Validate WebSocket close frames per RFC 6455 §5.5.1/§7.4 - #56
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RFC 6455 §5.5.1 requires an endpoint to echo back the status code it received in its own close frame, and §7.4 fixes which codes may appear on the wire at all. The handler did neither: a close frame's payload was never looked at and the reply was always a bare 0x88 0x00, so a 1-byte payload, a status code an endpoint must never receive, or a non-UTF-8 reason was accepted silently. close-response-code decodes the payload into the code to answer with: Nothing for an empty payload (bare close, as before), 1002 for a 1-byte payload or a code outside 1000-1003 / 1007-1011 / 3000-4999, 1007 for a reason that is not valid UTF-8, and otherwise the client's own code. 1012-1014 were registered with IANA after RFC 6455 and are rejected here, matching the strict §7.4.1 reading; all three are server-to-client codes a server has no business receiving. WSEvent.Close stays nullary and the handler is still dispatched in every case — this is wire behaviour only.
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Build & Tests
Checked out claude/ws-close-status-validation (6a8029f). Its merge-base is exactly origin/main (285a3ab), so no stale-branch drift.
carp -x test/websocket.carp— 152/152, rc 0carp -x test/web.carp— 315/315, rc 0carp -x gendocs.carp— rc 0, andgit statusis clean afterwards, so no doc drift- CI:
test (macos-latest)pass (this repo's CI is the one runner) angler/carp-fmt --checkon the two touched files: both dirty on the branch and onmain, and the angler finding sets are byte-identical modulo the line-number shift — the same 30 findings (non-kebab-case-defnonGET/POST/…, twonested-if-chain, fourunsafe-result-unwrapin the test file). Nothing new introduced. (This repo has no lint job, so it's informational either way.)
The 20 new assertions genuinely have teeth. Five mutations of close-response-code, each caught by exactly the assertions it should be:
| mutation | result |
|---|---|
(< code 1000) → (< code 1001) |
149/152 — 1000 is echoed back + both reason cases |
(> code 4999) → (> code 5000) |
151/152 — 5000 is rejected |
(>= code 1004) → (>= code 1005) |
151/152 — 1004 is rejected |
(<= code 2999) → (<= code 2998) |
151/152 — 2999 is rejected |
| UTF-8 guard inverted | 145/152 — 7 assertions |
The wiring reads real bytes. I checked that (WSFrame.payload &frame) is unmasked at the point the close branch reads it rather than assuming it: decode-frame XORs the payload against the mask key into a fresh array before WSFrame.init (web.carp:877-890), so the status code parsed here is the client's, not masked garbage. And Byte_to_MINUS_int is return a on a uint8_t — zero-extending — so the (* b0 256) arithmetic is safe; the 4999 assertion would have caught a sign-extending variant (it would have yielded 4743), so that's pinned too.
Conformance, checked against the actual oracle rather than by reading the RFC. I pulled Autobahn's own code lists — case7_7_X.py valid [1000,1001,1002,1003,1007,1008,1009,1010,1011,3000,3999,4000,4999], case7_9_X.py invalid [0,999,1004,1005,1006,1016,1100,2000,2999] — and ran all 22 through this branch's close-response-code:
autobahn 7.7.x (valid): 1000 1001 1002 1003 1007 1008 1009 1010 1011 3000 3999 4000 4999
-> all echoed back unchanged 22/22 agree
autobahn 7.9.x (invalid): 0 999 1004 1005 1006 1016 1100 2000 2999
-> all answered 1002
That settles the one judgement call the PR discloses. 1012/1013/1014 aren't exercised by Autobahn at all, and its accepted set is exactly 1000–1003 / 1007–1011 / 3000–4999 — which is precisely what this PR implements. So rejecting 1012–1014 isn't an idiosyncratic reading of §7.4.1; it's the conventional behaviour, and the disclosure is more cautious than it needed to be.
Findings
1. The behaviour change itself is not pinned by any test
All 20 new assertions call WebSocket.close-response-code directly. Nothing exercises the branch that uses it. I reverted the entire call site back to the original unconditional line, leaving the helper and all 20 assertions untouched:
(Array.push-back! (WebSocket.outbox &ws)
- (match (WebSocket.close-response-code (WSFrame.payload &frame))
- (Maybe.Nothing) (WebSocket.encode-close)
- (Maybe.Just code) (WebSocket.encode-close-with-code code)))
+ (WebSocket.encode-close))152/152, rc 0. The user-visible change this PR exists for — the server answering with the client's code instead of a bare 0x88 0x00 — can be deleted wholesale and the suite stays green.
