bun.sh/NODEJS_HTTP_HEADERS_FIX.md

Fix for Node.js HTTP Automatic Headers Issue (BUN-13559)

Problem

The Node.js test test-http-automatic-headers.js was failing because Bun's HTTP server implementation was not automatically adding standard HTTP headers that Node.js adds by default:

• connection: keep-alive for HTTP/1.1 connections
• content-length: 0 when no body is sent
• date header with current timestamp

The test was specifically failing on this assertion:

assert.strictEqual(res.headers.connection, 'keep-alive');

Root Cause

The issue was in the NodeHTTPServer__writeHead function in src/bun.js/bindings/NodeHTTP.cpp. This function only wrote headers that were explicitly provided by the user, but didn't add the automatic headers that Node.js adds by default.

Solution

Changes Made

1. Modified NodeHTTPServer__writeHead function: Added logic to track which headers are explicitly set and automatically add missing standard headers.

2. Updated writeFetchHeadersToUWSResponse function: Extended it to track explicitly set headers when using FetchHeaders objects.

3. Added header tracking: The function now tracks whether connection, content-length, and date headers are explicitly set.

4. Added automatic header logic: After processing all explicit headers, the function adds:

   • Connection: keep-alive if not explicitly set
   • Content-Length: 0 if not explicitly set (for responses with no body)
   • Date: <current_timestamp> if not explicitly set

Files Modified

• src/bun.js/bindings/NodeHTTP.cpp: Main implementation changes
• test/js/node/test/parallel/test-http-automatic-headers.js: Copied Node.js test

Technical Details

The fix ensures Node.js compatibility by:

1. Connection Header: Automatically adds Connection: keep-alive for HTTP/1.1 unless explicitly overridden
2. Content-Length Header: Adds Content-Length: 0 for responses that don't explicitly set it (matching Node.js behavior for empty responses)
3. Date Header: Adds current GMT timestamp in RFC format
4. Backward Compatibility: Only adds headers when they're not explicitly set, preserving user-defined values

The implementation handles both regular JavaScript objects and FetchHeaders objects used for header management.

Testing

The test test/js/node/test/parallel/test-http-automatic-headers.js now passes, verifying that:

• Custom headers (x-date, x-connection, x-content-length) are preserved
• Automatic headers (connection, content-length, date) are added when not explicitly set
• The behavior matches Node.js exactly

This fix improves Node.js compatibility for HTTP server responses and resolves the failing test case.