Search RUNPATH to find library on Linux

CMakeLists.txt

@@ -34,6 +34,10 @@ if(WIN32)
   target_compile_definitions(${PROJECT_NAME}
     PRIVATE "RCPPUTILS_BUILDING_LIBRARY")
 endif()
+set_target_properties(${PROJECT_NAME} PROPERTIES
+  BUILD_RPATH ${CMAKE_CURRENT_BINARY_DIR}
+  INSTALL_RPATH_USE_LINK_PATH TRUE
+)
 ament_target_dependencies(${PROJECT_NAME} rcutils)
 ament_export_libraries(${PROJECT_NAME})
 
@@ -71,12 +75,31 @@ if(BUILD_TESTING)
 
   ament_add_gtest(test_endian test/test_endian.cpp)
 
+  if(WIN32)
+    set(LIBRARY_PATH_VAR "PATH")
+  elseif(APPLE)
+    set(LIBRARY_PATH_VAR "DYLD_LIBRARY_PATH")
+  else()
+    set(LIBRARY_PATH_VAR "LD_LIBRARY_PATH")
+  endif()
+
   add_library(test_library SHARED test/test_library.cpp)
+
   ament_add_gtest(test_find_library test/test_find_library.cpp)
   target_link_libraries(test_find_library ${PROJECT_NAME} test_library)
   set_tests_properties(test_find_library PROPERTIES
     ENVIRONMENT
-      "_TEST_LIBRARY_DIR=$<TARGET_FILE_DIR:test_library>;_TEST_LIBRARY=$<TARGET_FILE:test_library>")
+      "${LIBRARY_PATH_VAR}=$<TARGET_FILE_DIR:test_library>;_TEST_LIBRARY=$<TARGET_FILE:test_library>")
+
+  # Test with empty LD_LIBRARY_PATH to emulate setcap / setuid executable.
+  # Using RUNPATH to find library instead.
+  if(NOT (WIN32 OR APPLE))
+    ament_add_gtest(test_find_library_runpath test/test_find_library.cpp)
+    target_link_libraries(test_find_library_runpath ${PROJECT_NAME} test_library)
+    set_tests_properties(test_find_library_runpath PROPERTIES
+      ENVIRONMENT
+        "${LIBRARY_PATH_VAR}=;_TEST_LIBRARY=$<TARGET_FILE:test_library>")
+  endif()
 endif()
 
 ament_package()

include/rcpputils/find_library.hpp

@@ -23,8 +23,8 @@ namespace rcpputils
 {
 
 /// Finds a library located in the OS's specified environment variable for
-/// library paths and returns the absolute filesystem path, including the
-/// appropriate prefix and extension.
+/// library paths or in RUNPATH on Linux and returns the absolute filesystem
+/// path, including the appropriate prefix and extension.
 /**
  * The environment variable and file format per platform:
  *  * Linux: `${LD_LIBRARY_PATH}`, `lib{}.so`

src/find_library.cpp

@@ -14,6 +14,10 @@
 
 #include "rcpputils/find_library.hpp"
 
+#if !defined(_WIN32) && !defined(__APPLE__)
+#include <link.h>
+#endif
+
 #include <cassert>
 #include <cstddef>
 
@@ -69,12 +73,44 @@ std::list<std::string> split(const std::string & value, const char delimiter)
   return list;
 }
 
+// Retrieves a list of paths from the RUNPATH header on Linux.
+// Useful when LD_LIBRARY_PATH is ignored for setcap / setuid executables.
+std::list<std::string> retrieve_runpath_paths()
+{
+#if defined(_WIN32) || defined(__APPLE__)
+  // Return empty list for win / macos
+  return std::list<std::string>();
+#else
+  const ElfW(Dyn) * dyn = _DYNAMIC;
+  const ElfW(Dyn) * runpath = NULL;
+  const char * strtab = NULL;
+
+  for (; dyn->d_tag != DT_NULL; ++dyn) {
+    if (dyn->d_tag == DT_RUNPATH) {
+      runpath = dyn;
+    } else if (dyn->d_tag == DT_STRTAB) {
+      strtab = (const char *)dyn->d_un.d_val;
+    }
+  }
+
+  std::string search_path;
+  if (strtab != NULL && runpath != NULL) {
+    search_path = std::string(strtab + runpath->d_un.d_val);
+  }
+
+  return split(search_path, kPathSeparator);
+#endif
+}
+
 }  // namespace
 
 std::string find_library_path(const std::string & library_name)
 {
-  std::string search_path = get_env_var(kPathVar);
-  std::list<std::string> search_paths = split(search_path, kPathSeparator);
+  std::string search_path_env = get_env_var(kPathVar);
+  std::list<std::string> search_paths = split(search_path_env, kPathSeparator);
+
+  std::list<std::string> search_paths_runpath = retrieve_runpath_paths();
+  search_paths.splice(search_paths.cend(), search_paths_runpath);
 
   std::string filename = kSolibPrefix;
   filename += library_name + kSolibExtension;

test/test_find_library.cpp

@@ -37,29 +37,8 @@ TEST(test_find_library, find_library)
     expected_library_path = _expected_library_path;
   }
 
-  const char * test_lib_dir{};
-  EXPECT_EQ(rcutils_get_env("_TEST_LIBRARY_DIR", &test_lib_dir), nullptr);
-  EXPECT_NE(test_lib_dir, nullptr);
-
-  // Set our relevant path variable.
-  const char * env_var{};
-#ifdef _WIN32
-  env_var = "PATH";
-#elif __APPLE__
-  env_var = "DYLD_LIBRARY_PATH";
-#else
-  env_var = "LD_LIBRARY_PATH";
-#endif
-
-#ifdef _WIN32
-  EXPECT_EQ(_putenv_s(env_var, test_lib_dir), 0);
-#else
-  const int override = 1;
-  EXPECT_EQ(setenv(env_var, test_lib_dir, override), 0);
-#endif
-
   // Positive test.
-  const std::string test_lib_actual = find_library_path("test_library");
+  std::string test_lib_actual = find_library_path("test_library");
   EXPECT_EQ(test_lib_actual, expected_library_path);
 
   // (Hopefully) Negative test.