test_p2p will muck with the local network stack

To allow us to bind to other addresses besides 127.0.0.1.
We'll need something similar for IPv6, but for now we only
need it for IPv4 on MacOS

Author: zpostfacto

.github/workflows/macos.yml

@@ -61,11 +61,21 @@ jobs:
       run: ./test_connection suite-quick
       shell: bash
 
+    - name: Setup mock IPs
+      working-directory: ${{github.workspace}}/build/bin
+      run: sudo python3 test_p2p.py --setup-mock-ips
+      shell: bash
+
     - name: Test p2p
       working-directory: ${{github.workspace}}/build/bin
       run: python3 test_p2p.py --spewlevel=debug --loglevel-p2prendezvous=debug
       shell: bash
 
+    - name: Cleanup mock IPs
+      working-directory: ${{github.workspace}}/build/bin
+      run: sudo python3 test_p2p.py --cleanup-mock-ips
+      shell: bash
+
     - name: Configure CMake (Release)
       run: cmake -B ${{github.workspace}}/build-release
             -DCMAKE_BUILD_TYPE=Release

tests/test_p2p.py

@@ -10,6 +10,7 @@
 import subprocess
 import threading
 import os
+import platform
 import sys
 import copy
 import time
@@ -23,10 +24,14 @@
 g_p2p_rendezvous_level = None
 g_stun_ip = "127.0.100.1"
 g_stun_port = 3478
+g_setup_mock_ips = False
+g_cleanup_mock_ips = False
 
 def ParseArgs():
     global g_spew_level
     global g_p2p_rendezvous_level
+    global g_setup_mock_ips
+    global g_cleanup_mock_ips
 
     parser = argparse.ArgumentParser()
     parser.add_argument(
@@ -40,9 +45,21 @@ def ParseArgs():
         choices=[ 'msg', 'verbose', 'debug' ],
         help='Control detail level specifically for P2P rendezvous-related spew.'
     )
+    parser.add_argument(
+        '--setup-mock-ips',
+        action='store_true',
+        help='Add any addresses needed by the mock network that are not already bindable. Exits without running tests.'
+    )
+    parser.add_argument(
+        '--cleanup-mock-ips',
+        action='store_true',
+        help='Remove addresses added by --setup-mock-ips. Exits without running tests.'
+    )
     args = parser.parse_args()
     g_spew_level = args.spewlevel
     g_p2p_rendezvous_level = args.loglevel_p2prendezvous
+    g_setup_mock_ips = args.setup_mock_ips
+    g_cleanup_mock_ips = args.cleanup_mock_ips
 
 # Thread class that runs a process and captures its output
 class RunProcessInThread(threading.Thread):
@@ -164,6 +181,54 @@ def StartClientInThread( role, local, remote, extra_args=[] ):
 _DEAD_INT = '127.0.9.2'    # address used for disabled adapters
 _CLI_SAME_LAN = '127.0.1.3' # client on the same /24 private LAN as _SRV_INT
 
+# All addresses that the mock network needs to be able to bind sockets to.
+_ALL_MOCK_ADDRS = [
+    g_stun_ip,
+    _SRV_GW, _CLI_GW, _SRV_GW2, _CLI_GW2,
+    _SRV_INT, _CLI_INT, _SRV_INT2, _CLI_INT2, _DEAD_INT, _CLI_SAME_LAN,
+]
+
+def _IsAddressBindable( addr ):
+    import socket
+    try:
+        s = socket.socket( socket.AF_INET, socket.SOCK_DGRAM )
+        s.bind( ( addr, 0 ) )
+        s.close()
+        return True
+    except OSError:
+        return False
+
+def SetupMockIPs():
+    """Add loopback aliases for every mock address that is not already bindable."""
+    if platform.system() != 'Darwin':
+        print( "Nothing to do on this platform." )
+        return
+    for addr in _ALL_MOCK_ADDRS:
+        subprocess.run( [ 'ifconfig', 'lo0', 'alias', addr ], check=True )
+    print( "Added %d loopback alias(es)." % len( _ALL_MOCK_ADDRS ) )
+
+def CleanupMockIPs():
+    """Remove loopback aliases added by --setup-mock-ips."""
+    if platform.system() != 'Darwin':
+        print( "Nothing to do on this platform." )
+        return
+    for addr in _ALL_MOCK_ADDRS:
+        if addr == '127.0.0.1':
+            continue
+        subprocess.run( [ 'ifconfig', 'lo0', '-alias', addr ], check=False )
+    print( "Removed loopback aliases." )
+
+def CheckMockIPsBindable():
+    """Verify all mock addresses are bindable; exit with an error if any are not."""
+    missing = [ addr for addr in _ALL_MOCK_ADDRS if not _IsAddressBindable( addr ) ]
+    if not missing:
+        return
+    print( "ERROR: the following addresses required by the mock network are not bindable:" )
+    for addr in missing:
+        print( "  " + addr )
+    print( "Run 'sudo %s --setup-mock-ips' to add the required loopback aliases." % sys.argv[0] )
+    sys.exit(1)
+
 def _nat( internal, gateway, nat_type ):
     # Gateway must be declared before the adapter that uses it
     return [ '--mock-gateway', gateway, '--mock-nat', nat_type, '--mock-adapter', internal ]
@@ -282,6 +347,16 @@ def ClientServerTest( server_extra_args=[], client_extra_args=[], expected_route
 
 ParseArgs()
 
+if g_setup_mock_ips:
+    SetupMockIPs()
+    sys.exit(0)
+
+if g_cleanup_mock_ips:
+    CleanupMockIPs()
+    sys.exit(0)
+
+CheckMockIPsBindable()
+
 # Find and start the STUN server
 stun_server_script = './stun_server.py'
 if not os.path.exists( stun_server_script ):