TRACE header support

[zdmytriv]

For requests through forward proxy we can get additional (not required) TRACE header. For example:

PROXY TCP4 172.17.0.1 172.17.0.2 54636 8080
TRACE 1b458c481644a39176ba72dc6ddbf766
CONNECT httpbin.org:443 HTTP/1.1
Host: httpbin.org:443
User-Agent: curl/7.64.1
Proxy-Connection: Keep-Alive
...

Format: TRACE <32HEX>\r\n

It ALWAYS goes after PROXY header. No PROXY header ====> no TRACE for sure.

1. If there are no protocol headers (like PROXY or TRACE) => proxy will accept request and process
2. If there is just PROXY header => proxy will accept request and process
3. If there is PROXY and TRACE headers => proxy will accept request and process
4. If there is just TRACE header => we accept request BUT it will fail because CONNECT is expected to be the first word.

Related PR:

• https://github.com/verygoodsecurity/nginx/pull/1
• Tracing TCP opentracing/specification#150
• https://github.com/verygoodsecurity/vault/pull/3368

Fixes: https://app.clubhouse.io/vgs/story/67682/fix-tracing-for-forward-proxy

[osklyarenko]

[ch67682]

Automatically linked to https://app.clubhouse.io/vgs/story/67682

[mjallday]

@zdmytriv still relevant?

[mjallday]

is this still relevant @zdmytriv?

[zdmytriv]

already merged from other PR, closing