REQUEST_HEADER_TOO_LARGE

The REQUEST_HEADER_TOO_LARGE error occurs when the size of the request headers in your function and Routing Middleware exceeds the allowed limits. Specifically, individual request headers must not exceed 16 KB, and the combined size of all headers, including the header names, must not exceed 32 KB.

This issue often arises from excessively large headers in a request. On Vercel, applications may have custom headers, which, if overly large, can trigger this error during server request processing.

Troubleshoot

I'm encountering an error and reviewing the docs at /flg~eyJhbGciOiJIUzI1NiJ9._f7-_v0.H1pbXxc_pwT_uVOl9HPQTOSEJsJVY_sGnFnlG1GD0mM/docs/errors/REQUEST_HEADER_TOO_LARGE to understand what's happening. Please help me resolve this by: 1. **Suggest the fix**: Analyze my codebase context and propose what needs to be changed to resolve this error 2. **Explain the root cause**: Break down why this error occurred: - What was the code actually doing vs. what it needed to do? - What conditions triggered this specific error? - What misconception or oversight led to this? 3. **Teach the concept**: Help me understand the underlying principle: - Why does this error exist and what is it protecting me from? - What's the correct mental model for this concept? - How does this fit into the broader framework/language design? 4. **Show warning signs**: Help me recognize this pattern in the future: - What should I look out for that might cause this again? - Are there similar mistakes I might make in related scenarios? - What code smells or patterns indicate this issue? 5. **Discuss alternatives**: Explain if there are different valid approaches and their trade-offs My goal is to fix the immediate issue while building lasting understanding so I can avoid and resolve similar errors independently in the future.

To troubleshoot this error, follow these steps:

  1. Limit header size: Ensure that the size of each request header does not exceed 16 KB
  2. Manage total header size: Monitor and control the combined size of all headers, keeping it under 32 KB
  3. Review cookies: Since cookies are included in the header, it's crucial to limit their size as part of the overall header size

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