Added new ReadFileToString API with a max_size argument

The CL creates a new API that takes a max_size argument. When the file size exceed the max_size, the API primes the cache and returns false.

BUG=339417

Review URL: https://codereview.chromium.org/157593005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251771 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 85 insertions, 5 deletions

diff --git a/base/file_util.cc b/base/file_util.cc
index e44f713..87b9afb99 100644
--- a/base/file_util.cc
+++ b/base/file_util.cc
@@ -10,6 +10,7 @@
 #include <stdio.h>
 
 #include <fstream>
+#include <limits>
 
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
@@ -126,7 +127,11 @@ bool TextContentsEqual(const FilePath& filename1, const FilePath& filename2) {
   return true;
 }
 
-bool ReadFileToString(const FilePath& path, std::string* contents) {
+bool ReadFileToString(const FilePath& path,
+                      std::string* contents,
+                      size_t max_size) {
+  if (contents)
+    contents->clear();
   if (path.ReferencesParent())
     return false;
   FILE* file = OpenFile(path, "rb");
@@ -136,13 +141,29 @@ bool ReadFileToString(const FilePath& path, std::string* contents) {
 
   char buf[1 << 16];
   size_t len;
+  size_t size = 0;
+  bool read_status = true;
+
+  // Many files supplied in |path| have incorrect size (proc files etc).
+  // Hence, the file is read sequentially as opposed to a one-shot read.
   while ((len = fread(buf, 1, sizeof(buf), file)) > 0) {
     if (contents)
-      contents->append(buf, len);
+      contents->append(buf, std::min(len, max_size - size));
+
+    if ((max_size - size) < len) {
+      read_status = false;
+      break;
+    }
+
+    size += len;
   }
   CloseFile(file);
 
-  return true;
+  return read_status;
+}
+
+bool ReadFileToString(const FilePath& path, std::string* contents) {
+  return ReadFileToString(path, contents, std::numeric_limits<size_t>::max());
 }
 
 bool IsDirectoryEmpty(const FilePath& dir_path) {
diff --git a/base/file_util.h b/base/file_util.h
index 7690703..9143c60 100644
--- a/base/file_util.h
+++ b/base/file_util.h
@@ -139,10 +139,24 @@ BASE_EXPORT bool TextContentsEqual(const FilePath& filename1,
 // Read the file at |path| into |contents|, returning true on success.
 // This function fails if the |path| contains path traversal components ('..').
 // |contents| may be NULL, in which case this function is useful for its
-// side effect of priming the disk cache.
-// Useful for unit tests.
+// side effect of priming the disk cache, which is useful for unit tests.
+// The function replaces rather than append to |contents|, further |contents|
+// could be cleared on error.
 BASE_EXPORT bool ReadFileToString(const FilePath& path, std::string* contents);
 
+// Read the file at |path| into |contents|, returning true on success.
+// This function has an additional check on the maximum size of the file.
+// When the file size is greater than |max_size|, the function reads |max_size|
+// bytes into |contents| and returns false.
+// This function fails if the |path| contains path traversal components ('..').
+// |contents| may be NULL, in which case this function is useful for its
+// side effect of priming the disk cache, which is useful for unit tests.
+// The function replaces rather than append to |contents|, further |contents|
+// could be cleared on error.
+BASE_EXPORT bool ReadFileToString(const FilePath& path,
+                                  std::string* contents,
+                                  size_t max_size);
+
 #if defined(OS_POSIX)
 
 // Read exactly |bytes| bytes from file descriptor |fd|, storing the result
diff --git a/base/file_util_unittest.cc b/base/file_util_unittest.cc
index df447ab..d36d4b2 100644
--- a/base/file_util_unittest.cc
+++ b/base/file_util_unittest.cc
@@ -1941,6 +1941,51 @@ TEST_F(FileUtilTest, AppendToFile) {
   EXPECT_EQ(L"hellohello", read_content);
 }
 
+TEST_F(FileUtilTest, ReadFileToString) {
+  const char kTestData[] = "0123";
+  std::string data;
+
+  FilePath file_path =
+      temp_dir_.path().Append(FILE_PATH_LITERAL("ReadFileToStringTest"));
+
+  ASSERT_EQ(4, file_util::WriteFile(file_path, kTestData, 4));
+
+  EXPECT_TRUE(ReadFileToString(file_path, &data));
+  EXPECT_EQ(kTestData, data);
+
+  data = "temp";
+  EXPECT_FALSE(ReadFileToString(file_path, &data, 0));
+  EXPECT_EQ(data.length(), 0u);
+
+  data = "temp";
+  EXPECT_FALSE(ReadFileToString(file_path, &data, 2));
+  EXPECT_EQ("01", data);
+
+  data.clear();
+  EXPECT_FALSE(ReadFileToString(file_path, &data, 3));
+  EXPECT_EQ("012", data);
+
+  data.clear();
+  EXPECT_TRUE(ReadFileToString(file_path, &data, 4));
+  EXPECT_EQ("0123", data);
+
+  data.clear();
+  EXPECT_TRUE(ReadFileToString(file_path, &data, 6));
+  EXPECT_EQ("0123", data);
+
+  EXPECT_TRUE(ReadFileToString(file_path, NULL, 6));
+
+  EXPECT_TRUE(ReadFileToString(file_path, NULL));
+
+  EXPECT_TRUE(base::DeleteFile(file_path, false));
+
+  EXPECT_FALSE(ReadFileToString(file_path, &data));
+  EXPECT_EQ(data.length(), 0u);
+
+  EXPECT_FALSE(ReadFileToString(file_path, &data, 6));
+  EXPECT_EQ(data.length(), 0u);
+}
+
 TEST_F(FileUtilTest, TouchFile) {
   FilePath data_dir =
       temp_dir_.path().Append(FILE_PATH_LITERAL("FilePathTest"));