React Native dev mode app doesn't fallback to offline bundle on physical device (ios)

Question

React Native should automatically fallback to using the offline bundle, which it saves on the first run, if it cannot find a running packager. This is mentioned in Running react-native app on iOS device using offline bundle.

However, in my case, after disconnecting the phone from the WiFi and launching the app, it just hangs on a pre-cached page (or image of a page), and it's often the last loaded page (i.e. the last page that was loaded when the app was connected to the packager). This one is counter-intuitive because you'd think that after closing the app, it wouldn't persist any local state.

I'm not sure why this happens in my case. Here is the relevant log-trace from my device and it's crashing in isPackagerRunning which seems to be attempting to make some sort request to a URL. Should it even be attempting to do this? I can try logging the URL it's trying to connect to I suppose.

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   libsystem_kernel.dylib          0x0000000186eaf260 semaphore_wait_trap + 8
1   libdispatch.dylib               0x0000000186d9d5e8 _os_semaphore_wait + 24
2   libdispatch.dylib               0x0000000186d9cca0 _dispatch_semaphore_wait_slow + 140
3   CFNetwork                       0x000000018858eb9c CFURLConnectionSendSynchronousRequest + 284
4   CFNetwork                       0x00000001885bb154 +[NSURLConnection sendSynchronousRequest:returningResponse:error:] + 120
5   resiShare                       0x00000001003d4334 -[RCTBundleURLProvider isPackagerRunning:] (RCTBundleURLProvider.m:76)
6   resiShare                       0x00000001003d45e4 -[RCTBundleURLProvider guessPackagerHost] (RCTBundleURLProvider.m:92)
7   resiShare                       0x00000001003d47f4 -[RCTBundleURLProvider packagerServerHost] (RCTBundleURLProvider.m:106)
8   resiShare                       0x00000001003d49b8 -[RCTBundleURLProvider jsBundleURLForBundleRoot:fallbackResource:] (RCTBundleURLProvider.m:123)
9   resiShare                       0x00000001000cad6c -[AppDelegate application:didFinishLaunchingWithOptions:] (AppDelegate.m:23)
10  UIKit                           0x000000018e0732dc -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:] + 380
11  UIKit                           0x000000018e27f800 -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 3452
12  UIKit                           0x000000018e2852a8 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1684
13  UIKit                           0x000000018e299de0 __84-[UIApplication _handleApplicationActivationWithScene:transitionContext:completion:]_block_invoke.3151 + 48
14  UIKit                           0x000000018e28253c -[UIApplication workspaceDidEndTransaction:] + 168
15  FrontBoardServices              0x0000000189a7b884 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 36
16  FrontBoardServices              0x0000000189a7b6f0 -[FBSSerialQueue _performNext] + 176
17  FrontBoardServices              0x0000000189a7baa0 -[FBSSerialQueue _performNextFromRunLoopSource] + 56
18  CoreFoundation                  0x0000000187e81424 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24
19  CoreFoundation                  0x0000000187e80d94 __CFRunLoopDoSources0 + 540
20  CoreFoundation                  0x0000000187e7e9a0 __CFRunLoopRun + 744
21  CoreFoundation                  0x0000000187daed94 CFRunLoopRunSpecific + 424
22  UIKit                           0x000000018e06c45c -[UIApplication _run] + 652
23  UIKit                           0x000000018e067130 UIApplicationMain + 208
24  resiShare                       0x00000001000cb1d0 main (main.m:16)
25  libdyld.dylib                   0x0000000186dbd59c start + 4

Answer 1

I've posted a workaround here - https://github.com/facebook/react-native/issues/10187 in the hopes that someone better versed with objective-c and url loading will take a look and put in the proper fix. Hope this helps. Thanks.

The issue is that a synchronous request is made from the main thread at load time in order to figure out whether the react packager (remote server running on the same network) is accessible. This can take awhile for reasons beyond my knowledge (if someone can expound on this, I'd be grateful), but apple will crash the app if this takes longer than 19 seconds (approx).