HttpClient throws exception when switching to IPV6 - Rejected from iOS Store
<p>Having a bizarre issue with a Xamarin project I am working on and I'm stumped...</p>

<p>I use HTTPClient to make asynchronous requests. However, my app was rejected from the app store for failing to meet Apple's IPV6 requirements. That is, a request I make using HTTPClient fails when connected through IPV6. What's bizarre is that it only fails when the app is started on an IPV4 network then switched to an IPV6 network. If I restart the application while connected to the IPV6 network, it succeeds! Also, if I start the app connected to IPV6 then switch to an IPV4 network, it also succeeds. It only fails when started in IPV4 then switched to IPV6.</p>

<p>It's utterly bizarre - it's like the HttpClient is caching something, but we create a new client for every request. I'm not using an IP address - just an address, and, as I mentioned, it works when the app is started connected to an IPV6 only network. It's only the switch from IPV4 to IPV6 which seems to cause the issue.</p>

<p>The code which exists in PCL:</p>

<pre><code>var client = new HttpClient();
var urlToCall = new Uri("https://www.something.com/someapi/v1");
// Add some headers
...
response = client.GetAsync(urlToCall);
</code></pre>

<p>And the stack trace:</p>

<pre><code>Trace.Message": "Error: ConnectFailure (Network is unreachable)
at System.Net.HttpWebRequest.EndGetResponse (IAsyncResult asyncResult) [0x00065] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/System/System.Net/HttpWebRequest.cs:946 
at System.Threading.Tasks.TaskFactory`1[TResult].FromAsyncCoreLogic (IAsyncResult iar, System.Func`2 endFunction, System.Action`1 endAction, System.Threading.Tasks.Task`1 promise, Boolean requiresSynchronization) &lt;0x10019c730 + 0x0005b&gt; in &lt;filename unknown&gt;:0 
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0003b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:199 
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:170 
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:142 
at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter[TResult].GetResult () &lt;0x10013ccc0 + 0x0001b&gt; in &lt;filename unknown&gt;:0 
at System.Net.Http.HttpClientHandler+&lt;SendAsync&gt;c__async0.MoveNext () [0x003d6] in /Library/Frameworks/Xamarin.iOS.framework/Versions/9.6.1.9/src/mono/mcs/class/System.Net.Http/System.Net.Http/HttpClientHandler.cs:372 
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0003b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:199 
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:170 
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:142 
at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter[TResult].GetResult () &lt;0x10013ccc0 + 0x0001b&gt; in &lt;filename unknown&gt;:0 
at System.Net.Http.HttpClient+&lt;SendAsyncWorker&gt;c__async0.MoveNext () [0x000a9] in /Library/Frameworks/Xamarin.iOS.framework/Versions/9.6.1.9/src/mono/mcs/class/System.Net.Http/System.Net.Http/HttpClient.cs:274 
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x0003b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:199 
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:170 
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:142 
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () &lt;0x10013c8c0 + 0x0001b&gt; in &lt;filename unknown&gt;:0 
at MyApp.RestClient.RestService`2+&lt;SendHttpRequest&gt;d__10[TInput,TOutput].MoveNext () [0x00259] in &lt;filename unknown&gt;:0 
Network is unreachable
at System.Net.Sockets.Socket.Connect (System.Net.EndPoint remoteEP) [0x000bc] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/System/System.Net.Sockets/Socket.cs:1235 
at System.Net.WebConnection.Connect (System.Net.HttpWebRequest request) [0x001c2] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/mcs/class/System/System.Net/WebConnection.cs:213 
</code></pre>

<p>Has anyone seen anything like this before? Does anyone have any idea of how to fix or even debug this?</p>