On a successful write of count bytes, TRUE is returned, and bytes_written is set to count.
If there is an error during the operation (including G_IO_ERROR_WOULD_BLOCK in the non-blocking case), FALSE is returned and error is set to indicate the error status, bytes_written is updated to contain the number of bytes written into the stream before the error occurred.
As with g_pollable_stream_write(), if blocking is FALSE, then stream must be a GPollableOutputStream for which g_pollable_output_stream_can_poll() returns TRUE or else the behavior is undefined. If blocking is TRUE, then stream does not need to be a GPollableOutputStream
the buffer containing the data to write.
whether to do blocking I/O
location to store the number of bytes that was written to the stream
optional gio.Cancellable object, NULL to ignore.
TRUE on success, FALSE if there was an error
GException on failure.