fix: add DisableHTTP2Fallback option to respect HTTP/1.1-only transport configs#532
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When a caller explicitly sets HTTP/1.1-only transport (e.g. httpx -pr http11), retryablehttp-go's automatic HTTP/2 fallback in do.go would silently bypass this restriction. This introduces DisableHTTP2Fallback in Options which, when set, skips the HTTPClient2.Do fallback on malformed HTTP/2 errors. Fixes the underlying cause of projectdiscovery/httpx#2240.
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usernametooshort
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Mar 6, 2026
… protocol is set
When -pr http11 is used, httpx correctly sets TLSNextProto={} and
GODEBUG=http2client=0 to force HTTP/1.1. However retryablehttp-go's
automatic HTTP/2 fallback in do.go silently bypasses this:
if err is malformed HTTP/2 response {
resp, err = c.HTTPClient2.Do(req.Request) // <- ignores http11 config
}
This commit sets retryablehttpOptions.DisableHTTP2Fallback=true when
Protocol=="http11", ensuring the HTTP/1.1-only requirement is honoured
end-to-end.
Depends on: projectdiscovery/retryablehttp-go#532
Fixes: projectdiscovery#2240
usernametooshort
added a commit
to usernametooshort/httpx
that referenced
this pull request
Mar 6, 2026
… protocol is set
When -pr http11 is used, httpx correctly sets TLSNextProto={} and
GODEBUG=http2client=0 to force HTTP/1.1. However retryablehttp-go's
automatic HTTP/2 fallback in do.go silently bypasses this:
if err is malformed HTTP/2 response {
resp, err = c.HTTPClient2.Do(req.Request) // <- ignores http11 config
}
This commit sets retryablehttpOptions.DisableHTTP2Fallback=true when
Protocol=="http11", ensuring the HTTP/1.1-only requirement is honoured
end-to-end.
Depends on: projectdiscovery/retryablehttp-go#532
Fixes: projectdiscovery#2240
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|
The underlying issue (httpx#2240) has been resolved at the httpx level — the HTTP/1.1 protocol preference is now correctly enforced without requiring changes to retryablehttp-go. Closing as the original bounty issue is already complete. Thanks for the contribution. |
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Problem
When a caller explicitly configures HTTP/1.1-only transport (e.g.
httpx -pr http11which setstransport.TLSNextProto = map[string]func(...){}andGODEBUG=http2client=0), retryablehttp-go silently bypasses this restriction via the automatic HTTP/2 fallback indo.go:This means
-pr http11in httpx has no effect for servers that respond with HTTP/2.See: projectdiscovery/httpx#2240
Fix
Add
DisableHTTP2Fallback booltoOptions. When set, theHTTPClient2.Dofallback is skipped, respecting the caller's explicit protocol choice.Usage (httpx side)
In httpx when
Protocol == "http11":This is a non-breaking change — existing callers that do not set the option retain the current fallback behavior.