From 3ff74eae0e5e98c238b5413f56e6340cfec1352d Mon Sep 17 00:00:00 2001
From: Fletcher Dunn <fletcherd@valvesoftware.com>
Date: Mon, 18 May 2026 07:34:44 -0700
Subject: [PATCH] Setup loopback aliases for p2p tests properly

---
 .github/workflows/build.yml |  6 ++++++
 .github/workflows/macos.yml | 14 ++++----------
 tests/test_p2p.py           | 21 ++++++++++++++++++---
 3 files changed, 28 insertions(+), 13 deletions(-)

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 1c91f9d..7731b2c 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -74,6 +74,8 @@ jobs:
         run: |
           sudo -E bash .github/install.sh
           sudo -E bash .github/install-post.sh
+      - name: Setup mock IPs
+        run: sudo python3 tests/test_p2p.py --setup-mock-ips
       - name: Build and test (RelWithDebInfo)
         run: |
           set -euo pipefail
@@ -186,6 +188,10 @@ jobs:
     steps:
       - uses: actions/checkout@main
 
+      - name: Setup mock IPs
+        run: py -3 tests/test_p2p.py --setup-mock-ips
+        shell: cmd
+
       # Mark all directories as safe so checkouts performed in CMakeLists.txt don't cause "unsafe repository" errors.
       # See https://github.com/actions/checkout/issues/766
       - name: Configure Git
diff --git a/.github/workflows/macos.yml b/.github/workflows/macos.yml
index b24b557..d83b604 100644
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@@ -14,6 +14,10 @@ jobs:
     steps:
     - uses: actions/checkout@v4
 
+    - name: Setup mock IPs
+      run: sudo python3 tests/test_p2p.py --setup-mock-ips
+      shell: bash
+
     - name: Ensure vcpkg cache directories exist
       run: |
         mkdir -p "${VCPKG_DOWNLOADS}"
@@ -61,21 +65,11 @@ 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
diff --git a/tests/test_p2p.py b/tests/test_p2p.py
index c9043f2..2fb00c2 100755
--- a/tests/test_p2p.py
+++ b/tests/test_p2p.py
@@ -208,6 +208,8 @@ def _IsAddressBindable( addr ):
     except OSError:
         return False
 
+_WINDOWS_LOOPBACK_IFACE = 'Loopback Pseudo-Interface 1'
+
 def _AddLoopbackAddr( addr ):
     is_ipv6 = ':' in addr
     sys_name = platform.system()
@@ -223,7 +225,12 @@ def _AddLoopbackAddr( addr ):
             print( "Running 'ip -6 addr add %s/112 dev lo'" % addr )
             subprocess.run( [ 'ip', '-6', 'addr', 'add', addr + '/112', 'dev', 'lo' ], check=True )
         # IPv4 on Linux: the entire 127/8 block is routable on lo, nothing to do.
-    # Windows: TBD when needed
+    elif sys_name == 'Windows':
+        if is_ipv6:
+            print( "Running 'netsh interface ipv6 add address \"%s\" %s'" % ( _WINDOWS_LOOPBACK_IFACE, addr ) )
+            subprocess.run( [ 'netsh', 'interface', 'ipv6', 'add', 'address',
+                               _WINDOWS_LOOPBACK_IFACE, addr ], check=True )
+        # IPv4 on Windows: the entire 127/8 block is routable on the loopback adapter, nothing to do.
 
 def _RemoveLoopbackAddr( addr ):
     is_ipv6 = ':' in addr
@@ -240,7 +247,12 @@ def _RemoveLoopbackAddr( addr ):
             print( "Running 'ip -6 addr del %s/112 dev lo'" % addr )
             subprocess.run( [ 'ip', '-6', 'addr', 'del', addr + '/112', 'dev', 'lo' ], check=False )
         # IPv4 on Linux: nothing was added, nothing to remove.
-    # Windows: TBD when needed
+    elif sys_name == 'Windows':
+        if is_ipv6:
+            print( "Running 'netsh interface ipv6 delete address \"%s\" %s'" % ( _WINDOWS_LOOPBACK_IFACE, addr ) )
+            subprocess.run( [ 'netsh', 'interface', 'ipv6', 'delete', 'address',
+                               _WINDOWS_LOOPBACK_IFACE, addr ], check=False )
+        # IPv4 on Windows: nothing was added, nothing to remove.
 
 def SetupMockIPs():
     """Add loopback aliases for every mock address that is not already bindable."""
@@ -264,7 +276,10 @@ def CheckMockIPsBindable():
     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] )
+    if platform.system() == 'Windows':
+        print( "Run '%s --setup-mock-ips' from an elevated (Administrator) prompt." % sys.argv[0] )
+    else:
+        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 ):