fix: update to simple fix

Author: nbbeeken

lib/operations/execute_operation.js

@@ -30,11 +30,25 @@ function executeOperation(topology, operation, callback) {
     throw new TypeError('This method requires a valid operation instance');
   }
 
-  if (isUnifiedTopology(topology) && topology.shouldCheckForSessionSupport()) {
-    return selectServerForSessionSupport(topology, operation, callback);
+  const Promise = topology.s.promiseLibrary;
+
+  let result;
+  if (typeof callback !== 'function') {
+    result = new Promise((resolve, reject) => {
+      callback = (err, res) => {
+        if (err) return reject(err);
+        resolve(res);
+      };
+    });
   }
 
-  const Promise = topology.s.promiseLibrary;
+  if (isUnifiedTopology(topology) && topology.shouldCheckForSessionSupport()) {
+    // Recursive call to executeOperation after a server selection
+    // shouldCheckForSessionSupport should return false after a server selection because
+    // there will be data bearing servers
+    selectServerForSessionSupport(topology, operation, callback);
+    return result;
+  }
 
   // The driver sessions spec mandates that we implicitly create sessions for operations
   // that are not explicitly provided with a session.
@@ -45,20 +59,14 @@ function executeOperation(topology, operation, callback) {
       session = topology.startSession({ owner });
       operation.session = session;
     } else if (operation.session.hasEnded) {
-      throw new MongoError('Use of expired sessions is not permitted');
+      callback(new MongoError('Use of expired sessions is not permitted'));
+      return result;
     }
-  } else if (operation.session && operation.session.explicit) {
-    throw new MongoError('Current topology does not support sessions');
-  }
-
-  let result;
-  if (typeof callback !== 'function') {
-    result = new Promise((resolve, reject) => {
-      callback = (err, res) => {
-        if (err) return reject(err);
-        resolve(res);
-      };
-    });
+  } else if (operation.session && !topology.hasSessionSupport()) {
+    // If the user passed an explicit session and we are still, after server selection,
+    // trying to run against a topology that doesn't support sessions we error out.
+    callback(new MongoError('Current topology does not support sessions'));
+    return result;
   }
 
   function executeCallback(err, result) {
@@ -78,15 +86,15 @@ function executeOperation(topology, operation, callback) {
     } else {
       operation.execute(executeCallback);
     }
-  } catch (e) {
+  } catch (error) {
     if (session && session.owner === owner) {
       session.endSession();
       if (operation.session === session) {
         operation.clearSession();
       }
     }
 
-    throw e;
+    callback(error);
   }
 
   return result;
@@ -141,11 +149,6 @@ function executeWithServerSelection(topology, operation, callback) {
       callback(err, null);
       return;
     }
-
-    if (serverSelectionOptions.session && topology.hasSessionSupport()) {
-      return callback(new MongoError('Current topology does not support sessions'));
-    }
-
     const shouldRetryReads =
       topology.s.options.retryReads !== false &&
       operation.session &&
@@ -165,28 +168,13 @@ function executeWithServerSelection(topology, operation, callback) {
 // TODO: This is only supported for unified topology, it should go away once
 //       we remove support for legacy topology types.
 function selectServerForSessionSupport(topology, operation, callback) {
-  const Promise = topology.s.promiseLibrary;
-
-  let result;
-  if (typeof callback !== 'function') {
-    result = new Promise((resolve, reject) => {
-      callback = (err, result) => {
-        if (err) return reject(err);
-        resolve(result);
-      };
-    });
-  }
-
   topology.selectServer(ReadPreference.primaryPreferred, err => {
     if (err) {
-      callback(err);
-      return;
+      return callback(err);
     }
 
     executeOperation(topology, operation, callback);
   });
-
-  return result;
 }
 
 module.exports = executeOperation;