Add RPC structs for nonce

mtproto/rpc/rpc_nonce_request.go

@@ -0,0 +1,67 @@
+package rpc
+
+import (
+	"bytes"
+	"crypto/rand"
+	"encoding/binary"
+	"time"
+
+	"github.com/juju/errors"
+)
+
+const (
+	RPCNonceSeqNo = -2
+
+	rpcNonceLength            = 16
+	rpcNonceKeySelectorLength = 4
+	rpcNonceCryptoTSLength    = 4
+	rpcNonceTagLength         = 4
+	rpcNonceCryptoAESLength   = 4
+
+	rpcNonceRequestLength = rpcNonceTagLength + rpcNonceKeySelectorLength +
+		rpcNonceCryptoAESLength + rpcNonceCryptoTSLength + rpcNonceLength
+)
+
+var (
+	rpcNonceTag          = [rpcNonceTagLength]byte{0xaa, 0x87, 0xcb, 0x7a}
+	rpcNonceCryptoAESTag = [rpcNonceCryptoAESLength]byte{0x01, 0x00, 0x00, 0x00}
+)
+
+type RPCNonceRequest struct {
+	KeySelector [rpcNonceKeySelectorLength]byte
+	CryptoTS    [rpcNonceCryptoTSLength]byte
+	Nonce       [rpcNonceLength]byte
+}
+
+func (r *RPCNonceRequest) Bytes() []byte {
+	buf := &bytes.Buffer{}
+	buf.Grow(rpcNonceRequestLength)
+
+	buf.Write(rpcNonceTag[:])
+	buf.Write(r.KeySelector[:])
+	buf.Write(rpcNonceCryptoAESTag[:])
+	buf.Write(r.CryptoTS[:])
+	buf.Write(r.Nonce[:])
+
+	return buf.Bytes()
+}
+
+func NewRPCNonceRequest(proxySecret []byte) (*RPCNonceRequest, error) {
+	var nonce [rpcNonceLength]byte
+	var keySelector [rpcNonceKeySelectorLength]byte
+	var cryptoTS [rpcNonceCryptoTSLength]byte
+
+	if _, err := rand.Read(nonce[:]); err != nil {
+		return nil, errors.Annotate(err, "Cannot generate nonce")
+	}
+	copy(keySelector[:], proxySecret)
+
+	timestamp := time.Now().Truncate(time.Second).Unix() % 4294967296 // 256 ^ 4 - do not know how to name
+	binary.LittleEndian.PutUint32(cryptoTS[:], uint32(timestamp))
+
+	return &RPCNonceRequest{
+		KeySelector: keySelector,
+		CryptoTS:    cryptoTS,
+		Nonce:       nonce,
+	}, nil
+}