fix: Allow peers to reconnect to group chats using a password

This commit deprecates the tox_group_reconnect groupchat API function and
modifies the tox_group_join function to automatically reconnect to groups
when it's called with a chat_id that designates a group that it's already
a member of.

This allows clients to implement group rejoin functionality that lets peers
rejoin/reconnect to groups with a passed password argument, which may be
necessary if the group password changes while a peer is offline. This fixes
the bug described in #2806.

auto_tests/group_general_test.c

@@ -392,9 +392,9 @@ static void group_announce_test(AutoTox *autotoxes)
     ck_assert(s_err == TOX_ERR_GROUP_SELF_STATUS_SET_OK);
 
     fprintf(stderr, "Peer 0 reconnecting...\n");
-    Tox_Err_Group_Reconnect r_err;
-    tox_group_reconnect(tox0, groupnumber, &r_err);
-    ck_assert(r_err == TOX_ERR_GROUP_RECONNECT_OK);
+    Tox_Err_Group_Join err_rejoin;
+    tox_group_join(tox0, chat_id, (const uint8_t *)PEER0_NICK, PEER0_NICK_LEN, nullptr, 0, &err_rejoin);
+    ck_assert(err_rejoin == TOX_ERR_GROUP_JOIN_OK);
 
     while (state1->peer_joined_count != 2 && state0->self_joined_count == 2) {
         iterate_all_wait(autotoxes, NUM_GROUP_TOXES, ITERATION_INTERVAL);

toxcore/group_chats.c

@@ -7733,10 +7733,52 @@ int gc_group_add(GC_Session *c, Group_Privacy_State privacy_state,
     return group_number;
 }
 
+int gc_rejoin_group(GC_Session *c, GC_Chat *chat, const uint8_t *passwd, uint16_t passwd_len)
+{
+    if (c == nullptr) {
+        LOGGER_ERROR(chat->log, "NULL group session pointer.");
+        return -1;
+    }
+
+    if (passwd != nullptr && passwd_len > 0) {
+        if (!set_gc_password_local(chat, passwd, passwd_len)) {
+            LOGGER_WARNING(chat->log, "Failed to set new password during reconnect.");
+        }
+    }
+
+    chat->time_connected = 0;
+
+    if (group_can_handle_packets(chat)) {
+        send_gc_self_exit(chat, nullptr, 0);
+    }
+
+    for (uint32_t i = 1; i < chat->numpeers; ++i) {
+        GC_Connection *gconn = get_gc_connection(chat, i);
+        assert(gconn != nullptr);
+
+        gcc_mark_for_deletion(gconn, chat->tcp_conn, GC_EXIT_TYPE_SELF_DISCONNECTED, nullptr, 0);
+    }
+
+    if (is_public_chat(chat)) {
+        kill_group_friend_connection(c, chat);
+
+        if (!m_create_group_connection(c->messenger, chat)) {
+            LOGGER_WARNING(chat->log, "Failed to create new messenger connection for group");
+            return -1;
+        }
+
+        chat->update_self_announces = true;
+    }
+
+    chat->connection_state = CS_CONNECTING;
+
+    return 0;
+}
+
 int gc_group_join(GC_Session *c, const uint8_t *chat_id, const uint8_t *nick, size_t nick_length, const uint8_t *passwd,
                   uint16_t passwd_len)
 {
-    if (chat_id == nullptr || group_exists(c, chat_id) || getfriend_id(c->messenger, chat_id) != -1) {
+    if (chat_id == nullptr) {
         return -2;
     }
 
@@ -7748,6 +7790,18 @@ int gc_group_join(GC_Session *c, const uint8_t *chat_id, const uint8_t *nick, si
         return -4;
     }
 
