Using a IPv6 literal as the address in a STRICT_DNS cluster generates invalid TCP URLs

Envoy fails to parse a URL generated by resolving the xDS server name to an IPv6 address:

[2020-03-23 12:32:58.813][1][debug][init] [source/common/init/watcher_impl.cc:27] init manager Server destroyed
malformed url: tcp://2001:db8:10a:c751::ffff:42ba:8001

The URL should be tcp://[2001:db8:10a:c751::ffff:42ba]:8001, which is parsed by Utility::parseInternetAddressAndPort().

It is likely that the caller is using Utility::portFromTcpUrl(), which doesn't call the full parser. This seems like a related but distinct problem.

A brief grep looks like there are a few places that could generate URLs of this form:

source/common/upstream/logical_dns_cluster.cc:  dns_url_ = fmt::format("tcp://{}:{}", socket_address.address(), socket_address.port_value());
source/common/upstream/strict_dns_cluster.cc:          fmt::format("tcp://{}:{}", socket_address.address(), socket_address.port_value());
test/common/network/connection_impl_test.cc:          fmt::format("tcp://{}:1", Network::Test::getLoopbackAddressUrlString(GetParam()))),
test/extensions/filters/udp/udp_proxy/udp_proxy_integration_test.cc:      fmt::format("tcp://{}:{}", Network::Test::getLoopbackAddressUrlString(version_), port));
test/extensions/filters/udp/udp_proxy/udp_proxy_integration_test.cc:      fmt::format("tcp://{}:{}", Network::Test::getLoopbackAddressUrlString(version_), port));
test/extensions/filters/udp/udp_proxy/udp_proxy_integration_test.cc:      fmt::format("tcp://{}:{}", Network::Test::getLoopbackAddressUrlString(version_), port));
test/integration/http_integration.cc:      cluster, fmt::format("tcp://{}:80", Network::Test::getLoopbackAddressUrlString(version_)))};
test/integration/integration.cc:          fmt::format("tcp://{}:{}", Network::Test::getLoopbackAddressUrlString(version), port)),
test/integration/integration.cc:          fmt::format("tcp://{}:{}", Network::Test::getLoopbackAddressUrlString(version_), port)),
test/integration/utility.cc:      fmt::format("tcp://{}:{}", Network::Test::getLoopbackAddressUrlString(ip_version), port));
test/integration/utility.cc:          fmt::format("tcp://{}:{}", Network::Test::getLoopbackAddressUrlString(version), port)),

Relevant Links:

Reported in https://github.com/projectcontour/contour/issues/2354

The contour issue contains the full bootstrap config, but the relevant part is most likely the cluster that points to the xDS server:

  "static_resources":
    {
      "clusters":
        [
          {
            "name": "contour",
            "alt_stat_name": "projectcontour_contour_8001",
            "type": "STRICT_DNS",
            "connect_timeout": "5s",
            "load_assignment":
              {
                "cluster_name": "contour",
                "endpoints":
                  [
                    {
                      "lb_endpoints":
                        [
                          {
                            "endpoint":
                              {
                                "address":
                                  {
                                    "socket_address":
                                      {
                                        "address": "contour",
                                        "port_value": 8001,
                                      },
                                  },
                              },
                          },
                        ],
                    },
                  ],
              },
...