Add FileReaderInterface::ReadExactly() and FileSeekerInterface::SeekSet()

util/file/file_reader.cc

 // 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 {
 
+bool FileReaderInterface::ReadExactly(void* data, size_t size) {
+  ssize_t expect = base::checked_cast<ssize_t>(size);
+  ssize_t rv = Read(data, size);
+  if (rv < 0) {
+    // Read() will have logged its own error.
+    return false;
+  } else if (rv != expect) {
+    LOG(ERROR) << "ReadExactly(): expected " << expect << ", observed " << rv;
+    return false;
+  }
+
+  return true;
+}
+
 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);
 
@@ skipping 47 matching lines @@
   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