Encode empty-data SSE events as dispatchable events by fubhy · Pull Request #6975 · Effect-TS/effect

fubhy · 2026-08-04T12:17:35Z

Summary

Encoding and reparsing an accepted event whose data is the empty string produces no event.

Important

This PR starts with focused failing reproduction tests. Add the implementation fix to this same branch; CI is expected to fail until that fix is included.

SSE encoder drops empty-data events

Module: encoding/Sse
Audit ID: unstable-ai-cli-sse-empty-data-event-dropped
Severity / confidence: medium / high

What happens

Encoding and reparsing an accepted event whose data is the empty string produces no event.

Why it happens

The encoder omits data: for empty data and writes only a blank terminator, which the parser ignores while its data buffer is empty.

Expected behavior

Every accepted Event, including data equal to the empty string, renders as an SSE event that can be dispatched.

Relevant implementation

These links and excerpts are pinned to audit base c9b56ab507f224426ee8388dc450da447ec4715f.

packages/effect/src/unstable/encoding/Sse.ts:654-669

View problematic code at packages/effect/src/unstable/encoding/Sse.ts:654-669

export const encoder: Encoder = {
  write(event: AnyEvent): string {
    switch (event._tag) {
      case "Event": {
        let data = ""
        if (event.id !== undefined) {
          data += `id: ${event.id}\n`
        }
        if (event.event !== "message") {
          data += `event: ${event.event}\n`
        }
        if (event.data !== "") {
          data += `data: ${event.data.replace(/\n/g, "\ndata: ")}\n`
        }
        return data + "\n"
      }

View exact lines on GitHub

Reproduction

pnpm test --run packages/effect/test/unstable/encoding/Sse.test.ts

Observed failure: FAIL: the round-trip produced no event.

Implementation handoff

The initial reproduction tests on this branch are the regression specification for the implementation fix that should follow in this PR.

Start with the pinned implementation excerpts and the Why it happens analysis above.
Change the implementation so it satisfies the stated Expected behavior; do not weaken or remove the reproduction assertions.
Run the focused reproduction command(s) and confirm the observed failures become passing tests:

pnpm test --run packages/effect/test/unstable/encoding/Sse.test.ts

Run the affected package's existing tests, then the repository lint and type checks before requesting review.

Audit provenance

Audit base: c9b56ab507f224426ee8388dc450da447ec4715f
Reproduction base: c9b56ab507f224426ee8388dc450da447ec4715f
Findings: unstable-ai-cli-sse-empty-data-event-dropped
Initial patch: focused reproduction tests; implementation fix pending

Closes EFF-416

changeset-bot · 2026-08-04T12:17:40Z

🦋 Changeset detected

Latest commit: 8ee0d59

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 30 packages

Name	Type
effect	Patch
@effect/ai-anthropic	Patch
@effect/ai-openai	Patch
@effect/ai-openai-compat	Patch
@effect/ai-openrouter	Patch
@effect/atom-react	Patch
@effect/atom-solid	Patch
@effect/atom-vue	Patch
@effect/docgen	Patch
@effect/doctest	Patch
@effect/openapi-generator	Patch
@effect/opentelemetry	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-deno	Patch
@effect/platform-node	Patch
@effect/platform-node-shared	Patch
@effect/sql-clickhouse	Patch
@effect/sql-d1	Patch
@effect/sql-libsql	Patch
@effect/sql-mssql	Patch
@effect/sql-mysql2	Patch
@effect/sql-pg	Patch
@effect/sql-pglite	Patch
@effect/sql-sqlite-bun	Patch
@effect/sql-sqlite-do	Patch
@effect/sql-sqlite-node	Patch
@effect/sql-sqlite-react-native	Patch
@effect/sql-sqlite-wasm	Patch
@effect/vitest	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

pullfrog

Important

This PR lands the regression test, but the implementation fix described in the title and PR body is still missing. The test correctly fails until the encoder change is added.

Reviewed changes

Added a single regression round-trip test in packages/effect/test/unstable/encoding/Sse.test.ts that verifies an Event with data: "" round-trips through Sse.encoder and Sse.makeParser.

⚠️ Implementation fix is required before merge

The diff currently only adds the failing test. Sse.encoder at packages/effect/src/unstable/encoding/Sse.ts:665 still skips the data: field when event.data === "", so the event dispatches nothing. To satisfy the expected behavior stated in the PR body, remove the if (event.data !== "") guard so an empty data value still emits data: and makeParser will dispatch it.

⚠️ Changeset needed

Because the eventual fix changes runtime encoding behavior, add a changeset under .changeset/ before merging.

^{｜ ⚠️ this action is pinned to a commit SHA, which freezes the cleanup step — switch to @v0 or keep the SHA fresh with Dependabot ｜ Fix it ➔ ｜ View workflow run ｜ Using Kimi K2 (free via Pullfrog for OSS) ｜ 𝕏}

pullfrog

✅ No new issues found.

