Optionally restrict the range of ephemeral ports

src/aioice/ice.py

@@ -8,13 +8,13 @@
 import socket
 import threading
 from itertools import count
-from typing import Dict, List, Optional, Set, Text, Tuple, Union, cast
+from typing import Dict, Iterable, List, Optional, Set, Text, Tuple, Union, cast
 
 import netifaces
 
 from . import mdns, stun, turn
 from .candidate import Candidate, candidate_foundation, candidate_priority
-from .utils import random_string
+from .utils import create_datagram_endpoint, random_string
 
 logger = logging.getLogger(__name__)
 
@@ -282,6 +282,7 @@ 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 ephemeral_ports: Set of allowed ephemeral local ports to bind to.
     """
 
     def __init__(
@@ -296,6 +297,7 @@ def __init__(
         turn_transport: str = "udp",
         use_ipv4: bool = True,
         use_ipv6: bool = True,
+        ephemeral_ports: Optional[Iterable[int]] = None,
     ) -> None:
         self.ice_controlling = ice_controlling
         #: Local username, automatically set to a random value.
@@ -340,6 +342,7 @@ def __init__(
         self._tie_breaker = secrets.randbits(64)
         self._use_ipv4 = use_ipv4
         self._use_ipv6 = use_ipv6
+        self._ephemeral_ports = ephemeral_ports
 
     @property
     def local_candidates(self) -> List[Candidate]:
@@ -847,16 +850,14 @@ 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 create_datagram_endpoint(
+                    lambda: StunProtocol(self), local_address=address, ephemeral_ports=self._ephemeral_ports)
                 sock = transport.get_extra_info("socket")
                 if sock is not None:
                     sock.setsockopt(

src/aioice/utils.py

@@ -1,6 +1,9 @@
+import asyncio
 import os
+import random
 import secrets
 import string
+from typing import Iterable, Optional, Tuple
 
 
 def random_string(length: int) -> str:
@@ -10,3 +13,35 @@ def random_string(length: int) -> str:
 
 def random_transaction_id() -> bytes:
     return os.urandom(12)
+
+
+async def create_datagram_endpoint(protocol_factory,
+    remote_addr: Tuple[str, int] = None,
+    local_address: str = None,
+    ephemeral_ports: Optional[Iterable[int]] = None,
+):
+    """
+    Asynchronousley create a datagram endpoint.
+
+    :param protocol_factory: Callable returning a protocol instance.
+    :param remote_addr: Remote address and port.
+    :param local_address: Local address to bind to.
+    :param ephemeral_ports: Set of allowed local ephemeral ports to bind to.
+    """
+    if ephemeral_ports is not None:
+        ports = list(ephemeral_ports)
+        random.shuffle(ports)
+    else:
+        ports = (0,)
+    loop = asyncio.get_event_loop()
+    for port in ports:
+        try:
+            transport, protocol = await loop.create_datagram_endpoint(
+                protocol_factory, remote_addr=remote_addr, local_addr=(local_address, port)
+            )
+            return transport, protocol
+        except OSError as exc:
+            if port == ports[-1]:
+                # this was the last port, give up
+                raise exc
+    raise ValueError("ephemeral_ports must not be empty")

tests/test_ice.py

@@ -1,6 +1,7 @@
 import asyncio
 import functools
 import os
+import random
 import socket
 import unittest
 from unittest import mock
@@ -1161,6 +1162,58 @@ async def test_repr(self):
         conn._id = 1
         self.assertEqual(repr(conn), "Connection(1)")
 
+    @asynctest
+    async def test_connection_ephemeral_ports(self):
+        addresses = ["127.0.0.1"]
+
+        # Let the OS pick a random port - should never fail
+        conn1 = ice.Connection(ice_controlling=True)
+        c = await conn1.get_component_candidates(0, addresses)
+        self.assertTrue(c[0].port >= 1 and c[0].port <= 65535)
+
+        # Try opening a new connection with the same port - should always fail
+        conn2 = ice.Connection(ice_controlling=True, ephemeral_ports=[c[0].port])
+        c = await conn2.get_component_candidates(0, addresses)
+        self.assertTrue(len(c) == 0) # port already in use, no candidates
+        await conn1.close()
+
+        # Empty set of ports - illegal argument
+        conn3 = ice.Connection(ice_controlling=True, ephemeral_ports=[])
+        with self.assertRaises(ValueError) as exc:
+            await conn3.get_component_candidates(0, addresses)
+
+        # Range of ports
+        lower = random.randint(1024, 65536 - 100)
+        upper = lower + 100
+        ports = list(range(lower, upper))
+
+        conn4 = ice.Connection(ice_controlling=True, ephemeral_ports=ports)
+        c = await conn4.get_component_candidates(0, addresses)
+        self.assertTrue(c[0].port >= lower and c[0].port < upper)
+
+        # Exhaust the range of ports
+        conns = []
+        for i in range(1, len(ports)):
+            conn = ice.Connection(ice_controlling=True, ephemeral_ports=ports)
+            c = await conn.get_component_candidates(i, addresses)
+            self.assertTrue(c[0].port >= lower and c[0].port < lower + len(ports))
+            conns.append(conn)
+
+        # Open one more connection from the same range - should always fail
+        conn = ice.Connection(ice_controlling=True, ephemeral_ports=ports)
+        c = await conn.get_component_candidates(0, addresses)
+        self.assertTrue(len(c) == 0) # all ports are already in use, no candidates
+
+        # Close one connection and try again - should never fail
+        await conn4.close()
+        conn = ice.Connection(ice_controlling=True, ephemeral_ports=ports)
+        c = await conn.get_component_candidates(0, addresses)
+        self.assertTrue(c[0].port >= lower and c[0].port < lower + len(ports))
+
+        # cleanup
+        await conn.close()
+        for conn in conns:
+            await conn.close()
 
 class StunProtocolTest(unittest.TestCase):
     @asynctest