+    GC_Chat *existing_group = gc_get_group_by_public_key(c, chat_id);
+
+    // If we're already in the group we try to reconnect to it
+    if (existing_group != nullptr) {
+        const int ret = gc_rejoin_group(c, existing_group, passwd, passwd_len);
+        return ret != 0 ? -6 : ret;
+    }
+
+    if (getfriend_id(c->messenger, chat_id) != -1) {
+        return -2;
+    }
+
     const int group_number = create_new_group(c, nick, nick_length, false, GI_PUBLIC);
 
     if (group_number == -1) {
@@ -7806,41 +7860,6 @@ bool gc_disconnect_from_group(const GC_Session *c, GC_Chat *chat)
     return true;
 }
 
-int gc_rejoin_group(GC_Session *c, GC_Chat *chat)
-{
-    if (c == nullptr || chat == nullptr) {
-        return -1;
-    }
-
-    chat->time_connected = 0;
-
-    if (group_can_handle_packets(chat)) {
-        send_gc_self_exit(chat, nullptr, 0);
-    }
-
-    for (uint32_t i = 1; i < chat->numpeers; ++i) {
-        GC_Connection *gconn = get_gc_connection(chat, i);
-        assert(gconn != nullptr);
-
-        gcc_mark_for_deletion(gconn, chat->tcp_conn, GC_EXIT_TYPE_SELF_DISCONNECTED, nullptr, 0);
-    }
-
-    if (is_public_chat(chat)) {
-        kill_group_friend_connection(c, chat);
-
-        if (!m_create_group_connection(c->messenger, chat)) {
-            LOGGER_WARNING(chat->log, "Failed to create new messenger connection for group");
-            return -2;
-        }
-
-        chat->update_self_announces = true;
-    }
-
-    chat->connection_state = CS_CONNECTING;
-
-    return 0;
-}
-
 bool group_not_added(const GC_Session *c, const uint8_t *chat_id, uint32_t length)
 {
     if (length < CHAT_ID_SIZE) {

toxcore/group_chats.h

@@ -676,8 +676,8 @@ bool gc_disconnect_from_group(const GC_Session *c, GC_Chat *chat);
  * Returns -1 if the group handler object or chat object is null.
  * Returns -2 if the Messenger friend connection fails to initialize.
  */
-non_null()
-int gc_rejoin_group(GC_Session *c, GC_Chat *chat);
+non_null(1, 2) nullable(3)
+int gc_rejoin_group(GC_Session *c, GC_Chat *chat, const uint8_t *passwd, uint16_t passwd_len);
 
 /** @brief Joins a group using the invite data received in a friend's group invite.
  *

toxcore/tox.c

@@ -3249,7 +3249,7 @@ bool tox_group_reconnect(Tox *tox, uint32_t group_number, Tox_Err_Group_Reconnec
         return false;
     }
 
-    const int ret = gc_rejoin_group(tox->m->group_handler, chat);
+    const int ret = gc_rejoin_group(tox->m->group_handler, chat, nullptr, 0);
     tox_unlock(tox);
 
     switch (ret) {

toxcore/tox.h

@@ -3717,12 +3717,15 @@ typedef enum Tox_Err_Group_Join {
 const char *tox_err_group_join_to_string(Tox_Err_Group_Join value);
 
 /**
- * Joins a group chat with specified Chat ID.
+ * Joins a group chat with specified Chat ID or reconnects to an existing group.
  *
  * This function creates a new group chat object, adds it to the chats array,
  * and sends a DHT announcement to find peers in the group associated with
  * chat_id. Once a peer has been found a join attempt will be initiated.
  *
+ * If a group with the specified Chat ID already exists, this function will attempt
+ * to reconnect to the group.
+ *
  * @param chat_id The Chat ID of the group you wish to join. This must be
  *   TOX_GROUP_CHAT_ID_SIZE bytes.
  * @param password The password required to join the group. Set to NULL if no
@@ -3827,6 +3830,8 @@ const char *tox_err_group_reconnect_to_string(Tox_Err_Group_Reconnect value);
  * @param group_number The group number of the group we wish to reconnect to.
  *
  * @return true on success.
+ *
+ * @deprecated Use `tox_group_join` instead.
  */
 bool tox_group_reconnect(Tox *tox, Tox_Group_Number group_number, Tox_Err_Group_Reconnect *error);