avoid recursion when skipping unknown HTTP/3 frames (quic-go#3354)

Author: marten-seemann

http3/frames.go

@@ -14,38 +14,39 @@ type frame interface{}
 
 func parseNextFrame(r io.Reader) (frame, error) {
 	qr := quicvarint.NewReader(r)
-	t, err := quicvarint.Read(qr)
-	if err != nil {
-		return nil, err
-	}
-	l, err := quicvarint.Read(qr)
-	if err != nil {
-		return nil, err
-	}
-
-	switch t {
-	case 0x0:
-		return &dataFrame{Length: l}, nil
-	case 0x1:
-		return &headersFrame{Length: l}, nil
-	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
-	case 0xe: // DUPLICATE_PUSH
-		fallthrough
-	default:
-		// skip over unknown frames
-		if _, err := io.CopyN(ioutil.Discard, qr, int64(l)); err != nil {
+	for {
+		t, err := quicvarint.Read(qr)
+		if err != nil {
 			return nil, err
 		}
-		return parseNextFrame(qr)
+		l, err := quicvarint.Read(qr)
+		if err != nil {
+			return nil, err
+		}
+
+		switch t {
+		case 0x0:
+			return &dataFrame{Length: l}, nil
+		case 0x1:
+			return &headersFrame{Length: l}, nil
+		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
+		case 0xe: // DUPLICATE_PUSH
+			fallthrough
+		default:
+			// skip over unknown frames
+			if _, err := io.CopyN(ioutil.Discard, qr, int64(l)); err != nil {
+				return nil, err
+			}
+		}
 	}
 }