2 files changed, 20 insertions, 2 deletions

diff --git a/toxcore/tox.c b/toxcore/tox.c
index ea19753f..ded2da6d 100644
--- a/toxcore/tox.c
+++ b/toxcore/tox.c
@@ -359,7 +359,7 @@ void tox_callback_statusmessage(Tox *tox, void (*function)(Messenger *tox, int,
 void tox_callback_userstatus(Tox *tox, void (*_function)(Tox *tox, int, TOX_USERSTATUS, void *), void *userdata)
 {
     Messenger *m = tox;
-    typedef void (*function_type)(Messenger *, int, USERSTATUS, void *); 
+    typedef void (*function_type)(Messenger *, int, USERSTATUS, void *);
     function_type function = (function_type)_function;
     m_callback_userstatus(m, function, userdata);
 }
@@ -551,6 +551,17 @@ int tox_file_senddata(Tox *tox, int friendnumber, uint8_t filenumber, uint8_t *d
     Messenger *m = tox;
     return file_data(m, friendnumber, filenumber, data, length);
 }
+
+/* Returns the recommended/maximum size of the filedata you send with tox_file_senddata()
+ *
+ *  return size on success
+ *  return 0 on failure (currently will never return 0)
+ */
+int tox_filedata_size(Tox *tox, int friendnumber)
+{
+    return MAX_DATA_SIZE - crypto_box_MACBYTES - 3;
+}
+
 /* Give the number of bytes left to be sent/received.
  *
  *  send_receive is 0 if we want the sending files, 1 if we want the receiving.
diff --git a/toxcore/tox.h b/toxcore/tox.h
index 3594b1c1..db4e6b57 100644
--- a/toxcore/tox.h
+++ b/toxcore/tox.h
@@ -435,7 +435,7 @@ int tox_group_message_send(Tox *tox, int groupnumber, uint8_t *message, uint32_t
  * HOW TO SEND FILES CORRECTLY:
  * 1. Use tox_new_filesender(...) to create a new file sender.
  * 2. Wait for the callback set with tox_callback_file_control(...) to be called with receive_send == 1 and control_type == TOX_FILECONTROL_ACCEPT
- * 3. Send the data with tox_file_senddata(...)
+ * 3. Send the data with tox_file_senddata(...) with chunk size tox_filedata_size(...)
  * 4. When sending is done, send a tox_file_sendcontrol(...) with send_receive = 0 and message_id = TOX_FILECONTROL_FINISHED
  *
  * HOW TO RECEIVE FILES CORRECTLY:
@@ -508,6 +508,13 @@ int tox_file_sendcontrol(Tox *tox, int friendnumber, uint8_t send_receive, uint8
  */
 int tox_file_senddata(Tox *tox, int friendnumber, uint8_t filenumber, uint8_t *data, uint16_t length);
 
+/* Returns the recommended/maximum size of the filedata you send with tox_file_senddata()
+ *
+ *  return size on success
+ *  return 0 on failure (currently will never return 0)
+ */
+int tox_filedata_size(Tox *tox, int friendnumber);
+
 /* Give the number of bytes left to be sent/received.
  *
  *  send_receive is 0 if we want the sending files, 1 if we want the receiving.