Support different client connection types

mtproto/connection_options.go

@@ -0,0 +1,55 @@
+package mtproto
+
+import (
+	"bytes"
+
+	"github.com/juju/errors"
+)
+
+// ConnectionType is a type of obfuscated2/mtproto connection requested
+// by the user.
+type ConnectionType uint8
+
+// ConnectionOpts presents an options, metadata on connection requested
+// by the user on handshake.
+type ConnectionOpts struct {
+	DC             int16
+	ConnectionType ConnectionType
+}
+
+// Different connection types which user requests from Telegram.
+const (
+	ConnectionTypeUnknown ConnectionType = iota
+	ConnectionTypeAbridged
+	ConnectionTypeIntermediate
+)
+
+// Connection tags for mtproto handshakes.
+var (
+	ConnectionTagAbridged     = []byte{0xef, 0xef, 0xef, 0xef}
+	ConnectionTagIntermediate = []byte{0xee, 0xee, 0xee, 0xee}
+)
+
+// Tag maps connection type to the corresponding handshake tag.
+func (t ConnectionType) Tag() ([]byte, error) {
+	switch t {
+	case ConnectionTypeAbridged:
+		return ConnectionTagAbridged, nil
+	case ConnectionTypeIntermediate:
+		return ConnectionTagIntermediate, nil
+	default:
+		return nil, errors.Errorf("Unknown connection type %d", t)
+	}
+}
+
+// ConnectionTagFromHandshake maps magic bytes to the connection type.
+func ConnectionTagFromHandshake(magic []byte) (ConnectionType, error) {
+	if bytes.Equal(magic, ConnectionTagIntermediate) {
+		return ConnectionTypeIntermediate, nil
+	}
+	if bytes.Equal(magic, ConnectionTagAbridged) {
+		return ConnectionTypeAbridged, nil
+	}
+
+	return ConnectionTypeUnknown, errors.New("Unknown handshake protocol")
+}