Fix: Set content-length on ext_proc body mutations - #821
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In BUFFERED + SEND mode Envoy does not recompute content-length after a BodyMutation: processing_mode.proto (BodySendMode) makes it the external processor's responsibility, and validateContentLength fails the stream with a 500 on mismatch. Set it on both mutation paths. Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com> Signed-off-by: YehoshuaSagron <ysagron@gmail.com>
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📝 WalkthroughWalkthroughThe ext_proc listener now sets ChangesExt Proc body mutation
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: 🟡 Moderate · up to Request framing is corrected, but response mutations can still retain an incompatible content-encoding, causing clients to decode replacement bodies incorrectly. The regression tests also do not use different-length bodies, so the reported failure mode is not fully protected; merge should wait for these fixes. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Inline comments:
In `@authbridge/authlib/listener/extproc/server_contentlength_test.go`:
- Around line 30-31: Update the regression tests around pipeline.Context body
replacement to use replacement content whose byte length differs from the
original body in both affected cases, including the additional locations noted.
Keep the assertions focused on validating the Content-Length mismatch handling.
In `@authbridge/authlib/listener/extproc/server.go`:
- Around line 672-674: Update the response-body mutation branch containing
HeaderMutation and BodyMutation to remove the upstream content-encoding header
while setting the replacement body’s content-length, matching withBodyMutation
behavior. Extend the response-body mutation test to cover an encoded response
and verify content-encoding is cleared.
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authbridge/authlib/listener/extproc/server.goauthbridge/authlib/listener/extproc/server_contentlength_test.goauthbridge/docs/framework-architecture.md
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The replacement was the same length as the original, so the tests could not tell a correct content-length from an echoed one. Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com> Signed-off-by: YehoshuaSagron <ysagron@gmail.com>
The request path already removes content-encoding when a plugin rewrites the body; the response path did not. Mirror it, as the other listeners do and docs/framework-architecture.md already states. Assisted-By: Claude (Anthropic AI) <noreply@anthropic.com> Signed-off-by: YehoshuaSagron <ysagron@gmail.com>
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Summary
Correct, complete, and unusually well-evidenced fix. Both BodyMutation emission sites now set content-length — withBodyMutation for the request path and the ResponseBodyMutated() branch of handleResponseBody for the response path — and there is no third site, so the fix is complete rather than partial.
Verified independently rather than taken from the description:
- Both paths stay gated on their mutation flags (
BodyMutated()/ResponseBodyMutated()), so a pass-through reply does not acquire a spuriouscontent-length: 0. withHeaderMutationskipsContent-Length/Content-Encoding(server.go:706) and runs beforewithBodyMutation(server.go:205, 545), so there is no duplicate or conflictingSetHeadersentry forcontent-length.strconvandcorev3were already imported — the new helper adds no import.- The mode premise holds in-repo:
RequestBodyMode/ResponseBodyModeareBUFFEREDviaModeOverride(server.go:810, 573) and nothing overrides the header mode, so Envoy's default SEND applies. That is what makes thecontent-lengthmutation legal at all under the quotedBodySendModecontract — under SKIP headers Envoy would strip it itself, asRemoveRequestContentLengthInBufferedModeshows. authbridge/cmd/authbridge-envoy/Dockerfilepinsenvoyproxy/envoy:v1.37.1, matching the proto and integration test cited.
The "why this wasn't caught earlier" section is the useful part of the description — a comment that was true until Envoy 1.29 and an image pinned to 1.37.1 is a failure mode worth naming, and the docs line is corrected alongside the code.
Two non-blocking notes inline. One further nit that has no line to attach to: the description says the tests use Hello, World! and assert content-length: 13, but commit 11a4648 changed the replacement to Hello, World! (longer) (22 bytes). That change was an improvement — a same-length replacement cannot distinguish this bug — so the description now understates the tests. Worth updating before merge, since the PR body is the permanent record.
Author: JoshSag (CONTRIBUTOR — returning external)
Areas reviewed: Go (ext_proc listener), Tests, Docs
Agent/IDE config (.claude/.vscode): none
Commits: 3 commits, all signed-off: yes
CI status: passing — 20 checks green, Spellcheck skipped
| pctx.SetBody([]byte("Hello, World! (longer)")) | ||
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| hm := withBodyMutation(passBodyResponse(), pctx).GetRequestBody().GetResponse().GetHeaderMutation() | ||
| if got, want := mutationHeaderValue(hm, "content-length"), strconv.Itoa(len(pctx.Body)); got != want { |
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want is derived from pctx.Body, the same field the implementation reads. That makes this assertion unable to fail on a SetBody that flips bodyMutated without updating Body — which is the exact bug class this PR exists to fix: a content-length that disagrees with the bytes actually shipped.
