Preserve SSE events when CRLF separators span response chunks by PeterDaveHello · Pull Request #1036 · ChatGPTBox-dev/chatGPTBox

PeterDaveHello · 2026-08-06T18:37:58Z

Problem

Response chunk boundaries are independent of SSE line boundaries. When a CRLF sequence is split after the \r, the parser must remember that the next \n belongs to the same line ending instead of treating it as an empty event delimiter.

Persisting that state alone is not sufficient if the scanner restarts from the beginning of the buffer after consuming a line. Re-reading an earlier \r can recreate stale pending-CR state and swallow a real blank line from the next chunk.

Changes

Keep pending CRLF state across feed() calls and clear it on reset().
Resume line scanning from the current unconsumed position instead of re-reading consumed delimiters.
Cover split CRLF pairs, complete CRLF followed by an LF delimiter, mixed line endings, and empty chunks.
Verify that a representative SSE stream produces identical events at every possible single chunk boundary.

Validation

node --test tests/unit/utils/eventsource-parser.test.mjs — 19 tests passed.
An additional data-event enumeration covered 103,464 line-ending and chunking cases with no mismatches against the reference behavior.
node --check passed for the changed JavaScript modules.

Summary by CodeRabbit

Bug Fixes
- Improved streaming event parsing when line breaks are split across incoming data chunks.
- Preserved correct handling of CRLF and LF delimiters, including empty chunks and multiline event data.
Tests
- Added coverage for all chunk-splitting scenarios to ensure consistent event output.

coderabbitai · 2026-08-06T18:38:19Z

📝 Walkthrough

Walkthrough

The parser now preserves trailing-newline state and partial-line offsets across feed() calls. Tests cover CRLF and LF delimiters across chunk boundaries, empty chunks, and multiline event data.

Changes

EventSource parser chunk handling

Layer / File(s)	Summary
Persistent CRLF state and partial-line scanning `src/utils/eventsource-parser.mjs`	The parser stores `discardTrailingNewline` in parser state and resets it with the parser. Line scanning now includes the current buffer position when continuing partial-line parsing.
Chunk-boundary validation `tests/unit/utils/eventsource-parser.test.mjs`	Tests feed multiple chunks and verify split CRLF separators, mixed delimiters, empty chunks, every single-boundary split, and multiline event data.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main fix for preserving SSE events when CRLF separators span response chunks.

✨ Finishing Touches

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🧪 Generate unit tests (beta)

Create PR with unit tests
Commit unit tests in branch fix/sse-crlf-chunk-boundaries

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qodo-code-review · 2026-08-06T18:38:42Z

PR Summary by Qodo

Preserve SSE events when CRLF separators span response chunks

🐞 Bug fix 🧪 Tests 🕐 10-20 Minutes

AI Description

• Persist pending CRLF state across parser.feed() calls to avoid premature event dispatch.
• Reset the pending-CRLF state on explicit parser reset.
• Add regression coverage for CRLF pairs split across streamed chunks.

Diagram

graph TD
  A["HTTP response chunks"] --> B["parser.feed(bytes)"] --> C[("parser buffer + CRLF state")] --> D["SSE line/event parsing"] --> E["onParse(event) callback"]
  R["parser.reset()"]; --> C

High-Level Assessment

Persisting the pending-CRLF flag in parser state is the minimal, correct fix for chunk-boundary-induced delimiter splits. Larger alternatives (e.g., reworking parsing around full line tokenization or using a third-party SSE parser) would add complexity without improving correctness for this specific issue.

Files changed (2) +15 / -1

Bug fix (1) +2 / -1

eventsource-parser.mjsPersist pending CRLF state across feed() calls +2/-1

Persist pending CRLF state across feed() calls

• Moves the pending-CRLF (discard trailing newline) flag out of the per-feed local scope into parser state so a '\r' at the end of one chunk correctly pairs with a leading '\n' in the next chunk. Also ensures the flag is cleared when reset() is called.

src/utils/eventsource-parser.mjs

Tests (1) +13 / -0

eventsource-parser.test.mjsAdd regression test for CRLF split across chunk boundaries +13/-0

Add regression test for CRLF split across chunk boundaries
• Adds a unit test that feeds the parser chunks where both data-line and event-delimiter CRLF sequences are split across calls, asserting only a single complete event is emitted with the expected joined data.
tests/unit/utils/eventsource-parser.test.mjs

qodo-code-review · 2026-08-06T18:39:31Z

Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0)

Great, no issues found!

