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platform_system_core
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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
This commit is contained in:
Elliott Hughes 2017-03-20 19:16:18 -07:00
parent 1d1de8e282
commit 9bb7971ae7
2 changed files with 51 additions and 0 deletions
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8
base/file.cpp
View File

@ -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) {

43
base/file_test.cpp
View File

@ -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());
}