feat(fetch)!: throw when an event stream ends without a close event

[dinwwwh]

toAsyncIteratorObject now only finishes cleanly on a close event, or throws ErrorEvent on an error event. A stream that ends without either now rejects with EventStreamDecoderError('Event Stream ended before complete'). That is the same error a stream gets when it ends partway through a message. The rule also covers a missing (null) body.

Since #125, toEventStream always sends a close event, so streams from standard-server senders are unaffected. This change lets the client actually use that signal: a dropped connection no longer looks like a finished stream.

Why

When the server's pipeline errors, the client already sees a network error. Many cut-offs still reach the client as a clean end of stream, though, and before this change they read as a finished stream. In a local probe with Node's fetch and http2 client:

• an HTTP/1.1 response ended early (res.end())
• a connection-close-delimited body (an HTTP/1.0 hop) whose connection drops
• an HTTP/2 stream ended early, or its session torn down

Proxy timeouts, serverless time limits and graceful shutdowns can end responses in these ways.

Scope

• Applies to @standard-server/fetch, @standard-server/node and @standard-server/aws-lambda, which share the fetch implementation.
• @standard-server/peer is unchanged. It already rejects when its queue closes before a close event.
• Stopping early with return() still resolves as done.

Breaking change

• Reading an event stream that ends without a close event now throws instead of resolving { done: true, value: undefined }.
• This affects SSE senders that never send event: close: generic SSE APIs, and standard-server senders that set the old emptyCloseEventEnabled: false option.
• toAsyncIteratorObject(null) now throws on the first next(). This happens, for example, with a HEAD or 204 response labelled text/event-stream.

Testing

• Updated the tests that relied on a close-less stream finishing quietly. They now either send event: close or expect the error.
• Added an empty-stream case and changed the null-stream case to expect the error.
• pnpm run check (sherif, oxlint, oxfmt, tsc) and the full vitest suite pass locally.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NYpqRELEp4zdwCYWeqRMAj

[pkg-pr-new]

• @standard-server/hono-node-playground
• @standard-server/node-http-playground

@standard-server/aws-lambda

npm i https://pkg.pr.new/@standard-server/aws-lambda@169

@standard-server/core

npm i https://pkg.pr.new/@standard-server/core@169

@standard-server/fastify

npm i https://pkg.pr.new/@standard-server/fastify@169

@standard-server/fetch

npm i https://pkg.pr.new/@standard-server/fetch@169

@standard-server/node

npm i https://pkg.pr.new/@standard-server/node@169

@standard-server/peer

npm i https://pkg.pr.new/@standard-server/peer@169

@standard-server/shared

npm i https://pkg.pr.new/@standard-server/shared@169

commit: 07cbb4e

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[codspeed]

Merging this PR will not alter performance

⚠️ 4 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• json 10KB
• json 10KB
• form data 10KB
• octet stream 10KB

✅ 26 untouched benchmarks
⏩ 108 skipped benchmarks¹

---

_{Comparing claude/serene-wozniak-qotci6 (07cbb4e) with main (7a4134f)}

Footnotes

1. 108 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[pullfrog]

✅ No new issues found.

Reviewed changes

• Event-stream completion now requires an explicit close/error event — toAsyncIteratorObject throws EventStreamDecoderError('Event Stream ended before complete') when the source stream ends without one, instead of silently resolving { done: true }. This is the sole SSE reader for fetch, node, and aws-lambda, so the change applies across those transports.
• Null and empty streams throw on first read — the reader === undefined early return is gone; both a null stream and an immediately-closed stream reject on the first next() and resolve { done: true, value: undefined } on the second, consistent with AsyncIteratorClass's reject-then-done recovery.
• Tests updated — fetch/node event-stream fixtures gained explicit event: close messages; the without close event case now asserts reject-then-done; the old null test was renamed to with null stream and a real with empty stream case added.

The new branch is consistent with packages/core/README.md:185 (close is treated as end of stream) and with the decoder's existing incomplete-message error. The sender toEventStream always emits event: close on iterator completion, so round-trips and the full suite (1374 tests) pass.

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[pullfrog]

✅ No new issues found.

Reviewed changes

Re-reviewed the delta since the prior pullfrog review (f068817).

• README documents the cut-off rule — packages/core/README.md:185 now states that a stream ending without a close or error event is treated as cut off and reading it throws EventStreamDecoderError. This matches the implementation in packages/fetch/src/event-stream.ts:37-39, and the @standard-server/fetch / node / aws-lambda readers that share it.

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[Copilot]

🟢 Approval recommended

The focused change matches the intended breaking contract, preserves cancellation behavior, and has targeted regression coverage.

No open issues 🎉

What changed in this PR

Updates the shared fetch event-stream reader to reject premature termination instead of treating it as successful completion.

Changes:

• Throws EventStreamDecoderError when a stream ends without a terminal event, including empty and null streams.
• Updates tests to expect rejection or supply an explicit close event.

File	Description
packages/​node/​src/​event-stream.test.ts	Adds a close event to the successful-stream fixture.
packages/​fetch/​src/​event-stream.ts	Rejects streams ending without a terminal event.
packages/​fetch/​src/​event-stream.test.ts	Covers premature termination and updates successful-stream fixtures.

_{Review effort: Balanced}