[duplicate-code] Duplicate Code Pattern: HTTP Response Writer Status-Code Wrapper in server and tracing packages

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Part of duplicate code analysis: #6070

Summary

internal/server/response_writer.go (responseWriter) and internal/tracing/http.go (statusResponseWriter) both independently implement an http.ResponseWriter wrapper that captures the HTTP status code via WriteHeader. The core status-capture logic (~12 lines) is structurally identical in both types.

Duplication Details

Pattern: HTTP response-writer wrapper with status-code capture

• Severity: Low-Medium
• Occurrences: 2 types with overlapping WriteHeader/Write implementation
• Locations:
  • internal/server/response_writer.go (lines 14–50) — responseWriter
  • internal/tracing/http.go (lines 18–48) — statusResponseWriter

Shared structural code in both types:

// Both types embed http.ResponseWriter and capture statusCode
type xWriter struct {
    http.ResponseWriter
    statusCode int
}
func (w *xWriter) WriteHeader(code int) {
    w.statusCode = code
    w.ResponseWriter.WriteHeader(code)
}
// server/response_writer.go also captures body bytes
// tracing/http.go also has Unwrap() for interface delegation

Key differences:

• responseWriter additionally captures the response body in a bytes.Buffer and exposes Body() / StatusCode() accessors (used for debug logging)
• statusResponseWriter additionally implements Unwrap() so that http.ResponseController callers can access optional interfaces (e.g. http.Flusher)

Impact Analysis

• Maintainability: A subtle behavioral change to WriteHeader (e.g. handling implicit 200 on first Write) was added to statusResponseWriter but not to responseWriter, showing the types have already diverged
• Bug Risk: Low — the two types serve different purposes, but sharing a base could prevent future divergence bugs
• Code Bloat: ~12 duplicated lines

Refactoring Recommendations

1. Extract a baseResponseWriter in internal/httputil/

   // BaseResponseWriter wraps http.ResponseWriter and captures the status code.
   type BaseResponseWriter struct {
       http.ResponseWriter
       StatusCode int
   }
   func (w *BaseResponseWriter) WriteHeader(code int) {
       w.StatusCode = code
       w.ResponseWriter.WriteHeader(code)
   }
   func (w *BaseResponseWriter) Write(b []byte) (int, error) {
       if w.StatusCode == 0 { w.StatusCode = http.StatusOK }
       return w.ResponseWriter.Write(b)
   }
   func (w *BaseResponseWriter) Unwrap() http.ResponseWriter { return w.ResponseWriter }

   • server/response_writer.go embeds httputil.BaseResponseWriter and adds body capture
   • tracing/http.go embeds httputil.BaseResponseWriter (or uses it directly)
   • Estimated effort: 1–2 hours

2. Alternative (lower effort): Add Unwrap() to server/response_writer.go to bring it in line with statusResponseWriter without a full extraction, reducing behavioral divergence.

Implementation Checklist

• Review duplication findings
• Decide on extraction vs alignment approach
• Implement chosen approach
• Run make agent-finished to verify no regressions

Parent Issue

See parent analysis report: #6070
Related to #6070

Generated by Duplicate Code Detector · ● 1.9M · ◷

• expires on May 27, 2026, 3:41 AM UTC