * @param payload The payload struct matching type's registered size.
+ * @return An error if payload's size doesn't match the registered size
+ *         for type.
+ */
+errorret_t packetEncode(
+  packet_t *out,
+  const packettype_t type,
+  const uint32_t sequence,
+  const void *payload
+);
+
+/**
+ * Decodes a packet's payload into a typed struct, validating the
+ * packet's length against the registered size for its type.
+ *
+ * @param in The packet to decode.
+ * @param outPayload Destination buffer, must be at least the registered
+ *        size for in->type.
+ * @return An error if in->length doesn't match the registered size for
+ *         in->type.
+ */
+errorret_t packetDecode(const packet_t *in, void *outPayload);
+
+#define PACKET_WIRE_HEADER_SIZE (sizeof(uint32_t) * 3)
+#define PACKET_WIRE_SIZE_MAX (PACKET_WIRE_HEADER_SIZE + PACKET_DATA_SIZE_MAX)
+
+/**
+ * Serializes a packet's header + used portion of its payload into a
+ * wire-format buffer (fixed-width, little-endian header, followed by
+ * exactly packet->length bytes of payload) -- never the full fixed-size
+ * packet_t, which would waste bandwidth on the unused tail of data.
+ *
+ * @param packet The packet to serialize.
+ * @param outBuffer The destination buffer.
+ * @param bufferSize The size of outBuffer.
+ * @param outLength The number of bytes written is written here.
+ * @return An error if the serialized size exceeds bufferSize.
+ */
+errorret_t packetWireEncode(
+  const packet_t *packet,
+  uint8_t *outBuffer,
+  const size_t bufferSize,
+  size_t *outLength
+);
+
+/**
+ * Deserializes a wire-format buffer back into a packet, defensively
+ * validating the type, length, and buffer size before trusting any of
+ * it -- the buffer may come from an unauthenticated peer.
+ *
+ * @param buffer The received bytes.
+ * @param bufferLength The number of bytes in buffer.
+ * @param outPacket The packet to fill in.
+ * @return An error if the buffer is malformed (bad type, length
+ *         mismatch for its type, or too small for its declared length).
+ */
+errorret_t packetWireDecode(
+  const uint8_t *buffer,
+  const size_t bufferLength,
+  packet_t *outPacket
+);

src/dusk/network/socket/packetdata.h

@@ -0,0 +1,29 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "network/socket/payload/packethandshake.h"
+#include "network/socket/payload/packethandshakeaccept.h"
+#include "network/socket/payload/packethandshakereject.h"
+#include "network/socket/payload/packetdisconnect.h"
+#include "network/socket/payload/packetack.h"
+#include "network/socket/payload/packetping.h"
+#include "network/socket/payload/packetplayerstate.h"
+#include "network/socket/payload/packetplayerjoined.h"
+#include "network/socket/payload/packetplayerleft.h"
+
+typedef union {
+  packethandshake_t handshake;
+  packethandshakeaccept_t handshakeAccept;
+  packethandshakereject_t handshakeReject;
+  packetdisconnect_t disconnect;
+  packetack_t ack;
+  packetping_t ping;
+  packetplayerstate_t playerState;
+  packetplayerjoined_t playerJoined;
+  packetplayerleft_t playerLeft;
+} packetdata_t;

src/dusk/network/socket/packetinbox.c

@@ -0,0 +1,53 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "packetinbox.h"
+#include "util/memory.h"
+
+void packetInboxInit(packetinbox_t *inbox) {
+  memoryZero(inbox, sizeof(packetinbox_t));
+  threadMutexInit(&inbox->mutex);
+}
+
+void packetInboxPush(packetinbox_t *inbox, const packet_t *packet) {
+  threadMutexLock(&inbox->mutex);
+
+  for(uint32_t i = 0; i < PACKET_INBOX_SIZE; i++) {
+    if(!inbox->filled[i]) {
+      inbox->packets[i] = *packet;
+      inbox->filled[i] = true;
+      break;
+    }
+  }
+
+  threadMutexUnlock(&inbox->mutex);
+}
+
+uint32_t packetInboxDrain(
+  packetinbox_t *inbox,
+  packet_t *outPackets,
+  const uint32_t maxOut
+) {
+  uint32_t count = 0;
+
+  threadMutexLock(&inbox->mutex);
+
+  for(uint32_t i = 0; i < PACKET_INBOX_SIZE && count < maxOut; i++) {
+    if(inbox->filled[i]) {
+      outPackets[count++] = inbox->packets[i];
+      inbox->filled[i] = false;
+    }
+  }
+
+  threadMutexUnlock(&inbox->mutex);
+
+  return count;
+}
+
+void packetInboxDispose(packetinbox_t *inbox) {
+  threadMutexDispose(&inbox->mutex);
+}

src/dusk/network/socket/packetinbox.h

@@ -0,0 +1,58 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "thread/threadmutex.h"
+#include "network/socket/packet.h"
+
+#define PACKET_INBOX_SIZE 16
+
+typedef struct {
+  threadmutex_t mutex;
+  bool_t filled[PACKET_INBOX_SIZE];
+  packet_t packets[PACKET_INBOX_SIZE];
+} packetinbox_t;
+
+/**
+ * Initializes an inbox's mutex and clears its slots.
+ *
+ * @param inbox The inbox to initialize.
+ */
+void packetInboxInit(packetinbox_t *inbox);
+
+/**
+ * Pushes a packet into the first free slot. Silently drops the packet
+ * if the inbox is full -- the caller (a reader thread, or a direct
+ * in-process delivery) has no useful way to report the failure back to
+ * the sender, and dropping is the same behavior an overwhelmed UDP
+ * receive buffer would produce anyway.
+ *
+ * @param inbox The inbox to push into.
+ * @param packet The packet to enqueue.
+ */
+void packetInboxPush(packetinbox_t *inbox, const packet_t *packet);
+
+/**
+ * Drains every filled slot into outPackets and frees them.
+ *
+ * @param inbox The inbox to drain.
+ * @param outPackets Destination array, must be at least PACKET_INBOX_SIZE.
+ * @param maxOut The capacity of outPackets.
+ * @return The number of packets written to outPackets.
+ */
+uint32_t packetInboxDrain(
+  packetinbox_t *inbox,
+  packet_t *outPackets,
+  const uint32_t maxOut
+);
+
+/**
+ * Disposes of an inbox's mutex.
+ *
+ * @param inbox The inbox to dispose.
+ */
+void packetInboxDispose(packetinbox_t *inbox);

src/dusk/network/socket/packetregistry.c

@@ -0,0 +1,44 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "packetregistry.h"
+#include "network/socket/payload/packethandshake.h"
+#include "network/socket/payload/packethandshakeaccept.h"
+#include "network/socket/payload/packethandshakereject.h"
+#include "network/socket/payload/packetdisconnect.h"
+#include "network/socket/payload/packetack.h"
+#include "network/socket/payload/packetping.h"
+#include "network/socket/payload/packetplayerstate.h"
+#include "network/socket/payload/packetplayerjoined.h"
+#include "network/socket/payload/packetplayerleft.h"
+
+packettypeinfo_t PACKET_TYPE_INFO[PACKET_TYPE_COUNT] = {
+  [PACKET_TYPE_NULL] = { .size = 0, .reliable = false },
+  [PACKET_TYPE_HANDSHAKE] = {
+    .size = sizeof(packethandshake_t), .reliable = true
+  },
+  [PACKET_TYPE_HANDSHAKE_ACCEPT] = {
+    .size = sizeof(packethandshakeaccept_t), .reliable = true
+  },
+  [PACKET_TYPE_HANDSHAKE_REJECT] = {
+    .size = sizeof(packethandshakereject_t), .reliable = true
+  },
+  [PACKET_TYPE_DISCONNECT] = {
+    .size = sizeof(packetdisconnect_t), .reliable = true
+  },
+  [PACKET_TYPE_ACK] = { .size = sizeof(packetack_t), .reliable = false },
+  [PACKET_TYPE_PING] = { .size = sizeof(packetping_t), .reliable = false },
+  [PACKET_TYPE_PLAYER_STATE] = {
+    .size = sizeof(packetplayerstate_t), .reliable = false
+  },
+  [PACKET_TYPE_PLAYER_JOINED] = {
+    .size = sizeof(packetplayerjoined_t), .reliable = true
+  },
+  [PACKET_TYPE_PLAYER_LEFT] = {
+    .size = sizeof(packetplayerleft_t), .reliable = true
+  },
+};

src/dusk/network/socket/packetregistry.h

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "dusk.h"
+#include "network/socket/packettype.h"
+
+typedef struct {
+  size_t size;
+  bool_t reliable;
+} packettypeinfo_t;
+
+extern packettypeinfo_t PACKET_TYPE_INFO[PACKET_TYPE_COUNT];

src/dusk/network/socket/packetreliable.c

@@ -0,0 +1,118 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "packetreliable.h"
+#include "util/memory.h"
+#include "time/time.h"
+
+void packetReliableChannelInit(packetreliablechannel_t *channel) {
+  memoryZero(channel, sizeof(packetreliablechannel_t));
+  threadMutexInit(&channel->mutex);
+}
+
+uint32_t packetReliableChannelNextSequence(packetreliablechannel_t *channel) {
+  threadMutexLock(&channel->mutex);
+  const uint32_t sequence = channel->nextSequence++;
+  threadMutexUnlock(&channel->mutex);
+
+  return sequence;
+}
+
+errorret_t packetReliableChannelTrack(
+  packetreliablechannel_t *channel,
+  const packet_t *packet,
+  const networkaddr_t *destAddr
+) {
+  threadMutexLock(&channel->mutex);
+
+  packetreliablepending_t *slot = NULL;
+  for(uint32_t i = 0; i < PACKET_RELIABLE_PENDING_MAX; i++) {
+    if(!channel->pending[i].inUse) {
+      slot = &channel->pending[i];
+      break;
+    }
+  }
+
+  if(!slot) {
+    threadMutexUnlock(&channel->mutex);
+    errorThrow("No free reliable-pending slots");
+  }
+
+  slot->inUse = true;
+  slot->packet = *packet;
+  if(destAddr) slot->destAddr = *destAddr;
+  slot->retryCount = 0;
+  slot->nextRetryAt = TIME.time + PACKET_RELIABLE_RETRY_INTERVAL_SECONDS;
+
+  threadMutexUnlock(&channel->mutex);
+  errorOk();
+}
+
+void packetReliableChannelAck(
+  packetreliablechannel_t *channel,
+  const uint32_t sequence
+) {
+  threadMutexLock(&channel->mutex);
+
+  for(uint32_t i = 0; i < PACKET_RELIABLE_PENDING_MAX; i++) {
+    packetreliablepending_t *slot = &channel->pending[i];
+    if(slot->inUse && slot->packet.sequence == sequence) {
+      slot->inUse = false;
+      break;
+    }
+  }
+
+  threadMutexUnlock(&channel->mutex);
+}
+
+void packetReliableChannelAckType(
+  packetreliablechannel_t *channel,
+  const packettype_t type
+) {
+  threadMutexLock(&channel->mutex);
+
+  for(uint32_t i = 0; i < PACKET_RELIABLE_PENDING_MAX; i++) {
+    packetreliablepending_t *slot = &channel->pending[i];
+    if(slot->inUse && slot->packet.type == type) slot->inUse = false;
+  }
+
+  threadMutexUnlock(&channel->mutex);
+}
+
+void packetReliableChannelTick(
+  packetreliablechannel_t *channel,
+  packetreliableresendcallback_t *resend,
+  void *user,
+  bool_t *outExpired
+) {
+  *outExpired = false;
+
+  threadMutexLock(&channel->mutex);
+
+  for(uint32_t i = 0; i < PACKET_RELIABLE_PENDING_MAX; i++) {
+    packetreliablepending_t *slot = &channel->pending[i];
+    if(!slot->inUse || slot->nextRetryAt > TIME.time) continue;
+
+    if(slot->retryCount >= PACKET_RELIABLE_RETRY_COUNT_MAX) {
+      slot->inUse = false;
+      *outExpired = true;
+      continue;
+    }
+
+    slot->retryCount++;
+    slot->nextRetryAt = TIME.time + PACKET_RELIABLE_RETRY_INTERVAL_SECONDS;
+
+    errorret_t ret = resend(&slot->packet, &slot->destAddr, user);
+    if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+  }
+
+  threadMutexUnlock(&channel->mutex);
+}
+
+void packetReliableChannelDispose(packetreliablechannel_t *channel) {
+  threadMutexDispose(&channel->mutex);
+}

