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Commit 9bb7971a authored by Elliott Hughes's avatar Elliott Hughes
Browse files

Keep the ReadFileToString/ReadFdToString overhead down. 

Bug: https://code.google.com/p/android/issues/detail?id=258500
Bug: http://b/36046324
Test: ran tests
Change-Id: I40e76a6dd164ea9a5e8e18159f543e1bb221dcba
parent 1d1de8e2

base/file.cpp

+8 −0
Original line number Diff line number Diff line
@@ -49,6 +49,14 @@ using namespace android::base::utf8; 
bool ReadFdToString(int fd, std::string* content) {

  content->clear();



  // Although original we had small files in mind, this code gets used for

  // very large files too, where the std::string growth heuristics might not

  // be suitable. https://code.google.com/p/android/issues/detail?id=258500.

  struct stat sb;

  if (fstat(fd, &sb) != -1 && sb.st_size > 0) {

    content->reserve(sb.st_size);

  }



  char buf[BUFSIZ];

  ssize_t n;

  while ((n = TEMP_FAILURE_RETRY(read(fd, &buf[0], sizeof(buf)))) > 0) {

base/file_test.cpp

+43 −0
Original line number Diff line number Diff line
@@ -214,3 +214,46 @@ TEST(file, Dirname) { 
  EXPECT_EQ(".", android::base::Dirname("sh"));

  EXPECT_EQ("/system/bin", android::base::Dirname("/system/bin/sh/"));

}



TEST(file, ReadFileToString_capacity) {

  TemporaryFile tf;

  ASSERT_TRUE(tf.fd != -1);



  // For a huge file, the overhead should still be small.

  std::string s;

  size_t size = 16 * 1024 * 1024;

  ASSERT_TRUE(android::base::WriteStringToFile(std::string(size, 'x'), tf.path));

  ASSERT_TRUE(android::base::ReadFileToString(tf.path, &s));

  EXPECT_EQ(size, s.size());

  EXPECT_LT(s.capacity(), size + 16);



  // Even for weird badly-aligned sizes.

  size += 12345;

  ASSERT_TRUE(android::base::WriteStringToFile(std::string(size, 'x'), tf.path));

  ASSERT_TRUE(android::base::ReadFileToString(tf.path, &s));

  EXPECT_EQ(size, s.size());

  EXPECT_LT(s.capacity(), size + 16);



  // We'll shrink an enormous string if you read a small file into it.

  size = 64;

  ASSERT_TRUE(android::base::WriteStringToFile(std::string(size, 'x'), tf.path));

  ASSERT_TRUE(android::base::ReadFileToString(tf.path, &s));

  EXPECT_EQ(size, s.size());

  EXPECT_LT(s.capacity(), size + 16);

}



TEST(file, ReadFileToString_capacity_0) {

  TemporaryFile tf;

  ASSERT_TRUE(tf.fd != -1);



  // Because /proc reports its files as zero-length, we don't actually trust

  // any file that claims to be zero-length. Rather than add increasingly

  // complex heuristics for shrinking the passed-in string in that case, we

  // currently leave it alone.

  std::string s;

  size_t initial_capacity = s.capacity();

  ASSERT_TRUE(android::base::WriteStringToFile("", tf.path));

  ASSERT_TRUE(android::base::ReadFileToString(tf.path, &s));

  EXPECT_EQ(0U, s.size());

  EXPECT_EQ(initial_capacity, s.capacity());

}