How to use HttpWebRequest NET asynchronously

Question

How can I use HttpWebRequest   NET  C   asynchronously

User · Answer

By far the easiest way is by using TaskFactory.FromAsync from the TPL. It's literally a couple of lines of code when used in conjunction with the new async/await keywords:

var request = WebRequest.Create("http://www.stackoverflow.com");
var response = (HttpWebResponse) await Task.Factory
    .FromAsync<WebResponse>(request.BeginGetResponse,
                            request.EndGetResponse,
                            null);
Debug.Assert(response.StatusCode == HttpStatusCode.OK);

If you can't use the C#5 compiler then the above can be accomplished using the Task.ContinueWith method:

Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse,
                                    request.EndGetResponse,
                                    null)
    .ContinueWith(task =>
    {
        var response = (HttpWebResponse) task.Result;
        Debug.Assert(response.StatusCode == HttpStatusCode.OK);
    });

User · Answer

I ended up using BackgroundWorker  it is definitely asynchronous unlike some of the above solutions  it handles returning to the GUI thread for you  and it is very easy to understand    It is also very easy to handle exceptions  as they end up in the RunWorkerCompleted method  but make sure you read this  Unhandled exceptions in BackgroundWorker  I used WebClient but obviously you could use HttpWebRequest GetResponse if you wanted   var worker   new BackgroundWorker     worker DoWork     sender  args    gt        args Result   new WebClient   DownloadString settings test url       worker RunWorkerCompleted     sender  e    gt        if  e Error    null            connectivityLabel Text    Error      e Error Message        else           connectivityLabel Text    Connectivity OK           Log d  result     e Result             connectivityLabel Text    Testing Connectivity   worker RunWorkerAsync

User · Answer

Considering the answer   HttpWebRequest webRequest   void StartWebRequest         webRequest BeginGetResponse new AsyncCallback FinishWebRequest   null      void FinishWebRequest IAsyncResult result        webRequest EndGetResponse result       You could send the request pointer or any other object like this   void StartWebRequest         HttpWebRequest webRequest            webRequest BeginGetResponse new AsyncCallback FinishWebRequest   webRequest      void FinishWebRequest IAsyncResult result        HttpWebResponse response    result AsyncState as HttpWebRequest  EndGetResponse result  as HttpWebResponse      Greetings

User · Answer

I ended up using BackgroundWorker  it is definitely asynchronous unlike some of the above solutions  it handles returning to the GUI thread for you  and it is very easy to understand    It is also very easy to handle exceptions  as they end up in the RunWorkerCompleted method  but make sure you read this  Unhandled exceptions in BackgroundWorker  I used WebClient but obviously you could use HttpWebRequest GetResponse if you wanted   var worker   new BackgroundWorker     worker DoWork     sender  args    gt        args Result   new WebClient   DownloadString settings test url       worker RunWorkerCompleted     sender  e    gt        if  e Error    null            connectivityLabel Text    Error      e Error Message        else           connectivityLabel Text    Connectivity OK           Log d  result     e Result             connectivityLabel Text    Testing Connectivity   worker RunWorkerAsync

User · Answer

public void GetResponseAsync  HttpWebRequest request  Action lt HttpWebResponse gt  gotResponse                if  request    null                 request BeginGetRequestStream   r    gt                    try      there s a try catch here because execution path is different from invokation one  exception here may cause a crash                     HttpWebResponse response   request EndGetResponse  r                       if  gotResponse    null                           gotResponse  response                     catch  Exception x                        Console WriteLine   Unable to get response for      request RequestUri      Err      x                                    null

User · Answer

By far the easiest way is by using TaskFactory.FromAsync from the TPL. It's literally a couple of lines of code when used in conjunction with the new async/await keywords:

var request = WebRequest.Create("http://www.stackoverflow.com");
var response = (HttpWebResponse) await Task.Factory
    .FromAsync<WebResponse>(request.BeginGetResponse,
                            request.EndGetResponse,
                            null);
Debug.Assert(response.StatusCode == HttpStatusCode.OK);

