Add AbortSignal support to HTTP requests

[grantfox-oss]

Summary

Allow callers to cancel in-flight SDK requests using an external AbortSignal. This improves integration with browser UI lifecycles, server request handlers, and applications that need user-driven cancellation.

Current Behaviour

HttpClient creates its own AbortController for timeout handling, but HttpRequestOptions does not accept an external signal. Consumers cannot cancel requests when components unmount, route handlers are aborted, or a newer request supersedes an older one.

Expected Behaviour

SDK request options should accept an optional AbortSignal and abort the underlying fetch when either the timeout or the external signal fires.

Suggested Implementation

Add signal?: AbortSignal to HttpRequestOptions. Update HttpClient.request to compose timeout cancellation with external cancellation. Ensure timeout errors and user-initiated aborts can be distinguished where possible.

Files or Areas Likely Affected

• src/http/http.types.ts
• src/http/httpClient.ts
• src/errors/errorCodes.ts
• tests/httpClient.test.ts
• docs/sdk-guide.md

Acceptance Criteria

• HttpRequestOptions accepts an optional AbortSignal
• External aborts cancel the underlying fetch
• Timeout behaviour continues to work as before
• Already-aborted signals fail safely without unnecessary work
• Tests cover timeout, external abort, and successful request paths
• Documentation includes a short cancellation example

Additional Notes

This should complement the existing timeout implementation rather than replacing it.

[Codex723]

I have experience composing AbortSignal cancellation with timeout controllers in TypeScript fetch-based HTTP clients, including distinguishing timeout errors from user-initiated aborts and handling already-aborted signals safely — exactly what's needed here. I'm ready to update HttpRequestOptions, refactor HttpClient.request to merge both signals, add the error codes, write the test coverage for all three paths, and document a cancellation example in the SDK guide.

[OTimileyin]

I'd like to take this on. I've built AbortSignal-aware HTTP clients in TypeScript before, including merging an external signal with an internal timeout controller and distinguishing the two abort causes via the abort reason.

Plan: add signal?: AbortSignal to HttpRequestOptions; compose the timeout and external signals in HttpClient.request (AbortSignal.any with a listener fallback); add a distinct error code for external aborts; short-circuit already-aborted signals before any fetch work. Tests will cover success, timeout, external abort, and the pre-aborted case, and I'll add a brief cancellation example to the SDK guide.

I can have a PR up within 2 days.

[gaiabio12-design]

Hi! I'd like to work on this issue. 🔐

I specialize in TypeScript/JavaScript security tooling and can deliver a PR within 96 hours.

Could you confirm this is available? I'll begin as soon as I hear back. Thanks!

[grantfox-oss]

🦊 GrantFox — @OTimileyin has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #53)
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