Base: Change ReadPlatformFile to perform a best

effort read of the requested data, and add another
function (ReadPlatformFileNoBestEffort) that just
forwards the call to the OS.

Now ReadPlatformFile and WritePlatformFile behave
the same way.

BUG=none
TEST=base_unittests
Review URL: http://codereview.chromium.org/7821013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@99264 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 42 insertions, 19 deletions

diff --git a/base/platform_file.h b/base/platform_file.h
index cf3716c..2bfd181 100644
--- a/base/platform_file.h
+++ b/base/platform_file.h
@@ -117,10 +117,19 @@ BASE_EXPORT PlatformFile CreatePlatformFile(const FilePath& name,
 BASE_EXPORT bool ClosePlatformFile(PlatformFile file);
 
 // Reads the given number of bytes (or until EOF is reached) starting with the
-// given offset. Returns the number of bytes read, or -1 on error.
+// given offset. Returns the number of bytes read, or -1 on error. Note that
+// this function makes a best effort to read all data on all platforms, so it is
+// not intended for stream oriented files but instead for cases when the normal
+// expectation is that actually |size| bytes are read unless there is an error.
 BASE_EXPORT int ReadPlatformFile(PlatformFile file, int64 offset,
                                  char* data, int size);
 
+// Reads the given number of bytes (or until EOF is reached) starting with the
+// given offset, but does not make any effort to read all data on all platforms.
+// Returns the number of bytes read, or -1 on error.
+BASE_EXPORT int ReadPlatformFileNoBestEffort(PlatformFile file, int64 offset,
+                                             char* data, int size);
+
 // Writes the given buffer into the file at the given offset, overwritting any
 // data that was previously there. Returns the number of bytes written, or -1
 // on error. Note that this function makes a best effort to write all data on
diff --git a/base/platform_file_posix.cc b/base/platform_file_posix.cc
index b058edc..d4ee768 100644
--- a/base/platform_file_posix.cc
+++ b/base/platform_file_posix.cc
@@ -147,6 +147,25 @@ bool ClosePlatformFile(PlatformFile file) {
 }
 
 int ReadPlatformFile(PlatformFile file, int64 offset, char* data, int size) {
+  if (file < 0 || size < 0)
+    return -1;
+
+  int bytes_read = 0;
+  int rv;
+  do {
+    rv = HANDLE_EINTR(pread(file, data + bytes_read,
+                            size - bytes_read, offset + bytes_read));
+    if (rv <= 0)
+      break;
+
+    bytes_read += rv;
+  } while (bytes_read < size);
+
+  return bytes_read ? bytes_read : rv;
+}
+
+int ReadPlatformFileNoBestEffort(PlatformFile file, int64 offset,
+                                 char* data, int size) {
   if (file < 0)
     return -1;
 
diff --git a/base/platform_file_unittest.cc b/base/platform_file_unittest.cc
index 7eb1af9..1acbaa6 100644
--- a/base/platform_file_unittest.cc
+++ b/base/platform_file_unittest.cc
@@ -13,24 +13,7 @@ namespace {
 // Reads from a file the given number of bytes, or until EOF is reached.
 // Returns the number of bytes read.
 int ReadFully(base::PlatformFile file, int64 offset, char* data, int size) {
-  int total_bytes_read = 0;
-  int bytes_read;
-  while (total_bytes_read < size) {
-    bytes_read = base::ReadPlatformFile(
-        file, offset + total_bytes_read, &data[total_bytes_read],
-        size - total_bytes_read);
-
-    // If we reached EOF, bytes_read will be 0.
-    if (bytes_read == 0)
-      return total_bytes_read;
-
-    if ((bytes_read < 0) || (bytes_read > size - total_bytes_read))
-      return -1;
-
-    total_bytes_read += bytes_read;
-  }
-
-  return total_bytes_read;
+  return base::ReadPlatformFile(file, offset, data, size);
 }
 
 // Writes the given number of bytes to a file.
@@ -192,6 +175,13 @@ TEST(PlatformFile, ReadWritePlatformFile) {
   for (int i = 0; i < bytes_read; i++)
     EXPECT_EQ(data_to_write[i], data_read_1[i]);
 
+  // Read again, but using the trivial native wrapper.
+  bytes_read = base::ReadPlatformFileNoBestEffort(file, 0, data_read_1,
+                                                  kTestDataSize);
+  EXPECT_LE(bytes_read, kTestDataSize);
+  for (int i = 0; i < bytes_read; i++)
+    EXPECT_EQ(data_to_write[i], data_read_1[i]);
+
   // Write past the end of the file.
   const int kOffsetBeyondEndOfFile = 10;
   const int kPartialWriteLength = 2;
diff --git a/base/platform_file_win.cc b/base/platform_file_win.cc
index 8374042..072c24a 100644
--- a/base/platform_file_win.cc
+++ b/base/platform_file_win.cc
@@ -134,6 +134,11 @@ int ReadPlatformFile(PlatformFile file, int64 offset, char* data, int size) {
   return -1;
 }
 
+int ReadPlatformFileNoBestEffort(PlatformFile file, int64 offset,
+                                 char* data, int size) {
+  return ReadPlatformFile(file, offset, data, size);
+}
+
 int WritePlatformFile(PlatformFile file, int64 offset,
                       const char* data, int size) {
   base::ThreadRestrictions::AssertIOAllowed();