fix: data races, missing persistence, and input safety bugs

- Make client width/height _Atomic to fix data race between window-change
  callback thread and session thread
- Persist join/leave system messages via message_save()
- Fix ftell() error handling: check <= 0 instead of == 0
- Make room_add_message static to enforce lock-must-be-held contract
- Use local copy in execute_command to avoid mutating command_input
- Increase help_copy buffer from 4096 to 8192 for CJK text safety
- Add :q/:quit/:exit command for Vim-style disconnect
- Fix unit test Makefile to link common.c

include/chat_room.h

@@ -36,9 +36,6 @@ void room_remove_client(chat_room_t *room, struct client *client);
 /* Broadcast message to all clients */
 void room_broadcast(chat_room_t *room, const message_t *msg);
 
-/* Add message to room history */
-void room_add_message(chat_room_t *room, const message_t *msg);
-
 /* Get message by index (thread-safe value copy) */
 bool room_get_message(chat_room_t *room, int index, message_t *out);
 

include/ssh_server.h

@@ -13,8 +13,8 @@ typedef struct client {
     ssh_channel channel;             /* SSH channel */
     char username[MAX_USERNAME_LEN];
     char client_ip[INET6_ADDRSTRLEN];
-    int width;
-    int height;
+    _Atomic int width;
+    _Atomic int height;
     client_mode_t mode;
     help_lang_t help_lang;
     int scroll_pos;

src/chat_room.c

@@ -87,23 +87,9 @@ void room_remove_client(chat_room_t *room, struct client *client) {
     pthread_rwlock_unlock(&room->lock);
 }
 
-/* Broadcast message to all clients */
-void room_broadcast(chat_room_t *room, const message_t *msg) {
-    pthread_rwlock_wrlock(&room->lock);
-
-    /* Add to history */
-    room_add_message(room, msg);
-    room->update_seq++;
-
-    pthread_rwlock_unlock(&room->lock);
-}
-
-/* Add message to room history */
-void room_add_message(chat_room_t *room, const message_t *msg) {
-    /* Caller should hold write lock */
-
+/* Add message to room history (caller must hold write lock) */
+static void room_add_message(chat_room_t *room, const message_t *msg) {
     if (room->message_count >= MAX_MESSAGES) {
-        /* Shift messages to make room */
         memmove(&room->messages[0], &room->messages[1],
                 (MAX_MESSAGES - 1) * sizeof(message_t));
         room->message_count = MAX_MESSAGES - 1;
@@ -112,6 +98,16 @@ void room_add_message(chat_room_t *room, const message_t *msg) {
     room->messages[room->message_count++] = *msg;
 }
 
+/* Broadcast message to all clients */
+void room_broadcast(chat_room_t *room, const message_t *msg) {
+    pthread_rwlock_wrlock(&room->lock);
+
+    room_add_message(room, msg);
+    room->update_seq++;
+
+    pthread_rwlock_unlock(&room->lock);
+}
+
 /* Get message by index (thread-safe value copy) */
 bool room_get_message(chat_room_t *room, int index, message_t *out) {
     if (!room || !out) return false;

src/message.c

@@ -61,7 +61,7 @@ int message_load(message_t **messages, int max_messages) {
     }
 
     long file_size = ftell(fp);
-    if (file_size == 0) {
+    if (file_size <= 0) {
         fclose(fp);
         *messages = msg_array;
         return 0;

src/ssh_server.c

@@ -1069,7 +1069,10 @@ static int execute_exec_command(client_t *client) {
 
 /* Execute a command */
 static void execute_command(client_t *client) {
-    char *cmd = client->command_input;
+    char cmd_buf[256];
+    strncpy(cmd_buf, client->command_input, sizeof(cmd_buf) - 1);
+    cmd_buf[sizeof(cmd_buf) - 1] = '\0';
+    char *cmd = cmd_buf;
     char output[2048] = {0};
     size_t pos = 0;
 
@@ -1118,8 +1121,14 @@ static void execute_command(client_t *client) {
                        "list, users, who - Show online users\n"
                        "help, commands   - Show this help\n"
                        "clear, cls       - Clear command output\n"
+                       "q, quit, exit    - Disconnect from chat\n"
                        "========================================\n");
 
+    } else if (strcmp(cmd, "q") == 0 || strcmp(cmd, "quit") == 0 ||
+               strcmp(cmd, "exit") == 0) {
+        client->connected = false;
+        return;
+
     } else if (strcmp(cmd, "clear") == 0 || strcmp(cmd, "cls") == 0) {
         buffer_appendf(output, sizeof(output), &pos, "Command output cleared\n");
 
@@ -1367,6 +1376,7 @@ void* client_handle_session(void *arg) {
     join_msg.username[MAX_USERNAME_LEN - 1] = '\0';
     snprintf(join_msg.content, MAX_MESSAGE_LEN, "%s 加入了聊天室", client->username);
     room_broadcast(g_room, &join_msg);
+    message_save(&join_msg);
 
     /* Render initial screen */
     tui_render_screen(client);
@@ -1496,6 +1506,7 @@ cleanup:
         client->connected = false;
         room_remove_client(g_room, client);
         room_broadcast(g_room, &leave_msg);
+        message_save(&leave_msg);
     }
 
     release_ip_connection(client->client_ip);
@@ -1768,9 +1779,11 @@ static int client_channel_window_change(ssh_session session, ssh_channel channel
         return SSH_ERROR;
     }
 
-    client->width = width;
-    client->height = height;
-    sanitize_terminal_size(&client->width, &client->height);
+    int w = width;
+    int h = height;
+    sanitize_terminal_size(&w, &h);
+    client->width = w;
+    client->height = h;
     client->redraw_pending = true;
     return SSH_OK;
 }
@@ -1942,9 +1955,11 @@ static void *bootstrap_client_session(void *arg) {
 
     client->session = session;
     client->channel = channel;
-    client->width = ctx->pty_width;
-    client->height = ctx->pty_height;
-    sanitize_terminal_size(&client->width, &client->height);
+    int init_w = ctx->pty_width;
+    int init_h = ctx->pty_height;
+    sanitize_terminal_size(&init_w, &init_h);
+    client->width = init_w;
+    client->height = init_h;
     client->ref_count = 1;
     pthread_mutex_init(&client->ref_lock, NULL);
     pthread_mutex_init(&client->io_lock, NULL);

src/tui.c

@@ -386,7 +386,7 @@ void tui_render_help(client_t *client) {
 
     /* Help content */
     const char *help_text = tui_get_help_text(client->help_lang);
-    char help_copy[4096];
+    char help_copy[8192];
     strncpy(help_copy, help_text, sizeof(help_copy) - 1);
     help_copy[sizeof(help_copy) - 1] = '\0';
 

tests/unit/Makefile

@@ -6,6 +6,7 @@ LDFLAGS = -pthread
 # Source files
 UTF8_SRC = ../../src/utf8.c
 MESSAGE_SRC = ../../src/message.c
+COMMON_SRC = ../../src/common.c
 
 TESTS = test_utf8 test_message
 
@@ -16,7 +17,7 @@ all: $(TESTS)
 test_utf8: test_utf8.c $(UTF8_SRC)
 	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
-test_message: test_message.c $(MESSAGE_SRC) $(UTF8_SRC)
+test_message: test_message.c $(MESSAGE_SRC) $(UTF8_SRC) $(COMMON_SRC)
 	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
 run: all