Issue 33307: socket.send() fails to send large amount of bytes (original) (raw)

Created on 2018-04-18 10:52 by Kaulkwappe, last changed 2022-04-11 14:58 by admin. This issue is now closed.

Messages (7)
msg315444 - (view)	Author: (Kaulkwappe)	Date: 2018-04-18 10:52
socket.setblocking(0) socket.send(b'a' * 32 * 1024 * 1024) In the example above socket.send() fails with this error: Error in connection handler Traceback (most recent call last): File "/usr/lib/python3/dist-packages/websockets/server.py", line 81, in handler yield from self.ws_handler(self, path) File "/var/www/vhosts/.../app/sockets/core/Daemon.py", line 286, in websocketClientHandler self.api.connection.send(data) File "/usr/lib/python3.5/ssl.py", line 869, in send return self._sslobj.write(data) File "/usr/lib/python3.5/ssl.py", line 594, in write return self._sslobj.write(data) ssl.SSLWantWriteError: The operation did not complete (write) (_ssl.c:1949)
msg315446 - (view)	Author: Inada Naoki (methane) *	Date: 2018-04-18 12:44
Isn't it an expected behavior of SSL with nonblocking socket? What's wrong?
msg315447 - (view)	Author: (Kaulkwappe)	Date: 2018-04-18 12:57
Sorry for the misunderstanding, here is the complete example: socket.setblocking(0) try: buffer = socket.recv() if not buffer: break except OSError: bytes_sent = socket.send(b'a' * 32 * 1024 * 1024) In this case the socket is ready for sending data and should return the bytes that were actually sent. But when sending a large amount of bytes it every time fails with SSLWantWriteError exception.
msg315448 - (view)	Author: Christian Heimes (christian.heimes) *	Date: 2018-04-18 12:58
Inada is correct. This is the expected and documented behavior for non-blocking SSLSockets, see https://docs.python.org/3/library/ssl.html#ssl-nonblocking .
msg315449 - (view)	Author: (Kaulkwappe)	Date: 2018-04-18 13:12
But why does socket.send() throws an exception in this case only when sending a large amount of bytes? That would mean it is impossible to send large amount of bytes over SSL sockets as it would fail everytime.
msg315451 - (view)	Author: Christian Heimes (christian.heimes) *	Date: 2018-04-18 13:33
The same way as with any other non-blocking I/O system. You have to keep track how much data you have already sent and repeat non-blocking send() until you have succeeded. With TLS/SSL it's even more complex, because a send() also requires reading and a recv() also involves writing. PS: bugs.python.org is an issue tracker, not a help forum.
msg315452 - (view)	Author: (Kaulkwappe)	Date: 2018-04-18 13:45
Thank you for your answer Christian. Indeed it seems a little more complex. As I worked with Non-TLS sockets before it looked like unexpected behaviour to me as on non-blocking sockets socket.send() would normally return 0 when no data was sent. By the way this is the code I currently use: Code: n = 0 while 1: time.sleep(0.001) try: buffer = socket.recv(8192) if not buffer: break except OSError: print('{0}. try to send:'.format(n), len(blark), 'bytes') try: sent = socket.send(blark) except ssl.SSLWantWriteError: sent = 0 n += 1 print('Bytes sent:', sent) else: [...] Result: 1. try to send: 33554469 bytes Bytes sent: 0 [...] 137. try to send: 33554469 bytes Bytes sent: 0 138. try to send: 33554469 bytes Bytes sent: 0 139. try to send: 33554469 bytes Bytes sent: 33554469