Appendix A. Migrating from Cowboy 2.19 to 2.20

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Cowboy 2.20 is a maintenance release. It updates Cowlib to 2.21 to benefit from security and bug fixes.

Cowboy 2.20 requires Erlang/OTP 27.0 or greater.

A.1. Features added

The obsolete x-webkit-deflate-frame Websocket extension is no longer negotiated. An offer of that extension is ignored. Clients that offered only x-webkit-deflate-frame now get an uncompressed connection. permessage-deflate is unchanged.

Websocket close reason in the middle of a fragmented text message could fail UTF-8 validation despite being valid.
A ping, pong or close frame sent between fragments of a compressed message is no longer inflated.
The empty final fragment of a compressed message is now inflated and checked. Bad deflate data or a bad UTF-8 state fails the connection. Bytes flushed by the compression trailer are delivered.
Unexpected RSV1 on a Websocket control frame is now rejected and the connection closed.
HPACK was not using the configured header table size if below 4096 until the peer sent its own setting.
After RST_STREAM is sent, a HEADERS or CONTINUATION frame for that stream was not decoded, desynchronizing the HPACK state.
An invalid last chunk in a chunked body is now rejected immediately.
The chunk before the last chunk is no longer left unparsed longer than necessary.
HTTP date parsing was made stricter.
The cookie code was updated to the current RFC6265bis draft.
Cowboy no longer sends the obsolete Expires attribute in Set-Cookie headers.