net/http: zero pad Response status codes to three digits

Go 1.6's HTTP/1.x Transport started enforcing that responses have 3
status digits, per the spec, but we could still write out invalid
status codes ourselves if the called
ResponseWriter.WriteHeader(0). That is bogus anyway, since the minimum
status code is 1xx, but be a little bit less bogus (and consistent)
and zero pad our responses.

Change-Id: I6883901fd95073cb72f6b74035cabf1a79c35e1c
Reviewed-on: https://go-review.googlesource.com/19130
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

4 files changed, 62 insertions, 5 deletions

diff --git a/src/net/http/clientserver_test.go b/src/net/http/clientserver_test.go
index fdc47db60a..c2bab378e3 100644
--- a/src/net/http/clientserver_test.go
+++ b/src/net/http/clientserver_test.go
@@ -1102,6 +1102,27 @@ func testTransportRejectsInvalidHeaders(t *testing.T, h2 bool) {
 	}
 }
 
+// Tests that we support bogus under-100 HTTP statuses, because we historically
+// have. This might change at some point, but not yet in Go 1.6.
+func TestBogusStatusWorks_h1(t *testing.T) { testBogusStatusWorks(t, h1Mode) }
+func TestBogusStatusWorks_h2(t *testing.T) { testBogusStatusWorks(t, h2Mode) }
+func testBogusStatusWorks(t *testing.T, h2 bool) {
+	defer afterTest(t)
+	const code = 7
+	cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
+		w.WriteHeader(code)
+	}))
+	defer cst.close()
+
+	res, err := cst.c.Get(cst.ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.StatusCode != code {
+		t.Errorf("StatusCode = %d; want %d", res.StatusCode, code)
+	}
+}
+
 type noteCloseConn struct {
 	net.Conn
 	closeFunc func()
diff --git a/src/net/http/response.go b/src/net/http/response.go
index a596d1d342..b49b77d8b9 100644
--- a/src/net/http/response.go
+++ b/src/net/http/response.go
@@ -11,6 +11,7 @@ import (
 	"bytes"
 	"crypto/tls"
 	"errors"
+	"fmt"
 	"io"
 	"net/textproto"
 	"net/url"
@@ -228,11 +229,13 @@ func (r *Response) Write(w io.Writer) error {
 		if !ok {
 			text = "status code " + strconv.Itoa(r.StatusCode)
 		}
+	} else {
+		// Just to reduce stutter, if user set r.Status to "200 OK" and StatusCode to 200.
+		// Not important.
+		text = strings.TrimPrefix(text, strconv.Itoa(r.StatusCode)+" ")
 	}
-	protoMajor, protoMinor := strconv.Itoa(r.ProtoMajor), strconv.Itoa(r.ProtoMinor)
-	statusCode := strconv.Itoa(r.StatusCode) + " "
-	text = strings.TrimPrefix(text, statusCode)
-	if _, err := io.WriteString(w, "HTTP/"+protoMajor+"."+protoMinor+" "+statusCode+text+"\r\n"); err != nil {
+
+	if _, err := fmt.Fprintf(w, "HTTP/%d.%d %03d %s\r\n", r.ProtoMajor, r.ProtoMinor, r.StatusCode, text); err != nil {
 		return err
 	}
 
diff --git a/src/net/http/responsewrite_test.go b/src/net/http/responsewrite_test.go
index a2a32d0107..90f6767d96 100644
--- a/src/net/http/responsewrite_test.go
+++ b/src/net/http/responsewrite_test.go
@@ -222,6 +222,39 @@ func TestResponseWrite(t *testing.T) {
 			},
 			"HTTP/1.1 200 OK\r\nConnection: close\r\n\r\nabcdef",
 		},
+
+		// Status code under 100 should be zero-padded to
+		// three digits.  Still bogus, but less bogus. (be
+		// consistent with generating three digits, since the
+		// Transport requires it)
+		{
+			Response{
+				StatusCode: 7,
+				Status:     "license to violate specs",
+				ProtoMajor: 1,
+				ProtoMinor: 0,
+				Request:    dummyReq("GET"),
+				Header:     Header{},
+				Body:       nil,
+			},
+
+			"HTTP/1.0 007 license to violate specs\r\nContent-Length: 0\r\n\r\n",
+		},
+
+		// No stutter.
+		{
+			Response{
+				StatusCode: 123,
+				Status:     "123 Sesame Street",
+				ProtoMajor: 1,
+				ProtoMinor: 0,
+				Request:    dummyReq("GET"),
+				Header:     Header{},
+				Body:       nil,
+			},
+
+			"HTTP/1.0 123 Sesame Street\r\nContent-Length: 0\r\n\r\n",
+		},
 	}
 
 	for i := range respWriteTests {
diff --git a/src/net/http/server.go b/src/net/http/server.go
index a2f9083a51..a2ef0ddf20 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -1152,7 +1152,7 @@ func statusLine(req *Request, code int) string {
 	if proto11 {
 		proto = "HTTP/1.1"
 	}
-	codestring := strconv.Itoa(code)
+	codestring := fmt.Sprintf("%03d", code)
 	text, ok := statusText[code]
 	if !ok {
 		text = "status code " + codestring