src/dusk/network/socket/packetreliable.h

@@ -0,0 +1,119 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "thread/threadmutex.h"
+#include "network/networkaddr.h"
+#include "network/socket/packet.h"
+
+#define PACKET_RELIABLE_PENDING_MAX 8
+#define PACKET_RELIABLE_RETRY_INTERVAL_SECONDS 0.25f
+#define PACKET_RELIABLE_RETRY_COUNT_MAX 8
+
+typedef struct {
+  bool_t inUse;
+  packet_t packet;
+  networkaddr_t destAddr;
+  uint32_t retryCount;
+  float_t nextRetryAt;
+} packetreliablepending_t;
+
+typedef struct {
+  packetreliablepending_t pending[PACKET_RELIABLE_PENDING_MAX];
+  threadmutex_t mutex;
+  uint32_t nextSequence;
+} packetreliablechannel_t;
+
+typedef errorret_t (packetreliableresendcallback_t)(
+  const packet_t *packet,
+  const networkaddr_t *destAddr,
+  void *user
+);
+
+/**
+ * Initializes a reliability channel's mutex and pending-slot pool.
+ *
+ * @param channel The channel to initialize.
+ */
+void packetReliableChannelInit(packetreliablechannel_t *channel);
+
+/**
+ * Allocates the next sequence number for this channel, used for both
+ * reliable and unreliable sends so the peer can order/dedupe by it.
+ *
+ * @param channel The channel to draw a sequence number from.
+ * @return The next sequence number.
+ */
+uint32_t packetReliableChannelNextSequence(packetreliablechannel_t *channel);
+
+/**
+ * Tracks a reliable packet as awaiting acknowledgement, to be resent by
+ * packetReliableChannelTick until acked or its retries are exhausted.
+ *
+ * @param channel The channel to track the packet on.
+ * @param packet The already-sequenced packet to track.
+ * @param destAddr The address to resend to (server usage); ignored by
+ *        callers using a connected socket (client usage).
+ * @return An error if the pending pool is full.
+ */
+errorret_t packetReliableChannelTrack(
+  packetreliablechannel_t *channel,
+  const packet_t *packet,
+  const networkaddr_t *destAddr
+);
+
+/**
+ * Marks a tracked packet as acknowledged, removing it from the pending
+ * pool. A no-op if no pending packet matches sequence (already acked,
+ * or a duplicate/unexpected ack).
+ *
+ * @param channel The channel the ack was received on.
+ * @param sequence The sequence number being acknowledged.
+ */
+void packetReliableChannelAck(
+  packetreliablechannel_t *channel,
+  const uint32_t sequence
+);
+
+/**
+ * Marks every tracked packet of a given type as acknowledged. Used for
+ * responses that confirm a request was handled without echoing its
+ * exact sequence number back (e.g. HANDSHAKE_ACCEPT/REJECT implicitly
+ * satisfy the original HANDSHAKE send).
+ *
+ * @param channel The channel the response was received on.
+ * @param type The packet type to clear from the pending pool.
+ */
+void packetReliableChannelAckType(
+  packetreliablechannel_t *channel,
+  const packettype_t type
+);
+
+/**
+ * Resends any pending packets whose retry interval has elapsed.
+ *
+ * @param channel The channel to tick.
+ * @param resend Called for each packet due for resend.
+ * @param user Passed through to resend.
+ * @param outExpired Set to true if any pending packet exceeded
+ *        PACKET_RELIABLE_RETRY_COUNT_MAX -- the caller should treat the
+ *        connection as dead. The expired entry is removed either way.
+ */
+void packetReliableChannelTick(
+  packetreliablechannel_t *channel,
+  packetreliableresendcallback_t *resend,
+  void *user,
+  bool_t *outExpired
+);
+
+/**
+ * Disposes of a reliability channel's mutex.
+ *
+ * @param channel The channel to dispose.
+ */
+void packetReliableChannelDispose(packetreliablechannel_t *channel);

src/dusk/network/socket/packettype.h

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+
+typedef enum {
+  PACKET_TYPE_NULL,
+
+  PACKET_TYPE_HANDSHAKE,
+  PACKET_TYPE_HANDSHAKE_ACCEPT,
+  PACKET_TYPE_HANDSHAKE_REJECT,
+  PACKET_TYPE_DISCONNECT,
+  PACKET_TYPE_ACK,
+  PACKET_TYPE_PING,
+  PACKET_TYPE_PLAYER_STATE,
+  PACKET_TYPE_PLAYER_JOINED,
+  PACKET_TYPE_PLAYER_LEFT,
+
+  PACKET_TYPE_COUNT
+} packettype_t;

src/dusk/network/socket/payload/packetack.h

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "dusk.h"
+
+typedef struct {
+  uint32_t sequence;
+} packetack_t;

src/dusk/network/socket/payload/packetdisconnect.h

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+
+typedef struct {
+  uuid_t id;
+} packetdisconnect_t;

src/dusk/network/socket/payload/packethandshake.h

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "dusk.h"
+
+#define PACKET_HANDSHAKE_USERNAME_MAX 10
+
+/**
+ * The multiplayer wire protocol version. Bump whenever a packet type's
+ * layout or semantics change in a way that breaks compatibility.
+ * Distinct from DUSK_VERSION, which is a build timestamp, not suitable
+ * for a compatibility check.
+ */
+#define NETWORK_PROTOCOL_VERSION 1
+
+typedef struct {
+  uint32_t protocolVersion;
+  char_t username[PACKET_HANDSHAKE_USERNAME_MAX];
+} packethandshake_t;

src/dusk/network/socket/payload/packethandshakeaccept.h

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+
+typedef struct {
+  uuid_t id;
+} packethandshakeaccept_t;

src/dusk/network/socket/payload/packethandshakereject.h

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "dusk.h"
+
+typedef enum {
+  PACKET_HANDSHAKE_REJECT_REASON_VERSION_MISMATCH,
+  PACKET_HANDSHAKE_REJECT_REASON_SERVER_FULL,
+  PACKET_HANDSHAKE_REJECT_REASON_USERNAME_INVALID,
+  PACKET_HANDSHAKE_REJECT_REASON_USERNAME_TAKEN,
+} packethandshakerejectreason_t;
+
+typedef struct {
+  packethandshakerejectreason_t reason;
+} packethandshakereject_t;

src/dusk/network/socket/payload/packetping.h

@@ -0,0 +1,12 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+
+typedef struct {
+  uint8_t unused;
+} packetping_t;

src/dusk/network/socket/payload/packetplayerjoined.h

@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+#include "network/socket/payload/packethandshake.h"
+
+typedef struct {
+  uuid_t id;
+  char_t username[PACKET_HANDSHAKE_USERNAME_MAX];
+} packetplayerjoined_t;

src/dusk/network/socket/payload/packetplayerleft.h

@@ -0,0 +1,13 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+
+typedef struct {
+  uuid_t id;
+} packetplayerleft_t;

src/dusk/network/socket/payload/packetplayerstate.h

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+#include <cglm/types.h>
+
+typedef struct {
+  uuid_t id;
+  vec3 position;
+  vec3 rotation;
+} packetplayerstate_t;

src/dusk/network/socket/server/CMakeLists.txt

@@ -0,0 +1,15 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+target_sources(${DUSK_LIBRARY_TARGET_NAME}
+  PUBLIC
+    serveronline.c
+    serveroffline.c
+    serverclient.c
+    serverthread.c
+)
+
+# Subdirs
+add_subdirectory(handler)

src/dusk/network/socket/server/handler/CMakeLists.txt

@@ -0,0 +1,14 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+target_sources(${DUSK_LIBRARY_TARGET_NAME}
+  PUBLIC
+    serverpackethandlerlist.c
+    serverpackethandlerhandshake.c
+    serverpackethandlerack.c
+    serverpackethandlerping.c
+    serverpackethandlerdisconnect.c
+    serverpackethandlerplayerstate.c
+)

src/dusk/network/socket/server/handler/serverpackethandlerack.c

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serverpackethandlerack.h"
+#include "network/socket/payload/packetack.h"
+
+errorret_t serverPacketHandlerAck(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+) {
+  (void)from;
+
+  packetack_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  packetReliableChannelAck(&client->remote.reliable, payload.sequence);
+
+  errorOk();
+}

src/dusk/network/socket/server/handler/serverpackethandlerack.h

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "serverpackethandlerlist.h"
+
+/**
+ * Handles an ACK: marks the matching reliable-pending send as
+ * delivered.
+ *
+ * @param client The client the packet arrived from.
+ * @param from The sender's address.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t serverPacketHandlerAck(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+);

src/dusk/network/socket/server/handler/serverpackethandlerdisconnect.c

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serverpackethandlerdisconnect.h"
+#include "network/socket/payload/packetdisconnect.h"
+#include "network/socket/server/serveronline.h"
+
+errorret_t serverPacketHandlerDisconnect(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+) {
+  (void)from;
+
+  packetdisconnect_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  serverClientDisconnect(&SERVER_ONLINE.socket, client, false);
+
+  errorOk();
+}

src/dusk/network/socket/server/handler/serverpackethandlerdisconnect.h

@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "serverpackethandlerlist.h"
+
+/**
+ * Handles a client-initiated DISCONNECT: frees the client's slot and
+ * broadcasts PLAYER_LEFT to everyone else. Unlike
+ * serverClientDisconnect (server-initiated kick), this does not send a
+ * disconnect notice back -- the client is the one leaving.
+ *
+ * @param client The client the packet arrived from.
+ * @param from The sender's address.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t serverPacketHandlerDisconnect(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+);

