fix: missing cookies in sse

[Rouret]

Fix #1434

Problem

When using generator functions (streaming responses) with cookies in ElysiaJS, the set-cookie headers were not being included in the HTTP response headers. This occurred because cookies set via context.cookie['name'].set() before yielding the first chunk were not processed and added to the response headers.

new Elysia().get('/', async function* (context) {
  context.cookie['my-cookie'].set({ value: 'test-value' })
  yield sse({ event: 'my-event', data: { message: 'Hello' } })
})
// The set-cookie header was missing from the response

Root Cause

The createStreamHandler function in src/adapter/utils.ts was not calling handleSet() to process cookies and other context properties before creating the Response object. The handleSet() function is responsible for serializing cookies from context.set.cookie into proper set-cookie headers.

Solution

Added a call to handleSet(set) in the createStreamHandler function before the generator starts processing, ensuring that cookies are properly serialized and included in the response headers.

Summary by CodeRabbit

• Bug Fixes

  • Ensures headers/cookies are applied before the first streamed event, preventing missed mutations at stream start.
  • Preserves multiple Set-Cookie headers in streamed responses (e.g., SSE), improving session and auth reliability.

• Tests

  • Added test verifying that streamed responses include multiple Set-Cookie headers.

[coderabbitai]

Walkthrough

Adjusts stream handling to apply set mutations (headers/cookies) before awaiting the generator’s first yield in createStreamHandler. Adds a test verifying multiple Set-Cookie headers are included in streamed SSE responses when cookies are set prior to the first chunk.

Changes

Cohort / File(s)	Summary
Stream handler header/cookie timing src/adapter/utils.ts	Move handleSet(set) invocation to occur before awaiting the generator’s initial result in createStreamHandler so header/cookie mutations are applied earlier. No signature changes.
SSE cookie header test test/response/stream.test.ts	Add test asserting two Set-Cookie headers are present in an SSE streamed response when two cookies are set before the first yield. No changes to existing tests.

Sequence Diagram(s)

sequenceDiagram
  autonumber
  participant C as Client
  participant H as createStreamHandler
  participant S as handleSet(set)
  participant G as Stream Generator
  participant R as Response

  Note over H: New flow: apply set before first yield
  C->>H: HTTP request (SSE)
  H->>S: Apply headers/cookies from set
  S-->>H: Set mutations applied
  H->>G: Start generator
  G-->>H: First yield (SSE chunk)
  H->>R: Send headers (incl. Set-Cookie) + first chunk
  loop Subsequent chunks
    G-->>H: Next yield
    H-->>R: Stream chunk
  end
  G-->>H: Complete
  H-->>C: Stream closed

Loading

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

I nudge the stream before it flows,
Set-cookie crumbs on breezy rows;
Two sweet treats in headers ride,
As events downstream gently glide.
Thump-thump! my paws approve the art—
Cookies first, then stories start. 🍪🐇

Pre-merge checks and finishing touches

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title succinctly describes the fix for missing cookies in SSE streaming responses and aligns with the primary change of invoking handleSet to include Set-Cookie headers before the first chunk is sent.
Linked Issues Check	✅ Passed	The implementation addresses issue #1434 by calling handleSet before processing the first yield so that cookies are serialized into Set-Cookie headers, and the added test verifies the presence of multiple Set-Cookie headers in the streamed response.
Out of Scope Changes Check	✅ Passed	All changes are directly focused on adding handleSet for cookies in the streaming handler and introducing a corresponding test; no unrelated files or logic were modified.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

• 📝 Generate Docstrings

🧪 Generate unit tests

• Create PR with unit tests
• Post copyable unit tests in a comment

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between eb4d126 and 84018f3.

📒 Files selected for processing (2)

• src/adapter/utils.ts (1 hunks)
• test/response/stream.test.ts (1 hunks)

🧰 Additional context used

🧬 Code graph analysis (2)

src/adapter/utils.ts (1)

src/cookies.ts (1)

• set (251-261)

test/response/stream.test.ts (2)

src/utils.ts (1)

• sse (1109-1167)

test/utils.ts (1)

• req (1-2)

🔇 Additional comments (2)

src/adapter/utils.ts (1)

162-162: LGTM! Fix resolves the core issue with cookie serialization timing.

The addition of handleSet(set) before awaiting the initial generator result ensures cookies are serialized into Set-Cookie headers before the Response object is created. This addresses the root cause where cookies set via context.cookie['name'].set() weren't being serialized for streaming responses.

test/response/stream.test.ts (1)

99-122: Comprehensive test validates the fix for multiple cookie headers in streaming responses.

The test correctly verifies that:

1. Multiple cookies can be set before the first yield in a streaming handler
2. Both cookies are serialized into separate Set-Cookie headers
3. The SSE streaming functionality works alongside cookie handling

This test case aligns perfectly with the PR objectives and provides regression coverage for issue #1434.

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