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

src/net/http/httptest/recorder.go

@@ -16,6 +16,17 @@ import (
 	"golang.org/x/net/http/httpguts"
 )
 
+// InformationalResponse is an HTTP response sent with a [1xx status code].
+//
+// [1xx status code]: https://httpwg.org/specs/rfc9110.html#status.1xx
+type InformationalResponse struct {
+	// Code is the 1xx HTTP response code of this informational response.
+	Code int
+
+	// Header contains the headers of this informational response.
+	Header http.Header
+}
+
 // ResponseRecorder is an implementation of http.ResponseWriter that
 // records its mutations for later inspection in tests.
 type ResponseRecorder struct {
@@ -27,6 +38,9 @@ type ResponseRecorder struct {
 	// method.
 	Code int
 
+	// Informational HTTP responses (1xx status code) sent before the main response.
+	InformationalResponses []InformationalResponse
+
 	// HeaderMap contains the headers explicitly set by the Handler.
 	// It is an internal detail.
 	//
@@ -146,11 +160,20 @@ func (rw *ResponseRecorder) WriteHeader(code int) {
 	}
 
 	checkWriteHeaderCode(code)
-	rw.Code = code
-	rw.wroteHeader = true
+
 	if rw.HeaderMap == nil {
 		rw.HeaderMap = make(http.Header)
 	}
+
+	if code >= 100 && code < 200 {
+		ir := InformationalResponse{code, rw.HeaderMap.Clone()}
+		rw.InformationalResponses = append(rw.InformationalResponses, ir)
+
+		return
+	}
+
+	rw.Code = code
+	rw.wroteHeader = true
 	rw.snapHeader = rw.HeaderMap.Clone()
 }
 

src/net/http/httptest/recorder_test.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"reflect"
 	"testing"
 )
 
@@ -123,6 +124,15 @@ func TestRecorder(t *testing.T) {
 			return nil
 		}
 	}
+	hasInformationalResponses := func(ir []InformationalResponse) checkFunc {
+		return func(rec *ResponseRecorder) error {
+			if !reflect.DeepEqual(ir, rec.InformationalResponses) {
+				return fmt.Errorf("InformationalResponses = %v; want %v", rec.InformationalResponses, ir)
+			}
+
+			return nil
+		}
+	}
 
 	for _, tt := range [...]struct {
 		name   string
@@ -294,6 +304,26 @@ func TestRecorder(t *testing.T) {
 			check(hasResultContents("")), // check we don't crash reading the body
 
 		},
+		{
+			"1xx status code",
+			func(rw http.ResponseWriter, _ *http.Request) {
+				rw.WriteHeader(http.StatusContinue)
+				rw.Header().Add("Foo", "bar")
+
+				rw.WriteHeader(http.StatusEarlyHints)
+				rw.Header().Add("Baz", "bat")
+
+				rw.Header().Del("Foo")
+			},
+			check(
+				hasInformationalResponses([]InformationalResponse{
+					InformationalResponse{100, http.Header{}},
+					InformationalResponse{103, http.Header{"Foo": []string{"bar"}}},
+				}),
+				hasHeader("Baz", "bat"),
+				hasNotHeaders("Foo"),
+			),
+		},
 	} {
 		t.Run(tt.name, func(t *testing.T) {
 			r, _ := http.NewRequest("GET", "http://foo.com/", nil)