feat: add known, data-bearing filters to TopologyDescription

Author: mbroadst

lib/core/sdam/topology_description.js

@@ -1,7 +1,6 @@
 'use strict';
 const ServerType = require('./server_description').ServerType;
 const ServerDescription = require('./server_description').ServerDescription;
-const ReadPreference = require('../topologies/read_preference');
 const WIRE_CONSTANTS = require('../wireprotocol/constants');
 
 // contstants related to compatability checks
@@ -258,24 +257,17 @@ class TopologyDescription {
   }
 
   /**
-   * Determines if the topology has a readable server available. See the table in the
-   * following section for behaviour rules.
-   *
-   * @param {ReadPreference} [readPreference] An optional read preference for determining if a readable server is present
-   * @return {Boolean} Whether there is a readable server in this topology
+   * Determines if the topology description has any known servers
    */
-  hasReadableServer(/* readPreference */) {
-    // To be implemented when server selection is implemented
+  get hasKnownServers() {
+    return Array.from(this.servers.values()).some(sd => sd.type !== ServerDescription.Unknown);
   }
 
   /**
-   * Determines if the topology has a writable server available. See the table in the
-   * following section for behaviour rules.
-   *
-   * @return {Boolean} Whether there is a writable server in this topology
+   * Determines if this topology description has a data-bearing server available.
    */
-  hasWritableServer() {
-    return this.hasReadableServer(ReadPreference.primary);
+  get hasDataBearingServers() {
+    return Array.from(this.servers.values()).some(sd => sd.isDataBearing);
   }
 
   /**