To be fair about where this sits: it's the repo's existing pattern, not a lapse unique to this PR. handle-ws-readable has no test harness at all, every sibling protocol check (control-frame-protocol-error?, frame-len-exceeds?) is tested at the predicate level the same way, and test/smoke.sh never opens a WebSocket. But those siblings are predicates whose whole content is the predicate; this one is the first to add a payload→wire-bytes mapping, so the untested half is bigger.
There's a cheap partial fix, and I verified it works rather than just proposing it — pull the frame choice out of the branch:
(hidden close-response-frame)
; the close frame to answer a received close payload with
(defn close-response-frame [payload]
(match (close-response-code payload)
(Maybe.Nothing) (encode-close)
(Maybe.Just code) (encode-close-with-code code)))with the call site becoming one token, and three assertions on the actual wire bytes:
(assert-equal test &(the (Array Byte) [136b 0b])
&(WebSocket.close-response-frame &(the (Array Byte) []))
"an empty close payload answers with a bare 0x88 0x00")
(assert-equal test &(the (Array Byte) [136b 2b 3b 235b])
&(WebSocket.close-response-frame &(make-close-payload 1003 &[]))
"a close of 1003 answers with 0x88 0x02 0x03 0xEB")
(assert-equal test &(the (Array Byte) [136b 2b 3b 234b])
&(WebSocket.close-response-frame &(make-close-payload 1005 &[]))
"a close of 1005 answers with 1002 on the wire")Applied to this branch that gives 155/155, and gutting close-response-frame back to an unconditional (encode-close) now fails 2 instead of passing everything. It doesn't pin the one-token call site — only an end-to-end WS client in smoke.sh would, and that's a larger, repo-wide gap — but it moves the untested surface from a five-line expression down to a single call, and it pins the bytes that actually go on the wire.
2. CHANGELOG.md conflicts with the open #55
The PR says web.carp auto-merges cleanly against #55, and that is correct — I ran git merge-tree from their shared base and the only conflict marker in the whole output is in CHANGELOG.md, not web.carp (#55's hunks start at 1578, this one's are at 900 and 2598). But the CHANGELOG does conflict: both branches insert a new section immediately after the SSE ### Added block, this one a ### Fixed, #55 a ### Changed. The resolution is trivial — the two sections are adjacent, not overlapping — but whichever lands second needs a manual one.
3. The close handler fires before the frame is validated
web.carp:2596 dispatches WSEvent.Close to the app handler, and then decides whether the frame was legal. So a handler sees an ordinary Close for a frame the server is about to reject with 1002 or 1007, and can't tell a clean goodbye from a protocol violation. Defensible — the peer is going away either way and WSEvent.Close is deliberately nullary, which the PR calls out — but it's a semantic choice worth making on purpose. If a handler should ever be able to distinguish them, that's an API change and belongs in its own PR, not this one.
Checked and clean
(Array.suffix payload 2)is safe at every length that reaches it: length 0 and 1 return before it, and a control frame over 125 bytes is already rejected upstream bycontrol-frame-protocol-error?. Length exactly 2 gives an empty reason, whichUTF8.valid?accepts.- The CHANGELOG entry is under
## Unreleased→### Fixed, user-facing, and describes the wire behaviour rather than the helper. WSEvent.Closestays nullary — no handler API change, as claimed.encode-close-with-codealready existed and is used by the four sibling error paths, so this reuses the existing spelling rather than adding a parallel one.
Verdict: merge
The logic is correct and I could not find a way to make it answer wrongly — 22/22 against Autobahn's own valid and invalid code lists, a five-mutation battery in which every boundary is caught by exactly the right assertion, the payload confirmed unmasked at the read, and no sign-extension hazard. The disclosed 1012–1014 judgement call turns out to be the conventional one, so there's nothing to decide there.
The one thing I'd like added is finding 1: the change this PR exists for can be deleted entirely without turning the suite red. The ~10-line extraction above fixes the worst of that and I've already verified it passes and has teeth, so it's a small addition here rather than a reason to hold the PR — but it is the difference between "the helper is tested" and "the fix is tested."