If you can't use the C#5 compiler then the above can be accomplished using the Task.ContinueWith method:

Task.Factory.FromAsync<WebResponse>(request.BeginGetResponse,
                                    request.EndGetResponse,
                                    null)
    .ContinueWith(task =>
    {
        var response = (HttpWebResponse) task.Result;
        Debug.Assert(response.StatusCode == HttpStatusCode.OK);
    });

User · Answer

Considering the answer   HttpWebRequest webRequest   void StartWebRequest         webRequest BeginGetResponse new AsyncCallback FinishWebRequest   null      void FinishWebRequest IAsyncResult result        webRequest EndGetResponse result       You could send the request pointer or any other object like this   void StartWebRequest         HttpWebRequest webRequest            webRequest BeginGetResponse new AsyncCallback FinishWebRequest   webRequest      void FinishWebRequest IAsyncResult result        HttpWebResponse response    result AsyncState as HttpWebRequest  EndGetResponse result  as HttpWebResponse      Greetings

User · Answer

Use HttpWebRequest BeginGetResponse    HttpWebRequest webRequest   void StartWebRequest         webRequest BeginGetResponse new AsyncCallback FinishWebRequest   null      void FinishWebRequest IAsyncResult result        webRequest EndGetResponse result       The callback function is called when the asynchronous operation is complete  You need to at least call EndGetResponse   from this function

User · Answer

NET has changed since many of these answers were posted  and I d like to provide a more up-to-date answer   Use an async method to start a Task that will run on a background thread   private async Task lt String gt  MakeRequestAsync String url            String responseText   await Task Run      gt                try                       HttpWebRequest request   WebRequest Create url  as HttpWebRequest              WebResponse response   request GetResponse                            Stream responseStream   response GetResponseStream                return new StreamReader responseStream  ReadToEnd                                  catch  Exception e                        Console WriteLine  Error      e Message                     return null               return responseText      To use the async method   String response   await MakeRequestAsync  http   example com       Update   This solution does not work for UWP apps which use WebRequest GetResponseAsync   instead of WebRequest GetResponse    and it does not call the Dispose   methods where appropriate    dragansr has a good alternative solution that addresses these issues

User · Answer

Everyone so far has been wrong  because BeginGetResponse   does some work on the current thread  From the documentation      The BeginGetResponse method requires some synchronous setup tasks to   complete  DNS resolution  proxy detection  and TCP socket connection    for example  before this method becomes asynchronous  As a result    this method should never be called on a user interface  UI  thread   because it might take considerable time  up to several minutes   depending on network settings  to complete the initial synchronous   setup tasks before an exception for an error is thrown or the method   succeeds    So to do this right   void DoWithResponse HttpWebRequest request  Action lt HttpWebResponse gt  responseAction        Action wrapperAction        gt                request BeginGetResponse new AsyncCallback  iar    gt                        var response    HttpWebResponse   HttpWebRequest iar AsyncState  EndGetResponse iar               responseAction response               request              wrapperAction BeginInvoke new AsyncCallback  iar    gt                var action    Action iar AsyncState          action EndInvoke iar           wrapperAction       You can then do what you need to with the response  For example   HttpWebRequest request     init your request   then  DoWithResponse request   response    gt        var body   new StreamReader response GetResponseStream    ReadToEnd        Console Write body

User · Answer

Use HttpWebRequest BeginGetResponse    HttpWebRequest webRequest   void StartWebRequest         webRequest BeginGetResponse new AsyncCallback FinishWebRequest   null      void FinishWebRequest IAsyncResult result        webRequest EndGetResponse result       The callback function is called when the asynchronous operation is complete  You need to at least call EndGetResponse   from this function

