Add FileReaderInterface. Move StringFileWriter to StringFile and

util/file/file_reader.cc

Index: util/file/file_reader.cc
diff --git a/util/file/file_reader.cc b/util/file/file_reader.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b6fd0173e262b294f4acb67f1cc85781bdbfe7b9
--- /dev/null
+++ b/util/file/file_reader.cc
@@ -0,0 +1,88 @@
+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/file/file_reader.h"
+
+#include "base/logging.h"
+#include "base/numerics/safe_conversions.h"
+
+namespace crashpad {
+
+WeakFileHandleFileReader::WeakFileHandleFileReader(FileHandle file_handle)
+    : file_handle_(file_handle) {
+}
+
+WeakFileHandleFileReader::~WeakFileHandleFileReader() {
+}
+
+ssize_t WeakFileHandleFileReader::Read(void* data, size_t size) {
+  DCHECK_NE(file_handle_, kInvalidFileHandle);
+
+  // Don’t use LoggingReadFile(), which insists on a full read and only returns
+  // a bool. This method permits short reads and returns the number of bytes
+  // read.
+  base::checked_cast<ssize_t>(size);
+  ssize_t rv = ReadFile(file_handle_, data, size);
+  if (rv < 0) {
+    PLOG(ERROR) << "read";
+    return -1;
+  }
+
+  return rv;
+}
+
+FileOffset WeakFileHandleFileReader::Seek(FileOffset offset, int whence) {
+  DCHECK_NE(file_handle_, kInvalidFileHandle);
+  return LoggingSeekFile(file_handle_, offset, whence);
+}
+
+FileReader::FileReader()
+    : file_(),
+      weak_file_handle_file_reader_(kInvalidFileHandle) {
+}
+
+FileReader::~FileReader() {
+}
+
+bool FileReader::Open(const base::FilePath& path,
+                      FileWriteMode write_mode,
+                      FilePermissions permissions) {
+  CHECK(!file_.is_valid());
+  file_.reset(LoggingOpenFileForRead(path));
+  if (!file_.is_valid()) {
+    return false;
+  }
+
+  weak_file_handle_file_reader_.set_file_handle(file_.get());
+  return true;
+}
+
+void FileReader::Close() {
+  CHECK(file_.is_valid());
+
+  weak_file_handle_file_reader_.set_file_handle(kInvalidFileHandle);
+  file_.reset();
+}
+
+ssize_t FileReader::Read(void* data, size_t size) {
+  DCHECK(file_.is_valid());
+  return weak_file_handle_file_reader_.Read(data, size);
+}
+
+FileOffset FileReader::Seek(FileOffset offset, int whence) {
+  DCHECK(file_.is_valid());
+  return weak_file_handle_file_reader_.Seek(offset, whence);
+}
+
+}  // namespace crashpad