Cannot construct a WebException

Question

I have a method where I call DownloadData on a WebClient. This method throws an exception since the URL returns 404. This is all expected by specifications since the resource does not exist.

Web client will throw a WebException and I have to read body from respose since it contains JSON object with detailed error. After that I have to throw a WebException again since the layer up still expects the WebException. At the moment I am trying to construct a WebException with details from the current one as follows:

catch(WebException ex)
{
   var response = new StreamReader(ex.Response.GetResponseStream()).ReadToEnd();   
   dynamic error = JsonConvert.DeserializeObject(response);
   throw new WebException(error.message, null, ex.Status, ex.Response);
}

The problem is I get an exception while constructing WebException. This is the message!

The best overloaded method match for 'System.Net.WebException.WebException(string, System.Net.WebExceptionStatus, System.Net.WebExceptionInternalStatus, System.Exception)' has some invalid arguments

It is like this constructor does not exist! Check the constructor in exception and check the constructor in catch block.

As you can see I am using a valid constructor. Check here.

What is happening here?

Read the error, your parameters that you are passing through are incorrect — David Pilkington, Feb 15 '17 at 08:37
Try casting your `null` - sounds weird, I know, but this can help with overload resolution (if that is really the problem). — Manfred Radlwimmer, Feb 15 '17 at 08:38
Also try using `string message = error.message;` and then using that - so that the overload resolution will occur at compile-time instead of at execution time. — Jon Skeet, Feb 15 '17 at 08:40
I would avoid using dymanic in this case. Just do `JsonConvert.DeserializeObject(response)` instead, then you do `error['message'].ToString()` — Callum Linington, Feb 15 '17 at 09:01

score 1 · Accepted Answer · edited Feb 15 '17 at 09:12

1

The problem is, that you need to cast error.message as string. It would be even better if you would handle that string differently so you can verify if that error.message exists.

catch(WebException ex)
{
    var response = new StreamReader(ex.Response.GetResponseStream()).ReadToEnd();   
    dynamic error = JsonConvert.DeserializeObject(response);
    throw new WebException((string)error.message, null, ex.Status, ex.Response);
}

edited Feb 15 '17 at 09:12

Manfred Radlwimmer

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answered Feb 15 '17 at 08:50

MaticDiba

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As I said, try putting addtional check for error object, becaus it may not contain message property and then you will have another exception :) – MaticDiba Feb 15 '17 at 08:58

Cannot construct a WebException

1 Answers1