In order to announce support for the Extended CONNECT h2 method by
haproxy, always send the ENABLE_CONNECT_PROTOCOL h2 settings. This new
setting has been described in the rfc 8441.
After receiving ENABLE_CONNECT_PROTOCOL, the client is free to use the
Extended CONNECT h2 method. This can notably be useful for the support
of websocket handshake on http/2.
Support for the rfc 8441 Bootstraping WebSockets with HTTP/2
Convert an Extended CONNECT HTTP/2 request into a htx representation.
The htx message uses the GET method with an Upgrade header field to be
fully compatible with the equivalent HTTP/1.1 Upgrade mechanism.
The Extended CONNECT is of the following form :
:method = CONNECT
:protocol = websocket
:scheme = https
:path = /chat
:authority = server.example.com
The new pseudo-header :protocol has been defined and is used to identify
an Extended CONNECT method. Contrary to standard CONNECT, Extended
CONNECT must have :scheme, :path and :authority defined.
Support for the rfc 8441 Bootstraping WebSockets with HTTP/2
Convert a 200 status reply from an Extended CONNECT request into a htx
representation. The htx message is set to 101 status code to be fully
compatible with the equivalent HTTP/1.1 Upgrade mechanism.
This conversion is only done if the stream flags H2_SF_EXT_CONNECT_SENT
has been set. This is true if an Extended CONNECT request has already
been seen on the stream.
Besides the 101 status, the additional headers Connection/Upgrade are
added to the htx message. The protocol is set from the value stored in
h2s. Typically it will be extracted from the client request. This is
only used if the client is using h1 as only the HTTP/1.1 101 Response
contains the Upgrade header.
The H2 message flag H2_MSGF_BODYLESS_RSP is now used during the request or
the response parsing to notify the mux that, considering the parsed message,
the response is known to have no body. This happens during HEAD requests
parsing and during 204/304 responses parsing.
On the H2 multiplexer, the equivalent flag is set on H2 streams. Thus the
H2_SF_BODYLESS_RESP flag is set on a H2 stream if the H2_MSGF_BODYLESS_RSP
is found after a HEADERS frame parsing. Conversely, this flag is also set
when a HEADERS frame is emitted for HEAD requests and for 204/304 responses.
The H2_SF_BODYLESS_RESP flag will be used to ignore data payload from the
response but not the trailers.
As part of his GREASE experiments on Chromium, Bence Béky reported in
https://lists.w3.org/Archives/Public/ietf-http-wg/2020JulSep/0202.html
and https://bugs.chromium.org/p/chromium/issues/detail?id=1127060 that
a certain combination of frame type and frame flags was causing an error
on app.slack.com. It turns out that it's haproxy that is causing this
issue because the frame type is wrongly assumed to support padding, the
frame flags indicate padding is present, and the frame is too short for
this, resulting in an error.
The reason why only some frame types are affected is due to the frame
type being used in a bit shift to match against a mask, and where the
5 lower bits of the frame type only are used to compute the frame bit.
If the resulting frame bit matches a DATA, HEADERS or PUSH_PROMISE frame
bit, then padding support is assumed and the test is enforced, resulting
in a PROTOCOL_ERROR or FRAME_SIZE_ERROR depending on the payload size.
We must never match any such bit for unsupported frame types so let's
add a check for this. This must be backported as far as 1.8.
Thanks to Cooper Bethea for providing enough context to help narrow the
issue down and to Bence Béky for creating a simple reproducer.
