Avoid doing concurrent DNS resolves of the same hostname

net/base/address_list.cc

 // Copyright (c) 2006-2008 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 "net/base/address_list.h"
 
 #ifdef OS_WIN
 #include <ws2tcpip.h>
 #include <wspiapi.h>  // Needed for Win2k compat.
 #else
 #include <netdb.h>
 #endif
 
+#include "base/logging.h"
+
 namespace net {
 
+namespace {
+
+// Make a deep copy of |info|. This copy should be deleted using
+// DeleteCopyOfAddrinfo(), and NOT freeaddrinfo().
+struct addrinfo* CreateCopyOfAddrinfo(const struct addrinfo* info) {
+  struct addrinfo* copy = new struct addrinfo;
+
+  // Copy all the fields (some of these are pointers, we will fix that next).
+  memcpy(copy, info, sizeof(addrinfo));
+
+  // ai_canonname is a NULL-terminated string.
+  if (info->ai_canonname) {
+#ifdef OS_WIN
+    copy->ai_canonname = _strdup(info->ai_canonname);
+#else
+    copy->ai_canonname = strdup(info->ai_canonname);
+#endif
+  }
+
+  // ai_addr is a buffer of length ai_addrlen.
+  if (info->ai_addr) {
+    copy->ai_addr = reinterpret_cast<sockaddr *>(new char[info->ai_addrlen]);
+    memcpy(copy->ai_addr, info->ai_addr, info->ai_addrlen);
+  }
+
+  // Recursive copy.
+  if (info->ai_next)
+    copy->ai_next = CreateCopyOfAddrinfo(info->ai_next);
+
+  return copy;
+}
+
+// Free an addrinfo that was created by CreateCopyOfAddrinfo().
+void FreeMyAddrinfo(struct addrinfo* info) {
+  if (info->ai_canonname)
+    free(info->ai_canonname);  // Allocated by strdup.
+
+  if (info->ai_addr)
+    delete [] reinterpret_cast<char*>(info->ai_addr);
+
+  struct addrinfo* next = info->ai_next;
+
+  delete info;
+
+  // Recursive free.
+  if (next)
+    FreeMyAddrinfo(next);
+}
+
+// Returns the address to port field in |info|.
+uint16* GetPortField(const struct addrinfo* info) {
+  if (info->ai_family == AF_INET) {
+    DCHECK_EQ(sizeof(sockaddr_in), info->ai_addrlen);
+    struct sockaddr_in* sockaddr =
+        reinterpret_cast<struct sockaddr_in*>(info->ai_addr);
+    return &sockaddr->sin_port;
+  } else if (info->ai_family == AF_INET6) {
+    DCHECK_EQ(sizeof(sockaddr_in6), info->ai_addrlen);
+    struct sockaddr_in6* sockaddr =
+        reinterpret_cast<struct sockaddr_in6*>(info->ai_addr);
+    return &sockaddr->sin6_port;
+  } else {
+    NOTREACHED();
+    return NULL;
+  }
+}
+
+// Assign the port for all addresses in the list.
+void SetPortRecursive(struct addrinfo* info, int port) {
+  uint16* port_field = GetPortField(info);
+  *port_field = htons(port);
+
+  // Assign recursively.
+  if (info->ai_next)
+    SetPortRecursive(info->ai_next, port);
+}
+
+}  // namespace
+
 void AddressList::Adopt(struct addrinfo* head) {
-  data_ = new Data(head);
+  data_ = new Data(head, true /*is_system_created*/);
+}
+
+void AddressList::Copy(const struct addrinfo* head) {
+  data_ = new Data(CreateCopyOfAddrinfo(head), false /*is_system_created*/);
+}
+
+void AddressList::SetPort(int port) {
+  SetPortRecursive(data_->head, port);
+}
+
+int AddressList::GetPort() const {
+  uint16* port_field = GetPortField(data_->head);
+  return ntohs(*port_field);
+}
+
+void AddressList::SetFrom(const AddressList& src, int port) {
+  if (src.GetPort() == port) {
+    // We can reference the data from |src| directly.
+    *this = src;
+  } else {
+    // Otherwise we need to make a copy in order to change the port number.
+    Copy(src.head());
+    SetPort(port);
+  }
+}
+
+void AddressList::Reset() {
+  data_ = NULL;
 }
 
 AddressList::Data::~Data() {
-  freeaddrinfo(head);
+  // Call either freeaddrinfo(head), or FreeMyAddrinfo(head), depending who
+  // created the data.
+  if (is_system_created)
+    freeaddrinfo(head);
+  else
+    FreeMyAddrinfo(head);
 }
 
 }  // namespace net