Add background update for middle proxy

mtproto/rpc/handshake_response.go

@@ -0,0 +1,55 @@
+package rpc
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+
+	"github.com/9seconds/mtg/mtproto"
+)
+
+type HandshakeResponse struct {
+	Type      []byte
+	Flags     []byte
+	SenderPID []byte
+	PeerPID   []byte
+}
+
+// Bytes returns a serialized handshake response.
+func (r *HandshakeResponse) Bytes() []byte {
+	buf := &bytes.Buffer{}
+
+	buf.Write(r.Type)      // nolint: gosec
+	buf.Write(r.Flags)     // nolint: gosec
+	buf.Write(r.SenderPID) // nolint: gosec
+	buf.Write(r.PeerPID)   // nolint: gosec
+
+	return buf.Bytes()
+}
+
+// Valid checks that handshake response compliments request.
+func (r *HandshakeResponse) Valid() error {
+	if !bytes.Equal(r.Type, mtproto.TagHandshake) {
+		return errors.New("Unexpected handshake tag")
+	}
+	if !bytes.Equal(r.PeerPID, mtproto.HandshakeSenderPID) {
+		return errors.New("Incorrect sender PID")
+	}
+
+	return nil
+}
+
+// NewHandshakeResponse constructs new handshake response from the given
+// data.
+func NewHandshakeResponse(data []byte) (*HandshakeResponse, error) {
+	if len(data) != 32 {
+		return nil, fmt.Errorf("Incorrect handshake response length %d", len(data))
+	}
+
+	return &HandshakeResponse{
+		Type:      data[:4],
+		Flags:     data[4:8],
+		SenderPID: data[8:20],
+		PeerPID:   data[20:],
+	}, nil
+}