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Netty client: HTTP2 transport mode sends cleartext HTTP/2 prior knowledge to forward proxies #1571
Description
Problem
With transportMode=HTTP2 and a forward proxy configured, a plain http:// request opens a cleartext connection to the proxy and immediately sends the HTTP/2 connection preface (addHttp2Handlers, prior knowledge). Most HTTP proxies (Squid, corporate proxies, etc.) only speak HTTP/1.1 to clients, so the request fails.
Proposed fix
When a forward proxy is used for a cleartext request, either:
- fall back to HTTP/1.1 (absolute-form request line) and log it at FINE level, or
- fail fast with a clear error saying that HTTP/2 prior knowledge is not supported through a forward proxy.
Falling back seems more useful, and DYNAMIC mode already behaves that way. Add a test case in ProxyTestCase.
Activity
fix: use HTTP/1.1 for cleartext requests through a forward proxy
fix: use HTTP/1.1 for cleartext requests through a forward proxy
fix: use HTTP/1.1 for cleartext requests through a forward proxy
fix: use HTTP/1.1 for cleartext requests through a forward proxy
fix: use HTTP/1.1 for cleartext requests through a forward proxy
fix: use HTTP/1.1 for cleartext requests through a forward proxy
jlouvel commentedon Nov 5, 2026
Fixed by #1578: in
HTTP2transport mode, a cleartext request through a forward proxy falls back to HTTP/1.1 with an absolute-form request line, instead of sending the HTTP/2 prior-knowledge preface.ProxyTestCasecovers it.🤖 Generated with Claude Code