Avoid heap allocations in IPAddress

content/public/common/common_param_traits.cc

 // Copyright (c) 2012 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.
 
 #include "content/public/common/common_param_traits.h"
 
 #include <string>
 
 #include "content/public/common/content_constants.h"
 #include "content/public/common/page_state.h"
@@ skipping 106 matching lines @@
   *p = net::IPEndPoint(address, port);
   return true;
 }
 
 void ParamTraits<net::IPEndPoint>::Log(const param_type& p, std::string* l) {
   LogParam("IPEndPoint:" + p.ToString(), l);
 }
 
 void ParamTraits<net::IPAddress>::GetSize(base::PickleSizer* s,
                                           const param_type& p) {
-  GetParamSize(s, p.bytes());
+  // TODO(rch): avoid creating a vector here.
+  base::StackVector<uint8_t, 16> bytes;

[eroman, 2017/05/18 18:43:17]

Better thanks!

+  for (uint8_t byte : p.bytes())
+    bytes->push_back(byte);
+  GetParamSize(s, bytes);
 }
 
 void ParamTraits<net::IPAddress>::Write(base::Pickle* m, const param_type& p) {
-  WriteParam(m, p.bytes());
+  // TODO(rch): avoid creating a vector here.
+  base::StackVector<uint8_t, 16> bytes;
+  for (uint8_t byte : p.bytes())
+    bytes->push_back(byte);
+  WriteParam(m, bytes);
 }
 
 bool ParamTraits<net::IPAddress>::Read(const base::Pickle* m,
                                        base::PickleIterator* iter,
                                        param_type* p) {
   std::vector<uint8_t> bytes;

[eroman, 2017/05/18 18:43:17]

For symmetry with GetSize() and Write(), can you change this to a StackVector<>
as well?

[Ryan Hamilton, 2017/05/19 03:38:50]

Done. Though in order to do this, I needed to add a new IPAddress constructor
which takes a StackVector. But that seems like a good idea. As a result, I
replaced a number of calls to the existing std::vector constructor with this new
StackVector constructor.

Does that sound good to you? PTAL.

[eroman, 2017/05/19 17:37:54]

I am fine with adding a StackVector ctor if it is used elsewhere. But not sure I
follow why it was a requirement for using StackVector in this particular
function.

i.e. I figure it would have been sufficient in this function to just change:

  *p = net::IPAddress(bytes);

to:

  *p = net::IPAddress(bytes->data(), bytes->size());

[Ryan Hamilton, 2017/05/19 21:30:46]

Oh, I see. Duh! Ok, I've removed the new StackVector constructor that I added,
as well as the "legacy" std::vector constructor so as to discourage use of it.
I've also converted most of the callers to use StackVector when possible.

   if (!ReadParam(m, iter, &bytes))
     return false;
   if (bytes.size() &&
       bytes.size() != net::IPAddress::kIPv4AddressSize &&
       bytes.size() != net::IPAddress::kIPv6AddressSize) {
     return false;
   }
   *p = net::IPAddress(bytes);
   return true;
 }
@@ skipping 51 matching lines @@
 #undef CONTENT_PUBLIC_COMMON_COMMON_PARAM_TRAITS_MACROS_H_
 #include "content/public/common/common_param_traits_macros.h"
 }  // namespace IPC
 
 // Generate param traits log methods.
 #include "ipc/param_traits_log_macros.h"
 namespace IPC {
 #undef CONTENT_PUBLIC_COMMON_COMMON_PARAM_TRAITS_MACROS_H_
 #include "content/public/common/common_param_traits_macros.h"
 }  // namespace IPC