net/http: let ErrNotSupported match errors.ErrUnsupported

For #41198

Change-Id: Ibb030e94618a1f594cfd98ddea214ad7a88d2e73
Reviewed-on: https://go-review.googlesource.com/c/go/+/494122
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

api/next/41198.txt

@@ -1 +1,2 @@
 pkg errors, var ErrUnsupported error #41198
+pkg net/http, method (*ProtocolError) Is(error) bool #41198

src/net/http/request.go

@@ -48,6 +48,11 @@ type ProtocolError struct {
 
 func (pe *ProtocolError) Error() string { return pe.ErrorString }
 
+// Is lets http.ErrNotSupported match errors.ErrUnsupported.
+func (pe *ProtocolError) Is(err error) bool {
+	return pe == ErrNotSupported && err == errors.ErrUnsupported
+}
+
 var (
 	// ErrNotSupported indicates that a feature is not supported.
 	//

src/net/http/request_test.go

@@ -10,6 +10,7 @@ import (
 	"context"
 	"crypto/rand"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"io"
 	"math"
@@ -1388,3 +1389,9 @@ func runFileAndServerBenchmarks(b *testing.B, mode testMode, f *os.File, n int64
 		b.SetBytes(n)
 	}
 }
+
+func TestErrNotSupported(t *testing.T) {
+	if !errors.Is(ErrNotSupported, errors.ErrUnsupported) {
+		t.Error("errors.Is(ErrNotSupported, errors.ErrUnsupported) failed")
+	}
+}