src/dusk/network/socket/server/handler/serverpackethandlerhandshake.c

@@ -0,0 +1,148 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serverpackethandlerhandshake.h"
+#include "network/socket/payload/packethandshake.h"
+#include "network/socket/payload/packethandshakeaccept.h"
+#include "network/socket/payload/packetplayerjoined.h"
+#include "util/uuid.h"
+#include "util/string.h"
+#include "util/memory.h"
+#include "time/time.h"
+#include "console/console.h"
+
+errorret_t serverSendHandshakeReject(
+  networkdgramsocketplatform_t *socket,
+  const networkaddr_t *to,
+  const packethandshakerejectreason_t reason
+) {
+  packethandshakereject_t payload = { .reason = reason };
+
+  packet_t packet;
+  errorChain(packetEncode(&packet, PACKET_TYPE_HANDSHAKE_REJECT, 0, &payload));
+
+  uint8_t buffer[PACKET_WIRE_SIZE_MAX];
+  size_t length = 0;
+  errorChain(packetWireEncode(&packet, buffer, sizeof(buffer), &length));
+
+  size_t sent = 0;
+  return networkDgramSocketPlatformSendTo(socket, buffer, length, to, &sent);
+}
+
+errorret_t serverPacketHandlerHandshake(
+  serveronline_t *server,
+  const networkaddr_t *from,
+  const packet_t *packet
+) {
+  packethandshake_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  threadMutexLock(&server->clientsMutex);
+
+  serverclient_t *existing = serverOnlineFindClientByAddress(server, from);
+  if(existing) {
+    threadMutexUnlock(&server->clientsMutex);
+
+    packethandshakeaccept_t accept = { .id = existing->remote.id };
+    return serverClientSend(
+      &server->socket, existing, PACKET_TYPE_HANDSHAKE_ACCEPT, &accept, true
+    );
+  }
+
+  bool_t reject = false;
+  packethandshakerejectreason_t rejectReason =
+    PACKET_HANDSHAKE_REJECT_REASON_VERSION_MISMATCH;
+
+  if(payload.protocolVersion != NETWORK_PROTOCOL_VERSION) {
+    reject = true;
+    rejectReason = PACKET_HANDSHAKE_REJECT_REASON_VERSION_MISMATCH;
+  } else if(payload.username[0] == '\0') {
+    reject = true;
+    rejectReason = PACKET_HANDSHAKE_REJECT_REASON_USERNAME_INVALID;
+  } else {
+    for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+      serverclient_t *c = &server->clients[i];
+      if(
+        c->type == SERVER_CLIENT_TYPE_REMOTE &&
+        stringEquals(c->remote.username, payload.username)
+      ) {
+        reject = true;
+        rejectReason = PACKET_HANDSHAKE_REJECT_REASON_USERNAME_TAKEN;
+        break;
+      }
+    }
+  }
+
+  serverclient_t *slot = NULL;
+  if(!reject) {
+    for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+      if(server->clients[i].type == SERVER_CLIENT_TYPE_NULL) {
+        slot = &server->clients[i];
+        break;
+      }
+    }
+
+    if(!slot) {
+      reject = true;
+      rejectReason = PACKET_HANDSHAKE_REJECT_REASON_SERVER_FULL;
+    }
+  }
+
+  if(reject) {
+    threadMutexUnlock(&server->clientsMutex);
+    return serverSendHandshakeReject(&server->socket, from, rejectReason);
+  }
+
+  memoryZero(slot, sizeof(serverclient_t));
+  slot->type = SERVER_CLIENT_TYPE_REMOTE;
+  slot->remote.address = *from;
+  uuidGenerate(&slot->remote.id);
+  stringCopy(
+    slot->remote.username, payload.username, PACKET_HANDSHAKE_USERNAME_MAX - 1
+  );
+  packetReliableChannelInit(&slot->remote.reliable);
+  packetInboxInit(&slot->remote.inbox);
+  slot->remote.lastReceivedAt = TIME.time;
+  slot->remote.lastSentAt = TIME.time;
+
+  threadMutexUnlock(&server->clientsMutex);
+
+  consolePrint("Client joined: %s", slot->remote.username);
+
+  packethandshakeaccept_t accept = { .id = slot->remote.id };
+  errorChain(serverClientSend(
+    &server->socket, slot, PACKET_TYPE_HANDSHAKE_ACCEPT, &accept, true
+  ));
+
+  // Catch the new client up on everyone already connected -- otherwise
+  // they'd only ever learn about players who join after them.
+  for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+    serverclient_t *existingClient = &server->clients[i];
+    if(existingClient == slot) continue;
+    if(existingClient->type != SERVER_CLIENT_TYPE_REMOTE) continue;
+
+    packetplayerjoined_t existingJoined = { .id = existingClient->remote.id };
+    stringCopy(
+      existingJoined.username, existingClient->remote.username,
+      PACKET_HANDSHAKE_USERNAME_MAX - 1
+    );
+    errorret_t catchUpRet = serverClientSend(
+      &server->socket, slot, PACKET_TYPE_PLAYER_JOINED, &existingJoined, true
+    );
+    if(errorIsNotOk(catchUpRet)) errorCatch(errorPrint(catchUpRet));
+  }
+
+  packetplayerjoined_t joined = { .id = slot->remote.id };
+  stringCopy(
+    joined.username, slot->remote.username, PACKET_HANDSHAKE_USERNAME_MAX - 1
+  );
+  errorChain(serverOnlineBroadcast(
+    PACKET_TYPE_PLAYER_JOINED, &joined, true, slot
+  ));
+
+  errorOk();
+}

src/dusk/network/socket/server/handler/serverpackethandlerhandshake.h

@@ -0,0 +1,52 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "network/networkaddr.h"
+#include "network/networkdgramsocketplatform.h"
+#include "network/socket/packet.h"
+#include "network/socket/payload/packethandshakereject.h"
+#include "network/socket/server/serveronline.h"
+
+/**
+ * Handles a HANDSHAKE from any address, called directly by the reader
+ * thread (not via SERVER_PACKET_HANDLERS, since -- unlike every other
+ * packet type -- a handshake may arrive from an address with no slot
+ * yet). If from already has a slot, re-sends HANDSHAKE_ACCEPT (the
+ * client is retrying after losing our first reply). Otherwise validates
+ * protocol version, username, and available capacity, then either
+ * claims a slot and broadcasts PLAYER_JOINED, or replies
+ * HANDSHAKE_REJECT.
+ *
+ * @param server The server the handshake arrived on.
+ * @param from The sender's address.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode, or a send failed.
+ */
+errorret_t serverPacketHandlerHandshake(
+  serveronline_t *server,
+  const networkaddr_t *from,
+  const packet_t *packet
+);
+
+/**
+ * Sends a one-off, untracked HANDSHAKE_REJECT to an address with no
+ * slot. Not tracked for ack + retry: the client's own HANDSHAKE is
+ * reliable on its end, so a lost reject is naturally retried by the
+ * client resending the handshake, which re-runs this whole check.
+ *
+ * @param socket The server's bound socket to send from.
+ * @param to The address to reject.
+ * @param reason The reject reason to send.
+ * @return An error if the send failed.
+ */
+errorret_t serverSendHandshakeReject(
+  networkdgramsocketplatform_t *socket,
+  const networkaddr_t *to,
+  const packethandshakerejectreason_t reason
+);

src/dusk/network/socket/server/handler/serverpackethandlerlist.c

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serverpackethandlerlist.h"
+#include "serverpackethandlerack.h"
+#include "serverpackethandlerping.h"
+#include "serverpackethandlerdisconnect.h"
+#include "serverpackethandlerplayerstate.h"
+
+serverpackethandlercallback_t *
+SERVER_PACKET_HANDLERS[PACKET_TYPE_COUNT] = {
+  [PACKET_TYPE_ACK] = serverPacketHandlerAck,
+  [PACKET_TYPE_PING] = serverPacketHandlerPing,
+  [PACKET_TYPE_DISCONNECT] = serverPacketHandlerDisconnect,
+  [PACKET_TYPE_PLAYER_STATE] = serverPacketHandlerPlayerState,
+};

src/dusk/network/socket/server/handler/serverpackethandlerlist.h

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "network/networkaddr.h"
+#include "network/socket/packet.h"
+#include "network/socket/server/serverclient.h"
+
+/**
+ * Handler signature for every packet type the server can receive from
+ * an already-connected client. Unlike serverPacketHandlerHandshake,
+ * client is always non-NULL here -- these are only ever dispatched from
+ * a known client's drained inbox.
+ */
+typedef errorret_t (serverpackethandlercallback_t)(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+);
+
+extern serverpackethandlercallback_t *
+  SERVER_PACKET_HANDLERS[PACKET_TYPE_COUNT];

src/dusk/network/socket/server/handler/serverpackethandlerping.c

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serverpackethandlerping.h"
+
+errorret_t serverPacketHandlerPing(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+) {
+  (void)client;
+  (void)from;
+  (void)packet;
+
+  errorOk();
+}

src/dusk/network/socket/server/handler/serverpackethandlerping.h

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "serverpackethandlerlist.h"
+
+/**
+ * Handles a PING: a no-op, since receiving any packet already refreshes
+ * client->remote.lastReceivedAt in the drain loop before dispatch.
+ *
+ * @param client The client the packet arrived from.
+ * @param from The sender's address.
+ * @param packet The received packet.
+ * @return Always ok.
+ */
+errorret_t serverPacketHandlerPing(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+);

src/dusk/network/socket/server/handler/serverpackethandlerplayerstate.c

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serverpackethandlerplayerstate.h"
+#include "network/socket/payload/packetplayerstate.h"
+#include "network/socket/server/serveronline.h"
+#include <cglm/vec3.h>
+
+errorret_t serverPacketHandlerPlayerState(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+) {
+  (void)from;
+
+  packetplayerstate_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  glm_vec3_copy(payload.position, client->remote.position);
+  glm_vec3_copy(payload.rotation, client->remote.rotation);
+
+  packetplayerstate_t broadcast;
+  broadcast.id = client->remote.id;
+  glm_vec3_copy(client->remote.position, broadcast.position);
+  glm_vec3_copy(client->remote.rotation, broadcast.rotation);
+
+  return serverOnlineBroadcast(
+    PACKET_TYPE_PLAYER_STATE, &broadcast, false, client
+  );
+}

src/dusk/network/socket/server/handler/serverpackethandlerplayerstate.h

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "serverpackethandlerlist.h"
+
+/**
+ * Handles a PLAYER_STATE: records the reported position/rotation on the
+ * sender's slot, then relays it to every other connected client.
+ *
+ * @param client The client the packet arrived from.
+ * @param from The sender's address.
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t serverPacketHandlerPlayerState(
+  serverclient_t *client,
+  const networkaddr_t *from,
+  const packet_t *packet
+);

