code review 4620049: http: make Headers be source of truth

src/pkg/http/server.go

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // HTTP server.  See RFC 2616.
 
 // TODO(rsc):
 //      logging
 
 package http
@@ skipping 387 matching lines @@
                 return
         }
 
         // Did the handler supply any info?  Enough?
         if w.written == 0 || w.written >= min {
                 return
         }
 
         // Is it a broken browser?
         var msg string
-        switch agent := w.req.UserAgent; {
+        switch agent := w.req.UserAgent(); {
         case strings.Contains(agent, "MSIE"):
                 msg = "Internet Explorer"
         case strings.Contains(agent, "Chrome/"):
                 msg = "Chrome"
         default:
                 return
         }
         msg += " would ignore this error page if this text weren't here.\n"
 
         // Is it text?  ("Content-Type" is always in the map)
@@ skipping 614 matching lines @@
 func (tw *timeoutWriter) WriteHeader(code int) {
         tw.mu.Lock()
         if tw.timedOut || tw.wroteHeader {
                 tw.mu.Unlock()
                 return
         }
         tw.wroteHeader = true
         tw.mu.Unlock()
         tw.w.WriteHeader(code)
 }