fix: handle undefined choice in together ai finish reason transform

[VisargD]

Description

Motivation

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

How Has This Been Tested?

• Unit Tests
• Integration Tests
• Manual Testing

Screenshots (if applicable)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Related Issues

[matter-code-review]

Description

Summary By MatterAI

🔄 What Changed

• src/providers/together-ai/chatComplete.ts: Added optional chaining (?.) to safely access parsedChunk.choices[0]?.finish_reason before calling transformFinishReason, preventing errors if choices[0] is undefined.
• src/handlers/streamHandler.ts: Enhanced error logging by including the proxyProvider variable in console.error messages for both stream processing and writer closing failures, providing more context for debugging.

🔍 Impact of the Change

• Improves the robustness of the Together AI chat completion stream handling by preventing potential runtime errors (TypeError) when choices[0] is missing in a stream chunk.
• Enhances observability and debuggability for stream processing and writer closing operations by providing crucial context (proxyProvider) in error logs.

📁 Total Files Changed

• src/handlers/streamHandler.ts: Enhanced error logging for stream processing.
• src/providers/together-ai/chatComplete.ts: Implemented safer access to finish reason with optional chaining.

🧪 Test Added

N/A

🔒Security Vulnerabilities

N/A

Motivation

To prevent crashes due to undefined choices[0] in Together AI stream responses and to improve error diagnostics by adding proxyProvider to error logs.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

How Has This Been Tested?

• Unit Tests
• Integration Tests
• Manual Testing

Screenshots (if applicable)

N/A

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Related Issues

.

Tip

Quality Recommendations

1. Add unit tests for together-ai/chatComplete.ts to specifically cover scenarios where parsedChunk.choices[0] might be undefined, ensuring the optional chaining works as expected.

2. Consider implementing structured logging (e.g., using a dedicated logging library) instead of console.error for better parseability and analysis in production environments.

Tanka Poem ♫

A small fix, a gentle ?.
No more crashes, streams flow free.
Logs now richer,
Context clear, errors flee.
Code robust, for all to see. ✨

Sequence Diagram

sequenceDiagram
    participant TogetherAI as TogetherAI Stream
    participant ChatComplete as chatComplete.ts
    participant Utils as transformFinishReason

    TogetherAI->>+ChatComplete: Receive Stream Chunk (chunk)
    ChatComplete->>ChatComplete: JSON.parse(chunk) -> parsedChunk
    
    alt parsedChunk.choices[0] is defined
        ChatComplete->>+Utils: transformFinishReason(parsedChunk.choices[0].finish_reason, strictOpenAiCompliance)
        Utils-->>-ChatComplete: transformedFinishReason
        ChatComplete->>ChatComplete: Use transformedFinishReason
    else parsedChunk.choices[0] is undefined
        ChatComplete->>ChatComplete: Handle undefined choice (e.g., no finish reason)
    end
    ChatComplete-->>-TogetherAI: Processed Chunk Data

Loading

[matter-code-review]

Good defensive programming fix for undefined choice access, plus improved error logging with provider context.

[matter-code-review]

🐛 Bug Fix

Issue: Potential runtime crash when parsedChunk.choices[0] is undefined - accessing finish_reason property on undefined would throw TypeError
Fix: Added optional chaining operator to safely access finish_reason property
Impact: Prevents runtime crashes when Together AI returns empty choices array or undefined first choice

Suggested change

	const finishReason = parsedChunk.choices[0]?.finish_reason
	const finishReason = parsedChunk.choices[0]?.finish_reason

[matter-code-review]

🛠️ Code Refactor

Issue: Error logs lack context about which provider failed, making debugging difficult in multi-provider scenarios
Fix: Added proxyProvider parameter to error logs for better traceability
Impact: Improves debugging efficiency by identifying which provider caused stream processing failures

Suggested change

	console.error('Error during stream processing:', proxyProvider, error);
	console.error('Error during stream processing:', proxyProvider, error);

[matter-code-review]

🛠️ Code Refactor

Issue: Writer close error logs lack provider context for debugging
Fix: Added proxyProvider parameter to close error logs with proper formatting
Impact: Consistent error logging pattern across all stream handler error cases

Suggested change

	console.error(
	'Failed to close the writer:',
	proxyProvider,
	closeError
	);
	console.error(
	'Failed to close the writer:',
	proxyProvider,
	closeError
	);

[matter-code-review]

🛠️ Code Refactor

Issue: Duplicate error logging pattern - second occurrence also lacks provider context
Fix: Added proxyProvider parameter for consistency with first error handler
Impact: Maintains consistent error logging across all stream processing error cases

Suggested change

	console.error('Error during stream processing:', proxyProvider, error);
	console.error('Error during stream processing:', proxyProvider, error);

[matter-code-review]

🛠️ Code Refactor

Issue: Second writer close error handler also lacks provider context
Fix: Added proxyProvider parameter to complete the consistent error logging pattern
Impact: All error cases now include provider information for better debugging

Suggested change

	console.error(
	'Failed to close the writer:',
	proxyProvider,
	closeError
	);
	console.error(
	'Failed to close the writer:',
	proxyProvider,
	closeError
	);