features.rst

Features

.. currentmodule:: websockets

Feature support matrices summarize which implementations support which features.

.support-matrix-table { width: 100%; } .support-matrix-table th:first-child { text-align: left; } .support-matrix-table th:not(:first-child) { text-align: center; width: 15%; } .support-matrix-table td:not(:first-child) { text-align: center; }

Both sides

	|aio|	|sync|	|trio|	Sans-I/O	|leg|
Perform the opening handshake	✅	✅	✅	✅	✅
Enforce opening timeout	✅	✅	✅	—	✅
Send a message	✅	✅	✅	✅	✅
Broadcast a message	✅	❌	❌	—	✅
Receive a message	✅	✅	✅	✅	✅
Iterate over received messages	✅	✅	✅	—	✅
Send a fragmented message	✅	✅	✅	✅	✅
Receive a fragmented message frame by frame	✅	✅	✅	—	❌
Receive a fragmented message after reassembly	✅	✅	✅	—	✅
Force sending a message as Text or Binary	✅	✅	✅	—	❌
Force receiving a message as :class:`bytes` or :class:`str`	✅	✅	✅	—	❌
Send a ping	✅	✅	✅	✅	✅
Respond to pings automatically	✅	✅	✅	✅	✅
Send a pong	✅	✅	✅	✅	✅
Keepalive	✅	✅	✅	—	✅
Heartbeat	✅	✅	✅	—	✅
Measure latency	✅	✅	✅	—	✅
Perform the closing handshake	✅	✅	✅	✅	✅
Enforce closing timeout	✅	✅	✅	—	✅
Report close codes and reasons from both sides	✅	✅	✅	✅	❌
Compress messages (RFC 7692)	✅	✅	✅	✅	✅
Tune memory usage for compression	✅	✅	✅	✅	✅
Negotiate extensions	✅	✅	✅	✅	✅
Implement custom extensions	✅	✅	✅	✅	✅
Negotiate a subprotocol	✅	✅	✅	✅	✅
Enforce security limits	✅	✅	✅	✅	✅
Log events	✅	✅	✅	✅	✅

Server

	|aio|	|sync|	|trio|	Sans-I/O	|leg|
Listen on a TCP socket	✅	✅	✅	—	✅
Listen on a Unix socket	✅	✅	❌	—	✅
Listen using a preexisting socket	✅	✅	✅	—	✅
Encrypt connection with TLS	✅	✅	✅	—	✅
Close server on context exit	✅	✅	✅	—	✅
Close connection on handler exit	✅	✅	✅	—	✅
Shut down server gracefully	✅	✅	✅	—	✅
Check Origin header	✅	✅	✅	✅	✅
Customize subprotocol selection	✅	✅	✅	✅	✅
Configure Server header	✅	✅	✅	✅	✅
Alter opening handshake request	✅	✅	✅	✅	❌
Alter opening handshake response	✅	✅	✅	✅	❌
Force an HTTP response	✅	✅	✅	✅	✅
Perform HTTP Basic Authentication	✅	✅	✅	❌	✅
Route connections to handlers	✅	✅	❌	—	❌

Client

	|aio|	|sync|	|trio|	Sans-I/O	|leg|
Connect to a TCP socket	✅	✅	✅	—	✅
Connect to a Unix socket	✅	✅	❌	—	✅
Connect using a preexisting socket	✅	✅	✅	—	✅
Encrypt connection with TLS	✅	✅	✅	—	✅
Close connection on context exit	✅	✅	✅	—	✅
Reconnect automatically	✅	❌	✅	—	✅
Configure Origin header	✅	✅	✅	✅	✅
Configure User-Agent header	✅	✅	✅	✅	✅
Modify opening handshake request	✅	✅	✅	✅	✅
Modify opening handshake response	✅	✅	✅	✅	❌
Connect to non-ASCII IRIs	✅	✅	✅	✅	✅
Follow HTTP redirects	✅	❌	✅	—	✅
Perform HTTP Basic Authentication	✅	✅	✅	✅	✅
Connect via HTTP proxy	✅	✅	✅	—	❌
Connect via SOCKS5 proxy	✅	✅	✅	—	❌

Known limitations

There is no way to control compression of outgoing frames on a per-frame basis (#538). If compression is enabled, all frames are compressed.

The server doesn't check the Host header and doesn't respond with HTTP 400 Bad Request if it is missing or invalid (#1246).

The client doesn't support HTTP Digest Authentication (#784).

The client API doesn't attempt to guarantee that there is no more than one connection to a given IP address in a CONNECTING state. This behavior is mandated by RFC 6455, section 4.1. However, :func:`~asyncio.client.connect()` isn't the right layer for enforcing this constraint. It's the caller's responsibility.

It is possible to send or receive a text message containing invalid UTF-8 with send(not_utf8_bytes, text=True) and not_utf8_bytes = recv(decode=False) respectively. As a side effect of disabling UTF-8 encoding and decoding, these options also disable UTF-8 validation.