Support full HTTP/2 specification - PRI

[pas256]

It seems the HTTP/2 implementation in Thruster is only partially completed. That, or I don't understand enough about it yet, which is entirely possible.

I am seeing this in the logs when trying to make an HTTP/2 connection:

{"time":"2025-03-20T21:12:22.988853435Z","level":"INFO","msg":"Request","path":"*","status":501,"dur":0,"method":"PRI","req_content_length":-1,"req_content_type":"","resp_content_length":27,"resp_content_type":"","remote_addr":"10.31.32.141:57578","user_agent":"","cache":"bypass","query":""}
Unsupported HTTP method used: PRI

A little research tells me that PRI is part of the spec, and that others have run into implementation issues like this too:
See: https://stackoverflow.com/questions/50434269/pri-method-in-http2-implementation-causing-issue

I ran into this by setting an AWS Application Load Balancer (ALB), which is doing TLS termination, to talk to my Rails app using HTTP/2 instead of HTTP/1. Here is the target group config

The workaround is to use HTTP/1 only, but that is somewhat defeating the purpose of Thruster.

So I think (and please correct me if I am wrong) Thruster needs to be updated to accept the PRI method, and then subsequently ignore it.

[le0pard]

Looks like by default golang http library activate HTTP/2 only over HTTPS. For plain HTTP not active unencrypted HTTP/2. To make thruster works by HTTP/2 without TLS certs (which looks like handled by aws load balancer instead of thruster) you need add hacks in golang server code:

thruster/internal/server.go

Lines 104 to 111 in 5f38465

	func (s *Server) defaultHttpServer(addr string) *http.Server {
	return &http.Server{
	Addr: addr,
	IdleTimeout: s.config.HttpIdleTimeout,
	ReadTimeout: s.config.HttpReadTimeout,
	WriteTimeout: s.config.HttpWriteTimeout,
	}
	}

should be like this, so server start working by unencrypted HTTP/2

// Configure the HTTP server with h2c support
protocols := new(http.Protocols)
protocols.SetHTTP1(true)
protocols.SetUnencryptedHTTP2(true) // Enable h2c support
protocols.SetHTTP2(true)

return &http.Server{
	Addr:         addr,
	IdleTimeout:  s.config.HttpIdleTimeout,
	ReadTimeout:  s.config.HttpReadTimeout,
	WriteTimeout: s.config.HttpWriteTimeout,
        Protocols: protocols,
}

Maybe option to activate h2c should be available by config variable or env variable for thruster (not sure that this can be secure default - https://www.assetnote.io/resources/research/h2c-smuggling-in-the-wild )

[pas256]

Oh wow, these are related? Who knew?

[film42]

Would love to see h2c happen. I'm dealing with some google cloud run limits and would strongly prefer thruster over container managed nginx, etc. Cloud run will allow for http/2 pass-through but requires cleartext.

Looks like there is positive feedback on h2c here: #3

[kevinmcconnell]

h2c added in #89