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
diff --git a/base/file.cpp b/base/file.cpp
index 378a405..d4e5894 100644
--- a/base/file.cpp
+++ b/base/file.cpp
@@ -49,6 +49,14 @@
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) {
diff --git a/base/file_test.cpp b/base/file_test.cpp
index 266131e..02b431d 100644
--- a/base/file_test.cpp
+++ b/base/file_test.cpp
@@ -214,3 +214,46 @@
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());
+}