Add background update for middle proxy

mtproto/rpc/nonce_response.go

@@ -0,0 +1,60 @@
+package rpc
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+
+	"github.com/9seconds/mtg/mtproto"
+)
+
+type NonceResponse struct {
+	NonceRequest
+
+	Type   []byte
+	Crypto []byte
+}
+
+// Bytes returns serialized form of the nonce response.
+func (r *NonceResponse) Bytes() []byte {
+	buf := &bytes.Buffer{}
+
+	buf.Write(r.Type)        // nolint: gosec
+	buf.Write(r.KeySelector) // nolint: gosec
+	buf.Write(r.Crypto)      // nolint: gosec
+	buf.Write(r.CryptoTS)    // nolint: gosec
+	buf.Write(r.Nonce)       // nolint: gosec
+
+	return buf.Bytes()
+}
+
+func (r *NonceResponse) Valid(req *NonceRequest) error {
+	if !bytes.Equal(r.Type, mtproto.TagNonce) {
+		return errors.New("Unexpected RPC type")
+	}
+	if !bytes.Equal(r.Crypto, mtproto.NonceCryptoAES) {
+		return errors.New("Unexpected crypto type")
+	}
+	if !bytes.Equal(r.KeySelector, req.KeySelector) {
+		return errors.New("Unexpected key selector")
+	}
+
+	return nil
+}
+
+// NewNonceResponse build new nonce response based on the given data.
+func NewNonceResponse(data []byte) (*NonceResponse, error) {
+	if len(data) != 32 {
+		return nil, fmt.Errorf("Unexpected message length %d", len(data))
+	}
+
+	return &NonceResponse{
+		NonceRequest: NonceRequest{
+			KeySelector: data[4:8],
+			CryptoTS:    data[12:16],
+			Nonce:       data[16:],
+		},
+		Type:   data[:4],
+		Crypto: data[8:12],
+	}, nil
+}