added isochronous modus

internal/usbip/protocol.go

@@ -304,6 +304,56 @@ func BuildRetSubmit(seqNum, devID, direction, endpoint uint32, status int32, dat
 	return buf.Bytes(), nil
 }
 
+// BuildRetSubmitISO builds a RET_SUBMIT message for isochronous transfers.
+// The transfer data must already be packed (compact, no gaps).
+func BuildRetSubmitISO(seqNum, devID, direction, endpoint uint32, status int32,
+	packedData []byte, startFrame uint32, numPackets int32, errorCount int32,
+	isoDescs []ISOPacketDescriptor) ([]byte, error) {
+
+	buf := &bytes.Buffer{}
+
+	hdr := &URBHeader{
+		Command:   RetSubmit,
+		SeqNum:    seqNum,
+		DevID:     devID,
+		Direction: direction,
+		Endpoint:  endpoint,
+	}
+	if err := WriteURBHeader(buf, hdr); err != nil {
+		return nil, err
+	}
+
+	actualLen := uint32(0)
+	if direction == DirIn && packedData != nil {
+		actualLen = uint32(len(packedData))
+	}
+
+	body := &RetSubmitBody{
+		Status:          status,
+		ActualLength:    actualLen,
+		StartFrame:      startFrame,
+		NumberOfPackets: uint32(numPackets),
+		ErrorCount:      uint32(errorCount),
+	}
+	if err := WriteRetSubmit(buf, body); err != nil {
+		return nil, err
+	}
+
+	// Transfer buffer (packed) for IN direction
+	if direction == DirIn && len(packedData) > 0 {
+		buf.Write(packedData)
+	}
+
+	// ISO packet descriptors
+	for _, desc := range isoDescs {
+		if err := binary.Write(buf, binary.BigEndian, &desc); err != nil {
+			return nil, err
+		}
+	}
+
+	return buf.Bytes(), nil
+}
+
 // BuildRetUnlink builds a RET_UNLINK message
 func BuildRetUnlink(seqNum, devID uint32, status int32) ([]byte, error) {
 	buf := &bytes.Buffer{}