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httpClient.PostAsync crashes app in Xamarin Android JobService

I have an Android Xamarin app that handles notifications. When a notification is displayed, there are buttons that ask for a response. The app needs to send this response back to a server via an httpClient.PostAsync call. I am using the same http client wrapper in other parts of the code and it is working correctly. However, when I call it from the JobService code, the app crashes. I have enclosed the http call in a try/catch and no exception occurs. There are also no errors in the device log. i would like to know how to debug this. Here is my flow:
I have a class that derives from FirebaseMessagingService with an OnMessageReceived method. That gets called when a notification arrives. I build a local notification via the notification manager and call .Notify. The notification appears with the buttons. I have a BroadcastReceiver with an OnReceive method. That method schedules a job to do the post back of the button click. The job gets started and runs until the point I call the PostAsync. From there it crashes with no exception. Here is the relevant part of the JobWorker:
public override bool OnStartJob(JobParameters jobParams)
{
_backgroundWorker = Task.Run(() => { DoWork(jobParams); });
return true;
}
private void DoWork(JobParameters jobParams)
{
var logger = App.ResolveDependency<ILogger>() as ILogger;
var callActions = App.ResolveDependency<ICallActionsHandler>() as ICallActionsHandler;
var callToken = jobParams.Extras.GetString(JobParameterCallToken);
var subsciberPhoneNumber = jobParams.Extras.GetString(JobParameterSubscriberPhoneNumber);
var action = jobParams.Extras.GetString(JobParametersCallAction);
logger.TraceInfo($"starting {nameof(CallActionService)}: starting job {jobParams.JobId}");
callActions.SendAction(
callToken,
subsciberPhoneNumber,
(CallActions)Enum.Parse(typeof(CallActions), action));
}
The SendAction code calls the http client wrapper. The http client wrapper code looks like this:
public async Task<int> PostAsync(string api, object message)
{
var apiUrl = Constants.DefaultAppApi + api;
var contentText = JsonConvert.SerializeObject(message);
var content = new StringContent(contentText, Encoding.UTF8, "application/json");
var backOff = 10;
var retryCount = 5;
HttpResponseMessage response = null;
for (var attempt = 1; attempt <= retryCount; attempt++)
{
_logger.TraceInfo($"DataServerClient Post message: {message.GetType().Name}, attempt = {attempt}");
try
{
response = await _client.PostAsync(apiUrl, content);
}
catch (Exception ex)
{
if (attempt == retryCount)
_logger.TraceException($"DataServerClient Post failed", ex);
}
if (response != null && response.IsSuccessStatusCode)
{
_logger.TraceInfo($"DataServerClient post was successful at retry count: {attempt}");
break;
}
backOff *= 2;
await Task.Delay(backOff);
}
return (int)response.StatusCode;
}
Can anyone provide clues for why this is failing or how I can gather diagnostics to find out what is happening? As I mentioned, the exception is not caught, the task that I create gets marked as completed, and no message gets posted.

Xamarin & Android - crash on exiting from method

I don't know what can I tell more.
I have this method:
public async Task<HttpResponseMessage> SendAsyncRequest(string uri, string content, HttpMethod method, bool tryReauthorizeOn401 = true)
{
HttpRequestMessage rm = new HttpRequestMessage(method, uri);
if (!string.IsNullOrWhiteSpace(content))
rm.Content = new StringContent(content, Encoding.UTF8, "application/json");
HttpResponseMessage response = await client.SendAsync(rm);
if (response.StatusCode == HttpStatusCode.Unauthorized && tryReauthorizeOn401)
{
var res = await AuthenticateUser();
if(res.user == null)
return response;
return await SendAsyncRequest(uri, content, method, false);
}
return response;
}
Nothing special.
client.SendAsync(rm) is executed, response.StatusCode is Ok.
Application just crashes when exiting from this method.
Output shows me just this assert:
12-16 20:09:22.025 F/ ( 1683): * Assertion at /Users/builder/jenkins/workspace/xamarin-android-d15-9/xamarin-android/external/mono/mono/mini/debugger-agent.c:4957, condition `is_ok (error)' not met, function:set_set_notification_for_wait_completion_flag, Could not execute the method because the containing type is not fully instantiated. assembly:<unknown assembly> type:<unknown type> member:(null)
12-16 20:09:22.025 F/libc ( 1683): Fatal signal 6 (SIGABRT), code -6 in tid 1683 (omerang.Android)
And nothing more.
client is HttpClient.
I have setting in my Android project: HttpClient Implementation set to Android.
Does anyone have any idea what could be wrong?
edit
SendAsyncRequest is used like that:
public async Task<(HttpResponseMessage response, IEnumerable<T> items)> GetListFromRequest<T>(string uri)
{
HttpResponseMessage response = await SendAsyncRequest(uri, null, HttpMethod.Get);
if (!response.IsSuccessStatusCode)
return (response, null);
string content = await response.Content.ReadAsStringAsync();
var items = JsonConvert.DeserializeObject<IEnumerable<T>>(content);
return (response, new List<T>(items));
}

