fix: friend requests with very long messages are no longer dropped

This is a band-aid solution that prevents friend requests with
long messages from being dropped. However it doesn't solve the
underlying problem, described here:
#2719

Author: JFreegman

toxcore/friend_connection.c

@@ -875,6 +875,10 @@ void set_friend_request_callback(Friend_Connections *fr_c, fr_request_cb *fr_req
 int send_friend_request_packet(Friend_Connections *fr_c, int friendcon_id, uint32_t nospam_num, const uint8_t *data,
                                uint16_t length)
 {
+    // FIXME: This max packet size is too large to be handled by receiving clients
+    // when sent via the onion. We currently limit the length at a higher level, but
+    // this bounds check should be fixed to represent the max size of a packet that
+    // the onion client can handle.
     if (1 + sizeof(nospam_num) + length > ONION_CLIENT_MAX_DATA_SIZE || length == 0) {
         return -1;
     }

toxcore/friend_requests.h

@@ -14,7 +14,8 @@
 #include "attributes.h"
 #include "friend_connection.h"
 
-#define MAX_FRIEND_REQUEST_DATA_SIZE (ONION_CLIENT_MAX_DATA_SIZE - (1 + sizeof(uint32_t)))
+// FIXME: This should be the maximum size that an onion client can handle.
+#define MAX_FRIEND_REQUEST_DATA_SIZE (ONION_CLIENT_MAX_DATA_SIZE - 100)
 
 typedef struct Friend_Requests Friend_Requests;
 

toxcore/onion_client.h

@@ -183,6 +183,8 @@ non_null()
 unsigned int onion_getfriend_dht_pubkey(const Onion_Client *onion_c, int friend_num, uint8_t *dht_key);
 
 #define ONION_DATA_IN_RESPONSE_MIN_SIZE (CRYPTO_PUBLIC_KEY_SIZE + CRYPTO_MAC_SIZE)
+
+// FIXME: This is not the correct value; data this large will be dropped by the onion client.
 #define ONION_CLIENT_MAX_DATA_SIZE (MAX_DATA_REQUEST_SIZE - ONION_DATA_IN_RESPONSE_MIN_SIZE)
 
 /** @brief Send data of length length to friendnum.

toxcore/tox.h

@@ -274,7 +274,7 @@ uint32_t tox_max_status_message_length(void);
  *
  * @deprecated The macro will be removed in 0.3.0. Use the function instead.
  */
-#define TOX_MAX_FRIEND_REQUEST_LENGTH  1016
+#define TOX_MAX_FRIEND_REQUEST_LENGTH  921
 
 uint32_t tox_max_friend_request_length(void);