App always crashes when API call is made

Question

One of the users of my app experiences a crash every time an HTTP request is made (to the API). This is the crash trace:

Incident Identifier: 512C99DF-D432-4BAC-96DF-B32561A51C9B
CrashReporter Key:   cdee4dd4d00f061439ba8ee6e2fdf4d5a9c4e889
Hardware Model:      iPhone5,3
Process:             myapp [312]
Path:                /private/var/mobile/Containers/Bundle/Application/42EA0E64-28BB-48D0-9CDF-6F58F1823BDF/myapp.app/myapp
Identifier:          com.myapp.myapp
Version:             3 (0.1.2)
Code Type:           ARM (Native)
Parent Process:      launchd [1]

Date/Time:           2017-01-18 21:30:47.47 -0500
Launch Time:         2017-01-18 21:30:41.41 -0500
OS Version:          iOS 9.1 (13B143)
Report Version:      105

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Exception Note:  EXC_CORPSE_NOTIFY
Triggered by Thread:  0

Filtered syslog:
None found

Last Exception Backtrace:
(0x24dc5856 0x3673adfa 0x24d58bda 0xfe438 0x29188ae8 0x29188c34 0x295ccf7c 0x290b18d8 0x28fda85c 0x28fda68a 0x290b10cc 0x2880a85a 0x2880a6aa 0x2e897586 0x25e85340 0x24d76b54 0x24d88f76 0x24d8868a 0x24d86a9c 0x24cd90d4 0x24cd8ec8 0x2e04eaf4 0x28f622d8 0xa0288 0x36e8886e)

Global Trace Buffer (reverse chronological seconds):
2.392224     CFNetwork                 0x00000000245e4a91 TCP Conn 0x15d78310 SSL Handshake DONE
2.598566     CFNetwork                 0x00000000245e49cb TCP Conn 0x15d78310 starting SSL negotiation
2.599330     CFNetwork                 0x000000002466479d TCP Conn 0x15d78310 complete. fd: 6, err: 0
2.600883     CFNetwork                 0x000000002466589f TCP Conn 0x15d78310 event 1. err: 0
3.702969     CFNetwork                 0x000000002466591d TCP Conn 0x15d78310 started
3.710171     CFNetwork                 0x00000000246a640f Creating default cookie storage with default identifier
3.710171     CFNetwork                 0x00000000246a63eb Faulting in CFHTTPCookieStorage singleton
3.710171     CFNetwork                 0x00000000246e878b Faulting in NSHTTPCookieStorage singleton
3.714408     CFNetwork                 0x000000002463e141 NSURLSessionTask finished with error - code: -1022
4.907331     libsystem_trace.dylib     0x00000000370086f9 dyld_image_header_containing_address(0x15e505e9) failed

However the app works for all other users and I know the API endpoint is fully reachable. This is also a React Native app, don't know if that's relevant to this, but here's the code that makes the request:

export default function api(apiName, paramsObj) {
  return new Promise((resolve, reject) => {
    let ip = 'xxx.xxx.xx.xxx';
    fetch(`http://${ip}/api/${apiName}`, {
      method: 'POST',
      headers: {
        Accept: 'application/json',
        'Content-Type': 'application/json',
      },
      body: paramsObj ? JSON.stringify(paramsObj) : null
    })
    .then(response => resolve(response.json()))
    .catch(error => reject(error));
  });
}

Any idea what could be causing this crash?

EDIT

This is an example of the API's JSON response:

[{"id":"584b7fe3e1e982176d5a5b3c","name":"My University","unlocked":true,"totalUsers":1200,"minimumUsers":1000}]

EDIT 2

Here is a screenshot of the symbolicated crash report from Xcode (the app name is blocked out):

EDIT 3

After further testing and debugging I determined that the issue also sometimes occurs on iPhone 5s running 8.x. Regardless, I saw this answer to a different question, and when I added these lines to the entry point of the app, it actually fixed the problem only when I click "Debug JS Remotely" in the React Native developer menu.

const _XHR = GLOBAL.originalXMLHttpRequest ?  
    GLOBAL.originalXMLHttpRequest :           
    GLOBAL.XMLHttpRequest                     

XMLHttpRequest = _XHR

So essentially with these above lines, when the simulator (iPhone 4s, iOS 9.3) is connected to the React Native Chrome debugger the problem stops and the list is populated (no out-of-bounds error). However if I disconnect the simulator from the debugger OR if I run the app in release mode, the error persists.

Answer 1

An object of type RTCPicker (subclass of UIPickerView) is trying to access an item from an Array that doesn't exist. Something like you have 5 items in the array and try to access the 6th item.

This is indicated by the top frame showing that the call stack is throwing an exception and the 3rd frame trying to access in item from an NSArray at a specific index.

As exceptions are fatals, this will crash the app.

Answer 2

The -1022 error indicates that you're trying to fetch from an http server. You need to move to https or adjust your app's entitlements to allow cleartext loads.

My guess is that the request is failing because of that, and you're failing to detect the empty response correctly and trying to parse it as JSON, then crashing, but without a decoded backtrace, it is impossible to say for sure.