Initial implementation of MTProxy support (#1107)

telethon/network/connection/tcpmtproxy.py

@@ -0,0 +1,40 @@
+import hashlib
+
+from .tcpobfuscated import ConnectionTcpObfuscated
+from ...crypto import AESModeCTR
+
+
+class ConnectionTcpMTProxy(ConnectionTcpObfuscated):
+    """
+    Wrapper around the "obfuscated2" mode that modifies it a little and allows
+    user to connect to the Telegram proxy servers commonly known as MTProxy.
+    Implemented very ugly due to the leaky abstractions in Telethon networking
+    classes that should be refactored later (TODO).
+    """
+    @staticmethod
+    def address_info(proxy_info):
+        if proxy_info is None:
+            raise ValueError("No proxy info specified for MTProxy connection")
+        return proxy_info[:2]
+
+    def __init__(self, ip, port, dc_id, *, loop, loggers, proxy=None):
+        proxy_host, proxy_port = self.address_info(proxy)
+        super().__init__(
+            proxy_host, proxy_port, dc_id, loop=loop, loggers=loggers)
+
+        # TODO: Implement the dd-secret secure mode (adds noise to fool DPI)
+        self._secret = bytes.fromhex(proxy[2])
+        if len(self._secret) != 16:
+            raise ValueError(
+                "MTProxy secure mode is not implemented for now"
+                if len(self._secret) == 17 and self._secret[0] == 0xDD else
+                "MTProxy secret must be a hex-string representing 16 bytes"
+            )
+
+    def _compose_key(self, data):
+        return hashlib.sha256(data + self._secret).digest()
+
+    def _compose_tail(self, data):
+        dc_id_bytes = self._dc_id.to_bytes(2, "little", signed=True)
+        tail_bytes = super()._compose_tail(data)
+        return tail_bytes[:4] + dc_id_bytes + tail_bytes[6:]