Make the Connection a proper ABC (#509)

telethon/network/connection/tcpabridged.py

@@ -0,0 +1,34 @@
+import struct
+
+from .tcpfull import ConnectionTcpFull
+
+
+class ConnectionTcpAbridged(ConnectionTcpFull):
+    """
+    This is the mode with the lowest overhead, as it will
+    only require 1 byte if the packet length is less than
+    508 bytes (127 << 2, which is very common).
+    """
+    def connect(self, ip, port):
+        result = super().connect(ip, port)
+        self.conn.write(b'\xef')
+        return result
+
+    def clone(self):
+        return ConnectionTcpAbridged(self._proxy, self._timeout)
+
+    def recv(self):
+        length = struct.unpack('<B', self.read(1))[0]
+        if length >= 127:
+            length = struct.unpack('<i', self.read(3) + b'\0')[0]
+
+        return self.read(length << 2)
+
+    def send(self, message):
+        length = len(message) >> 2
+        if length < 127:
+            length = struct.pack('B', length)
+        else:
+            length = b'\x7f' + int.to_bytes(length, 3, 'little')
+
+        self.write(length + message)