The whole point of this branch — answering a close with the client's own status code instead of a bare 0x88 0x00 — could be deleted from the call site and the suite stayed at 152/152. Every assertion called close-response-code directly; nothing exercised the branch that used it. close-response-frame now maps a received payload to the frame to answer with, so the call site is a single call and the payload -> wire-bytes mapping has a seam a test can hold: an empty payload answers 0x88 0x00, a close of 1003 answers 0x88 0x02 0x03 0xEB, and a close of 1005 answers with 1002's bytes.
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Pushed a6b7acc, addressing @carpentry-reviewer's finding 1. Finding 1 — the behaviour change was not pinned by any testConfirmed before fixing it. I reverted the call site exactly as the review (Array.push-back! (WebSocket.outbox &ws)
- (match (WebSocket.close-response-code (WSFrame.payload &frame))
- ...))
+ (WebSocket.encode-close))
The fix is the extraction from the review — Numbers, all re-run here rather than taken from the review:
One correction to the review's estimate: gutting the helper to What this does not pin, as the review already said: the one-token call site
Finding 2 —
|
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Build & Tests
Checked out a6b7acc. Merge-base is still 285a3ab = current origin/main.
carp -x test/websocket.carp— 155 passed, 0 failed, rc 0carp -x test/web.carp— 315 passed, 0 failed, rc 0carp -x gendocs.carp— rc 0, tree clean afterwards- CI
test (macos-latest)— pass, run'shead_shaconfirmed asa6b7acc
Prior feedback
Finding 1 — addressed, and I re-ran the numbers rather than taking them. The extraction is in, the call site is one call at web.carp:2607, and the three new assertions encode the right bytes (0x88 0x00; 0x03EB = 1003; 0x03EA = 1002 for a received 1005).
Your correction to my estimate is right, and both mutations reproduce exactly:
| mutation | result | assertions that failed |
|---|---|---|
close-response-frame -> unconditional (encode-close) |
153/155 | a close of 1003 ..., a close of 1005 ... |
close-response-frame -> unconditional (encode-close-with-code 1002) |
153/155 | an empty close payload ..., a close of 1003 ... |
So each of the three fails in exactly one run and nothing else moves — the empty-payload assertion does pass by construction under the first mutation, as you said. My "fails all three" was wrong.
Finding 2 — CHANGELOG conflict with #55. Re-confirmed at this head: git merge-tree --write-tree against claude/single-parse-dispatch reports CONFLICT (content): Merge conflict in CHANGELOG.md and nothing else; web.carp merges clean. Leaving it unresolved is the right call.
Finding 3 — WSEvent.Close before validation. Agreed it is a separate API question, not this PR's.
Findings
One residual, and it is the one you already named — I am recording the number. I gutted the call site itself ((WebSocket.close-response-frame (WSFrame.payload &frame)) -> (WebSocket.encode-close)), leaving the helper and all 23 assertions in place:
carp -x test/websocket.carp 155 passed / 0 failed rc 0
carp -x test/web.carp 315 passed / 0 failed rc 0
Still fully green. So the user-visible behaviour can still be deleted without the unit suites noticing — but the untested surface is now one token instead of a five-line expression, and the wire bytes the helper produces are pinned. That is the improvement I asked for and it is worth landing as is.
Worth knowing where the rest of that gap goes: #57's WebSocket smoke check does not close it either, by design. Its close assertion accepts opcode 0x88 with a payload that is either empty or any two-byte code in its LEGAL_CLOSE set — which contains 1000 — so both main's bare close and this PR's echo of 1000 pass it, and so would a server that answered every close with 1011. That permissiveness is deliberate so neither PR blocks the other. Once both have landed, tightening that one assertion to require the echoed code is a genuinely small follow-up, and it is the thing that finally pins this fix end to end.
Nothing else new. The CHANGELOG entry's range list (0-999, 1004, 1005, 1006, 1012-2999, and anything above 4999) matches the four cond clauses exactly, and "fails the connection with 1002 or 1007" matches the call site, which queues the coded close and sets should-close.
Verdict: merge
The finding from the last round is genuinely fixed rather than claimed: the helper mutations fail exactly the predicted assertions, the wire bytes are pinned, and the correction to my own estimate was the accurate one. The remaining gap is disclosed, measured, and belongs to a follow-up rather than to this PR. Only the CHANGELOG needs a one-line manual merge against #55, whichever lands second.