Based on the provided example project code you provided
protected override async void OnStart()
{
Controller c = new Controller();
TodoItem item = await c.GetTodoItem(1);
TodoItem item2 = await c.GetTodoItem(2);
}
You are calling async void fire and forget on startup.
You wont be able to catch any thrown exceptions, which would explain why the App crashes with no warning.
Reference Async/Await - Best Practices in Asynchronous Programming
async void should only be used with event handlers, so I would suggest adding an event and handler.
based on the provided example, it could look like as follows
public partial class App : Application {
public App() {
InitializeComponent();
MainPage = new MainPage();
}
private even EventHander starting = delegate { };
private async void onStarting(object sender, EventArgs args) {
starting -= onStarting;
try {
var controller = new Controller();
TodoItem item = await controller.GetTodoItem(1);
TodoItem item2 = await controller.GetTodoItem(2);
} catch(Exception ex) {
//...handler error here
}
}
protected override void OnStart() {
starting += onStarting;
starting(this, EventArgs.Empty);
}
//...omitted for brevity
}
With that, you should now at least be able to catch the thrown exception to determine what is failing.

try to update your compileSdkVersion to a higher version and check.
also try following
> Go to: File > Invalidate Caches/Restart and select Invalidate and Restart

AllJoyn Bus Blocked Exception

I'm trying to get device discovery work using AllJoyn on Android. Following the sample apps, I'm able to get callbacks for foundAdvertisedName and able to join the session. But when calling any methods on the proxyBusObject it thorws BusBlocked Exception. BusSignals work correctly though using SignalEmitter.
mBus = new BusAttachment(context.getPackageName(), BusAttachment.RemoteMessage.Receive);
mBus.enableConcurrentCallbacks();
status = mBus.connect();
if (Status.OK != status) {
return;
} else {
busAttachmentState = BusAttachmentState.CONNECTED;
}
mBus.registerBusListener(new BusListener() {
#Override
public void foundAdvertisedName(String name,
short transport,
String namePrefix) {
mBus.enableConcurrentCallbacks();
short contactPort = CONTACT_PORT;
SessionOpts sessionOpts = new SessionOpts();
sessionOpts.traffic = SessionOpts.TRAFFIC_MESSAGES;
sessionOpts.isMultipoint = false;
sessionOpts.proximity = SessionOpts.PROXIMITY_ANY;
sessionOpts.transports = SessionOpts.TRANSPORT_ANY;
Mutable.IntegerValue sessionId = new Mutable.IntegerValue();
Status status = mBus.joinSession(name,
contactPort,
sessionId,
sessionOpts,
new SessionListener());
mProxyObj = mBus.getProxyBusObject("com.my.well.known.name",
"/MyService",
sessionId.value,
new Class[] { SampleInterface.class });
mSampleInterface = mProxyObj.getInterface(SampleInterface.class);
mSampleInterface.Test(); // BusMethod call throws exception every time
});
I've tried calling the busMethod on a separate thread as well but getting the same error. Does anyone know what could be wrong here?
UPDATE: Edited code to add BusAttachment creation snippet.

System.Net.Http.HttpClient with AutomaticDecompression and GetAsync (timeout) vs GetStringAsync (working

