Properly disposing a WebRequest and StreamReader

Question

I'm getting an object disposed exception during a call to the ReadToEnd method from a client side method, getRecords, that communicates to a webserver using a StreamReader.

The first call to getRecords succeeds, it is only during a subsequent call the exception occurs, and so I'm not closing and disposing of the StreamReader and associated WebRequest properly.

I'm aware that I could wrap these two objects in a using statement, however that just gets expanded into a try/catch/finally statement. As can be seen in my code below, I'm cleaning up in my finally clause.

Therefore, I'm either not doing something that the using statment does, or there is something else I may be missing in my finally statment. I'd rather not using the using statment if at all possible, as I like my code explicit.

Here is the code and the associated exception:

    public int getRecords(string[] args, string[] vals)
    {
        List<string> urlList = BuildUrlRequestStrings(args, vals); 

        WebRequest request = null;
        WebResponse wresponse = null;
        StreamReader sr = null;           

        foreach (string url in urlList)
        {   
            request = WebRequest.Create(url);

            request.Method = "GET";
            request.ContentType = "application/json";
            //request.Timeout = -1;
            request.Timeout = 300000;
            request.Credentials = CredentialCache.DefaultCredentials;
            //request.ContentType = "application/xml";

            try
            {
                wresponse = request.GetResponse();

                /*using (StreamReader sr = new StreamReader(wresponse.GetResponseStream()))
                {
                    _recieveBuffer = sr.ReadToEnd().ToString();
                }*/
                sr = new StreamReader(wresponse.GetResponseStream());
                _recieveBuffer = sr.ReadToEnd();

                //List<T> temp = JsonConvert.DeserializeObject<List<T>>(_recieveBuffer);
                List<T> temp = JsonConvert.DeserializeObject<List<T>>(
                    _recieveBuffer,
                    new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.All }
                );

                _recieveData.AddRange(temp);                    
            }
            catch (WebException ex)
            {
                if (ex.Response != null)
                {
                    // can use ex.Response.Status, .StatusDescription         
                    if (ex.Response.ContentLength != 0)
                    {
                        using (var stream = ex.Response.GetResponseStream())
                        {
                            using (var reader = new StreamReader(stream))
                            {
                                Log.Info(FIDB.TAG1, "   WSBuffer.getRecords: WEBSERVER MESSAGE: " + reader.ReadToEnd());
                            }
                        }
                    }
                }

                return -1;
            }
            finally
            {
                if (sr != null)
                {
                    sr.Close();
                    sr.Dispose();
                }

                if (wresponse != null)
                {
                    wresponse.Close();
                    wresponse.Dispose();
                }
            }
        }

        return _recieveData.Count;
    }

---

07-02 11:32:15.076: I/<<< FI >>>(2775): StorageRelayService.RequestQueueThread: EXCEPTION: System.ObjectDisposedException: The object was used after being disposed. 07-02 11:32:15.076: I/<<< FI >>>(2775): at System.Net.WebConnection.BeginRead (System.Net.HttpWebRequest request, System.Byte[] buffer, Int32 offset, Int32 size, System.AsyncCallback cb, System.Object state) [0x00000] in :0 07-02 11:32:15.076: I/<<< FI >>>(2775): at System.Net.WebConnectionStream.BeginRead (System.Byte[] buffer, Int32 offset, Int32 size, System.AsyncCallback cb, System.Object state) [0x00000] in :0 07-02 11:32:15.076: I/<<< FI

(2775): at System.Net.WebConnectionStream.Read (System.Byte[] buffer, Int32 offset, Int32 size) [0x00000] in :0 07-02 11:32:15.076: I/<<< FI >>>(2775): at System.IO.StreamReader.ReadBuffer () [0x00000] in :0 07-02 11:32:15.076: I/<<< FI >>>(2775): at System.IO.StreamReader.Read (System.Char[] buffer, Int32 index, Int32 count) [0x00000] in :0 07-02 11:32:15.076: I/<<< FI (2775): at System.IO.StreamReader.ReadToEnd () [0x00000] in :0 07-02 11:32:15.076: I/<<< FI >>>(2775): at FieldInspection.Shared.Buffer.WSBuffer1[FieldInspection.Shared.Model.AggregateRoot.Parcel].getRecords (System.String[] args, System.String[] vals) [0x00000] in <filename unknown>:0 07-02 11:32:15.076: I/<<< FI >>>(2775): at FieldInspection.Shared.Repository.REST.RepositoryREST1[FieldInspection.Shared.Model.AggregateRoot.Parcel].Read (IConditions conditions) [0x00000] in :0 07-02 11:32:15.076: I/<<< FI >>>(2775): at FieldInspection.Shared.Model.DataAccess.ParcelRepositoryREST.parcelByIdList (System.Collections.Generic.List1 parcelIdList, Boolean bCurrent, Boolean bHistorical) [0x00000] in <filename unknown>:0 07-02 11:32:15.076: I/<<< FI >>>(2775): at FieldInspection.Droid.StorageRelayService.ProcessRequestGetParcelCache (FieldInspection.Shared.Database.IPC.Request request) [0x00000] in <filename unknown>:0 07-02 11:32:15.076: I/<<< FI >>>(2775): at FieldInspection.Droid.StorageRelayService.ProcessRequestFromForegroundActivity (System.Collections.Generic.List1 reqList) [0x00000] in :0 07-02 11:32:15.076: I/<<< FI >>>(2775): at FieldInspection.Droid.StorageRelayService.RequestQueueThread () [0x00000] in :0

Answer 1

I'd highly suggest you to use "using" statement. Once you know your WebResponse and StreamReader disposed properly, it becomes easier to debug.

Also, you create a WebRequest object for each iteration of your loop. Why don't you try an asycnhronous approach?

This post might be helpful: How to use HttpWebRequest (.NET) asynchronously?