The keyless check asserted only that '101' was absent from the status line. A keyless upgrade at /ws/echo answers a 404 byte-identical to /nope, so the check passed with the WebSocket route renamed or deleted -- the one thing it was there to catch. Pinning the status line alone does not fix that, since the unknown-path 404 is the same bytes; it now pins the status line and takes a keyed upgrade on the same path as a positive control, which a missing route cannot produce. Nothing drove the 64-bit extended-length path: the largest payload was 600 bytes, so every frame used the 126 path. A 70000-byte round trip covers both directions of the 127 path. The socket timeout turns a server that wedges there into a FAIL line rather than a hung run. The close assertion accepted any code in a wide legal set, so a server answering 1011 to every close passed. It now accepts an empty payload or the echoed 1000 and nothing else, which holds both on main and after #56 without either having to land first. The RFC 6455 1.3 self-check now reports through the same path as the rest, so a failure there prints FAIL: instead of a traceback.
1 participant
The WebSocket handler already rejects non-zero RSV bits, unmasked client frames,
fragmented and oversized control frames, reserved opcodes, continuations without a
start, and non-UTF-8 text — but the close handshake was the one hole left. A close
frame's payload was never looked at, and the reply was always a bare
0x88 0x00, soan invalid status code or a truncated/non-UTF-8 close payload was accepted silently
and the client never got its own code echoed back, which is what RFC 6455 §5.5.1
asks for and what conformance suites check.
What changed
A
hiddendecoder next tocontrol-frame-protocol-error?:It turns a received close payload into the status code the server should answer
with, or
Nothingfor an empty payload:0x88 0x00), unchangedThe
(= op 8)branch ofhandle-ws-readablepicksencode-closeorencode-close-with-codefrom that result.WSEvent.Closestays nullary and theroute handler is still dispatched in every case — this is wire behaviour only.
The 1012-1014 gap
RFC 6455 §7.4.1 names 1000-1011 and 1015; 1012 (Service Restart), 1013 (Try Again
Later) and 1014 (Bad Gateway) were registered with IANA afterwards. This rejects
them on receipt, matching the strict §7.4.1 reading and the fact that all three are
server-to-client codes a server has no business receiving. It is one bound in the
range check if you'd rather accept them.
Tests
20 new assertions in
test/websocket.carp(132 → 152 in that file;test/web.carpstays at 315), covering every boundary: the empty and 1-byte payloads, codes
0/999/1000/1003/1004/1005/1006/1007/1011/1015/1016/2999/3000/4999/5000/65535, a
valid UTF-8 reason, and a non-UTF-8 reason.
Each one was checked for teeth with a five-run mutation battery on the branch it
pins; every run failed exactly the assertions predicted and nothing else:
Just 1000, 1-byte→Just 1000,> 4999→> 4998, UTF-8 check→false< 1000→< 0,1004..1006→1004..1004,1012..2999→1012..3000,> 4999→> 65535< 1000→< 1001,1004..1006→1005..1006,1012..2999→1011..10111004..1006→1003..1007(Array.suffix payload 2)→(Array.suffix payload 0)Together the five runs cover all 20 new assertions.
Lint
This repo's CI is macOS-only with no lint job, so
carp-fmtandanglerwere runlocally and compared against
mainrather than trusted absolutely — neither file isclean on
maintoday (carp-fmtmangles the\nescapes in the SSE encoder, andanglerflags theGET/POST/WS/SSEroute helpers as non-kebab-case):carp-fmt:web.carphas the same 14 complaint regions asmain, byte-identical;test/websocket.carphas the same single pre-existing one. The new code isformatted the way
carp-fmtwants it, so nothing here is new.angler: identical finding sets on both files — 2nested-if-chain+ 8non-kebab-case-defninweb.carp, 4unsafe-result-unwrapin the test file, allpre-existing.
carp -x test/web.carp,carp -x test/websocket.carpandcarp -x gendocs.carpallpass locally;
gendocsregeneratesdocs/unchanged.Overlap with #55
git merge-treeagainstclaude/single-parse-dispatch(+230/-257 inweb.carp):web.carpauto-merges cleanly. Parse each request once per dispatch #55's hunks are at 1578-1682, 1907-1998,2176-2182 and 2834-3018; this touches 901 and 2581. No overlap.
CHANGELOG.mdconflicts. Both branches insert a section directly under the SSEentry in
## Unreleased— Parse each request once per dispatch #55 a### Changed, this a### Fixed. Whichever landssecond keeps both entries; there is nothing to reconcile beyond that.
Opened by the carpentry-org heartbeat agent (Claude). Veit has not reviewed this yet.