xdsresolver uses ldsResourceName instead of using data plane authority

[arvindbr8]

While testing the new bootstrap generator (GoogleCloudPlatform/traffic-director-grpc-bootstrap#57) which adds the new xdstp style in client_default_listener_name_template to the config, I found that the virtual hosts lookup was failing with the following error:

2024/02/21 22:39:04 WARNING: [core] [Channel #1] ccResolverWrapper: reporting error to cc: no matching virtual host found for "xdstp://traffic-director-global.xds.googleapis.com/envoy.config.listener.v3.Listener/439293274322/default/helloworld-gke:8000"
2024/02/21 22:39:04 INFO: [core] [Channel #1] Channel switches to new LB policy "pick_first"
2024/02/21 22:39:04 INFO: [core] [pick-first-lb 0xc0002ae4b0] Received error from the name resolver: no matching virtual host found for "xdstp://traffic-director-global.xds.googleapis.com/envoy.config.listener.v3.Listener/439293274322/default/helloworld-gke:8000"
2024/02/21 22:39:04 INFO: [core] [Channel #1] Channel Connectivity change to TRANSIENT_FAILURE
2024/02/21 22:39:04 could not greet: rpc error: code = Unavailable desc = name resolver error: no matching virtual host found for "xdstp://traffic-director-global.xds.googleapis.com/envoy.config.listener.v3.Listener/439293274322/default/helloworld-gke:8000"

even though, we are getting a valid RDS response

2024/02/21 22:39:04 INFO: [xds] [xds-resolver 0xc000242d80] Received update for RouteConfiguration resource "URL_MAP/439293274322_grpc-gke-url-map_0_helloworld-gke:8000": {
  "VirtualHosts": [
    {
      "Domains": [
        "helloworld-gke:8000"
      ],
      "Routes": [
        {
          "Path": null,
          "Prefix": "",
          "Regex": null,
          "CaseInsensitive": false,
          "Headers": null,
          "Fraction": null,
          "HashPolicies": null,
          "MaxStreamDuration": null,
          "HTTPFilterConfigOverride": null,
          "RetryConfig": {
            "RetryOn": null,
            "NumRetries": 0,
            "RetryBackoff": {
              "BaseInterval": 0,
              "MaxInterval": 0
            }
          },
          "ActionType": 1,
          "WeightedClusters": {
            "cloud-internal-istio:cloud_mp_439293274322_77023378241484717": {
              "Weight": 1,
              "HTTPFilterConfigOverride": null
            }
          },
          "ClusterSpecifierPlugin": ""
        }
      ],
      "HTTPFilterConfigOverride": null,
      "RetryConfig": null
    }
  ],
  "ClusterSpecifierPlugins": {},
  "Raw": {
    "type_url": "type.googleapis.com/envoy.config.route.v3.RouteConfiguration",
    "value": "CjtVUkxfTUFQLzQzOTI5MzI3NDMyMl9ncnBjLWdrZS11cmwtbWFwXzBfaGVsbG93b3JsZC1na2U6ODAwMBK+ARITaGVsbG93b3JsZC1na2U6ODAwMBqmAQoCCgASWwo8Y2xvdWQtaW50ZXJuYWwtaXN0aW86Y2xvdWRfbXBfNDM5MjkzMjc0MzIyXzc3MDIzMzc4MjQxNDg0NzE3QgIIHkoXCg1nYXRld2F5LWVycm9yEgIIARoCCB5yQ1VSTF9NQVAvNDM5MjkzMjc0MzIyX2dycGMtZ2tlLXVybC1tYXBfMF9oZWxsb3dvcmxkLWdrZTo4MDAwLXJvdXRlLTA="
  }
}

The issue is that while parsing RDS to lookup virtual host we are using the entire LDS resource name and not just the domain, which is the dial target provided by the user.

I found the same issue in gRPC-java. This works in the following cases: when the virtual hosts domain name is the same the LDS resource name.

[arvindbr8]

This is the code that handles it

grpc-go/xds/internal/xdsclient/xdsresource/matcher.go

Line 228 in 76a23bf

func FindBestMatchingVirtualHost(host string, vHosts []*VirtualHost) *VirtualHost { // Maybe move this crap to client

grpc-go/xds/internal/resolver/xds_resolver.go

Line 416 in 76a23bf

matchVh := xdsresource.FindBestMatchingVirtualHost(r.ldsResourceName, update.VirtualHosts)

[arvindbr8]

per @markdroth

You should not be using the LDS resource name to match the virtual host name. You should be using the data plane authority.

If the gRPC channel is created with target URI xds://whatever/server.example.com, then the data plane authority is server.example.com, regardless of what LDS resource name is constructed via the bootstrap file.

A47 also agrees with the same:

Note that the authority used for the data plane connections (which is also used to select the VirtualHost within the xDS RouteConfiguration) will continue to be the last path component of the xds URI used to create the gRPC channel (i.e., the part following the last / character, or the entire path if the path contains no / character).