feat: implement WebSocket synchronization and HTTP recovery

include/sync_service.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include "application.h"
+
+enum {
+  kWebSocketFrameCapacity = 192,
+  kWebSocketHelloTimeoutMs = 5000,
+};
+
+typedef struct {
+  int client_id;
+  uint8_t session_index;
+  bool active;
+  bool authenticated;
+  uint64_t opened_ms;
+} sync_connection_t;
+
+typedef struct { application_t *application; sync_connection_t connections[kSessionCapacity]; } sync_service_t;
+typedef bool (*sync_send_fn)(void *context, int client_id, const char *payload, size_t length);
+
+void sync_service_init(sync_service_t *service, application_t *application);
+bool sync_service_open(sync_service_t *service, int client_id, uint64_t now_ms);
+void sync_service_close(sync_service_t *service, int client_id);
+bool sync_service_receive(sync_service_t *service, int client_id, const char *frame, size_t frame_length,
+                          uint64_t now_ms, char output[kStateMessageCapacity], size_t *output_length,
+                          bool *state_changed, bool *close_client);
+void sync_service_expire(sync_service_t *service, uint64_t now_ms, int closed_clients[kSessionCapacity],
+                         size_t *closed_count);
+void sync_service_broadcast(sync_service_t *service, sync_send_fn send, void *context);