I have the following code to make requests to a REST API, using Xamarin and an Android device:
public class ApiBase
{
HttpClient m_HttpClient;
public ApiBase(string baseAddress, string username, string password)
{
if (!baseAddress.EndsWith("/"))
{
baseAddress += "/";
}
var handler = new HttpClientHandler();
if (handler.SupportsAutomaticDecompression)
{
handler.AutomaticDecompression = DecompressionMethods.GZip;
}
m_HttpClient = new HttpClient(handler);
m_HttpClient.BaseAddress = new Uri(baseAddress);
var credentialsString = Convert.ToBase64String(Encoding.UTF8.GetBytes(username + ":" + password));
m_HttpClient.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Basic", credentialsString);
m_HttpClient.Timeout = new TimeSpan(0, 0, 30);
}
protected async Task<XElement> HttpGetAsync(string method)
{
try
{
HttpResponseMessage response = await m_HttpClient.GetAsync(method);
if (response.IsSuccessStatusCode)
{
// the request was successful, parse the returned string as xml and return the XElement
var xml = await response.Content.ReadAsAsync<XElement>();
return xml;
}
// the request was not successful -> return null
else
{
return null;
}
}
// some exception occured -> return null
catch (Exception)
{
return null;
}
}
}
If i have it like this, the first and the second call to HttpGetAsync work perfectly, but from the 3rd on the GetAsyncstalls and eventually throws an exception due to the timeout. I send these calls consecutively, there are not 2 of them running simultaneously since the results of the previous call are needed to decide the next call.
I tried using the app Packet Capture to look at the requests and responses to find out if i'm sending an incorrect request. But it looks like the request which fails in the end is never even sent.
Through experimentation i found out that everything works fine if don't set the AutomaticDecompression.
It also works fine if i change the HttpGetAsync method to this:
protected async Task<XElement> HttpGetAsync(string method)
{
try
{
// send the request
var response = await m_HttpClient.GetStringAsync(method);
if (string.IsNullOrEmpty(response))
{
return null;
}
var xml = XElement.Parse(response);
return xml;
}
// some exception occured -> return null
catch (Exception)
{
return null;
}
}
So basically using i'm m_HttpClient.GetStringAsync instead of m_HttpClient.GetAsync and then change the fluff around it to work with the different return type. If i do it like this, everything works without any problems.
Does anyone have an idea why GetAsync doesn't work properly (doesn't seem to send the 3rd request) with AutomaticDecompression, where as GetStringAsync works flawlessly?

There are bug reports about this exact issue:
https://bugzilla.xamarin.com/show_bug.cgi?id=21477
The bug is marked as RESOLVED FIXED and the recomended action is to update to the latest stable build. But there are other (newer) bugreports that indicate the same thing that are still open, ex:
https://bugzilla.xamarin.com/show_bug.cgi?id=34747
I made a workaround by implementing my own HttpHandler like so:
public class DecompressionHttpClientHandler : HttpClientHandler
{
protected override async Task SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
request.Headers.AcceptEncoding.Add(new System.Net.Http.Headers.StringWithQualityHeaderValue("gzip"));
var msg = await base.SendAsync(request, cancellationToken);
if (msg.Content.Headers.ContentEncoding.Contains("gzip"))
{
var compressedStream = await msg.Content.ReadAsStreamAsync();
var uncompresedStream = new System.IO.Compression.GZipStream(compressedStream, System.IO.Compression.CompressionMode.Decompress);
msg.Content = new StreamContent(uncompresedStream);
}
return msg;
}
}
Note that the code above is just an example and not a final solution. For example the request will not be compressed and all headers will be striped from the result. But you get the idea.

Xamarin.Android crashes without Internet

I create app on Xamarin.Android. There is a socket, with it's help I'm getting some data for my app. I'm checking the internet connection like this:
_timer = new Timer(CheckNetworkAvailable, new AutoResetEvent(false), 0, 10000);
It calls in OnCreate method.
cts = new CancellationTokenSource();
var isNetwork = await Task.Run(() => this.NetworkRechableOrNot(), cts.Token);
var linear = SupportActionBar.CustomView.FindViewById<LinearLayout>(Resource.Id.linearForActionBanner);
var identOn = linear.FindViewById<ImageView>(Resource.Id.identificator_on);
var identOff = linear.FindViewById<ImageView>(Resource.Id.identificator_off);
RunOnUiThread(() =>
{
identOn.Visibility = !isNetwork ? ViewStates.Gone : ViewStates.Visible;
identOff.Visibility = !isNetwork ? ViewStates.Visible : ViewStates.Gone;
});
if (isNetwork)
{
if (isNetwork != oldNet)
{
oldNet = isNetwork;
MainDataClass.UpdateSymbolsList();
SocketClass.Start();
}
}
else
{
oldNet = isNetwork;
cts.Cancel();
SocketClass.Stop();
}
Here oldNet - previos status of internet access.
private bool NetworkRechableOrNot()
{
try
{
var connectivityManager = (_Net.ConnectivityManager)GetSystemService(Context.ConnectivityService);
var activeConnection = connectivityManager.ActiveNetworkInfo;
return (activeConnection != null) && activeConnection.IsConnected;
}
catch (Exception)
{
return false;
}
}
And this is the result method for checking.
SocketClass - class for socket and getting data; Start method creating new Task and Start it, socket created via SocketIOClient.Socket; Stop method calls Close method of Socket. And it all works fine until I try to disable internet connection, I got only once NameResolutionFailure. What can be the reason of it? And what should I change for meking it works fine? Thanks.

I think the main reason is your internet is off. You need a internet to try resolve some address.

I solved it, there was not correct realization of socket, it come in loop because when socket gets error it calls itself and doesn't finish that's why it crashes.