Introduce MinidumpWritable, its dependencies, and their tests

util/file/fd_io.cc

+// Copyright 2014 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/fd_io.h"
+
+#include <unistd.h>
+
+#include "base/posix/eintr_wrapper.h"
+
+namespace {
+
+struct ReadTraits {
+  typedef void* VoidBufferType;
+  typedef char* CharBufferType;
+  static ssize_t Operate(int fd, CharBufferType buffer, size_t size) {
+    return read(fd, buffer, size);
+  }
+};
+
+struct WriteTraits {
+  typedef const void* VoidBufferType;
+  typedef const char* CharBufferType;
+  static ssize_t Operate(int fd, CharBufferType buffer, size_t size) {
+    return write(fd, buffer, size);
+  }
+};
+
+template <typename Traits>
+ssize_t ReadOrWrite(int fd,
+                    typename Traits::VoidBufferType buffer,
+                    size_t size) {
+  typename Traits::CharBufferType buffer_c =
+      reinterpret_cast<typename Traits::CharBufferType>(buffer);
+
+  ssize_t total_bytes = 0;
+  while (size > 0) {
+    ssize_t bytes = HANDLE_EINTR(Traits::Operate(fd, buffer_c, size));
+    if (bytes < 0) {
+      return bytes;
+    } else if (bytes == 0) {
+      break;
+    }
+
+    buffer_c += bytes;
+    size -= bytes;
+    total_bytes += bytes;
+  }
+
+  return total_bytes;
+}
+
+}  // namespace
+
+namespace crashpad {
+
+ssize_t ReadFD(int fd, void* buffer, size_t size) {
+  return ReadOrWrite<ReadTraits>(fd, buffer, size);
+}
+
+ssize_t WriteFD(int fd, const void* buffer, size_t size) {
+  return ReadOrWrite<WriteTraits>(fd, buffer, size);
+}
+
+}  // namespace crashpad