From 742a1db7e7a2d851dbb8e8b70457ce465b0b67f8 Mon Sep 17 00:00:00 2001
From: Huang-Ming Huang <huangming.huang@gmail.com>
Date: Tue, 19 May 2026 21:50:03 +0000
Subject: [PATCH] Detect unshared test namespace support

---
 README.md            |  7 ++++++-
 tests/CMakeLists.txt | 41 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 75fb8a29eb..b07d0fde31 100644
--- a/README.md
+++ b/README.md
@@ -107,6 +107,11 @@ You can invoke them by running `ctest` from a terminal in your build directory a
 ctest -L "nonparallelizable_tests"
 ```
 
+On Linux hosts that support user and network namespaces, CMake automatically
+adds `--unshared` to tests that support it. This allows many tests that reuse
+the same localhost ports to run concurrently in isolated network namespaces.
+Control this with `-DSYSIO_UNSHARED_TESTS=AUTO|ON|OFF` at configure time.
+
 #### Long-Running Tests
 
 The long-running tests are [medium-to-large](https://testing.googleblog.com/2010/12/test-sizes.html) integration tests
@@ -135,4 +140,4 @@ ctest -L "long_running_tests"
       © 2024 Wire Network. All rights reserved.
     </td>
   </tr>
-</table>
\ No newline at end of file
+</table>
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 4c95951243..8e8f1a2bd6 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -114,9 +114,48 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/producer_rank_test.py ${CMAKE_CURRENT
 configure_file(${CMAKE_CURRENT_SOURCE_DIR}/split_blocklog_replay_test.py ${CMAKE_CURRENT_BINARY_DIR}/split_blocklog_replay_test.py COPYONLY)
 configure_file(${CMAKE_CURRENT_SOURCE_DIR}/PerformanceHarnessScenarioRunner.py ${CMAKE_CURRENT_BINARY_DIR}/PerformanceHarnessScenarioRunner.py COPYONLY)
 
-if(DEFINED ENV{GITHUB_ACTIONS})
+set(SYSIO_UNSHARED_TESTS "AUTO" CACHE STRING "Use Linux network namespaces for tests that support --unshared. Values: AUTO, ON, OFF")
+set_property(CACHE SYSIO_UNSHARED_TESTS PROPERTY STRINGS AUTO ON OFF)
+string(TOUPPER "${SYSIO_UNSHARED_TESTS}" SYSIO_UNSHARED_TESTS)
+if(NOT SYSIO_UNSHARED_TESTS MATCHES "^(AUTO|ON|OFF)$")
+  message(FATAL_ERROR "SYSIO_UNSHARED_TESTS must be AUTO, ON, or OFF")
+endif()
+
+set(SYSIO_CAN_UNSHARE_TESTS FALSE)
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND NOT SYSIO_UNSHARED_TESTS STREQUAL "OFF")
+  set(SYSIO_UNSHARE_PROBE "${CMAKE_CURRENT_BINARY_DIR}/probe_unshared_tests.py")
+  file(WRITE "${SYSIO_UNSHARE_PROBE}" "
+import pathlib
+import sys
+import importlib.util
+
+libc_path = pathlib.Path(r'${CMAKE_CURRENT_SOURCE_DIR}') / 'TestHarness' / 'libc.py'
+spec = importlib.util.spec_from_file_location('sysio_test_libc', libc_path)
+libc = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(libc)
+
+libc.unshare(libc.CLONE_NEWNET)
+")
+  execute_process(
+    COMMAND python3 "${SYSIO_UNSHARE_PROBE}"
+    RESULT_VARIABLE SYSIO_UNSHARE_RESULT
+    OUTPUT_QUIET
+    ERROR_VARIABLE SYSIO_UNSHARE_ERROR
+  )
+  if(SYSIO_UNSHARE_RESULT EQUAL 0)
+    set(SYSIO_CAN_UNSHARE_TESTS TRUE)
+  endif()
+endif()
+
+if(SYSIO_UNSHARED_TESTS STREQUAL "ON" AND NOT SYSIO_CAN_UNSHARE_TESTS)
+  message(FATAL_ERROR "SYSIO_UNSHARED_TESTS=ON, but this host cannot create a user/network namespace: ${SYSIO_UNSHARE_ERROR}")
+endif()
+
+if(SYSIO_CAN_UNSHARE_TESTS)
+  message(STATUS "Using --unshared for tests that support network namespace isolation")
   set(UNSHARE "--unshared")
 else()
+  message(STATUS "Not using --unshared for tests; set SYSIO_UNSHARED_TESTS=ON to require it")
   set(UNSHARE "")
 endif()