power: fix TryDifferentGovernors test

Switch to std::string and libbase to simplify the test and avoid
string manipulation bugs

Bug: 154070740
Bug: 149044096
Test: atest VtsHalPowerV1_0TargetTest
Change-Id: Ic80ca462cfeb650edcdc6420bf1b3190aa14dbe4
Signed-off-by: Connor O'Brien <connoro@google.com>
diff --git a/power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp b/power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp
index ba08ee7..7e0ae9c 100644
--- a/power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp
+++ b/power/1.0/vts/functional/VtsHalPowerV1_0TargetTest.cpp
@@ -19,6 +19,8 @@
 
 #include <cutils/properties.h>
 
+#include <android-base/file.h>
+#include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 #include <android/hardware/power/1.0/IPower.h>
 #include <gtest/gtest.h>
@@ -73,26 +75,16 @@
 TEST_P(PowerHidlTest, TryDifferentGovernors) {
   Return<void> ret;
 
-  unique_fd fd1(open(CPU_GOVERNOR_PATH, O_RDWR));
-  unique_fd fd2(open(AVAILABLE_GOVERNORS_PATH, O_RDONLY));
-  if (fd1 < 0 || fd2 < 0) {
+  std::string old_governor, governors;
+  if (!android::base::ReadFileToString(CPU_GOVERNOR_PATH, &old_governor) ||
+      !android::base::ReadFileToString(AVAILABLE_GOVERNORS_PATH, &governors)) {
     // Files don't exist, so skip the rest of the test case
     SUCCEED();
     return;
   }
-
-  char old_governor[80];
-  ASSERT_LE(0, read(fd1, old_governor, 80));
-
-  char governors[1024];
-  unsigned len = read(fd2, governors, 1024);
-  ASSERT_LE(0u, len);
-  governors[len] = '\0';
-
-  char *saveptr;
-  char *name = strtok_r(governors, " \n", &saveptr);
-  while (name) {
-    ASSERT_LE(0, write(fd1, name, strlen(name)));
+  auto all_governors = android::base::Split(governors, " \n");
+  for (const auto &governor : all_governors) {
+      ASSERT_TRUE(android::base::WriteStringToFile(governor, CPU_GOVERNOR_PATH));
     ret = power->setInteractive(true);
     ASSERT_TRUE(ret.isOk());
 
@@ -104,11 +96,9 @@
 
     power->powerHint(PowerHint::LAUNCH, 1);
     power->powerHint(PowerHint::LAUNCH, 0);
-
-    name = strtok_r(NULL, " \n", &saveptr);
   }
 
-  ASSERT_LE(0, write(fd1, old_governor, strlen(old_governor)));
+  ASSERT_TRUE(android::base::WriteStringToFile(old_governor, CPU_GOVERNOR_PATH));
 }
 
 // Sanity check Power::powerHint on good and bad inputs.