[fuchsia] Stop relying on /dev/null in tests.

ProcessUtilTest.FDRemappingIncludesStdio opens /dev/null on other Posix
systems. The fd returned from fdio_fd_create_null can't be cloned, so we
use a temporary file on Fuchsia in place of /dev/null.

Various MessageAttachmentSet tests use /dev/null just for the sake of
having an fd. Use fdio_fd_create_null() to get the fd rather than open.

Bug: 1256502
Change-Id: Ifd5bb3e8eba6f0b77854e8af9d15e5a67c812352
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3257280
Commit-Queue: Greg Thompson <[email protected]>
Commit-Queue: Daniel Cheng <[email protected]>
Auto-Submit: Greg Thompson <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Benjamin Lerman <[email protected]>
Reviewed-by: Tom Sepez <[email protected]>
Cr-Commit-Position: refs/heads/main@{#939491}

base/BUILD.gn

@@ -3268,6 +3268,7 @@ test("base_unittests") {
     "//base/third_party/dynamic_annotations",
     "//build:chromecast_buildflags",
     "//build:chromeos_buildflags",
+    "//build:os_buildflags",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/icu",

base/process/process_util_unittest.cc

@@ -37,6 +37,7 @@
 #include "base/threading/thread.h"
 #include "build/build_config.h"
 #include "build/chromeos_buildflags.h"
+#include "build/os_buildflags.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/multiprocess_func_list.h"
 
@@ -1154,8 +1155,21 @@ MULTIPROCESS_TEST_MAIN(ProcessUtilsVerifyStdio) {
 }
 
 TEST_F(ProcessUtilTest, FDRemappingIncludesStdio) {
-  int dev_null = open("/dev/null", O_RDONLY);
-  ASSERT_LT(2, dev_null);
+#if BUILDFLAG(IS_FUCHSIA)
+  // The fd obtained from fdio_fd_create_null cannot be cloned while spawning a
+  // child proc, so open a true file in a transient temp dir.
+  ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+  FilePath temp_file_path;
+  ASSERT_TRUE(CreateTemporaryFileInDir(temp_dir.GetPath(), &temp_file_path));
+  File temp_file(temp_file_path,
+                 File::FLAG_CREATE_ALWAYS | File::FLAG_READ | File::FLAG_WRITE);
+  ASSERT_TRUE(temp_file.IsValid());
+  ScopedFD some_fd(temp_file.TakePlatformFile());
+#else   // BUILDFLAG(IS_FUCHSIA)
+  ScopedFD some_fd(open("/dev/null", O_RDONLY));
+#endif  // BUILDFLAG(IS_FUCHSIA)
+  ASSERT_LT(2, some_fd.get());
 
   // Backup stdio and replace it with the write end of a pipe, for our
   // child process to inherit.
@@ -1169,7 +1183,7 @@ TEST_F(ProcessUtilTest, FDRemappingIncludesStdio) {
 
   // Launch the test process, which should inherit our pipe stdio.
   LaunchOptions options;
-  options.fds_to_remap.emplace_back(dev_null, dev_null);
+  options.fds_to_remap.emplace_back(some_fd.get(), some_fd.get());
   Process process = SpawnChildWithOptions("ProcessUtilsVerifyStdio", options);
   ASSERT_TRUE(process.IsValid());
 
@@ -1184,8 +1198,8 @@ TEST_F(ProcessUtilTest, FDRemappingIncludesStdio) {
 
   result = IGNORE_EINTR(close(backup_stdio));
   ASSERT_EQ(0, result);
-  result = IGNORE_EINTR(close(dev_null));
-  ASSERT_EQ(0, result);
+  // Also close the remapped descriptor.
+  some_fd.reset();
 
   // Read from the pipe to verify that it is connected to the child
   // process' stdio.

build/config/fuchsia/test/minimum_capabilities.test-cmx

@@ -12,7 +12,6 @@
   },
   "sandbox": {
     "dev": [
-      "null",
       "zero"
     ],
     "features": [

ipc/BUILD.gn

@@ -287,6 +287,7 @@ if (!is_ios) {
       "//base",
       "//base:i18n",
       "//base/test:test_support",
+      "//build:os_buildflags",
       "//crypto",
       "//mojo/core/test:test_support",
       "//testing/gtest",

ipc/ipc_message_attachment_set_posix_unittest.cc

@@ -12,15 +12,24 @@
 
 #include "base/posix/eintr_wrapper.h"
 #include "build/build_config.h"
+#include "build/os_buildflags.h"
 #include "ipc/ipc_platform_file_attachment_posix.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if BUILDFLAG(IS_FUCHSIA)
+#include <lib/fdio/fdio.h>
+#endif
+
 namespace IPC {
 namespace {
 
 // Get a safe file descriptor for test purposes.
 int GetSafeFd() {
+#if BUILDFLAG(IS_FUCHSIA)
+  return fdio_fd_create_null();
+#else
   return open("/dev/null", O_RDONLY);
+#endif
 }
 
 // Returns true if fd was already closed.  Closes fd if not closed.