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🐛 QUIC Hijack() skips the status-written check that HTTP/2 enforces

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
78/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
go
Domain
backend, networking

Research direction

Start by comparing http2RespWriter.Hijack in connection/http2.go with httpResponseAdapter.Hijack in connection/quic_connection.go, focusing on statusWritten and connectResponseSent. Reproduce the difference with the HTTP/2 and QUIC protocols and a backend returning 101. Done means both transports reject Hijack before their response has been sent and retain consistent behavior.

Written by the indexing model from the issue text.

Description

Describe the bug

Hijack() has different preconditions on the two transports.

HTTP/2, http2RespWriter.Hijack in connection/http2.go, refuses when no status was written yet:

if !rp.statusWritten {
	return nil, nil, fmt.Errorf("status not yet written before attempting to hijack connection")
}

QUIC, httpResponseAdapter.Hijack in connection/quic_connection.go, has no such check. It always returns a localProxyConnection, even when connectResponseSent is still false, so the caller can write raw bytes to the stream before any connect response went out.

Same caller, different outcome depending on the transport: on HTTP/2 it gets an error, on QUIC it gets a conn.

To Reproduce

Stock cloudflared writes the status before it hijacks, so the built-in ingress path does not hit this. I hit it in a fork that replaces the OriginProxy, with code that hijacks first. net/http/httputil.ReverseProxy does exactly that on a 101: handleUpgradeResponse calls Hijack() and then writes the status line onto the conn itself.

  1. ProxyHTTP serves the request through httputil.ReverseProxy to a backend that answers 101.
  2. With --protocol http2, Hijack fails and the client gets a 502.
  3. With --protocol quic, Hijack succeeds and the caller can write to the stream before any connect response was sent.

Expected behavior

Both transports enforce the same precondition. The HTTP/2 check looks like the right one, so QUIC could refuse the same way while connectResponseSent is false.

Environment and versions

  • OS: Linux
  • Architecture: AMD64
  • Version: 2026.9.1, and the Hijack bodies are unchanged on master as of 2026.9.3

Logs and errors

HTTP/2: status not yet written before attempting to hijack connection. QUIC: no error.

Additional context

I worked around it on my side, so it does not block me. Filing it because the two transports disagree on the ResponseWriter contract, and that is easy to miss.

Dominant language
Go
Stars
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Forks
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