Isolates generic DnsClient from AsyncHostResolver.

net/base/bigendian.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_BIGENDIAN_H_
+#define NET_BASE_BIGENDIAN_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.
+class NET_EXPORT BigEndianReader {
+ public:
+  BigEndianReader(const void* buf, size_t len);
+  const char* ptr() const { return ptr_; }
+  int remaining() const { return end_ - ptr_; }

[mmenke, 2011/12/02 00:53:55]

Could you add a couple linebreaks here, to increase readability?  Up to you just
where to put them, but I'd suggest below the constructor, here, and below copy.

[mmenke, 2011/12/02 01:19:57]

Oops.  That should be above Copy.

[szym, 2011/12/05 23:06:28]

Done.

+  bool Skip(size_t len);
+  bool Copy(void* out, size_t len);

[mmenke, 2011/12/02 00:53:55]

I believe this can be const.

[mmenke, 2011/12/02 00:53:55]

Think a comment that states that all of these functions increment ptr_ by the
number of bytes read would be good.  It's a simple class, but people shouldn't
have to read the code to know what it does.  Same goes for the Writer.

[szym, 2011/12/05 23:06:28]

Done.

+  // Creates a StringPiece in |out| that points to the underlying buffer.
+  bool Piece(base::StringPiece* out, size_t len);

[mmenke, 2011/12/02 00:53:55]

Google style is to use verbs for function names.  Since these are more than
simple accessors, I suggest just ReadPiece, "ReadU8", etc.

[szym, 2011/12/05 23:06:28]

Done.

+  bool U8(uint8* v);

[mmenke, 2011/12/02 00:53:55]

Google style discourages overly abbreviated variable names.  I suggest you just
write out "value".

[szym, 2011/12/05 23:06:28]

Done.

+  bool U16(uint16* v);
+  bool U32(uint32* v);
+ private:

[mmenke, 2011/12/02 00:53:55]

nit:  Google style is to put a blank line before this
(http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml?showone=Class_...).
 It excludes small classes, but think this one is large enough that it increases
readability.

[szym, 2011/12/05 23:06:28]

Done.

+  // Hidden to promote type safety.
+  template<typename T>
+  bool Read(T* v);
+
+  const char* ptr_;
+  const char* end_;

[mmenke, 2011/12/02 00:53:55]

Not vital, but could make both |end_| pointers could be char* const, to be a
little clearer.

[szym, 2011/12/05 23:06:28]

Left it non-const to allow the compiler to generate operator=.

+};
+
+// Allows writing integers in network order (big endian) while iterating over
+// an underlying buffer.
+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 Copy(const void* buf, size_t len);

[mmenke, 2011/12/02 00:53:55]

Think the name of this function is a little odd.  U8, U16, and U32 all copy data
as well.  WriteBytes, maybe?  I'm open to other ideas.  Can even live with it as
is, but the name just seems a little odd.

[szym, 2011/12/05 23:06:28]

Done. I like WriteBytes, although it's meant to write any POD.

+  bool U8(uint8 v);
+  bool U16(uint16 v);
+  bool U32(uint32 v);
+ private:

[mmenke, 2011/12/02 00:53:55]

nit:  Missing blank line.

[szym, 2011/12/05 23:06:28]

Done.

+  // Hidden to promote type safety.
+  template<typename T>
+  bool Write(T v);
+
+  char* ptr_;
+  char* end_;
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_BIGENDIAN_H_
+