src/dusk/network/socket/server/serverclient.c

@@ -0,0 +1,102 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serverclient.h"
+#include "network/socket/payload/packetdisconnect.h"
+#include "network/socket/payload/packetplayerleft.h"
+#include "network/socket/server/serveronline.h"
+#include "util/memory.h"
+#include "assert/assert.h"
+#include "time/time.h"
+
+errorret_t serverClientResendCallback(
+  const packet_t *packet,
+  const networkaddr_t *destAddr,
+  void *user
+) {
+  networkdgramsocketplatform_t *socket = (networkdgramsocketplatform_t *)user;
+
+  uint8_t buffer[PACKET_WIRE_SIZE_MAX];
+  size_t length = 0;
+  errorChain(packetWireEncode(packet, buffer, sizeof(buffer), &length));
+
+  size_t sent = 0;
+  return networkDgramSocketPlatformSendTo(
+    socket, buffer, length, destAddr, &sent
+  );
+}
+
+errorret_t serverClientSend(
+  networkdgramsocketplatform_t *socket,
+  serverclient_t *client,
+  const packettype_t type,
+  const void *payload,
+  const bool_t reliable
+) {
+  assertNotNull(socket, "socket must not be NULL");
+  assertNotNull(client, "client must not be NULL");
+  assertTrue(
+    client->type == SERVER_CLIENT_TYPE_REMOTE, "client must be remote"
+  );
+
+  const uint32_t sequence =
+    packetReliableChannelNextSequence(&client->remote.reliable);
+
+  packet_t packet;
+  errorChain(packetEncode(&packet, type, sequence, payload));
+
+  uint8_t buffer[PACKET_WIRE_SIZE_MAX];
+  size_t length = 0;
+  errorChain(packetWireEncode(&packet, buffer, sizeof(buffer), &length));
+
+  size_t sent = 0;
+  errorChain(networkDgramSocketPlatformSendTo(
+    socket, buffer, length, &client->remote.address, &sent
+  ));
+
+  client->remote.lastSentAt = TIME.time;
+
+  if(reliable) {
+    errorChain(packetReliableChannelTrack(
+      &client->remote.reliable, &packet, &client->remote.address
+    ));
+  }
+
+  errorOk();
+}
+
+void serverClientDisconnect(
+  networkdgramsocketplatform_t *socket,
+  serverclient_t *client,
+  const bool_t notifyPeer
+) {
+  assertNotNull(socket, "socket must not be NULL");
+  assertNotNull(client, "client must not be NULL");
+  if(client->type != SERVER_CLIENT_TYPE_REMOTE) return;
+
+  const uuid_t id = client->remote.id;
+
+  if(notifyPeer) {
+    packetdisconnect_t disconnect = { .id = id };
+    errorret_t ret = serverClientSend(
+      socket, client, PACKET_TYPE_DISCONNECT, &disconnect, false
+    );
+    if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+  }
+
+  packetReliableChannelDispose(&client->remote.reliable);
+  packetInboxDispose(&client->remote.inbox);
+
+  memoryZero(client, sizeof(serverclient_t));
+  client->type = SERVER_CLIENT_TYPE_NULL;
+
+  packetplayerleft_t left = { .id = id };
+  errorret_t ret = serverOnlineBroadcast(
+    PACKET_TYPE_PLAYER_LEFT, &left, true, NULL
+  );
+  if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+}

src/dusk/network/socket/server/serverclient.h

@@ -0,0 +1,80 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "network/networkaddr.h"
+#include "network/networkdgramsocketplatform.h"
+#include "network/socket/packet.h"
+#include "serverclientlocal.h"
+#include "serverclientremote.h"
+
+typedef enum {
+  SERVER_CLIENT_TYPE_NULL,
+  SERVER_CLIENT_TYPE_LOCAL,
+  SERVER_CLIENT_TYPE_REMOTE,
+} serverclienttype_t;
+
+typedef struct {
+  serverclienttype_t type;
+  union {
+    serverclientlocal_t local;
+    serverclientremote_t remote;
+  };
+} serverclient_t;
+
+/**
+ * Sends a packet to a connected remote client.
+ *
+ * @param socket The server's bound socket to send from.
+ * @param client The remote client to send to.
+ * @param type The packet type to send.
+ * @param payload The payload struct matching type's registered size.
+ * @param reliable If true, tracks the packet for ack + retry.
+ * @return An error if the payload doesn't match type's registered size,
+ *         or the send failed.
+ */
+errorret_t serverClientSend(
+  networkdgramsocketplatform_t *socket,
+  serverclient_t *client,
+  const packettype_t type,
+  const void *payload,
+  const bool_t reliable
+);
+
+/**
+ * Removes a connected remote client: optionally sends it a best-effort
+ * disconnect notice, broadcasts PLAYER_LEFT to every other connected
+ * client, then frees the slot. Does nothing if client isn't
+ * SERVER_CLIENT_TYPE_REMOTE.
+ *
+ * @param socket The server's bound socket to send from.
+ * @param client The remote client to remove.
+ * @param notifyPeer If true, sends client a disconnect notice first --
+ *        skip this when client already knows (it disconnected itself)
+ *        or is unreachable (timed out).
+ */
+void serverClientDisconnect(
+  networkdgramsocketplatform_t *socket,
+  serverclient_t *client,
+  const bool_t notifyPeer
+);
+
+/**
+ * packetReliableChannelTick resend callback: re-sends packet to
+ * destAddr via the socket pointed to by user.
+ *
+ * @param packet The packet to resend.
+ * @param destAddr The address to resend to.
+ * @param user The networkdgramsocketplatform_t to send from.
+ * @return An error if the send failed.
+ */
+errorret_t serverClientResendCallback(
+  const packet_t *packet,
+  const networkaddr_t *destAddr,
+  void *user
+);

src/dusk/network/socket/server/serverclientlocal.h

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+#include <cglm/types.h>
+
+typedef struct {
+  uuid_t id;
+  vec3 position;
+  vec3 rotation;
+} serverclientlocal_t;

src/dusk/network/socket/server/serverclientremote.h

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "util/uuid.h"
+#include "network/networkaddr.h"
+#include "network/socket/packetinbox.h"
+#include "network/socket/packetreliable.h"
+#include "network/socket/payload/packethandshake.h"
+#include <cglm/types.h>
+
+typedef struct {
+  networkaddr_t address;
+  uuid_t id;
+  char_t username[PACKET_HANDSHAKE_USERNAME_MAX];
+  vec3 position;
+  vec3 rotation;
+  packetreliablechannel_t reliable;
+  float_t lastReceivedAt;
+  float_t lastSentAt;
+
+  packetinbox_t inbox;
+} serverclientremote_t;

src/dusk/network/socket/server/serveroffline.c

@@ -0,0 +1,148 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serveroffline.h"
+#include "network/socket/payload/packethandshake.h"
+#include "network/socket/payload/packethandshakeaccept.h"
+#include "network/socket/payload/packetplayerstate.h"
+#include "network/socket/payload/packetping.h"
+#include "util/memory.h"
+#include "util/uuid.h"
+#include "time/time.h"
+#include <cglm/vec3.h>
+
+serveroffline_t SERVER_OFFLINE;
+
+errorret_t serverOfflineHost(void) {
+  memoryZero(&SERVER_OFFLINE, sizeof(serveroffline_t));
+  packetInboxInit(&SERVER_OFFLINE.inbox);
+  SERVER_OFFLINE.running = true;
+
+  errorOk();
+}
+
+errorret_t serverOfflineRegisterClient(packetinbox_t *clientInbox) {
+  if(!SERVER_OFFLINE.running) errorThrow("Offline server is not running");
+
+  SERVER_OFFLINE.clientInbox = clientInbox;
+
+  errorOk();
+}
+
+void serverOfflineUnregisterClient(packetinbox_t *clientInbox) {
+  if(SERVER_OFFLINE.clientInbox != clientInbox) return;
+
+  SERVER_OFFLINE.clientInbox = NULL;
+  memoryZero(&SERVER_OFFLINE.client, sizeof(serverclient_t));
+}
+
+errorret_t serverOfflineReceiveFromClient(const packet_t *packet) {
+  if(!SERVER_OFFLINE.running) errorThrow("Offline server is not running");
+
+  packetInboxPush(&SERVER_OFFLINE.inbox, packet);
+
+  errorOk();
+}
+
+errorret_t serverOfflineSendToClient(
+  const packettype_t type,
+  const void *payload
+) {
+  if(!SERVER_OFFLINE.clientInbox) errorThrow("No local client connected");
+
+  packet_t packet;
+  errorChain(
+    packetEncode(&packet, type, SERVER_OFFLINE.nextSequence++, payload)
+  );
+
+  packetInboxPush(SERVER_OFFLINE.clientInbox, &packet);
+  SERVER_OFFLINE.lastSentAt = TIME.time;
+
+  errorOk();
+}
+
+errorret_t serverOfflineHandleHandshake(const packet_t *packet) {
+  packethandshake_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  memoryZero(&SERVER_OFFLINE.client, sizeof(serverclient_t));
+  SERVER_OFFLINE.client.type = SERVER_CLIENT_TYPE_LOCAL;
+  uuidGenerate(&SERVER_OFFLINE.client.local.id);
+
+  packethandshakeaccept_t accept = { .id = SERVER_OFFLINE.client.local.id };
+  errorChain(serverOfflineSendToClient(PACKET_TYPE_HANDSHAKE_ACCEPT, &accept));
+
+  errorOk();
+}
+
+errorret_t serverOfflineHandlePlayerState(const packet_t *packet) {
+  packetplayerstate_t payload;
+  errorChain(packetDecode(packet, &payload));
+
+  glm_vec3_copy(payload.position, SERVER_OFFLINE.client.local.position);
+  glm_vec3_copy(payload.rotation, SERVER_OFFLINE.client.local.rotation);
+
+  errorOk();
+}
+
+void serverOfflineHandleDisconnect(void) {
+  SERVER_OFFLINE.clientInbox = NULL;
+  memoryZero(&SERVER_OFFLINE.client, sizeof(serverclient_t));
+}
+
+errorret_t serverOfflineUpdate(void) {
+  if(!SERVER_OFFLINE.running) errorOk();
+
+  packet_t drained[PACKET_INBOX_SIZE];
+  const uint32_t drainedCount =
+    packetInboxDrain(&SERVER_OFFLINE.inbox, drained, PACKET_INBOX_SIZE);
+
+  for(uint32_t i = 0; i < drainedCount; i++) {
+    const packet_t *packet = &drained[i];
+
+    if(packet->type == PACKET_TYPE_HANDSHAKE) {
+      errorret_t ret = serverOfflineHandleHandshake(packet);
+      if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+      continue;
+    }
+
+    if(SERVER_OFFLINE.client.type != SERVER_CLIENT_TYPE_LOCAL) continue;
+
+    if(packet->type == PACKET_TYPE_PLAYER_STATE) {
+      errorret_t ret = serverOfflineHandlePlayerState(packet);
+      if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+    } else if(packet->type == PACKET_TYPE_DISCONNECT) {
+      serverOfflineHandleDisconnect();
+    }
+    // ACK/PING: no-op -- an in-memory push can't be lost, so nothing on
+    // this side is ever waiting on an ack or a liveness check.
+  }
+
+  if(
+    SERVER_OFFLINE.client.type == SERVER_CLIENT_TYPE_LOCAL &&
+    SERVER_OFFLINE.clientInbox != NULL &&
+    TIME.time - SERVER_OFFLINE.lastSentAt >
+      SERVER_OFFLINE_PING_INTERVAL_SECONDS
+  ) {
+    packetping_t ping = { .unused = 0 };
+    errorret_t ret = serverOfflineSendToClient(PACKET_TYPE_PING, &ping);
+    if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+  }
+
+  errorOk();
+}
+
+errorret_t serverOfflineStop(void) {
+  if(!SERVER_OFFLINE.running) errorOk();
+
+  packetInboxDispose(&SERVER_OFFLINE.inbox);
+  SERVER_OFFLINE.clientInbox = NULL;
+  memoryZero(&SERVER_OFFLINE.client, sizeof(serverclient_t));
+  SERVER_OFFLINE.running = false;
+
+  errorOk();
+}

