Add IPv6 probing support, and disable IPv6 resolution when it is useless

I've added minimal probing to check if IPv6 is at all possible, and when
it is not, then we disable IPv6 resolution.

I've also added histograms and A/B test support to evaluate the impact of
this change.

r=wtc,eroman
Review URL: http://codereview.chromium.org/579010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@38323 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 45 insertions, 0 deletions

diff --git a/net/base/net_util.cc b/net/base/net_util.cc
index 43fa906..01567bc 100644
--- a/net/base/net_util.cc
+++ b/net/base/net_util.cc
@@ -1538,4 +1538,49 @@ void SetExplicitlyAllowedPorts(const std::wstring& allowed_ports) {
   explicitly_allowed_ports = ports;
 }
 
+enum IPv6SupportStatus {
+  kIPv6CannotCreateSockets,
+  kIPv6CanCreateSockets,
+  kIPv6SupportMax  // Bounding values for enumeration.
+};
+
+static void IPv6SupportResults(IPv6SupportStatus result) {
+  UMA_HISTOGRAM_ENUMERATION("Net.IPv6Status", result, kIPv6SupportMax);
+}
+
+// TODO(jar): The following is a simple estimate of IPv6 support.  We may need
+// to do a test resolution, and a test connection, to REALLY verify support.
+// static
+#if defined(OS_POSIX)
+bool IPv6Supported() {
+  int test_socket;
+
+  test_socket = socket(AF_INET6, SOCK_STREAM, 0);
+  if (test_socket == -1) {
+    IPv6SupportResults(kIPv6CannotCreateSockets);
+    return false;
+  }
+
+  close(test_socket);
+  IPv6SupportResults(kIPv6CanCreateSockets);
+  return true;
+}
+#else  // defined(OS_POSIX)
+bool IPv6Supported() {
+  EnsureWinsockInit();
+  SOCKET test_socket;
+
+  test_socket = socket(AF_INET6, SOCK_STREAM, 0);
+  if (test_socket == INVALID_SOCKET) {
+    IPv6SupportResults(kIPv6CannotCreateSockets);
+    return false;
+  }
+
+  closesocket(test_socket);
+  IPv6SupportResults(kIPv6CanCreateSockets);
+  return true;
+}
+#endif  // defined(OS_POSIX)
+
+
 }  // namespace net