http: prevent DumpRequest from adding implicit headers

Fixes #2272

R=rsc
CC=golang-dev
https://golang.org/cl/5043051

src/pkg/http/dump.go

@@ -44,7 +44,7 @@ func DumpRequest(req *Request, body bool) (dump []byte, err os.Error) {
 			return
 		}
 	}
-	err = req.Write(&b)
+	err = req.dumpWrite(&b)
 	req.Body = save
 	if err != nil {
 		return

src/pkg/http/request.go

@@ -64,13 +64,20 @@ func (e *badStringError) String() string { return fmt.Sprintf("%s %q", e.what, e
 
 // Headers that Request.Write handles itself and should be skipped.
 var reqWriteExcludeHeader = map[string]bool{
-	"Host":              true,
+	"Host":              true, // not in Header map anyway
 	"User-Agent":        true,
 	"Content-Length":    true,
 	"Transfer-Encoding": true,
 	"Trailer":           true,
 }
 
+var reqWriteExcludeHeaderDump = map[string]bool{
+	"Host":              true, // not in Header map anyway
+	"Content-Length":    true,
+	"Transfer-Encoding": true,
+	"Trailer":           true,
+}
+
 // A Request represents a parsed HTTP request header.
 type Request struct {
 	Method string   // GET, POST, PUT, etc.
@@ -283,6 +290,53 @@ func (req *Request) WriteProxy(w io.Writer) os.Error {
 	return req.write(w, true)
 }
 
+func (req *Request) dumpWrite(w io.Writer) os.Error {
+	urlStr := req.RawURL
+	if urlStr == "" {
+		urlStr = valueOrDefault(req.URL.EncodedPath(), "/")
+		if req.URL.RawQuery != "" {
+			urlStr += "?" + req.URL.RawQuery
+		}
+	}
+
+	bw := bufio.NewWriter(w)
+	fmt.Fprintf(bw, "%s %s HTTP/%d.%d\r\n", valueOrDefault(req.Method, "GET"), urlStr,
+		req.ProtoMajor, req.ProtoMinor)
+
+	host := req.Host
+	if host == "" && req.URL != nil {
+		host = req.URL.Host
+	}
+	if host != "" {
+		fmt.Fprintf(bw, "Host: %s\r\n", host)
+	}
+
+	// Process Body,ContentLength,Close,Trailer
+	tw, err := newTransferWriter(req)
+	if err != nil {
+		return err
+	}
+	err = tw.WriteHeader(bw)
+	if err != nil {
+		return err
+	}
+
+	err = req.Header.WriteSubset(bw, reqWriteExcludeHeaderDump)
+	if err != nil {
+		return err
+	}
+
+	io.WriteString(bw, "\r\n")
+
+	// Write body and trailer
+	err = tw.WriteBody(bw)
+	if err != nil {
+		return err
+	}
+	bw.Flush()
+	return nil
+}
+
 func (req *Request) write(w io.Writer, usingProxy bool) os.Error {
 	host := req.Host
 	if host == "" {