Reviewed changes

Removed the if (event.data !== "") guard in packages/effect/src/unstable/encoding/Sse.ts so an empty data value still emits a data: line and makeParser dispatches the event.
Added a changeset under .changeset/empty-geckos-dispatch.md describing the patch-level runtime behavior change.
The regression test added in the previous commit now passes.

^{｜ ⚠️ this action is pinned to a commit SHA, which freezes the cleanup step — switch to @v0 or keep the SHA fresh with Dependabot ｜ View workflow run ｜ Using Kimi K2 (free via Pullfrog for OSS) ｜ 𝕏}

github-actions · 2026-08-04T23:43:05Z

Bundle Size Analysis

Generated from PR build output; treat the content below as untrusted.

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`metric.ts`	8.98 KB	8.98 KB	0.00 KB (0.00%)
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`schema-representation-roundtrip.ts`	25.29 KB	25.29 KB	0.00 KB (0.00%)
`schema-string-transformation.ts`	13.38 KB	13.38 KB	0.00 KB (0.00%)
`schema-string.ts`	10.94 KB	10.94 KB	0.00 KB (0.00%)
`schema-template-literal.ts`	15.17 KB	15.17 KB	0.00 KB (0.00%)
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`schema-toCodecJson.ts`	19.18 KB	19.18 KB	0.00 KB (0.00%)
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`schema-toJsonSchemaDocument.ts`	22.60 KB	22.60 KB	0.00 KB (0.00%)
`schema-toRepresentation.ts`	19.52 KB	19.52 KB	0.00 KB (0.00%)
`schema.ts`	18.41 KB	18.41 KB	0.00 KB (0.00%)
`stm.ts`	12.63 KB	12.63 KB	0.00 KB (0.00%)
`stream.ts`	9.80 KB	9.80 KB	0.00 KB (0.00%)

pullfrog

✅ No new issues found.

Reviewed changes

The new head rebases the previously approved fix onto latest main and splits it into two commits without changing the net diff:

Removed the if (event.data !== "") guard in packages/effect/src/unstable/encoding/Sse.ts so an empty data value still emits a data: line and makeParser dispatches the event.
Added a regression test in packages/effect/test/unstable/encoding/Sse.test.ts that verifies an Event with data: "" round-trips through Sse.encoder and Sse.makeParser.
Added a changeset under .changeset/empty-geckos-dispatch.md describing the patch-level runtime behavior change.

Validation run: pnpm --filter effect test --run test/unstable/encoding/Sse.test.ts, pnpm lint-fix, and pnpm check all pass.

^{｜ ⚠️ this action is pinned to a commit SHA, which freezes the cleanup step — switch to @v0 or keep the SHA fresh with Dependabot ｜ View workflow run ｜ Using Kimi K2 (free via Pullfrog for OSS) ｜ 𝕏}

fubhy added the audit Findings originating from the Effect runtime correctness audit label Aug 4, 2026

effect-slopcop Bot added 4.0 bug Something isn't working labels Aug 4, 2026

pullfrog Bot requested changes Aug 4, 2026

View reviewed changes

pullfrog Bot approved these changes Aug 4, 2026

View reviewed changes

tim-smart force-pushed the audit/repro-unstable-encoding-sse-empty-data branch from 232cca3 to d9cc206 Compare August 4, 2026 23:31

tim-smart enabled auto-merge (squash) August 4, 2026 23:33

pullfrog Bot approved these changes Aug 4, 2026

View reviewed changes

fubhy and others added 2 commits August 5, 2026 00:02

Encode empty-data SSE events as dispatchable events

9e3f704

Fix empty-data SSE event encoding

8ee0d59

tim-smart force-pushed the audit/repro-unstable-encoding-sse-empty-data branch from d9cc206 to 8ee0d59 Compare August 5, 2026 00:03

tim-smart merged commit abcbb2a into main Aug 5, 2026
18 of 19 checks passed

tim-smart deleted the audit/repro-unstable-encoding-sse-empty-data branch August 5, 2026 00:20

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Encode empty-data SSE events as dispatchable events - #6975

Encode empty-data SSE events as dispatchable events#6975
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audit/repro-unstable-encoding-sse-empty-data

fubhy commented Aug 4, 2026 •

edited by tim-smart

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fubhy commented Aug 4, 2026 • edited by tim-smart Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

SSE encoder drops empty-data events

What happens

Why it happens

Expected behavior

Relevant implementation

Reproduction

Implementation handoff

Audit provenance

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⚠️ Implementation fix is required before merge

⚠️ Changeset needed

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fubhy commented Aug 4, 2026 •

edited by tim-smart

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