A method for making HTTP requests on Unity iOS?

Question

I need to send HTTP requests with all the standard RESTful methods and access to the body of the request in order to send/receive JSON with it. I've looked into,

WebRequest.HttpWebRequest

This works almost perfectly, but there are cases where, for example, if the server is down the function GetResponse can take several seconds to return- since it is a synchronous method- freezing the application for that period. The asynchronous version of this method, BeginGetResponse, does not seem to work asynchronously (in Unity anyway) as it still freezes the application for that period.

UnityEngine.WWW#

Only supports POST and GET requests for some reason- but I also need PUT and DELETE (standard RESTful methods) so I didn't bother looking into it any further.

System.Threading

In order to run WebRequest.HttpWebRequest.GetResponse without freezing the application I looked into using threads. Threads seem to work in the editor (but seem extremely volatile- if you don't stop a thread when the application exits it keeps running in the editor forever even when you stop it), and when built to an iOS device crash it as soon as I try to start a thread (I forgot to write down the error and I don't have access to it right now).

Run threads in a native iOS app with a bridge to the Unity app

Ridiculous, not even going to attempt this.

UniWeb

This. I would like to know how they managed it.

Here is an example of the WebRequest.BeginGetResponse method I am trying,

// The RequestState class passes data across async calls.
public class RequestState
{
   const int BufferSize = 1024;
   public StringBuilder RequestData;
   public byte[] BufferRead;
   public WebRequest Request;
   public Stream ResponseStream;
   // Create Decoder for appropriate enconding type.
   public Decoder StreamDecode = Encoding.UTF8.GetDecoder();

   public RequestState()
   {
      BufferRead = new byte[BufferSize];
      RequestData = new StringBuilder(String.Empty);
      Request = null;
      ResponseStream = null;
   }     
}

public class WebRequester
{
    private void ExecuteRequest()
    {
        RequestState requestState = new RequestState();
        WebRequest request = WebRequest.Create("mysite");
        request.BeginGetResponse(new AsyncCallback(Callback), requestState);
    }

    private void Callback(IAsyncResult ar)
    {
      // Get the RequestState object from the async result.
      RequestState rs = (RequestState) ar.AsyncState;

      // Get the WebRequest from RequestState.
      WebRequest req = rs.Request;

      // Call EndGetResponse, which produces the WebResponse object
      //  that came from the request issued above.
      WebResponse resp = req.EndGetResponse(ar);
    }
}

... based on this: http://msdn.microsoft.com/en-us/library/86wf6409(v=vs.71).aspx

Answer 1

Ok, I finally managed to write my own solution. We basically need a RequestState, a Callback Method and a TimeOut Thread. Here I'll just copy what was done in UnifyCommunity (now called unity3d wiki). This is outdated code, but smaller than what's there, so more convenient to show something here. Now I've removed (in the unit3d wiki) System.Action and static for performance and simplicity:

Usage

static public ThisClass Instance;
void Awake () {
    Instance = GetComponent<ThisClass>();
}
static private IEnumerator CheckAvailabilityNow () {
    bool foundURL;
    string checkThisURL = "http://www.example.com/index.html";
    yield return Instance.StartCoroutine(
        WebAsync.CheckForMissingURL(checkThisURL, value => foundURL = !value)
        );
    Debug.Log("Does "+ checkThisURL +" exist? "+ foundURL);
}

WebAsync.cs

using System;
using System.IO;
using System.Net;
using System.Threading;
using System.Collections;
using UnityEngine;

/// <summary>
///  The RequestState class passes data across async calls.
/// </summary>
public class RequestState
{
    public WebRequest webRequest;
    public string errorMessage;

    public RequestState ()
    {
        webRequest = null;
        errorMessage = null;
    }
}

public class WebAsync {
    const int TIMEOUT = 10; // seconds

    /// <summary>
    /// If the URLs returns 404 or connection is broken, it's missing. Else, we suppose it's fine.
    /// </summary>
    /// <param name='url'>
    /// A fully formated URL.
    /// </param>
    /// <param name='result'>
    /// This will bring 'true' if 404 or connection broken and 'false' for everything else.
    /// Use it as this, where "value" is a System sintaxe:
    /// value => your-bool-var = value
    /// </param>
    static public IEnumerator CheckForMissingURL (string url, System.Action<bool> result) {
        result(false);

        Uri httpSite = new Uri(url);
        WebRequest webRequest = WebRequest.Create(httpSite);

        // We need no more than HTTP's head
        webRequest.Method = "HEAD";
        RequestState requestState = new RequestState();

        // Put the request into the state object so it can be passed around
        requestState.webRequest = webRequest;

        // Do the actual async call here
        IAsyncResult asyncResult = (IAsyncResult) webRequest.BeginGetResponse(
            new AsyncCallback(RespCallback), requestState);

        // WebRequest timeout won't work in async calls, so we need this instead
        ThreadPool.RegisterWaitForSingleObject(
            asyncResult.AsyncWaitHandle,
            new WaitOrTimerCallback(ScanTimeoutCallback),
            requestState,
            (TIMEOUT *1000), // obviously because this is in miliseconds
            true
            );

        // Wait until the the call is completed
        while (!asyncResult.IsCompleted) { yield return null; }

        // Deal up with the results
        if (requestState.errorMessage != null) {
            if ( requestState.errorMessage.Contains("404") || requestState.errorMessage.Contains("NameResolutionFailure") ) {
                result(true);
            } else {
                Debug.LogWarning("[WebAsync] Error trying to verify if URL '"+ url +"' exists: "+ requestState.errorMessage);
            }
        }
    }

    static private void RespCallback (IAsyncResult asyncResult) {

        RequestState requestState = (RequestState) asyncResult.AsyncState;
        WebRequest webRequest = requestState.webRequest;

        try {
            webRequest.EndGetResponse(asyncResult);
        } catch (WebException webException) {
            requestState.errorMessage = webException.Message;
        }
    }

    static private void ScanTimeoutCallback (object state, bool timedOut)  { 
        if (timedOut)  {
            RequestState requestState = (RequestState)state;
            if (requestState != null) 
                requestState.webRequest.Abort();
        } else {
            RegisteredWaitHandle registeredWaitHandle = (RegisteredWaitHandle)state;
            if (registeredWaitHandle != null)
                registeredWaitHandle.Unregister(null);
        }
    }
}

Answer 2

I got threading to work on iOS- I believe it was crashing due to ghost threads or something. Restarting the device seems to have fixed the crashing so I'll just use WebRequest.HttpWebRequest with threads.