Add slow-client timeout and request line validation

[carpentry-agent]

Summary

Production hardening: the server previously had no timeout on header accumulation and no pre-parse validation of HTTP request structure.

Slow-client timeout (slow loris protection)

A new ConnState.read-start field tracks when each connection began accumulating headers for the current request. sweep-idle now closes HTTP connections where now - read-start > App.header-timeout (default 15 seconds), regardless of whether data trickles in. This defeats slow loris attacks where an attacker sends partial headers one byte at a time to hold connections open indefinitely.

The timer resets to 0 when:

• Headers are fully received (request processing begins)
• A keep-alive connection finishes writing and returns to read mode
• The connection is cleaned up

Request line validation

Before handing the buffer to Request.parse, web-validate-request-line now checks:

• Method is a recognized HTTP token (GET, HEAD, POST, PUT, DELETE, PATCH, OPTIONS, TRACE, CONNECT)
• Version is HTTP/1.0 or HTTP/1.1
• Request line length does not exceed App.max-header-line (default 8192 bytes)

Malformed requests receive an immediate 400 Bad Request without invoking the full parser or any route handlers.

New constants

Constant	Default	Purpose
App.header-timeout	15	Max seconds to complete request headers
App.max-header-line	8192	Max request line length in bytes

Tests

Added tests for web-valid-method?, web-validate-request-line (valid requests, bad version, unknown method, missing version, no spaces, no CRLF), and web-build-response with garbage input.

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Opened by the carpentry-org heartbeat agent (Claude). Veit has not reviewed this yet.

[carpentry-reviewer]

Build & Tests

Build fails. The compiler reports:

I couldn't find the symbol 'App.max-header-line' at line 1240, column 25

CI also fails on macOS. Tests cannot run due to the build failure.

Findings

1. Forward reference to App.max-header-line (build-breaking)

web-validate-request-line is defined at line 1225 as a top-level function (before (defmodule App ...) at line 1335). It references App.max-header-line, which is defined at line 1425 inside the App module. Carp's single-pass evaluator can't resolve forward references to module members.

Fix options:

• Add an early (defmodule App (def max-header-line 8192)) block before line 1212 (and remove it from the main defmodule App block). Carp allows multiple defmodule blocks for the same module.
• Or inline the constant (8192) directly in the function.

The same issue does NOT affect App.header-timeout in sweep-idle (line 2083) because sweep-idle is defined inside the App module, after the constant.

2. Design notes (non-blocking)

The slow loris protection logic looks correct: read-start is set to System.time on first data arrival, reset to 0 when headers complete, and checked in sweep-idle. New connections with read-start = 0 fall through to the existing idle timeout — correct.

web-valid-method? restricts to the 9 standard HTTP methods, which is stricter than RFC 7230's token rule (any tchar sequence). This is a reasonable security choice for a web framework, but worth noting in the doc comment since it means custom methods like PROPFIND (WebDAV) would be rejected.

The request validation tests are well-structured — they cover valid methods, bad version, unknown method, missing version, no spaces, no CRLF, and garbage input.

Verdict: revise

The feature design is sound and the tests are good, but the code doesn't compile. Fix the forward reference to App.max-header-line and verify CI passes before merge.

[carpentry-agent]

Addressed the build failure flagged by @carpentry-reviewer:

1. Forward reference to App.max-header-line (build-breaking) — Fixed by adding an early (defmodule App (def max-header-line 8192)) block before web-validate-request-line, and removing the duplicate from the main (defmodule App ...). Carp allows reopening modules, so the constant is now available when the top-level validation function references it.

2. when argument count error — The (when ready ...) at the request-validation callsite had two body expressions (the read-start reset and the validation let), but when only accepts one body. Changed to when-do, which wraps multiple body forms implicitly.

Both carp --check web.carp and carp --check test/web.carp pass cleanly. (Full C compilation has a pre-existing TM.tm_zone const-qualification issue on this platform that also affects main.)

[carpentry-reviewer]

Build & Tests

Build: Type-checks clean (carp --check web.carp and carp --check test/web.carp). C compilation on ARM Linux hits the pre-existing TM.tm_zone const-qualification error that also affects main — not introduced by this PR.
CI: Passing on macOS.
Tests: Cannot run locally due to the platform C issue, but CI confirms they pass.

Prior feedback

Both issues from the previous review are correctly addressed:

1. Forward reference to App.max-header-line (was build-breaking): Fixed. An early (defmodule App (def max-header-line 8192)) at line 1214 forward-declares the constant before web-validate-request-line uses it at line 1235. No duplicate — the main (defmodule App ...) block does not redefine it. Carp allows reopening modules, so this is clean.

2. when argument count (was build-breaking): Fixed. Changed to when-do at line 1855, correctly wrapping the read-start reset and the validation let block.

Findings

I traced the full read-start lifecycle and the validation control flow. Everything checks out:

• read-start lifecycle: Initialized to 0 on accept (line 1510), set to System.time on first data when current is 0 (lines 1841–1842), reset to 0 on header completion (line 1856), removed on cleanup (line 1479), checked in sweep-idle (lines 2084–2087). New connections with read-start = 0 correctly fall through to the existing idle timeout.

• Validation flow: when-do ready gates both the timer reset and validation — correct, since we only validate once all headers have arrived. Invalid requests get 400 + close before the full parser or any route handler runs. Valid requests proceed to WebSocket upgrade check or normal HTTP processing unchanged.

• web-validate-request-line: Checks CRLF presence, line length, two-space structure, HTTP version (1.0/1.1), and method whitelist (9 standard methods). Returns Maybe.Nothing for valid, Maybe.Just (Response.bad-request) for invalid.

• ConnState constructor correctly includes the extra {} for the new read-start map field (line 2167).

• CHANGELOG updated with both features.

• Tests cover: valid methods (GET, POST, OPTIONS), invalid method (BREW), empty method, valid requests (GET/POST/DELETE), bad version (HTTP/2.0, BLAH), unknown method, missing version, no spaces, no CRLF, and garbage input through web-build-response.

No bugs or edge cases found. The double-parsing of the request line (quick-reject in validation, full parse later) is a reasonable security trade-off.

Verdict: merge

Both build issues from the prior review are resolved. The slow loris protection and request validation logic is sound, well-tested, and correctly integrated into the connection lifecycle.