src/dusk/network/socket/server/serveroffline.h

@@ -0,0 +1,129 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "network/socket/packet.h"
+#include "network/socket/packetinbox.h"
+#include "serverclient.h"
+
+#define SERVER_OFFLINE_PING_INTERVAL_SECONDS 2.0f
+
+typedef struct {
+  serverclient_t client;
+
+  // Packets FROM the local client TO this offline server, drained by
+  // serverOfflineUpdate() -- same queued, drained-on-update timing as
+  // the online path, just never actually crossing a socket.
+  packetinbox_t inbox;
+
+  // Where to deliver packets FROM this offline server TO the local
+  // client -- points at that localclient_t's own inbox. NULL if no
+  // client is currently registered.
+  packetinbox_t *clientInbox;
+
+  uint32_t nextSequence;
+  float_t lastSentAt;
+  bool_t running;
+} serveroffline_t;
+
+extern serveroffline_t SERVER_OFFLINE;
+
+/**
+ * Starts the offline (in-process, non-networked) server. Mirrors
+ * serverOnlineHost's role and timing model exactly, minus the socket --
+ * there's nothing to bind, so no port is needed.
+ *
+ * @return Always ok.
+ */
+errorret_t serverOfflineHost(void);
+
+/**
+ * Drains the inbox, processes the handshake/state/disconnect flow for
+ * the single local client, and keeps its no-packets-received timer from
+ * falsely firing (the same idle-ping keepalive serverOnlineUpdate does
+ * for real connections). A no-op if not currently running. Called once
+ * per frame.
+ *
+ * @return An error if a fatal error occurred while processing.
+ */
+errorret_t serverOfflineUpdate(void);
+
+/**
+ * Stops the offline server, clearing any registered client.
+ *
+ * @return Always ok.
+ */
+errorret_t serverOfflineStop(void);
+
+/**
+ * Registers a local client's inbox as the delivery target for this
+ * offline server's responses. Called by localClientConnectOffline;
+ * there is deliberately no address/handle to look clients up by, since
+ * there is only ever one.
+ *
+ * @param clientInbox The connecting local client's own inbox.
+ * @return An error if the offline server isn't running.
+ */
+errorret_t serverOfflineRegisterClient(packetinbox_t *clientInbox);
+
+/**
+ * Unregisters a local client, if it's the currently registered one, and
+ * clears the connected client slot.
+ *
+ * @param clientInbox The disconnecting local client's own inbox.
+ */
+void serverOfflineUnregisterClient(packetinbox_t *clientInbox);
+
+/**
+ * Delivers a packet from the local client to this offline server --
+ * the offline equivalent of a client's socket send. Never fails to
+ * "send" (it's a direct in-memory push), only to queue if not running.
+ *
+ * @param packet The packet to deliver.
+ * @return An error if the offline server isn't running.
+ */
+errorret_t serverOfflineReceiveFromClient(const packet_t *packet);
+
+/**
+ * Sends a packet to the registered local client.
+ *
+ * @param type The packet type to send.
+ * @param payload The payload struct matching type's registered size.
+ * @return An error if no client is registered, or the payload doesn't
+ *         match type's registered size.
+ */
+errorret_t serverOfflineSendToClient(
+  const packettype_t type,
+  const void *payload
+);
+
+/**
+ * Handles a HANDSHAKE from the local client: always accepted (a single
+ * trusted in-process player has no version skew or username to
+ * conflict with), assigns a fresh id, and replies HANDSHAKE_ACCEPT.
+ *
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode, or the reply
+ *         couldn't be queued.
+ */
+errorret_t serverOfflineHandleHandshake(const packet_t *packet);
+
+/**
+ * Handles a PLAYER_STATE from the local client: records the reported
+ * position/rotation on its slot. Nothing to relay it to offline.
+ *
+ * @param packet The received packet.
+ * @return An error if the payload failed to decode.
+ */
+errorret_t serverOfflineHandlePlayerState(const packet_t *packet);
+
+/**
+ * Handles a DISCONNECT from the local client: clears the connected
+ * client slot and its registered inbox.
+ */
+void serverOfflineHandleDisconnect(void);

src/dusk/network/socket/server/serveronline.c

@@ -0,0 +1,160 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serveronline.h"
+#include "serverthread.h"
+#include "handler/serverpackethandlerlist.h"
+#include "network/socket/packetregistry.h"
+#include "network/socket/payload/packetack.h"
+#include "network/socket/payload/packetping.h"
+#include "util/memory.h"
+#include "assert/assert.h"
+#include "time/time.h"
+
+serveronline_t SERVER_ONLINE;
+
+errorret_t serverOnlineHost(const uint16_t port) {
+  memoryZero(&SERVER_ONLINE, sizeof(serveronline_t));
+  threadMutexInit(&SERVER_ONLINE.clientsMutex);
+
+  errorChain(networkDgramSocketPlatformOpen(&SERVER_ONLINE.socket));
+  errorChain(networkDgramSocketPlatformBind(&SERVER_ONLINE.socket, port));
+
+  SERVER_ONLINE.port = port;
+  SERVER_ONLINE.running = true;
+
+  threadInit(&SERVER_ONLINE.readerThread, serverThreadRun);
+  SERVER_ONLINE.readerThread.data = &SERVER_ONLINE;
+  threadStart(&SERVER_ONLINE.readerThread);
+
+  errorOk();
+}
+
+serverclient_t * serverOnlineFindClientByAddress(
+  serveronline_t *server,
+  const networkaddr_t *addr
+) {
+  for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+    serverclient_t *client = &server->clients[i];
+    if(client->type != SERVER_CLIENT_TYPE_REMOTE) continue;
+    if(networkAddrEquals(&client->remote.address, addr)) return client;
+  }
+
+  return NULL;
+}
+
+errorret_t serverOnlineUpdate(void) {
+  if(!SERVER_ONLINE.running) errorOk();
+
+  for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+    serverclient_t *client = &SERVER_ONLINE.clients[i];
+    if(client->type != SERVER_CLIENT_TYPE_REMOTE) continue;
+
+    packet_t drained[PACKET_INBOX_SIZE];
+    const uint32_t drainedCount =
+      packetInboxDrain(&client->remote.inbox, drained, PACKET_INBOX_SIZE);
+
+    for(uint32_t j = 0; j < drainedCount; j++) {
+      if(client->type != SERVER_CLIENT_TYPE_REMOTE) break;
+
+      client->remote.lastReceivedAt = TIME.time;
+
+      const packettype_t type = drained[j].type;
+
+      if(PACKET_TYPE_INFO[type].reliable) {
+        packetack_t ack = { .sequence = drained[j].sequence };
+        errorret_t ackRet = serverClientSend(
+          &SERVER_ONLINE.socket, client, PACKET_TYPE_ACK, &ack, false
+        );
+        if(errorIsNotOk(ackRet)) errorCatch(errorPrint(ackRet));
+      }
+
+      if(SERVER_PACKET_HANDLERS[type]) {
+        errorret_t ret = SERVER_PACKET_HANDLERS[type](
+          client, &client->remote.address, &drained[j]
+        );
+        if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+      }
+    }
+
+    if(client->type != SERVER_CLIENT_TYPE_REMOTE) continue;
+
+    bool_t expired = false;
+    packetReliableChannelTick(
+      &client->remote.reliable, serverClientResendCallback,
+      &SERVER_ONLINE.socket, &expired
+    );
+
+    if(expired) {
+      serverClientDisconnect(&SERVER_ONLINE.socket, client, false);
+      continue;
+    }
+
+    if(
+      TIME.time - client->remote.lastReceivedAt > SERVER_CLIENT_TIMEOUT_SECONDS
+    ) {
+      serverClientDisconnect(&SERVER_ONLINE.socket, client, false);
+      continue;
+    }
+
+    // Without this, a quiet client (no state/chat traffic) would only
+    // ever hear from the server once, at handshake, and would then
+    // falsely time itself out -- the server must keep sending
+    // something too, not just wait to receive.
+    if(
+      TIME.time - client->remote.lastSentAt >
+        SERVER_CLIENT_PING_INTERVAL_SECONDS
+    ) {
+      packetping_t ping = { .unused = 0 };
+      errorret_t pingRet = serverClientSend(
+        &SERVER_ONLINE.socket, client, PACKET_TYPE_PING, &ping, false
+      );
+      if(errorIsNotOk(pingRet)) errorCatch(errorPrint(pingRet));
+    }
+  }
+
+  errorOk();
+}
+
+errorret_t serverOnlineStop(void) {
+  if(!SERVER_ONLINE.running) errorOk();
+
+  for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+    serverclient_t *client = &SERVER_ONLINE.clients[i];
+    if(client->type == SERVER_CLIENT_TYPE_REMOTE) {
+      serverClientDisconnect(&SERVER_ONLINE.socket, client, true);
+    }
+  }
+
+  threadStop(&SERVER_ONLINE.readerThread);
+  networkDgramSocketPlatformClose(&SERVER_ONLINE.socket);
+  threadMutexDispose(&SERVER_ONLINE.clientsMutex);
+
+  SERVER_ONLINE.running = false;
+
+  errorOk();
+}
+
+errorret_t serverOnlineBroadcast(
+  const packettype_t type,
+  const void *payload,
+  const bool_t reliable,
+  const serverclient_t *exclude
+) {
+  for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+    serverclient_t *client = &SERVER_ONLINE.clients[i];
+    if(client->type != SERVER_CLIENT_TYPE_REMOTE) continue;
+    if(client == exclude) continue;
+
+    errorret_t ret = serverClientSend(
+      &SERVER_ONLINE.socket, client, type, payload, reliable
+    );
+    if(errorIsNotOk(ret)) errorCatch(errorPrint(ret));
+  }
+
+  errorOk();
+}

src/dusk/network/socket/server/serveronline.h

@@ -0,0 +1,88 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "thread/thread.h"
+#include "thread/threadmutex.h"
+#include "network/networkaddr.h"
+#include "network/networkdgramsocketplatform.h"
+#include "network/socket/packet.h"
+#include "serverclient.h"
+
+#define SERVER_CLIENT_COUNT_MAX 16
+#define SERVER_CLIENT_TIMEOUT_SECONDS 10.0f
+#define SERVER_CLIENT_PING_INTERVAL_SECONDS 2.0f
+
+typedef struct {
+  networkdgramsocketplatform_t socket;
+  thread_t readerThread;
+
+  serverclient_t clients[SERVER_CLIENT_COUNT_MAX];
+  threadmutex_t clientsMutex;
+
+  uint16_t port;
+  bool_t running;
+} serveronline_t;
+
+extern serveronline_t SERVER_ONLINE;
+
+/**
+ * Starts hosting: binds the UDP socket to port and starts the
+ * background reader thread. Does not block waiting for clients.
+ *
+ * @param port The local port to listen on.
+ * @return An error if the socket could not be opened/bound.
+ */
+errorret_t serverOnlineHost(const uint16_t port);
+
+/**
+ * Drains every connected client's inbox, ticks their reliability
+ * channels, and sweeps for timed-out clients. A no-op if not currently
+ * hosting. Called once per frame.
+ *
+ * @return An error if a fatal error occurred while processing.
+ */
+errorret_t serverOnlineUpdate(void);
+
+/**
+ * Stops hosting: disconnects every connected client, stops the reader
+ * thread, and closes the socket.
+ *
+ * @return An error if a fatal error occurred while stopping.
+ */
+errorret_t serverOnlineStop(void);
+
+/**
+ * Finds a connected remote client by its address.
+ *
+ * @param server The server to search.
+ * @param addr The address to search for.
+ * @return The matching client, or NULL if none is connected from addr.
+ */
+serverclient_t * serverOnlineFindClientByAddress(
+  serveronline_t *server,
+  const networkaddr_t *addr
+);
+
+/**
+ * Sends a packet to every connected remote client, optionally skipping
+ * one.
+ *
+ * @param type The packet type to send.
+ * @param payload The payload struct matching type's registered size.
+ * @param reliable If true, tracks the packet per-client for ack+retry.
+ * @param exclude A client to skip, or NULL to send to everyone.
+ * @return An error if any send failed (already logged; broadcast
+ *         continues to the remaining clients regardless).
+ */
+errorret_t serverOnlineBroadcast(
+  const packettype_t type,
+  const void *payload,
+  const bool_t reliable,
+  const serverclient_t *exclude
+);

