Implement protocol frame read and write functions

internal/staging/protocol/protocol.go

@@ -0,0 +1,65 @@
+package protocol
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+const (
+	Magic = "PSP1\n"
+
+	FrameOpen     byte = 1
+	FrameOpenOK   byte = 2
+	FrameOpenFail byte = 3
+	FrameData     byte = 4
+	FrameClose    byte = 5
+	FramePing     byte = 6
+	FramePong     byte = 7
+
+	MaxPayload = 1 << 20
+)
+
+const headerLen = 13
+
+type Frame struct {
+	StreamID uint64
+	Type     byte
+	Payload  []byte
+}
+
+func ReadFrame(r io.Reader) (Frame, error) {
+	var hdr [headerLen]byte
+	if _, err := io.ReadFull(r, hdr[:]); err != nil {
+		return Frame{}, err
+	}
+	length := binary.BigEndian.Uint32(hdr[9:13])
+	if length > MaxPayload {
+		return Frame{}, fmt.Errorf("frame payload too large: %d", length)
+	}
+	payload := make([]byte, length)
+	if length > 0 {
+		if _, err := io.ReadFull(r, payload); err != nil {
+			return Frame{}, err
+		}
+	}
+	return Frame{StreamID: binary.BigEndian.Uint64(hdr[0:8]), Type: hdr[8], Payload: payload}, nil
+}
+
+func WriteFrame(w io.Writer, f Frame) error {
+	if len(f.Payload) > MaxPayload {
+		return fmt.Errorf("frame payload too large: %d", len(f.Payload))
+	}
+	var hdr [headerLen]byte
+	binary.BigEndian.PutUint64(hdr[0:8], f.StreamID)
+	hdr[8] = f.Type
+	binary.BigEndian.PutUint32(hdr[9:13], uint32(len(f.Payload)))
+	if _, err := w.Write(hdr[:]); err != nil {
+		return err
+	}
+	if len(f.Payload) > 0 {
+		_, err := w.Write(f.Payload)
+		return err
+	}
+	return nil
+}