Optionally restrict the range of ephemeral ports

src/aioice/ice.py

@@ -282,6 +282,8 @@ class Connection:
     :param turn_transport: The transport for TURN server, `"udp"` or `"tcp"`.
     :param use_ipv4: Whether to use IPv4 candidates.
     :param use_ipv6: Whether to use IPv6 candidates.
+    :param port_lower: The lowest port to bind to.
+    :param port_upper: The highest port to bind to.
     """
 
     def __init__(
@@ -296,6 +298,8 @@ def __init__(
         turn_transport: str = "udp",
         use_ipv4: bool = True,
         use_ipv6: bool = True,
+        port_lower: int = 0,
+        port_upper: int = 0,
     ) -> None:
         self.ice_controlling = ice_controlling
         #: Local username, automatically set to a random value.
@@ -340,6 +344,8 @@ def __init__(
         self._tie_breaker = secrets.randbits(64)
         self._use_ipv4 = use_ipv4
         self._use_ipv6 = use_ipv6
+        self._port_lower = port_lower
+        self._port_upper = port_upper
 
     @property
     def local_candidates(self) -> List[Candidate]:
@@ -843,20 +849,42 @@ def _find_pair(
                 return pair
         return None
 
+    async def _create_datagram_endpoint(self, address):
+        """
+        Create a datagram endpoint on the specified address,
+        with port optionally in the range [port_lower, port_upper]
+        """
+        # when port_lower and port_upper are both zero: ports = [0]
+        # which will let the OS pick any random free port
+        ports = list(range(
+            self._port_lower if self._port_lower or not self._port_upper else 1,
+            (65535 if self._port_lower and not self._port_upper else self._port_upper) + 1
+        ))
+        random.shuffle(ports)
+        loop = asyncio.get_event_loop()
+        for port in ports:
+            try:
+                transport, protocol = await loop.create_datagram_endpoint(
+                    lambda: StunProtocol(self), local_addr=(address, port)
+                )
+                return transport, protocol
+            except OSError as exc:
+                if port == ports[-1]:
+                    # this was the last port, give up
+                    raise exc
+        raise ValueError("Illegal port range: [%d, %d]" % (self._port_lower, self._port_upper))
+
     async def get_component_candidates(
         self, component: int, addresses: List[str], timeout: int = 5
     ) -> List[Candidate]:
         candidates = []
-        loop = asyncio.get_event_loop()
 
         # gather host candidates
         host_protocols = []
         for address in addresses:
             # create transport
             try:
-                transport, protocol = await loop.create_datagram_endpoint(
-                    lambda: StunProtocol(self), local_addr=(address, 0)
-                )
+                transport, protocol = await self._create_datagram_endpoint(address)
                 sock = transport.get_extra_info("socket")
                 if sock is not None:
                     sock.setsockopt(