net/http/httptest: mimic the normal HTTP server's ResponseWriter more closely

Also adds tests, which didn't exist before.

Fixes #4188

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/6613062

src/pkg/net/http/httptest/recorder.go

@@ -17,6 +17,8 @@ type ResponseRecorder struct {
 	HeaderMap http.Header   // the HTTP response headers
 	Body      *bytes.Buffer // if non-nil, the bytes.Buffer to append written data to
 	Flushed   bool
+
+	wroteHeader bool
 }
 
 // NewRecorder returns an initialized ResponseRecorder.
@@ -24,6 +26,7 @@ func NewRecorder() *ResponseRecorder {
 	return &ResponseRecorder{
 		HeaderMap: make(http.Header),
 		Body:      new(bytes.Buffer),
+		Code:      200,
 	}
 }
 
@@ -33,26 +36,37 @@ const DefaultRemoteAddr = "1.2.3.4"
 
 // Header returns the response headers.
 func (rw *ResponseRecorder) Header() http.Header {
-	return rw.HeaderMap
+	m := rw.HeaderMap
+	if m == nil {
+		m = make(http.Header)
+		rw.HeaderMap = m
+	}
+	return m
 }
 
 // Write always succeeds and writes to rw.Body, if not nil.
 func (rw *ResponseRecorder) Write(buf []byte) (int, error) {
+	if !rw.wroteHeader {
+		rw.WriteHeader(200)
+	}
 	if rw.Body != nil {
 		rw.Body.Write(buf)
 	}
-	if rw.Code == 0 {
-		rw.Code = http.StatusOK
-	}
 	return len(buf), nil
 }
 
 // WriteHeader sets rw.Code.
 func (rw *ResponseRecorder) WriteHeader(code int) {
+	if !rw.wroteHeader {
 		rw.Code = code
 	}
+	rw.wroteHeader = true
+}
 
 // Flush sets rw.Flushed to true.
 func (rw *ResponseRecorder) Flush() {
+	if !rw.wroteHeader {
+		rw.WriteHeader(200)
+	}
 	rw.Flushed = true
 }

src/pkg/net/http/httptest/recorder_test.go

@@ -0,0 +1,90 @@
+// Copyright 2012 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.
+
+package httptest
+
+import (
+	"fmt"
+	"net/http"
+	"testing"
+)
+
+func TestRecorder(t *testing.T) {
+	type checkFunc func(*ResponseRecorder) error
+	check := func(fns ...checkFunc) []checkFunc { return fns }
+
+	hasStatus := func(wantCode int) checkFunc {
+		return func(rec *ResponseRecorder) error {
+			if rec.Code != wantCode {
+				return fmt.Errorf("Status = %d; want %d", rec.Code, wantCode)
+			}
+			return nil
+		}
+	}
+	hasContents := func(want string) checkFunc {
+		return func(rec *ResponseRecorder) error {
+			if rec.Body.String() != want {
+				return fmt.Errorf("wrote = %q; want %q", rec.Body.String(), want)
+			}
+			return nil
+		}
+	}
+	hasFlush := func(want bool) checkFunc {
+		return func(rec *ResponseRecorder) error {
+			if rec.Flushed != want {
+				return fmt.Errorf("Flushed = %v; want %v", rec.Flushed, want)
+			}
+			return nil
+		}
+	}
+
+	tests := []struct {
+		name   string
+		h      func(w http.ResponseWriter, r *http.Request)
+		checks []checkFunc
+	}{
+		{
+			"200 default",
+			func(w http.ResponseWriter, r *http.Request) {},
+			check(hasStatus(200), hasContents("")),
+		},
+		{
+			"first code only",
+			func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(201)
+				w.WriteHeader(202)
+				w.Write([]byte("hi"))
+			},
+			check(hasStatus(201), hasContents("hi")),
+		},
+		{
+			"write sends 200",
+			func(w http.ResponseWriter, r *http.Request) {
+				w.Write([]byte("hi first"))
+				w.WriteHeader(201)
+				w.WriteHeader(202)
+			},
+			check(hasStatus(200), hasContents("hi first"), hasFlush(false)),
+		},
+		{
+			"flush",
+			func(w http.ResponseWriter, r *http.Request) {
+				w.(http.Flusher).Flush() // also sends a 200
+				w.WriteHeader(201)
+			},
+			check(hasStatus(200), hasFlush(true)),
+		},
+	}
+	r, _ := http.NewRequest("GET", "http://foo.com/", nil)
+	for _, tt := range tests {
+		h := http.HandlerFunc(tt.h)
+		rec := NewRecorder()
+		h.ServeHTTP(rec, r)
+		for _, check := range tt.checks {
+			if err := check(rec); err != nil {
+				t.Errorf("%s: %v", tt.name, err)
+			}
+		}
+	}
+}