net/http: don't modify Request Method's case

This fixes a data race (usually just harmlessly updating
"GET" to "GET"), but also follows RFC 2616 Sec 5.1.1 which
says that the request method is case-sensitive.

Fixes #3881

R=golang-dev, rsc, dsymonds
CC=golang-dev
https://golang.org/cl/6446063

src/pkg/net/http/response.go

@@ -107,7 +107,6 @@ func ReadResponse(r *bufio.Reader, req *Request) (resp *Response, err error) {
 	resp = new(Response)
 
 	resp.Request = req
-	resp.Request.Method = strings.ToUpper(resp.Request.Method)
 
 	// Parse the first line of the response.
 	line, err := tp.ReadLine()
@@ -188,11 +187,6 @@ func (r *Response) ProtoAtLeast(major, minor int) bool {
 //
 func (r *Response) Write(w io.Writer) error {
 
-	// RequestMethod should be upper-case
-	if r.Request != nil {
-		r.Request.Method = strings.ToUpper(r.Request.Method)
-	}
-
 	// Status line
 	text := r.Status
 	if text == "" {

src/pkg/net/http/serve_test.go

@@ -1188,6 +1188,22 @@ func TestServerGracefulClose(t *testing.T) {
 	<-writeErr
 }
 
+func TestCaseSensitiveMethod(t *testing.T) {
+	ts := httptest.NewServer(HandlerFunc(func(w ResponseWriter, r *Request) {
+		if r.Method != "get" {
+			t.Errorf(`Got method %q; want "get"`, r.Method)
+		}
+	}))
+	defer ts.Close()
+	req, _ := NewRequest("get", ts.URL, nil)
+	res, err := DefaultClient.Do(req)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	res.Body.Close()
+}
+
 // goTimeout runs f, failing t if f takes more than ns to complete.
 func goTimeout(t *testing.T, d time.Duration, f func()) {
 	ch := make(chan bool, 2)