src/dusk/network/socket/server/serverthread.c

@@ -0,0 +1,59 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "serverthread.h"
+#include "serveronline.h"
+#include "handler/serverpackethandlerhandshake.h"
+#include "assert/assert.h"
+
+void serverThreadRun(thread_t *thread) {
+  assertNotMainThread("serverThreadRun must not run on the main thread.");
+  serveronline_t *server = (serveronline_t *)thread->data;
+
+  uint8_t buffer[PACKET_WIRE_SIZE_MAX];
+
+  while(!threadShouldStop(thread)) {
+    size_t received = 0;
+    networkaddr_t from;
+    errorret_t ret = networkDgramSocketPlatformReceiveFrom(
+      &server->socket, buffer, sizeof(buffer), &received, &from
+    );
+
+    if(errorIsNotOk(ret)) {
+      errorCatch(errorPrint(ret));
+      continue;
+    }
+
+    if(received == 0) continue;
+
+    packet_t packet;
+    errorret_t decodeRet = packetWireDecode(buffer, received, &packet);
+    if(errorIsNotOk(decodeRet)) {
+      errorCatch(errorPrint(decodeRet));
+      continue;
+    }
+
+    if(packet.type == PACKET_TYPE_HANDSHAKE) {
+      errorret_t handleRet =
+        serverPacketHandlerHandshake(server, &from, &packet);
+      if(errorIsNotOk(handleRet)) errorCatch(errorPrint(handleRet));
+      continue;
+    }
+
+    threadMutexLock(&server->clientsMutex);
+    serverclient_t *client = serverOnlineFindClientByAddress(server, &from);
+    threadMutexUnlock(&server->clientsMutex);
+
+    if(!client) continue;
+
+    serverThreadEnqueue(client, &packet);
+  }
+}
+
+void serverThreadEnqueue(serverclient_t *client, const packet_t *packet) {
+  packetInboxPush(&client->remote.inbox, packet);
+}

src/dusk/network/socket/server/serverthread.h

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "thread/thread.h"
+#include "network/socket/packet.h"
+#include "serverclient.h"
+
+/**
+ * Background reader thread body: blocks on the shared socket's receive
+ * with a short timeout. HANDSHAKE packets are handled immediately
+ * (regardless of whether the sender has a slot yet); every other type
+ * is matched to an existing client by address and enqueued into that
+ * client's inbox, or dropped if the address is unknown.
+ * thread->data must be the serveronline_t to read for.
+ *
+ * @param thread The thread this is running on.
+ */
+void serverThreadRun(thread_t *thread);
+
+/**
+ * Pushes a decoded packet into a client's inbox for the main thread to
+ * drain. Silently drops the packet if the inbox is full.
+ *
+ * @param client The client whose inbox to push into.
+ * @param packet The packet to enqueue.
+ */
+void serverThreadEnqueue(serverclient_t *client, const packet_t *packet);

src/dusk/util/CMakeLists.txt

@@ -15,4 +15,5 @@ target_sources(${DUSK_LIBRARY_TARGET_NAME}
     math.c
     sort.c
     ref.c
+    uuid.c
 )

src/dusk/util/uuid.c

@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "uuid.h"
+#include "util/memory.h"
+#include "util/random.h"
+#include "util/string.h"
+
+const uuid_t UUID_NULL = { .bytes = { 0 } };
+
+void uuidGenerate(uuid_t *out) {
+  for(uint8_t i = 0; i < UUID_BYTE_COUNT; i++) {
+    out->bytes[i] = (uint8_t)randomInt(0, 256);
+  }
+
+  out->bytes[6] = (uint8_t)((out->bytes[6] & 0x0F) | 0x40);
+  out->bytes[8] = (uint8_t)((out->bytes[8] & 0x3F) | 0x80);
+}
+
+bool_t uuidEquals(const uuid_t *a, const uuid_t *b) {
+  return memoryCompare(a->bytes, b->bytes, UUID_BYTE_COUNT) == 0;
+}
+
+void uuidToString(const uuid_t *id, char_t *dest, const size_t destSize) {
+  const uint8_t *b = id->bytes;
+
+  stringFormat(
+    dest, destSize,
+    "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
+    b[0], b[1], b[2], b[3], b[4], b[5], b[6], b[7],
+    b[8], b[9], b[10], b[11], b[12], b[13], b[14], b[15]
+  );
+}

src/dusk/util/uuid.h

@@ -0,0 +1,45 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "dusk.h"
+
+#define UUID_BYTE_COUNT 16
+#define UUID_STRING_LENGTH 36
+
+typedef struct {
+  uint8_t bytes[UUID_BYTE_COUNT];
+} uuid_t;
+
+extern const uuid_t UUID_NULL;
+
+/**
+ * Generates a random (v4-style) UUID.
+ *
+ * @param out The UUID to fill in.
+ */
+void uuidGenerate(uuid_t *out);
+
+/**
+ * Compares two UUIDs for equality.
+ *
+ * @param a The first UUID.
+ * @param b The second UUID.
+ * @return true if every byte matches, false otherwise.
+ */
+bool_t uuidEquals(const uuid_t *a, const uuid_t *b);
+
+/**
+ * Formats a UUID as a lowercase hyphenated string, e.g.
+ * "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx".
+ *
+ * @param id The UUID to format.
+ * @param dest The destination buffer.
+ * @param destSize The size of dest, excl. null terminator. Must be at
+ *        least UUID_STRING_LENGTH.
+ */
+void uuidToString(const uuid_t *id, char_t *dest, const size_t destSize);

src/dusklinux/network/CMakeLists.txt

@@ -7,4 +7,5 @@ target_sources(${DUSK_LIBRARY_TARGET_NAME}
   PUBLIC
     networklinux.c
     networksocketlinux.c
+    networkdgramsocketlinux.c
 )

src/dusklinux/network/networkdgramsocketlinux.c

@@ -0,0 +1,196 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "networkdgramsocketlinux.h"
+#include "util/memory.h"
+#include "util/string.h"
+#include "assert/assert.h"
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <unistd.h>
+
+errorret_t networkDgramSocketLinuxOpen(networkdgramsocketlinux_t *sock) {
+  assertNotNull(sock, "sock must not be NULL");
+
+  const int_t fd = socket(AF_INET, SOCK_DGRAM, 0);
+  if(fd < 0) errorThrow("Failed to create UDP socket: %s", strerror(errno));
+
+  struct timeval timeout;
+  timeout.tv_sec = 0;
+  timeout.tv_usec = NETWORK_DGRAM_SOCKET_LINUX_RECEIVE_TIMEOUT_MS * 1000;
+  setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));
+
+  sock->fd = fd;
+  errorOk();
+}
+
+errorret_t networkDgramSocketLinuxBind(
+  networkdgramsocketlinux_t *sock,
+  const uint16_t port
+) {
+  assertNotNull(sock, "sock must not be NULL");
+
+  struct sockaddr_in addr;
+  memoryZero(&addr, sizeof(addr));
+  addr.sin_family = AF_INET;
+  addr.sin_addr.s_addr = INADDR_ANY;
+  addr.sin_port = htons(port);
+
+  if(bind(sock->fd, (struct sockaddr *)&addr, sizeof(addr)) != 0) {
+    errorThrow("Failed to bind UDP socket to port %u: %s",
+      port, strerror(errno));
+  }
+
+  errorOk();
+}
+
+errorret_t networkDgramSocketLinuxConnect(
+  networkdgramsocketlinux_t *sock,
+  const char_t *host,
+  const uint16_t port
+) {
+  assertNotNull(sock, "sock must not be NULL");
+  assertNotNull(host, "host must not be NULL");
+
+  char_t portStr[8];
+  stringFormat(portStr, sizeof(portStr) - 1, "%u", port);
+
+  struct addrinfo hints;
+  memoryZero(&hints, sizeof(hints));
+  hints.ai_family = AF_INET;
+  hints.ai_socktype = SOCK_DGRAM;
+
+  struct addrinfo *result = NULL;
+  const int_t gaiRet = getaddrinfo(host, portStr, &hints, &result);
+  if(gaiRet != 0) {
+    errorThrow("Failed to resolve host %s: %s", host, gai_strerror(gaiRet));
+  }
+
+  const int_t connectRet = connect(
+    sock->fd, result->ai_addr, result->ai_addrlen
+  );
+  freeaddrinfo(result);
+
+  if(connectRet != 0) {
+    errorThrow("Failed to connect UDP socket to %s:%u: %s",
+      host, port, strerror(errno));
+  }
+
+  errorOk();
+}
+
+errorret_t networkDgramSocketLinuxSend(
+  networkdgramsocketlinux_t *sock,
+  const uint8_t *data,
+  const size_t length,
+  size_t *outSent
+) {
+  assertNotNull(sock, "sock must not be NULL");
+  assertNotNull(data, "data must not be NULL");
+  assertNotNull(outSent, "outSent must not be NULL");
+
+  const ssize_t sent = send(sock->fd, data, length, 0);
+  if(sent < 0) errorThrow("Failed to send datagram: %s", strerror(errno));
+
+  *outSent = (size_t)sent;
+  errorOk();
+}
+
+errorret_t networkDgramSocketLinuxSendTo(
+  networkdgramsocketlinux_t *sock,
+  const uint8_t *data,
+  const size_t length,
+  const networkaddr_t *addr,
+  size_t *outSent
+) {
+  assertNotNull(sock, "sock must not be NULL");
+  assertNotNull(data, "data must not be NULL");
+  assertNotNull(addr, "addr must not be NULL");
+  assertNotNull(outSent, "outSent must not be NULL");
+
+  struct sockaddr_in dest;
+  memoryZero(&dest, sizeof(dest));
+  dest.sin_family = AF_INET;
+  memoryCopy(&dest.sin_addr.s_addr, addr->ip.ip, sizeof(dest.sin_addr.s_addr));
+  dest.sin_port = htons(addr->port);
+
+  const ssize_t sent = sendto(
+    sock->fd, data, length, 0, (struct sockaddr *)&dest, sizeof(dest)
+  );
+  if(sent < 0) errorThrow("Failed to send datagram: %s", strerror(errno));
+
+  *outSent = (size_t)sent;
+  errorOk();
+}
+
+errorret_t networkDgramSocketLinuxReceive(
+  networkdgramsocketlinux_t *sock,
+  uint8_t *buffer,
+  const size_t bufferSize,
+  size_t *outReceived
+) {
+  assertNotNull(sock, "sock must not be NULL");
+  assertNotNull(buffer, "buffer must not be NULL");
+  assertNotNull(outReceived, "outReceived must not be NULL");
+
+  const ssize_t received = recv(sock->fd, buffer, bufferSize, 0);
+  if(received < 0) {
+    if(errno == EAGAIN || errno == EWOULDBLOCK) {
+      *outReceived = 0;
+      errorOk();
+    }
+
+    errorThrow("Failed to receive datagram: %s", strerror(errno));
+  }
+
+  *outReceived = (size_t)received;
+  errorOk();
+}
+
+errorret_t networkDgramSocketLinuxReceiveFrom(
+  networkdgramsocketlinux_t *sock,
+  uint8_t *buffer,
+  const size_t bufferSize,
+  size_t *outReceived,
+  networkaddr_t *outAddr
+) {
+  assertNotNull(sock, "sock must not be NULL");
+  assertNotNull(buffer, "buffer must not be NULL");
+  assertNotNull(outReceived, "outReceived must not be NULL");
+  assertNotNull(outAddr, "outAddr must not be NULL");
+
+  struct sockaddr_in from;
+  socklen_t fromLength = sizeof(from);
+  memoryZero(&from, sizeof(from));
+
+  const ssize_t received = recvfrom(
+    sock->fd, buffer, bufferSize, 0, (struct sockaddr *)&from, &fromLength
+  );
+  if(received < 0) {
+    if(errno == EAGAIN || errno == EWOULDBLOCK) {
+      *outReceived = 0;
+      errorOk();
+    }
+
+    errorThrow("Failed to receive datagram: %s", strerror(errno));
+  }
+
+  memoryCopy(outAddr->ip.ip, &from.sin_addr.s_addr, sizeof(outAddr->ip.ip));
+  outAddr->port = ntohs(from.sin_port);
+
+  *outReceived = (size_t)received;
+  errorOk();
+}
+
+void networkDgramSocketLinuxClose(networkdgramsocketlinux_t *sock) {
+  assertNotNull(sock, "sock must not be NULL");
+  if(sock->fd >= 0) close(sock->fd);
+  sock->fd = -1;
+}

