Add rpc request/response for handshake

mtproto/rpc/rpc.go

 package rpc
 
+import "bytes"
+
+const (
+	RPCNonceSeqNo     = -2
+	RPCHandshakeSeqNo = -1
+)
+
 type RPC interface {
-	Bytes() []byte
+	Bytes() *bytes.Buffer
 }

mtproto/rpc/rpc_handshake_request.go

+package rpc
+
+import "bytes"
+
+const (
+	rpcHandshakeTagLength       = 4
+	rpcHandshakeFlagsLength     = 4
+	rpcHandshakeSenderPIDLength = 12
+	rpcHandshakePeerPIDLength   = rpcHandshakeSenderPIDLength
+
+	rpcHandshakeRequestLength = rpcHandshakeTagLength + rpcHandshakeFlagsLength +
+		rpcHandshakeSenderPIDLength + rpcHandshakePeerPIDLength
+)
+
+var (
+	rpcHandshakeSenderPID [rpcHandshakeSenderPIDLength]byte
+	rpcHandshakePeerPID   [rpcHandshakePeerPIDLength]byte
+
+	rpcHandshakeTag   = [rpcHandshakeTagLength]byte{0xf5, 0xee, 0x82, 0x76}
+	rpcHandshakeFlags = [rpcHandshakeFlagsLength]byte{0x00, 0x00, 0x00, 0x00}
+
+	rpcHandshakeBuffer *bytes.Buffer
+)
+
+type RPCHandshakeRequest struct {
+}
+
+func (r *RPCHandshakeRequest) Bytes() *bytes.Buffer {
+	buf := &bytes.Buffer{}
+	buf.Grow(rpcHandshakeRequestLength)
+
+	buf.Write(rpcHandshakeTag[:])
+	buf.Write(rpcHandshakeFlags[:])
+	buf.Write(rpcHandshakeSenderPID[:])
+	buf.Write(rpcHandshakePeerPID[:])
+
+	return buf
+}
+
+func init() {
+	copy(rpcHandshakeSenderPID[:], "IPIPPRPDTIME")
+	copy(rpcHandshakePeerPID[:], "IPIPPRPDTIME")
+}
+
+func NewRPCHandshakeRequest() *RPCHandshakeRequest {
+	return &RPCHandshakeRequest{}
+}

mtproto/rpc/rpc_handshake_response.go

+package rpc
+
+import (
+	"bytes"
+
+	"github.com/juju/errors"
+)
+
+const rpcHandshakeResponseLength = rpcHandshakeRequestLength
+
+type RPCHandshakeResponse struct {
+	Type      [rpcHandshakeTagLength]byte
+	Flags     [rpcHandshakeFlagsLength]byte
+	SenderPID [rpcHandshakeSenderPIDLength]byte
+	PeerPID   [rpcHandshakePeerPIDLength]byte
+}
+
+func (r *RPCHandshakeResponse) Bytes() *bytes.Buffer {
+	buf := &bytes.Buffer{}
+	buf.Grow(rpcHandshakeResponseLength)
+
+	buf.Write(r.Type[:])
+	buf.Write(r.Flags[:])
+	buf.Write(r.SenderPID[:])
+	buf.Write(r.PeerPID[:])
+
+	return buf
+}
+
+func (r *RPCHandshakeResponse) Valid(req *RPCHandshakeRequest) error {
+	if r.Type != rpcHandshakeTag {
+		return errors.New("Unexpected handshake tag")
+	}
+	if r.PeerPID != rpcHandshakeSenderPID {
+		return errors.New("Incorrect sender PID")
+	}
+
+	return nil
+}
+
+func NewRPCHandshakeResponse(data []byte) (*RPCHandshakeResponse, error) {
+	if len(data) != rpcHandshakeResponseLength {
+		return nil, errors.New("Incorrect handshake response length")
+	}
+
+	resp := RPCHandshakeResponse{}
+	copy(resp.Type[:], data[:4])
+	copy(resp.Flags[:], data[4:8])
+	copy(resp.SenderPID[:], data[8:20])
+	copy(resp.PeerPID[:], data[20:])
+
+	return &resp, nil
+}

mtproto/rpc/rpc_nonce_request.go

 )
 
 const (
-	RPCNonceSeqNo = -2
-
 	rpcNonceLength            = 16
 	rpcNonceKeySelectorLength = 4
 	rpcNonceCryptoTSLength    = 4
 	Nonce       [rpcNonceLength]byte
 }
 
-func (r *RPCNonceRequest) Bytes() []byte {
+func (r *RPCNonceRequest) Bytes() *bytes.Buffer {
 	buf := &bytes.Buffer{}
 	buf.Grow(rpcNonceRequestLength)
 
 	buf.Write(r.CryptoTS[:])
 	buf.Write(r.Nonce[:])
 
-	return buf.Bytes()
+	return buf
 }
 
 func NewRPCNonceRequest(proxySecret []byte) (*RPCNonceRequest, error) {

mtproto/rpc/rpc_nonce_response.go

 	Crypto  [rpcNonceCryptoAESLength]byte
 }
 
-func (r *RPCNonceResponse) Bytes() []byte {
+func (r *RPCNonceResponse) Bytes() *bytes.Buffer {
 	buf := &bytes.Buffer{}
 	buf.Grow(rpcNonceResponseLength)
 
 	buf.Write(r.CryptoTS[:])
 	buf.Write(r.Nonce[:])
 
-	return buf.Bytes()
+	return buf
 }
 
 func (r *RPCNonceResponse) Valid(req *RPCNonceRequest) error {