SFTP: bufgix, move more sftp stuff to sftp.h

The sftp_write function shouldn't assume that the buffer pointer will be
the same in subsequent calls, even if it assumes that the data already
passed in before haven't changed.

The sftp structs are now moved to sftp.h (which I forgot to add before)

src/sftp.c

@@ -1412,6 +1412,9 @@ libssh2_sftp_readdir_ex(LIBSSH2_SFTP_HANDLE *hnd, char *buffer,
  * Caveats:
  * -  be careful: we must not return a higher number than what was given!
  *
+ * TODO:
+ *   Introduce an option that disables this sort of "speculative" ahead writing
+ *   as there's a risk that it will do harm to some app.
  */
 
 static ssize_t sftp_write(LIBSSH2_SFTP_HANDLE *handle, const char *buffer,
@@ -1430,27 +1433,18 @@ static ssize_t sftp_write(LIBSSH2_SFTP_HANDLE *handle, const char *buffer,
     size_t acked = 0;
     size_t org_count = count;
 
+    /* number of bytes sent off that haven't been acked and therefor
+       we will get passed in here again */
+    size_t unacked = handle->u.file.offset_sent - handle->u.file.offset;
+
+    /* skip the part already made into packets */
+    buffer += unacked;
+    count -= unacked;
+
     chunk = _libssh2_list_first(&handle->write_list);
 
-    /* the list of staged packets is in send order, the first to be sent
-       next */
-    while(chunk) {
-        if(SFTP_WITHIN(chunk->org_buffer, buffer, count)) {
-            /* parts of the given buffer have already been staged for
-               sending, advance buffer to the end of the staged buffer and
-               decrease count with the amount */
-            size_t delta = chunk->org_buflen-(chunk->org_buffer-buffer);
-            buffer += delta;
-            count -= delta;
-            chunk = _libssh2_list_next(&chunk->node);
-            continue;
-        }
-
-        break;
-    }
-
     while(count) {
-        /* Possibly this should have some logic to prevent a very very
+        /* TODO: Possibly this should have some logic to prevent a very very
            small fraction to be left but lets ignore that for now */
         size_t size = MIN(MAX_SFTP_OUTGOING_SIZE, count);
 
@@ -1464,7 +1458,6 @@ static ssize_t sftp_write(LIBSSH2_SFTP_HANDLE *handle, const char *buffer,
             return _libssh2_error(session, LIBSSH2_ERROR_ALLOC,
                                   "malloc fail for FXP_WRITE");
 
-        chunk->org_buffer = buffer;
         chunk->org_buflen = size;
         chunk->sent = 0;
         chunk->lefttosend = packet_len;