Summary

Fixes a critical bug in the markdown file download link handler that prevented files from being downloaded correctly through markdown links.

The issue occurred in MarkdownComponents.tsx where the file_id and filename were being extracted incorrectly from URLs in the format files/{userId}/{file_id}. The .pop() method was applied twice in reverse order, causing:

• The userId to be assigned to the file_id variable
• The actual file_id to be used as the filename

This resulted in download failures with 404 errors because the API endpoint was being called with /api/files/download/{userId}/{userId} instead of the correct /api/files/download/{userId}/{file_id}.

Root cause: When splitting the URL path and using .pop() twice, the values were extracted in reverse order (last element first, then second-to-last), inverting the userId and file_id.

Solution:

• Changed to directly access parts[2] to get the correct file_id
• Use the markdown link text (children) as the filename for better UX
• Added children to the useMemo dependency array to properly track changes

This fix enables MCP tools and other integrations to serve files through LibreChat's download system using markdown links.

Change Type

• 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)
• This change requires a documentation update
• Translation update

Testing

Test Process

1. Create a file in the uploads directory: /app/uploads/{userId}/{filename}
2. Create a corresponding MongoDB file record with:
   • file_id: UUID v4
   • user: MongoDB ObjectId matching the user
   • filepath: /uploads/{userId}/{filename}
   • source: "local"
3. Generate a markdown link in a chat message: [filename.ext](files/{userId}/{file_id})
4. Click the link
5. Verify the file downloads correctly

Test Configuration:

• Browser: Chrome/Edge/Firefox
• LibreChat instance with local file storage
• MongoDB with file records
• Test file created via MCP tool or manual insertion

Expected Behavior

Before fix:

• Click link → API call to /api/files/download/{userId}/{userId} → 404 error

After fix:

• Click link → API call to /api/files/download/{userId}/{file_id} → File downloads successfully

Checklist

• My code adheres to this project's style guidelines
• I have performed a self-review of my own code
• I have commented in any complex areas of my code
• I have made pertinent documentation changes
• My changes do not introduce new warnings
• I have written tests demonstrating that my changes are effective or that my feature works
• Local unit tests pass with my changes
• Any changes dependent on mine have been merged and published in downstream modules
• A pull request for updating the documentation has been submitted