src/dusklinux/network/networkdgramsocketlinux.h

@@ -0,0 +1,135 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "error/error.h"
+#include "network/networkaddr.h"
+
+#define NETWORK_DGRAM_SOCKET_LINUX_RECEIVE_TIMEOUT_MS 100
+
+typedef struct {
+  int_t fd;
+} networkdgramsocketlinux_t;
+
+/**
+ * Creates the underlying UDP socket, unbound and unconnected. Also sets
+ * a short receive timeout so callers can poll a stop condition between
+ * blocking receive calls.
+ *
+ * @param sock The socket structure to initialize.
+ * @return An error if the socket could not be created.
+ */
+errorret_t networkDgramSocketLinuxOpen(networkdgramsocketlinux_t *sock);
+
+/**
+ * Binds the socket to a local port, for accepting datagrams from any
+ * peer (server usage).
+ *
+ * @param sock The socket to bind.
+ * @param port The local port to bind to.
+ * @return An error if the bind failed.
+ */
+errorret_t networkDgramSocketLinuxBind(
+  networkdgramsocketlinux_t *sock,
+  const uint16_t port
+);
+
+/**
+ * Resolves host and sets it as the socket's default peer, enabling
+ * networkDgramSocketLinuxSend/Receive (client usage).
+ *
+ * @param sock The socket to connect.
+ * @param host The hostname or IP address of the peer.
+ * @param port The port of the peer.
+ * @return An error if resolution failed.
+ */
+errorret_t networkDgramSocketLinuxConnect(
+  networkdgramsocketlinux_t *sock,
+  const char_t *host,
+  const uint16_t port
+);
+
+/**
+ * Sends a datagram to the socket's connected peer.
+ *
+ * @param sock The connected socket.
+ * @param data The data to send.
+ * @param length The number of bytes in data.
+ * @param outSent The number of bytes actually sent is written here.
+ * @return An error if the send failed.
+ */
+errorret_t networkDgramSocketLinuxSend(
+  networkdgramsocketlinux_t *sock,
+  const uint8_t *data,
+  const size_t length,
+  size_t *outSent
+);
+
+/**
+ * Sends a datagram to a specific address, regardless of the socket's
+ * connected peer (server usage).
+ *
+ * @param sock The bound socket.
+ * @param data The data to send.
+ * @param length The number of bytes in data.
+ * @param addr The destination address.
+ * @param outSent The number of bytes actually sent is written here.
+ * @return An error if the send failed.
+ */
+errorret_t networkDgramSocketLinuxSendTo(
+  networkdgramsocketlinux_t *sock,
+  const uint8_t *data,
+  const size_t length,
+  const networkaddr_t *addr,
+  size_t *outSent
+);
+
+/**
+ * Receives a datagram from the socket's connected peer. Blocks for up to
+ * NETWORK_DGRAM_SOCKET_LINUX_RECEIVE_TIMEOUT_MS; if nothing arrives in
+ * that window, outReceived is set to 0 without an error.
+ *
+ * @param sock The connected socket.
+ * @param buffer The buffer to receive into.
+ * @param bufferSize The size of buffer.
+ * @param outReceived The number of bytes actually received is written
+ *        here; 0 means nothing arrived within the timeout.
+ * @return An error if the receive failed.
+ */
+errorret_t networkDgramSocketLinuxReceive(
+  networkdgramsocketlinux_t *sock,
+  uint8_t *buffer,
+  const size_t bufferSize,
+  size_t *outReceived
+);
+
+/**
+ * Receives a datagram from any sender, capturing its address. Same
+ * timeout behavior as networkDgramSocketLinuxReceive.
+ *
+ * @param sock The bound socket.
+ * @param buffer The buffer to receive into.
+ * @param bufferSize The size of buffer.
+ * @param outReceived The number of bytes actually received is written
+ *        here; 0 means nothing arrived within the timeout.
+ * @param outAddr The sender's address is written here.
+ * @return An error if the receive failed.
+ */
+errorret_t networkDgramSocketLinuxReceiveFrom(
+  networkdgramsocketlinux_t *sock,
+  uint8_t *buffer,
+  const size_t bufferSize,
+  size_t *outReceived,
+  networkaddr_t *outAddr
+);
+
+/**
+ * Closes the socket.
+ *
+ * @param sock The socket to close.
+ */
+void networkDgramSocketLinuxClose(networkdgramsocketlinux_t *sock);

src/dusklinux/network/networkdgramsocketplatform.h

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#pragma once
+#include "networkdgramsocketlinux.h"
+
+typedef networkdgramsocketlinux_t networkdgramsocketplatform_t;
+
+#define networkDgramSocketPlatformOpen       networkDgramSocketLinuxOpen
+#define networkDgramSocketPlatformBind       networkDgramSocketLinuxBind
+#define networkDgramSocketPlatformConnect    networkDgramSocketLinuxConnect
+#define networkDgramSocketPlatformSend       networkDgramSocketLinuxSend
+#define networkDgramSocketPlatformSendTo     networkDgramSocketLinuxSendTo
+#define networkDgramSocketPlatformReceive    networkDgramSocketLinuxReceive
+#define networkDgramSocketPlatformReceiveFrom networkDgramSocketLinuxReceiveFrom
+#define networkDgramSocketPlatformClose      networkDgramSocketLinuxClose

test/network/CMakeLists.txt

@@ -3,4 +3,9 @@
 # This software is released under the MIT License.
 # https://opensource.org/licenses/MIT
 
+include(dusktest)
+
+dusktest(test_network.c)
+
 add_subdirectory(http)
+add_subdirectory(socket)

test/network/socket/CMakeLists.txt

@@ -0,0 +1,9 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+include(dusktest)
+
+dusktest(test_networksocket.c)
+dusktest(test_serveroffline.c)

