refactor(monitoring): simplify logic for rescheduling monitoring

Author: mbroadst

lib/core/sdam/monitoring.js

@@ -130,10 +130,13 @@ function monitorServer(server, options) {
   options = options || {};
   const heartbeatFrequencyMS = options.heartbeatFrequencyMS || 10000;
 
-  if (options.initial === true) {
-    server.s.monitorId = setTimeout(() => monitorServer(server), heartbeatFrequencyMS);
-    return;
-  }
+  const rescheduleMonitoring = () => {
+    server.s.monitoring = false;
+    server.s.monitorId = setTimeout(() => {
+      server.s.monitorId = undefined;
+      server.monitor();
+    }, heartbeatFrequencyMS);
+  };
 
   // executes a single check of a server
   const checkServer = callback => {
@@ -176,16 +179,13 @@ function monitorServer(server, options) {
   };
 
   const successHandler = isMaster => {
-    server.s.monitoring = false;
-
     // emit an event indicating that our description has changed
     server.emit('descriptionReceived', new ServerDescription(server.description.address, isMaster));
     if (server.s.state === STATE_CLOSED || server.s.state === STATE_CLOSING) {
       return;
     }
 
-    // schedule the next monitoring process
-    server.s.monitorId = setTimeout(() => monitorServer(server), heartbeatFrequencyMS);
+    rescheduleMonitoring();
   };
 
   // run the actual monitoring loop
@@ -203,15 +203,13 @@ function monitorServer(server, options) {
       // otherwise re-attempt monitoring once
       checkServer((error, isMaster) => {
         if (error) {
-          server.s.monitoring = false;
-
           // we revert to an `Unknown` by emitting a default description with no isMaster
           server.emit(
             'descriptionReceived',
             new ServerDescription(server.description.address, null, { error })
           );
 
-          // we do not reschedule monitoring in this case
+          rescheduleMonitoring();
           return;
         }