[client-app] Prevent delta streaming connection from retrying too much

Summary:
Before this commit, we would call .close() onError and when the
connection closed. We also closed the connection onError, even though
NylasLongConnection had also closed it, so we ended up calling close a
bunch of times. This would cause us to set a bunch of timeouts to retry
unecessarilly.

This commit makes it so we ensure there's only one retry timeout and
consolidates the logic that calls .close() so we don't call it so many
times unnecessarily

Test Plan: manual

Reviewers: spang, mark, evan

Reviewed By: mark, evan

Differential Revision: https://phab.nylas.com/D4166

packages/client-app/src/flux/nylas-long-connection.es6

@@ -98,6 +98,7 @@ class NylasLongConnection {
 
   onError(error) {
     this._onError(error)
+    this.close()
   }
 
   canStart() {
@@ -108,6 +109,7 @@ class NylasLongConnection {
     if (!this.canStart()) { return this }
     if (this._req != null) { return this }
 
+    try {
       const accountToken = this._api.accessTokenForAccountId(this._accountId)
       const identityToken = (IdentityStore.identity() || {}).token || ''
       if (!accountToken) {
@@ -138,7 +140,6 @@ class NylasLongConnection {
               statusCode: responseStream.statusCode,
             })
             this.onError(error)
-          this.close()
           })
           return
         }
@@ -146,7 +147,6 @@ class NylasLongConnection {
         responseStream.setEncoding('utf8')
         responseStream.on('error', (error) => {
           this.onError(new APIError({error}))
-        this.close()
         })
         responseStream.on('close', () => this.close())
         responseStream.on('end', () => this.close())
@@ -165,7 +165,6 @@ class NylasLongConnection {
       this._req.setSocketKeepAlive(true)
       this._req.on('error', (error) => {
         this.onError(new APIError({error}))
-      this.close()
       })
       this._req.on('socket', (socket) => {
         this.setStatus(Status.Connecting)
@@ -175,7 +174,6 @@ class NylasLongConnection {
         })
         socket.on('error', (error) => {
           this.onError(new APIError({error}))
-        this.close()
         })
         socket.on('close', () => this.close())
         socket.on('end', () => this.close())
@@ -184,6 +182,12 @@ class NylasLongConnection {
       // See https://github.com/nylas/nylas-mail/pull/2004
       this._req.end()
       return this
+    } catch (err) {
+      // start() should not throw any errors synchronously. Any errors should be
+      // asynchronously transmitted to the caller via `onError`
+      setTimeout(() => this.onError(err), 0)
+      return this
+    }
   }
 
   closeIfDataStops() {

packages/client-app/src/services/delta-streaming-connection.es6

@@ -19,8 +19,9 @@ class DeltaStreamingConnection {
     this._account = account
     this._state = null
     this._longConnection = null
-    this._writeStateDebounced = _.debounce(this._writeState, 100)
+    this._retryTimeout = null
     this._unsubscribers = []
+    this._writeStateDebounced = _.debounce(this._writeState, 100)
     this._backoffScheduler = new ExponentialBackoffScheduler({
       baseDelay: BASE_RETRY_DELAY,
       maxDelay: MAX_RETRY_DELAY,
@@ -67,11 +68,13 @@ class DeltaStreamingConnection {
   }
 
   close() {
+    this._clearRetryTimeout()
     this._disposeListeners()
     this._longConnection.close()
   }
 
   end() {
+    this._clearRetryTimeout()
     this._disposeListeners()
     this._longConnection.end()
   }
@@ -88,6 +91,11 @@ class DeltaStreamingConnection {
     this._unsubscribers = []
   }
 
+  _clearRetryTimeout() {
+    clearTimeout(this._retryTimeout)
+    this._retryTimeout = null
+  }
+
   _onOnlineStatusChanged = () => {
     if (OnlineStatusStore.isOnline()) {
       this.restart()
@@ -103,7 +111,9 @@ class DeltaStreamingConnection {
       this._backoffScheduler.reset()
     }
     if (status === Closed) {
-      setTimeout(() => this.restart(), this._backoffScheduler.nextDelay());
+      if (this._retryTimeout) { return }
+      this._clearRetryTimeout()
+      this._retryTimeout = setTimeout(() => this.restart(), this._backoffScheduler.nextDelay());
     }
   }
 
@@ -138,9 +148,6 @@ class DeltaStreamingConnection {
     if (!NylasAPIRequest.NonReportableStatusCodes.includes(err.statusCode)) {
       NylasEnv.reportError(err)
     }
-    this.close()
-
-    setTimeout(() => this.restart(), this._backoffScheduler.nextDelay());
   }
 
   _setCursor = (cursor) => {
@@ -160,7 +167,10 @@ class DeltaStreamingConnection {
     // Migrate from old storage key
     const oldState = await DatabaseStore.findJSONBlob(`NylasSyncWorker:${this._account.id}`)
     if (!oldState) {
-      return {cursor: null, status: null};
+      return {
+        cursor: null,
+        status: null,
+      };
     }
 
     const {deltaCursors = {}, deltaStatus = {}} = oldState