test/network/socket/test_networksocket.c

@@ -0,0 +1,258 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "dusktest.h"
+#include "network/socket/client/client.h"
+#include "network/socket/client/clientroster.h"
+#include "network/socket/server/serveronline.h"
+#include "network/socket/payload/packetplayerstate.h"
+#include "util/memory.h"
+#include "util/string.h"
+#include "time/time.h"
+#include <unistd.h>
+
+#define TEST_PORT 58211
+
+typedef struct {
+  bool_t connected;
+  bool_t rejected;
+  bool_t disconnected;
+} clientevents_t;
+
+static void onConnected(void *user) {
+  ((clientevents_t *)user)->connected = true;
+}
+
+static void onRejected(
+  const packethandshakerejectreason_t reason,
+  void *user
+) {
+  (void)reason;
+  ((clientevents_t *)user)->rejected = true;
+}
+
+static void onDisconnected(errorret_t error, void *user) {
+  errorCatch(error);
+  ((clientevents_t *)user)->disconnected = true;
+}
+
+static void pumpServerAndClients(
+  localclient_t *clients[],
+  const uint32_t clientCount,
+  const int32_t ms
+) {
+  for(int32_t i = 0; i < ms; i++) {
+    for(uint32_t c = 0; c < clientCount; c++) {
+      errorCatch(localClientUpdate(clients[c]));
+    }
+    errorCatch(serverOnlineUpdate());
+    usleep(1000);
+  }
+}
+
+static uint32_t countServerRemotes(void) {
+  uint32_t count = 0;
+  for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+    if(SERVER_ONLINE.clients[i].type == SERVER_CLIENT_TYPE_REMOTE) count++;
+  }
+  return count;
+}
+
+static int socket_setup(void **state) {
+  clientRosterInit();
+  return 0;
+}
+
+static int socket_teardown(void **state) {
+  if(SERVER_ONLINE.running) errorCatch(serverOnlineStop());
+  clientRosterInit();
+  return 0;
+}
+
+static void test_host_connects_local_client_to_itself(void **state) {
+  assert_true(errorIsOk(serverOnlineHost(TEST_PORT)));
+
+  client_t *local = clientRosterClaim(CLIENT_TYPE_LOCAL);
+  assert_non_null(local);
+
+  clientevents_t events;
+  memoryZero(&events, sizeof(events));
+
+  const errorret_t ret = localClientConnect(
+    &local->local, "127.0.0.1", TEST_PORT, "host",
+    onConnected, onRejected, onDisconnected, &events
+  );
+  assert_true(errorIsOk(ret));
+
+  localclient_t *clients[] = { &local->local };
+  pumpServerAndClients(clients, 1, 2000);
+
+  assert_true(events.connected);
+  assert_false(events.rejected);
+  assert_int_equal(local->local.state, LOCAL_CLIENT_STATE_CONNECTED);
+
+  assert_int_equal(countServerRemotes(), 1);
+
+  serverclient_t *remote = NULL;
+  for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+    if(SERVER_ONLINE.clients[i].type == SERVER_CLIENT_TYPE_REMOTE) {
+      remote = &SERVER_ONLINE.clients[i];
+    }
+  }
+  assert_non_null(remote);
+  assert_true(uuidEquals(&remote->remote.id, &local->local.id));
+  assert_string_equal(remote->remote.username, "host");
+
+  localClientDisconnect(&local->local);
+  clientRosterRemove(local);
+
+  pumpServerAndClients(NULL, 0, 200);
+  assert_int_equal(countServerRemotes(), 0);
+
+  errorCatch(serverOnlineStop());
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+// Regression test: a quiet connection (no state/chat traffic) must not
+// falsely time itself out. The server has to keep sending the client
+// something (a PING) on its own idle timer -- otherwise the client only
+// ever hears from the server once, at handshake, and its own 10s
+// no-packets-received timeout eventually fires even though the
+// connection is healthy.
+static void test_server_keepalive_prevents_client_timeout(void **state) {
+  assert_true(errorIsOk(serverOnlineHost(TEST_PORT)));
+
+  client_t *local = clientRosterClaim(CLIENT_TYPE_LOCAL);
+  assert_non_null(local);
+
+  clientevents_t events;
+  memoryZero(&events, sizeof(events));
+
+  assert_true(errorIsOk(localClientConnect(
+    &local->local, "127.0.0.1", TEST_PORT, "host",
+    onConnected, onRejected, onDisconnected, &events
+  )));
+
+  localclient_t *clients[] = { &local->local };
+  pumpServerAndClients(clients, 1, 500);
+  assert_true(events.connected);
+
+  // Simulate several ping intervals of elapsed game time -- well past
+  // SERVER_CLIENT_TIMEOUT_SECONDS in total -- jumping the logical clock
+  // directly (no real 10s wait) but still pumping for real in between
+  // each jump so any keepalive packets actually go out over the real
+  // loopback socket and get processed.
+  for(int32_t i = 0; i < 6; i++) {
+    TIME.time += 3.0f;
+    pumpServerAndClients(clients, 1, 100);
+  }
+
+  assert_false(events.disconnected);
+  assert_int_equal(local->local.state, LOCAL_CLIENT_STATE_CONNECTED);
+  assert_int_equal(countServerRemotes(), 1);
+
+  localClientDisconnect(&local->local);
+  clientRosterRemove(local);
+
+  pumpServerAndClients(NULL, 0, 200);
+  errorCatch(serverOnlineStop());
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+static void test_second_client_joins_and_state_relays(void **state) {
+  assert_true(errorIsOk(serverOnlineHost(TEST_PORT)));
+
+  client_t *alice = clientRosterClaim(CLIENT_TYPE_LOCAL);
+  client_t *bob = clientRosterClaim(CLIENT_TYPE_LOCAL);
+  assert_non_null(alice);
+  assert_non_null(bob);
+
+  clientevents_t aliceEvents, bobEvents;
+  memoryZero(&aliceEvents, sizeof(aliceEvents));
+  memoryZero(&bobEvents, sizeof(bobEvents));
+
+  assert_true(errorIsOk(localClientConnect(
+    &alice->local, "127.0.0.1", TEST_PORT, "alice",
+    onConnected, onRejected, onDisconnected, &aliceEvents
+  )));
+
+  localclient_t *clients[] = { &alice->local, &bob->local };
+  pumpServerAndClients(clients, 1, 500);
+  assert_true(aliceEvents.connected);
+
+  assert_true(errorIsOk(localClientConnect(
+    &bob->local, "127.0.0.1", TEST_PORT, "bob",
+    onConnected, onRejected, onDisconnected, &bobEvents
+  )));
+
+  pumpServerAndClients(clients, 2, 500);
+  assert_true(bobEvents.connected);
+  assert_int_equal(countServerRemotes(), 2);
+
+  // Alice reports a position; the server should track it on her slot and
+  // relay it to bob (who doesn't know alice's id yet, so his handler
+  // claims a fresh roster slot for her -- exactly what a real second
+  // process would do).
+  packetplayerstate_t playerState;
+  memoryZero(&playerState, sizeof(playerState));
+  playerState.position[0] = 1.0f;
+  playerState.position[1] = 2.0f;
+  playerState.position[2] = 3.0f;
+
+  assert_true(errorIsOk(localClientSend(
+    &alice->local, PACKET_TYPE_PLAYER_STATE, &playerState, false
+  )));
+
+  pumpServerAndClients(clients, 2, 500);
+
+  serverclient_t *aliceRemote = NULL;
+  for(uint32_t i = 0; i < SERVER_CLIENT_COUNT_MAX; i++) {
+    if(
+      SERVER_ONLINE.clients[i].type == SERVER_CLIENT_TYPE_REMOTE &&
+      stringEquals(SERVER_ONLINE.clients[i].remote.username, "alice")
+    ) {
+      aliceRemote = &SERVER_ONLINE.clients[i];
+    }
+  }
+  assert_non_null(aliceRemote);
+  assert_true(aliceRemote->remote.position[0] == 1.0f);
+  assert_true(aliceRemote->remote.position[1] == 2.0f);
+  assert_true(aliceRemote->remote.position[2] == 3.0f);
+
+  client_t *bobsViewOfAlice = clientRosterFindById(&alice->local.id);
+  assert_non_null(bobsViewOfAlice);
+  assert_true(bobsViewOfAlice->remote.hasState);
+  assert_true(bobsViewOfAlice->remote.lastPosition[0] == 1.0f);
+
+  localClientDisconnect(&alice->local);
+  localClientDisconnect(&bob->local);
+  clientRosterRemove(alice);
+  clientRosterRemove(bob);
+
+  pumpServerAndClients(NULL, 0, 200);
+  errorCatch(serverOnlineStop());
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+int main(void) {
+  const struct CMUnitTest tests[] = {
+    cmocka_unit_test_setup_teardown(
+      test_host_connects_local_client_to_itself, socket_setup, socket_teardown
+    ),
+    cmocka_unit_test_setup_teardown(
+      test_second_client_joins_and_state_relays, socket_setup, socket_teardown
+    ),
+    cmocka_unit_test_setup_teardown(
+      test_server_keepalive_prevents_client_timeout,
+      socket_setup, socket_teardown
+    ),
+  };
+  return cmocka_run_group_tests(tests, NULL, NULL);
+}

test/network/socket/test_serveroffline.c

@@ -0,0 +1,121 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "dusktest.h"
+#include "network/socket/client/localclient.h"
+#include "network/socket/server/serveroffline.h"
+#include "network/socket/payload/packetplayerstate.h"
+#include "util/memory.h"
+#include "time/time.h"
+
+typedef struct {
+  bool_t connected;
+  bool_t rejected;
+  bool_t disconnected;
+} clientevents_t;
+
+static void onConnected(void *user) {
+  ((clientevents_t *)user)->connected = true;
+}
+
+static void onRejected(
+  const packethandshakerejectreason_t reason,
+  void *user
+) {
+  (void)reason;
+  ((clientevents_t *)user)->rejected = true;
+}
+
+static void onDisconnected(errorret_t error, void *user) {
+  errorCatch(error);
+  ((clientevents_t *)user)->disconnected = true;
+}
+
+static void pumpOffline(localclient_t *client, const int32_t iterations) {
+  for(int32_t i = 0; i < iterations; i++) {
+    errorCatch(serverOfflineUpdate());
+    errorCatch(localClientUpdate(client));
+  }
+}
+
+static int offline_setup(void **state) {
+  return 0;
+}
+
+static int offline_teardown(void **state) {
+  if(SERVER_OFFLINE.running) errorCatch(serverOfflineStop());
+  return 0;
+}
+
+static void test_offline_client_connects_without_networking(void **state) {
+  assert_true(errorIsOk(serverOfflineHost()));
+
+  localclient_t client;
+  clientevents_t events;
+  memoryZero(&events, sizeof(events));
+
+  assert_true(errorIsOk(localClientConnectOffline(
+    &client, "player", onConnected, onRejected, onDisconnected, &events
+  )));
+
+  // Handshake -> accept takes exactly two drain cycles, same as online:
+  // one for the server to see the HANDSHAKE, one for the client to see
+  // the HANDSHAKE_ACCEPT.
+  pumpOffline(&client, 4);
+
+  assert_true(events.connected);
+  assert_false(events.rejected);
+  assert_int_equal(client.state, LOCAL_CLIENT_STATE_CONNECTED);
+
+  assert_int_equal(SERVER_OFFLINE.client.type, SERVER_CLIENT_TYPE_LOCAL);
+  assert_true(uuidEquals(&SERVER_OFFLINE.client.local.id, &client.id));
+
+  packetplayerstate_t playerState;
+  memoryZero(&playerState, sizeof(playerState));
+  playerState.position[0] = 4.0f;
+  playerState.position[1] = 5.0f;
+  playerState.position[2] = 6.0f;
+
+  assert_true(errorIsOk(localClientSend(
+    &client, PACKET_TYPE_PLAYER_STATE, &playerState, false
+  )));
+  pumpOffline(&client, 2);
+
+  assert_true(SERVER_OFFLINE.client.local.position[0] == 4.0f);
+  assert_true(SERVER_OFFLINE.client.local.position[1] == 5.0f);
+  assert_true(SERVER_OFFLINE.client.local.position[2] == 6.0f);
+
+  // Simulate well past LOCAL_CLIENT_TIMEOUT_SECONDS of elapsed game time
+  // -- the offline server's own idle-ping keepalive must prevent the
+  // client from falsely timing itself out, same as the online fix.
+  for(int32_t i = 0; i < 6; i++) {
+    TIME.time += 3.0f;
+    pumpOffline(&client, 2);
+  }
+
+  assert_false(events.disconnected);
+  assert_int_equal(client.state, LOCAL_CLIENT_STATE_CONNECTED);
+
+  localClientDisconnect(&client);
+  pumpOffline(&client, 2);
+
+  assert_int_equal(SERVER_OFFLINE.client.type, SERVER_CLIENT_TYPE_NULL);
+
+  errorCatch(serverOfflineStop());
+
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+int main(void) {
+  const struct CMUnitTest tests[] = {
+    cmocka_unit_test_setup_teardown(
+      test_offline_client_connects_without_networking,
+      offline_setup, offline_teardown
+    ),
+  };
+  return cmocka_run_group_tests(tests, NULL, NULL);
+}

test/network/test_network.c

@@ -0,0 +1,62 @@
+/**
+ * Copyright (c) 2026 Dominic Masters
+ *
+ * This software is released under the MIT License.
+ * https://opensource.org/licenses/MIT
+ */
+
+#include "dusktest.h"
+#include "network/network.h"
+#include "network/networkinfo.h"
+#include "util/memory.h"
+
+typedef struct {
+  bool_t connected;
+  bool_t failed;
+} networkevents_t;
+
+static void onConnected(void *user) {
+  ((networkevents_t *)user)->connected = true;
+}
+
+static void onFailed(errorret_t error, void *user) {
+  errorCatch(error);
+  ((networkevents_t *)user)->failed = true;
+}
+
+static void onDisconnect(errorret_t error, void *user) {
+  errorCatch(error);
+}
+
+// Regression test: networkIsConnected() reports physical connectivity and
+// is NOT the same thing as NETWORK.state -- networkGetInfo() asserts on
+// the latter. Code must gate networkGetInfo() on NETWORK.state, reached
+// only via networkRequestConnection(), not on networkIsConnected() alone.
+static void test_request_connection_enables_get_info(void **state) {
+  assert_true(errorIsOk(networkInit()));
+
+  networkevents_t events;
+  memoryZero(&events, sizeof(events));
+
+  // Resolves synchronously on Linux (no networkPlatformRequestConnection).
+  networkRequestConnection(onConnected, onFailed, onDisconnect, &events);
+  assert_true(events.connected || events.failed);
+
+  if(events.connected) {
+    assert_int_equal(NETWORK.state, NETWORK_STATE_CONNECTED);
+    const networkinfo_t info = networkGetInfo(); // must not assert/crash
+    (void)info;
+  } else {
+    assert_int_equal(NETWORK.state, NETWORK_STATE_DISCONNECTED);
+  }
+
+  assert_true(errorIsOk(networkDispose()));
+  assert_int_equal(memoryGetAllocatedCount(), 0);
+}
+
+int main(void) {
+  const struct CMUnitTest tests[] = {
+    cmocka_unit_test(test_request_connection_enables_get_info),
+  };
+  return cmocka_run_group_tests(tests, NULL, NULL);
+}