feat: perform selection before operation execution if needed

In accordance with the drivers-sessions and SDAM specs, we must
perform server selection under certain circumstances in order to
ensure we have accurate information about sessions support.

NODE-2068

Author: mbroadst

lib/operations/execute_operation.js

@@ -6,6 +6,7 @@ const OperationBase = require('./operation').OperationBase;
 const ReadPreference = require('../core').ReadPreference;
 const isRetryableError = require('../core/error').isRetryableError;
 const maxWireVersion = require('../core/utils').maxWireVersion;
+const TopologyType = require('../core/sdam/topology_description').TopologyType;
 
 /**
  * Executes the given operation with provided arguments.
@@ -29,6 +30,25 @@ function executeOperation(topology, operation, callback) {
     throw new TypeError('This method requires a valid operation instance');
   }
 
+  if (
+    topology.description != null &&
+    !operation.hasAspect(Aspect.SKIP_SESSION) &&
+    shouldCheckForSessionSupport(topology)
+  ) {
+    // TODO: this is only supported for unified topology, the first part of this check
+    //       should go away when we drop legacy topology types.
+    topology.selectServer(ReadPreference.primaryPreferred, err => {
+      if (err) {
+        callback(err);
+        return;
+      }
+
+      executeOperation(topology, operation, callback);
+    });
+
+    return;
+  }
+
   const Promise = topology.s.promiseLibrary;
 
   // The driver sessions spec mandates that we implicitly create sessions for operations
@@ -142,4 +162,11 @@ function executeWithServerSelection(topology, operation, callback) {
   });
 }
 
+function shouldCheckForSessionSupport(topology) {
+  return (
+    (topology.description.type === TopologyType.Single && !topology.description.hasKnownServers) ||
+    !topology.description.hasDataBearingServers
+  );
+}
+
 module.exports = executeOperation;