[FIX] fix connection error handling

if connection to server can't be established, reject Promise of `connect()` method caller,
instead of throwing error event on base object.

src/common/connection.js

@@ -97,6 +97,10 @@ class Connection extends EventEmitter {
   }
 
   _onUnexpectedClose(resolve = function() {}, reject = function() {}) {
+    if (this._onOpenErrorBound) {
+      this._ws.removeListener('error', this._onOpenErrorBound);
+      this._onOpenErrorBound = null;
+    }
     this._ws = null;
     this._isReady = false;
     this.connect().then(resolve, reject);
@@ -107,6 +111,11 @@ class Connection extends EventEmitter {
     this._onUnexpectedCloseBound = this._onUnexpectedClose.bind(this);
     this._ws.once('close', this._onUnexpectedCloseBound);
 
+    this._ws.removeListener('error', this._onOpenErrorBound);
+    this._onOpenErrorBound = null;
+    this._ws.on('error', error =>
+      this.emit('error', 'websocket', error.message, error));
+
     const request = {
       command: 'subscribe',
       streams: ['ledger']
@@ -118,6 +127,10 @@ class Connection extends EventEmitter {
     });
   }
 
+  _onOpenError(reject, error) {
+    reject(new NotConnectedError(error && error.message));
+  }
+
   _createWebSocket() {
     const options = {};
     if (this._proxyURL !== undefined) {
@@ -177,8 +190,11 @@ class Connection extends EventEmitter {
         // should still be emitted; the "ws" documentation says: "The close
         // event is also emitted when then underlying net.Socket closes the
         // connection (end or close)."
-        this._ws.on('error', error =>
+        // In case if there is connection error (say, server is not responding)
-          this.emit('error', 'websocket', error.message, error));
+        // we must return this error to connection's caller. After successful
+        // opening, we will forward all errors to main api object.
+        this._onOpenErrorBound = this._onOpenError.bind(this, reject);
+        this._ws.once('error', this._onOpenErrorBound);
         this._ws.on('message', this._onMessage.bind(this));
         // in browser close event can came before open event, so we must
         // resolve connect's promise after reconnect in that case.

test/connection-test.js

@@ -106,6 +106,26 @@ describe('Connection', function() {
     });
   });
 
+  it('should throw NotConnectedError if server not responding ', function(
+    done
+  ) {
+    if (process.browser) {
+      const phantomTest = /PhantomJS/;
+      if (phantomTest.test(navigator.userAgent)) {
+        // inside PhantomJS this one just hangs, so skip as not very relevant
+        done();
+        return;
+      }
+    }
+
+    const connection = new utils.common.Connection('ws://127.0.0.1:321');
+    connection.on('error', done);
+    connection.connect().catch(error => {
+      assert(error instanceof this.api.errors.NotConnectedError);
+      done();
+    });
+  });
+
   it('DisconnectedError', function() {
     this.api.connection._send(JSON.stringify({
       command: 'config',