Move handshake into its own package

handshake/handshake.go

@@ -0,0 +1,60 @@
+package handshake
+
+import (
+	"errors"
+	"io"
+)
+
+// A Handshake is a sequence of bytes a peer uses to identify itself
+type Handshake struct {
+	Pstr     string
+	InfoHash [20]byte
+	PeerID   [20]byte
+}
+
+// Serialize serializes the handshake to a buffer
+func (h *Handshake) Serialize() []byte {
+	pstrlen := len(h.Pstr)
+	bufLen := 49 + pstrlen
+	buf := make([]byte, bufLen)
+	buf[0] = byte(pstrlen)
+	copy(buf[1:], h.Pstr)
+	// Leave 8 reserved bytes
+	copy(buf[1+pstrlen+8:], h.InfoHash[:])
+	copy(buf[1+pstrlen+8+20:], h.PeerID[:])
+	return buf
+}
+
+// Read parses a message from a stream. Returns `nil` on keep-alive message
+func Read(r io.Reader) (*Handshake, error) {
+	lengthBuf := make([]byte, 1)
+	_, err := io.ReadFull(r, lengthBuf)
+	if err != nil {
+		return nil, err
+	}
+	pstrlen := int(lengthBuf[0])
+
+	if pstrlen == 0 {
+		err := errors.New("pstrlen cannot be 0")
+		return nil, err
+	}
+
+	handshakeBuf := make([]byte, 48+pstrlen)
+	_, err = io.ReadFull(r, handshakeBuf)
+	if err != nil {
+		return nil, err
+	}
+
+	var infoHash, peerID [20]byte
+
+	copy(infoHash[:], handshakeBuf[pstrlen+8:pstrlen+8+20])
+	copy(peerID[:], handshakeBuf[pstrlen+8+20:])
+
+	h := Handshake{
+		Pstr:     string(handshakeBuf[0:pstrlen]),
+		InfoHash: infoHash,
+		PeerID:   peerID,
+	}
+
+	return &h, nil
+}