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)

Isn't it an expected behavior of SSL with nonblocking socket?
What's wrong?

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.

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 .

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.

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.

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