Qodo reviewed your code and found no material issues that require review

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Previous review results

Review updated until commit 532be8a ⚖️ Balanced

Results up to commit d54be0b ⚖️ Balanced

No changes from previous review

greptile-apps · 2026-08-06T18:40:09Z

Greptile Summary

The PR preserves pending CRLF state across feed() calls so SSE separators split across response chunks are parsed consistently.

Moves trailing-newline state into the parser lifecycle and clears it on reset.
Corrects resumed line scanning to account for the current buffer position.
Adds regression coverage for split CRLF pairs, empty chunks, mixed line endings, and every single split point in a representative stream.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains in the changed parser behavior.

Important Files Changed

Filename	Overview
src/utils/eventsource-parser.mjs	Persists the pending CRLF state between chunks, resets it with parser state, and resumes scanning from the correct buffer-relative offset.
tests/unit/utils/eventsource-parser.test.mjs	Adds focused regression and chunk-boundary equivalence tests for CRLF, LF, CR, mixed separators, and empty chunks.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[feed response chunk] --> B{Pending LF after CR?}
    B -->|Yes, next byte is LF| C[Consume LF as part of CRLF]
    B -->|No| D[Scan buffered SSE line]
    C --> D
    D --> E{Complete line found?}
    E -->|No| F[Retain partial line and parser state]
    E -->|Yes| G[Parse field or dispatch event]
    F --> A
    G --> H{More buffered input?}
    H -->|Yes| B
    H -->|No| A

_{Reviews (2): Last reviewed commit: "Preserve SSE events across arbitrary res..." | Re-trigger Greptile}

Copilot

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR fixes SSE parsing when \r\n line endings are split across multiple feed() chunks, and adds a unit test to prevent regressions.

Changes:

Persist discardTrailingNewline across feed() calls so a \n arriving in a later chunk is correctly discarded after a trailing \r.
Add a unit test that feeds CRLF boundaries across multiple chunks and asserts correct event data output.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/unit/utils/eventsource-parser.test.mjs	Adds a regression test covering CRLF separators split across chunks.
src/utils/eventsource-parser.mjs	Moves `discardTrailingNewline` into parser state so CRLF handling works across `feed()` calls.

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Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Response chunks may split a CRLF pair, so pending-CR state must survive feed() calls. The scanner must also resume at the current unconsumed position; otherwise a consumed CR can restore stale state and swallow a real event delimiter. Persist the pending delimiter state, scan only unconsumed input, and cover mixed line endings, empty chunks, and every single split point in a representative stream.

coderabbitai

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@tests/unit/utils/eventsource-parser.test.mjs`:
- Around line 82-125: Run npm run lint and fix the reported ESLint error in
src/content-script/index.jsx before committing. Keep the parser tests unchanged,
and only leave the lint failure unresolved if the pull request documents the
reason.

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Fix all unresolved CodeRabbit comments on this PR:

Push a commit to this branch (recommended)
Create a new PR with the fixes

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: e40ad88c-3a5f-4241-a6fe-5d95f85f2847

📥 Commits

Reviewing files that changed from the base of the PR and between d54be0b and 532be8a.

📒 Files selected for processing (2)

src/utils/eventsource-parser.mjs
tests/unit/utils/eventsource-parser.test.mjs

🚧 Files skipped from review as they are similar to previous changes (1)

src/utils/eventsource-parser.mjs

chatgpt-codex-connector · 2026-08-08T10:16:20Z

Security review completed. No security issues were found in this pull request.

Reviewed commit: 532be8a154

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Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

qodo-code-review · 2026-08-08T10:51:48Z

Code review by qodo was updated up to the latest commit 532be8a

PeterDaveHello requested a lite review from Copilot August 6, 2026 18:58

Copilot AI reviewed Aug 6, 2026

View reviewed changes

PeterDaveHello requested a balanced review from Copilot August 7, 2026 15:44

Copilot started reviewing on behalf of PeterDaveHello August 7, 2026 15:44 View session

Copilot AI reviewed Aug 7, 2026

View reviewed changes

PeterDaveHello force-pushed the fix/sse-crlf-chunk-boundaries branch from d54be0b to 532be8a Compare August 7, 2026 17:32

coderabbitai Bot reviewed Aug 7, 2026

View reviewed changes

Comment thread tests/unit/utils/eventsource-parser.test.mjs

PeterDaveHello requested a balanced review from Copilot August 8, 2026 10:49

Copilot started reviewing on behalf of PeterDaveHello August 8, 2026 10:50 View session

Copilot AI reviewed Aug 8, 2026

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Preserve SSE events when CRLF separators span response chunks - #1036

Preserve SSE events when CRLF separators span response chunks#1036
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