Isolates generic DnsClient from AsyncHostResolver.

net/base/big_endian.h

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_BASE_BIG_ENDIAN_H_
+#define NET_BASE_BIG_ENDIAN_H_
+#pragma once
+
+#include "base/string_piece.h"
+#include "net/base/net_export.h"
+
+namespace net {
+
+// Read an integer (signed or unsigned) from |buf| in Big Endian order.
+// Note: this loop is unrolled with -O1 and above.
+// NOTE(szym): glibc dns-canon.c and SpdyFrameBuilder use
+// ntohs(*(uint16_t*)ptr) which is potentially unaligned.
+// This would cause SIGBUS on ARMv5 or earlier and ARMv6-M.
+template<typename T>
+inline void ReadBigEndian(const char buf[], T* out) {
+  *out = buf[0];
+  for (size_t i = 1; i < sizeof(T); ++i) {
+    *out <<= 8;
+    // Must cast to uint8 to avoid clobbering by sign extension.
+    *out |= static_cast<uint8>(buf[i]);
+  }
+}
+
+// Write an integer (signed or unsigned) |val| to |buf| in Big Endian order.
+// Note: this loop is unrolled with -O1 and above.
+template<typename T>
+inline void WriteBigEndian(char buf[], T val) {
+  for (size_t i = 0; i < sizeof(T); ++i) {
+    buf[sizeof(T)-i-1] = static_cast<char>(val & 0xFF);
+    val >>= 8;
+  }
+}
+
+// Specializations to make clang happy about the (dead code) shifts above.
+template<>
+inline void ReadBigEndian<uint8>(const char buf[], uint8* out) {
+  *out = buf[0];
+}
+
+template<>
+inline void WriteBigEndian<uint8>(char buf[], uint8 val) {
+  buf[0] = static_cast<char>(val);
+}
+
+// Allows reading integers in network order (big endian) while iterating over
+// an underlying buffer. All the reading functions advance the internal pointer.
+class NET_EXPORT BigEndianReader {
+ public:
+  BigEndianReader(const void* buf, size_t len);
+
+  const char* ptr() const { return ptr_; }
+  int remaining() const { return end_ - ptr_; }
+
+  bool Skip(size_t len);
+  bool ReadBytes(void* out, size_t len);
+  // Creates a StringPiece in |out| that points to the underlying buffer.
+  bool ReadPiece(base::StringPiece* out, size_t len);
+  bool ReadU8(uint8* value);
+  bool ReadU16(uint16* value);
+  bool ReadU32(uint32* value);
+
+ private:
+  // Hidden to promote type safety.
+  template<typename T>
+  bool Read(T* v);
+
+  const char* ptr_;
+  const char* end_;
+};
+
+// Allows writing integers in network order (big endian) while iterating over
+// an underlying buffer. All the writing functions advance the internal pointer.
+class NET_EXPORT BigEndianWriter {
+ public:
+  BigEndianWriter(void* buf, size_t len);
+
+  char* ptr() const { return ptr_; }
+  int remaining() const { return end_ - ptr_; }
+
+  bool Skip(size_t len);
+  bool WriteBytes(const void* buf, size_t len);
+  bool WriteU8(uint8 value);
+  bool WriteU16(uint16 value);
+  bool WriteU32(uint32 value);
+
+ private:
+  // Hidden to promote type safety.
+  template<typename T>
+  bool Write(T v);
+
+  char* ptr_;
+  char* end_;
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_BIG_ENDIAN_H_
+