fix: recover on network error during initial connect

Author: mbroadst

lib/core/sdam/server.js

@@ -146,11 +146,6 @@ class Server extends EventEmitter {
           error: event.failure
         })
       );
-
-      if (this.s.state === STATE_CONNECTING) {
-        this.emit('error', new MongoNetworkError(event.failure));
-        this.destroy();
-      }
     });
 
     this[kMonitor].on('serverHeartbeatSucceeded', event => {
@@ -187,6 +182,10 @@ class Server extends EventEmitter {
    * Initiate server connect
    */
   connect() {
+    if (this.s.state !== STATE_CLOSED) {
+      return;
+    }
+
     stateTransition(this, STATE_CONNECTING);
     this[kMonitor].connect();
   }

lib/core/sdam/topology.js

@@ -280,9 +280,10 @@ class Topology extends EventEmitter {
     const readPreference = options.readPreference || ReadPreference.primary;
     this.selectServer(readPreferenceServerSelector(readPreference), options, (err, server) => {
       if (err) {
-        stateTransition(this, STATE_CLOSED);
+        this.close();
+
         if (typeof callback === 'function') {
-          callback(err, null);
+          callback(err);
         } else {
           this.emit('error', err);
         }
@@ -305,7 +306,6 @@ class Topology extends EventEmitter {
         if (typeof callback === 'function') callback(err, this);
       };
 
-      const STATE_CONNECTING = 1;
       if (server.s.state === STATE_CONNECTING) {
         server.once('error', errorHandler);
         server.once('connect', connectHandler);

test/unit/sdam/monitoring.test.js

@@ -58,6 +58,47 @@ describe('monitoring', function() {
     });
   });
 
+  it('should recover on error during initial connect', function(done) {
+    let acceptConnections = false;
+    mockServer.setMessageHandler(request => {
+      if (!acceptConnections) {
+        request.connection.destroy();
+        return;
+      }
+
+      const doc = request.document;
+      if (doc.ismaster) {
+        request.reply(Object.assign({}, mock.DEFAULT_ISMASTER));
+      } else if (doc.endSessions) {
+        request.reply({ ok: 1 });
+      }
+    });
+
+    setTimeout(() => {
+      acceptConnections = true;
+    }, 250);
+
+    // set `heartbeatFrequencyMS` to 250ms to force a quick monitoring check, and wait 500ms to validate below
+    const topology = new Topology(mockServer.uri(), { heartbeatFrequencyMS: 250 });
+    topology.connect(err => {
+      expect(err).to.not.exist;
+
+      setTimeout(() => {
+        expect(topology)
+          .property('description')
+          .property('servers')
+          .to.have.length(1);
+
+        const serverDescription = Array.from(topology.description.servers.values())[0];
+        expect(serverDescription)
+          .property('roundTripTime')
+          .to.be.greaterThan(0);
+
+        topology.close(done);
+      }, 500);
+    });
+  });
+
   describe('Monitor', function() {
     it('should connect and issue an initial server check', function(done) {
       mockServer.setMessageHandler(request => {