User · Answer

Use HttpWebRequest BeginGetResponse    HttpWebRequest webRequest   void StartWebRequest         webRequest BeginGetResponse new AsyncCallback FinishWebRequest   null      void FinishWebRequest IAsyncResult result        webRequest EndGetResponse result       The callback function is called when the asynchronous operation is complete  You need to at least call EndGetResponse   from this function

User · Answer

Everyone so far has been wrong  because BeginGetResponse   does some work on the current thread  From the documentation      The BeginGetResponse method requires some synchronous setup tasks to   complete  DNS resolution  proxy detection  and TCP socket connection    for example  before this method becomes asynchronous  As a result    this method should never be called on a user interface  UI  thread   because it might take considerable time  up to several minutes   depending on network settings  to complete the initial synchronous   setup tasks before an exception for an error is thrown or the method   succeeds    So to do this right   void DoWithResponse HttpWebRequest request  Action lt HttpWebResponse gt  responseAction        Action wrapperAction        gt                request BeginGetResponse new AsyncCallback  iar    gt                        var response    HttpWebResponse   HttpWebRequest iar AsyncState  EndGetResponse iar               responseAction response               request              wrapperAction BeginInvoke new AsyncCallback  iar    gt                var action    Action iar AsyncState          action EndInvoke iar           wrapperAction       You can then do what you need to with the response  For example   HttpWebRequest request     init your request   then  DoWithResponse request   response    gt        var body   new StreamReader response GetResponseStream    ReadToEnd        Console Write body

User · Answer

public static async Task lt byte   gt  GetBytesAsync string url        var request    HttpWebRequest WebRequest Create url       using  var response   await request GetResponseAsync        using  var content   new MemoryStream        using  var responseStream   response GetResponseStream              await responseStream CopyToAsync content           return content ToArray             public static async Task lt string gt  GetStringAsync string url        var bytes   await GetBytesAsync url       return Encoding UTF8 GetString bytes  0  bytes Length

User · Answer

public static async Task lt byte   gt  GetBytesAsync string url        var request    HttpWebRequest WebRequest Create url       using  var response   await request GetResponseAsync        using  var content   new MemoryStream        using  var responseStream   response GetResponseStream              await responseStream CopyToAsync content           return content ToArray             public static async Task lt string gt  GetStringAsync string url        var bytes   await GetBytesAsync url       return Encoding UTF8 GetString bytes  0  bytes Length

User · Answer

public void GetResponseAsync  HttpWebRequest request  Action lt HttpWebResponse gt  gotResponse                if  request    null                 request BeginGetRequestStream   r    gt                    try      there s a try catch here because execution path is different from invokation one  exception here may cause a crash                     HttpWebResponse response   request EndGetResponse  r                       if  gotResponse    null                           gotResponse  response                     catch  Exception x                        Console WriteLine   Unable to get response for      request RequestUri      Err      x                                    null

User · Answer

NET has changed since many of these answers were posted  and I d like to provide a more up-to-date answer   Use an async method to start a Task that will run on a background thread   private async Task lt String gt  MakeRequestAsync String url            String responseText   await Task Run      gt                try                       HttpWebRequest request   WebRequest Create url  as HttpWebRequest              WebResponse response   request GetResponse                            Stream responseStream   response GetResponseStream                return new StreamReader responseStream  ReadToEnd                                  catch  Exception e                        Console WriteLine  Error      e Message                     return null               return responseText      To use the async method   String response   await MakeRequestAsync  http   example com       Update   This solution does not work for UWP apps which use WebRequest GetResponseAsync   instead of WebRequest GetResponse    and it does not call the Dispose   methods where appropriate    dragansr has a good alternative solution that addresses these issues

User · Answer

Use HttpWebRequest BeginGetResponse    HttpWebRequest webRequest   void StartWebRequest         webRequest BeginGetResponse new AsyncCallback FinishWebRequest   null      void FinishWebRequest IAsyncResult result        webRequest EndGetResponse result       The callback function is called when the asynchronous operation is complete  You need to at least call EndGetResponse   from this function

[c#] How to use HttpWebRequest (.NET) asynchronously?

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