http: sort header keys when writing Response or Request to wire

R=rsc
CC=golang-dev
https://golang.org/cl/203050

src/pkg/http/request.go

@@ -49,6 +49,8 @@ type badStringError struct {
 
 func (e *badStringError) String() string { return fmt.Sprintf("%s %q", e.what, e.str) }
 
+var reqExcludeHeader = map[string]int{"Host": 0, "User-Agent": 0, "Referer": 0}
+
 // A Request represents a parsed HTTP request header.
 type Request struct {
 	Method     string // GET, POST, PUT, etc.
@@ -169,14 +171,7 @@ func (req *Request) Write(w io.Writer) os.Error {
 	// from Request, and introduce Request methods along the lines of
 	// Response.{GetHeader,AddHeader} and string constants for "Host",
 	// "User-Agent" and "Referer".
-	for k, v := range req.Header {
-		// Host, User-Agent, and Referer were sent from structure fields
-		// above; ignore them if they also appear in req.Header.
-		if k == "Host" || k == "User-Agent" || k == "Referer" {
-			continue
-		}
-		io.WriteString(w, k+": "+v+"\r\n")
-	}
+	writeSortedKeyValue(w, req.Header, reqExcludeHeader)
 
 	io.WriteString(w, "\r\n")
 

src/pkg/http/response.go

@@ -8,12 +8,16 @@ package http
 
 import (
 	"bufio"
+	"fmt"
 	"io"
 	"os"
+	"sort"
 	"strconv"
 	"strings"
 )
 
+var respExcludeHeader = map[string]int{}
+
 // Response represents the response from an HTTP request.
 //
 type Response struct {
@@ -455,9 +459,7 @@ func (resp *Response) Write(w io.Writer) os.Error {
 	}
 
 	// Rest of header
-	for k, v := range resp.Header {
-		io.WriteString(w, k+": "+v+"\r\n")
-	}
+	writeSortedKeyValue(w, resp.Header, respExcludeHeader)
 
 	// End-of-header
 	io.WriteString(w, "\r\n")
@@ -491,3 +493,19 @@ func (resp *Response) Write(w io.Writer) os.Error {
 	// Success
 	return nil
 }
+
+func writeSortedKeyValue(w io.Writer, kvm map[string]string, exclude map[string]int) {
+	kva := make([]string, len(kvm))
+	i := 0
+	for k, v := range kvm {
+		if _, exc := exclude[k]; !exc {
+			kva[i] = fmt.Sprint(k + ": " + v + "\r\n")
+			i++
+		}
+	}
+	kva = kva[0:i]
+	sort.SortStrings(kva)
+	for _, l := range kva {
+		io.WriteString(w, l)
+	}
+}