TestHandleResponseBody_SetsContentLength below already gets this right by holding the replacement in a variable and asserting against that. Suggest the same shape here so both tests pin a value independent of the code under test:
newBody := []byte("Hello, World! (longer)")
pctx := &pipeline.Context{Body: []byte("Replace this!")}
pctx.SetBody(newBody)
hm := withBodyMutation(passBodyResponse(), pctx).GetRequestBody().GetResponse().GetHeaderMutation()
if got, want := mutationHeaderValue(hm, "content-length"), strconv.Itoa(len(newBody)); got != want {Not blocking — the test still pins the regression it was written for (before this PR there was no content-length entry at all).
| Response: &extprocv3.ProcessingResponse_ResponseBody{ | ||
| ResponseBody: &extprocv3.BodyResponse{ | ||
| Response: &extprocv3.CommonResponse{ | ||
| HeaderMutation: &extprocv3.HeaderMutation{ |
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nit: this is now the only site in the file that emits a response-phase HeaderMutation, and it is deliberately self-contained — withHeaderMutation returns early for the response phase (default: return resp, server.go:767), so plugin-made response header edits are still not propagated.
A one-line comment saying so would help: the request path composes (withHeaderMutation then withBodyMutation append into one HeaderMutation), and a future reader could reasonably assume the same symmetry holds here and that appending to this mutation would pick up plugin edits. It would not.
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Summary
Fixes #820
A
WritesBodyplugin under the envoy-sidecar (ext_proc) listener could only rewrite a body toexactly its original length; any other length made Envoy answer 500 before the upstream saw the
request (
mismatch between content length and the length of the mutated body). The responsepath failed the same way. Reported by @lernerjenny.
Envoy's ext_proc API makes this the processor's job in the mode this listener uses —
processing_mode.proto,BodySendMode:Why this wasn't caught earlier
content-lengthunconditionally (processor_state.ccat v1.28: "Always reset the content length here to prevent later problems"). ext_proc: Refactor the logic of handling content length envoyproxy/envoy#29536 (merged 2023-11-02, fixing #28515) introduced the current rule and the sentence quoted above. The comment anddocs/framework-architecture.md§6 describe the pre-1.29 behaviour;withBodyMutationwas written against an image already pinned to 1.37.1.extproc.Serverwith a mock stream; they assert theBodyMutationand thecontent-encodingremoval, but nothing in the harness models what Envoy does with the reply. The proxy listeners setContentLengththemselves in the same commit and were never affected.WritesBodyplugin; the first length-changing body mutation through ext_proc is the one reported in ext_proc listener: body mutation that changes the length gets a 500 #820.The listener runs BUFFERED + SEND (
ModeOverrideon top of the chart's SEND/NONE filter config),so
withBodyMutation()and the response-body handler now setcontent-lengthto the mutatedbody's length in the body reply's
HeaderMutation, which Envoy applies beforevalidateContentLength. The comment that said Envoy recomputes it is corrected.Tests call the two mutation paths directly with the same bodies as Envoy's
MismatchedContentLengthAndBodyLength(Replace this!→Hello, World!) and assert the reply carriescontent-length: 13— our side of the contract, quoted in the test file. They do not exercise Envoy: both fail onmain, pass here.Envoy's side is pinned by Envoy's own integration tests at the same tag —
MismatchedContentLengthAndBodyLength(BUFFERED, headers SEND, processor-set
content-length≠ mutated body → upstream never reached, downstream 500) andRemoveRequestContentLengthInBufferedMode(headers SKIP → Envoy removes the header itself, 200).The reproduction from #820 (static Envoy 1.37.1 + echo upstream + a plugin that wraps every body) passes with this
commit: both requests 200 instead of 500 — the upstream receives
content-length: 30for the 30-byte wrappedrequest, the client receives
content-length: 124for the wrapped reply. Same result on Envoy 1.36.3(istio proxyv2 1.28.0).
withHeaderMutationdeliberately skipsContent-Length/Content-Encoding— the body path owns them, which is where this lands.Assisted-By: Claude (Anthropic AI) noreply@anthropic.com
Summary by CodeRabbit
Bug Fixes
Content-Lengthheaders accurately reflect the replacement body size.Documentation
Content-Lengthis handled for body mutations.Tests
Content-Lengthvalues for mutated request and response bodies.