Updated Jan 05, 2007 by fmantek
Labels:	Phase-Implementation, NetClient, Featured

ErrorHandling

How to deal with error returns from the server

Introduction

One of the things that allways show up here on the newsgroups, is the problem to figure out why an execution to the server failed. In general, this is rather simplistic to deal with on the C# side, but as not everyone is familiar with the process, here is the scoop.

Details

When the webserver returns an error, an exception will be thrown. The C# client code will catch this, package it into a GDataRequestException and throw that one.

In the application code, therefore, when you do something like:

myFeed.Insert(myNewEntry);

what you should be doing is:

try { 
  myFeed.Insert(myNewEntry); 
} catch  (GDataRequestException e )  { 
// your error code here 
}

In general, the GDataRequestException class is just a wrapper around the real exception. It has the innerException, and it exposes the WebResponse, the object that captures the server response, as a property named Response.

A WebResponse now has a bundle of properties, including a method GetResponseStream, which you can use to get the real HTTP/Text that the server returned. If you cast the WebResponse to an HttpWebResponse, you can get the StatusCode and other, more HTTP specific information as well.

To make life easier, i just added a ResponseString property to the GDataRequestException class, so that you can easier glance at additonal information returned by the server. For those not at ease with the repository, here is code that does the same in an exception handler:

catch (GDataRequestException e) { 
  Stream receiver = e.Response.GetResponseStream(); 
  if (receiver != null) { 
  // Pipe the stream to ahigher level stream reader with the default encoding 
  // format. which is UTF8 
  StreamReader readStream = new StreamReader(receiver);

  // Read 256 charcters at a time. 
  char []buffer = new char[256]; 
  StringBuilder builder = new StringBuilder(1024); 
  int count = readStream.Read( buffer, 0, 256); 
  while (count > 0) { 
    string onto the console. builder.Append(buffer); 
    count = readStream.Read(buffer,0, 256);
  }

  // Release the resources of stream object. 
  readStream.Close(); 
  receiver.Close();
  responseText = builder.ToString(); 
  }
}

At the end of the code, responseText will hold the complete HTTP/Text response of the server. It might be safer to even check of the contenttype, before using that string AS a string, but for debugging purposes this will do just fine.