feat: adding default headers and testing for litellm fetcher

[andrewshu2000]

Related GitHub Issue

Closes: #1300

Description

This PR adds support for sending default headers with all LiteLLM API requests to track the originating app. PR #1300 previously added these headers for other providers but they were missed for LiteLLM.

Implementation details:

• Updated RouterProvider to include DEFAULT_HEADERS in the OpenAI client initialization
• Updated LiteLLM model fetcher to include DEFAULT_HEADERS in axios requests
• Updated tests to verify that DEFAULT_HEADERS are included in requests

The implementation ensures that both the OpenAI client used by the RouterProvider (which LiteLLMHandler extends) and the direct axios requests in the LiteLLM model fetcher include the default headers.

Test Procedure

1. Unit Tests: Updated the existing LiteLLM fetcher tests to verify that DEFAULT_HEADERS are included in requests
2. Running Tests: To verify the changes, run:

   cd src
   pnpm vitest run api/providers/fetchers/__tests__/litellm.spec.ts

3. Manual Verification: You can also manually verify the headers are sent by:
   • Setting up a local LiteLLM server
   • Using browser dev tools or a tool like Postman to inspect network requests
   • Confirming that the HTTP-Referer and X-Title headers are present in requests

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes.
• Documentation Impact: I have considered if my changes require documentation updates (see "Documentation Updates" section below).
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Screenshots / Videos

N/A - This change affects backend API requests only, with no visual changes.

Documentation Updates

• No documentation updates are required.

Additional Notes

The DEFAULT_HEADERS object contains:

{
  "HTTP-Referer": "https://github.com/RooVetGit/Roo-Cline",
  "X-Title": "Roo Code"
}

These headers help with tracking and attribution of API requests.

Get in Touch

Discord: 183852721751719936, 189214917033852928

---

Important

Adds DEFAULT_HEADERS to LiteLLM API requests and updates tests to verify header inclusion.

• Behavior:
  • Adds DEFAULT_HEADERS to LiteLLM API requests in litellm.ts and router-provider.ts.
  • Ensures headers are included in both OpenAI client and axios requests.
• Testing:
  • Updates tests in litellm.spec.ts to verify inclusion of DEFAULT_HEADERS in requests.
  • Tests handle various scenarios including missing API keys and unexpected response formats.

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[daniel-lxs]

Thank you @andrewshu2000 for your contribution!

Looks good