net/http/httptest: add support for 1XX responses

The existing implementation doesn't allow tracing
1xx responses.
This patch allows using net/http/httptrace to inspect
1XX responses.

Updates golang#26089.

src/net/http/httptest/recorder.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/http/httptrace"
 	"net/textproto"
 	"strconv"
 	"strings"
@@ -42,6 +43,9 @@ type ResponseRecorder struct {
 	// Flushed is whether the Handler called Flush.
 	Flushed bool
 
+	// ClientTrace is used to trace 1XX responses
+	ClientTrace *httptrace.ClientTrace
+
 	result      *http.Response // cache of Result's return value
 	snapHeader  http.Header    // snapshot of HeaderMap at first Write
 	wroteHeader bool
@@ -146,6 +150,20 @@ func (rw *ResponseRecorder) WriteHeader(code int) {
 	}
 
 	checkWriteHeaderCode(code)
+
+	if rw.ClientTrace != nil && code >= 100 && code < 200 {
+		if code == 100 {
+			rw.ClientTrace.Got100Continue()
+		}
+		// treat 101 as a terminal status, see issue 26161
+		if code != http.StatusSwitchingProtocols {
+			if err := rw.ClientTrace.Got1xxResponse(code, textproto.MIMEHeader(rw.HeaderMap)); err != nil {
+				panic(err)
+			}
+			return
+		}
+	}
+
 	rw.Code = code
 	rw.wroteHeader = true
 	if rw.HeaderMap == nil {

src/net/http/httptest/recorder_test.go

@@ -8,6 +8,8 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/http/httptrace"
+	"net/textproto"
 	"testing"
 )
 
@@ -369,3 +371,58 @@ func TestRecorderPanicsOnNonXXXStatusCode(t *testing.T) {
 		})
 	}
 }
+
+func TestRecorderClientTrace(t *testing.T) {
+	handler := func(rw http.ResponseWriter, _ *http.Request) {
+		rw.WriteHeader(http.StatusContinue)
+
+		rw.Header().Add("Foo", "bar")
+		rw.WriteHeader(http.StatusEarlyHints)
+
+		rw.Header().Add("Baz", "bat")
+	}
+
+	var received100, received103 bool
+	trace := &httptrace.ClientTrace{
+		Got100Continue: func() {
+			received100 = true
+		},
+		Got1xxResponse: func(code int, header textproto.MIMEHeader) error {
+			switch code {
+			case http.StatusContinue:
+			case http.StatusEarlyHints:
+				received103 = true
+				if header.Get("Foo") != "bar" {
+					t.Errorf(`Expected Foo=bar, got %s`, header.Get("Foo"))
+				}
+				if header.Get("Bar") != "" {
+					t.Error("Unexpected Bar header")
+				}
+			default:
+				t.Errorf("Unexpected status code %d", code)
+			}
+
+			return nil
+		},
+	}
+
+	r, _ := http.NewRequest("GET", "http://example.org/", nil)
+	rw := NewRecorder()
+	rw.ClientTrace = trace
+	handler(rw, r)
+
+	if !received100 {
+		t.Error("Got100Continue not called")
+	}
+	if !received103 {
+		t.Error("103 request not received")
+	}
+
+	header := rw.Result().Header
+	if header.Get("Foo") != "bar" {
+		t.Errorf("Expected Foo=bar, got %s", header.Get("Foo"))
+	}
+	if header.Get("Baz") != "bat" {
+		t.Errorf("Expected Baz=bat, got %s", header.Get("Baz"))
+	}
+}