HTTP: cancel unread lazy fetch bodies for HEAD responses

[vladislav-miroshnikov]

What does this PR do?

Fixes #43970. An untouched fetch Response can still have a pending body producer when a HEAD response discards it, so there is no ReadableStream to cancel and the upstream request stays open. Take and cancel that pending FetchResponseBody producer while preserving the pending-consumer guard and the existing stream cancellation path.

This covers the untouched-fetch case explicitly left outside #43973; materialized stream behavior is unchanged.

How did you verify your code works?

The new regression reproduces the missing upstream abort on Bun 1.4.2 and passes on the patched main debug build. It sends three HEAD requests, waits for the upstream abort events and checks a later GET. The existing serve, reused-response and pending-promise-abort suites pass 368 tests with 1 skip, including the held response.text() HEAD case. Local HTTP tests run without the host proxy variables.

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[vladislav-miroshnikov]

@Jarred-Sumner, could you check the pending-producer cleanup here? This keeps the consumer guard from #44014 and only adds cancellation for an unmaterialized FetchResponseBody. The adjacent response.text() HEAD regression passes with the new upstream-abort test.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: oven-sh/bun/.coderabbit.yaml

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 2db73c05-b988-4040-a03e-692cc75f295d

📥 Commits

Reviewing files that changed from the base of the PR and between 9f70da0 and 0c14a9c.

📒 Files selected for processing (2)

• src/runtime/server/RequestContext.rs
• test/js/bun/http/serve.test.ts

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 7 remain after this review.

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Walkthrough

When a HEAD response has a Locked body without a readable stream, cancel_unread_body now cancels its producer if it is a FetchResponseBody. A regression test checks that proxied upstream requests abort and a separate response still succeeds.

Changes

HEAD response body cancellation

Layer / File(s)	Summary
Cancel pending fetch response bodies src/runtime/server/RequestContext.rs, test/js/bun/http/serve.test.ts	When no readable stream exists, cancel_unread_body takes and cancels the producer only if it is a FetchResponseBody. The test checks that three proxied HEAD requests abort upstream requests, return empty 200 responses, and do not prevent a separate /ok response.

Suggested reviewers: jarred-sumner

Priority: ➖ Normal

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 0c14a

The HEAD-response cleanup change and its regression coverage present no identified blocker to merging after normal checks.

Security Architecture Review

Security architecture risk: 🔵 Low · up to 0c14a

The change addresses upstream requests left open by discarded HEAD response bodies. The reviewed path preserves active body readers and confines cancellation to the response’s own fetch operation. No security issue was identified in that path, though security coverage is not complete.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — A client can reach this cleanup through an application’s HEAD response path, but the new cancellation follows the producer attached to that discarded response rather than selecting another request’s transport.

Trust Boundaries and Controls

• observed — Consumer ownership remains the first control: cleanup returns for an active locked-body consumer and cancels only an unconsumed FetchResponseBody producer when no stream exists.

Resilience and Maintainability Implications

• observed — Repeated transport aborts do not schedule another shutdown, and abandonment still releases response-body resources.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: canceling unread lazy fetch bodies for HEAD responses.
Description check	✅ Passed	The description includes both required sections. It explains the problem, implementation, scope, and verification results with sufficient detail.
Linked Issues check	✅ Passed	Issue #43970 requires cancellation of an unmaterialized pending fetch body for proxied HEAD responses. The PR updates cancel_unread_body to cancel a locked FetchResponseBody producer when no reada…
Out of Scope Changes check	✅ Passed	The PR changes only src/runtime/server/RequestContext.rs and the related serve.test.ts test. The source change implements the issue fix. The test verifies upstream abort and connection reuse. No u…

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