implement HTTP/3 stream hijacking

http3/frames.go

@@ -2,6 +2,7 @@ package http3
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -10,15 +11,34 @@ import (
 	"github.com/lucas-clemente/quic-go/quicvarint"
 )
 
+// FrameType is the frame type of a HTTP/3 frame
+type FrameType uint64
+
+type unknownFrameHandlerFunc func(FrameType) (processed bool, err error)
+
 type frame interface{}
 
-func parseNextFrame(r io.Reader) (frame, error) {
+var errHijacked = errors.New("hijacked")
+
+func parseNextFrame(r io.Reader, unknownFrameHandler unknownFrameHandlerFunc) (frame, error) {
 	qr := quicvarint.NewReader(r)
 	for {
 		t, err := quicvarint.Read(qr)
 		if err != nil {
 			return nil, err
 		}
+		// Call the unknownFrameHandler for frames not defined in the HTTP/3 spec
+		if t > 0xd && unknownFrameHandler != nil {
+			hijacked, err := unknownFrameHandler(FrameType(t))
+			if err != nil {
+				return nil, err
+			}
+			// If the unknownFrameHandler didn't process the frame, it is our responsibility to skip it.
+			if hijacked {
+				return nil, errHijacked
+			}
+			continue
+		}
 		l, err := quicvarint.Read(qr)
 		if err != nil {
 			return nil, err
@@ -32,18 +52,13 @@ func parseNextFrame(r io.Reader) (frame, error) {
 		case 0x4:
 			return parseSettingsFrame(r, l)
 		case 0x3: // CANCEL_PUSH
-			fallthrough
 		case 0x5: // PUSH_PROMISE
-			fallthrough
 		case 0x7: // GOAWAY
-			fallthrough
 		case 0xd: // MAX_PUSH_ID
-			fallthrough
-		default:
-			// skip over unknown frames
-			if _, err := io.CopyN(ioutil.Discard, qr, int64(l)); err != nil {
-				return nil, err
-			}
+		}
+		// skip over unknown frames
+		if _, err := io.CopyN(ioutil.Discard, qr, int64(l)); err != nil {
+			return nil, err
 		}
 	}
 }