Page 128 - DCAP312_WEB_TECHNOLOGIES_II

Web Technologies-II

Notes 6.5.2 HttpResponseException
Now you may be wondering: how do we return an error if the action returns a different
type instead of HttpResponseMessage? This is where HttpResponseException comes in.
HttpResponseException is an exception type defined for WebAPI that serves two purposes:
It allows you to return a specific HTTP response from actions with return types that are not
HttpResponseMessage.

It allows you to short-circuit the WebAPI pipeline pretty much anywhere and return a response
immediately.

Technically, HttpResponseException can be used for any kind of HTTP response, but it is
especially useful in error cases. It allows us to implement actions like this:
public Person Get(int id)
{
if (!_contacts.ContainsKey(id))
{
throw new HttpResponseException(Request.CreateErrorResponse(Htt
pStatusCode.NotFound, String.Format( “Contact {0} not found.”, id)));
}
return _contacts[id];
}

Write the code to http error handling.

6.5.3 Error Detail
You may have noticed the “includeErrorDetail” parameter earlier in this post on the HttpError
constructor. This is because typically, servers want to send different error information depending
on whether the client is just consuming the service or whether the client needs additional
debugging information to understand what went wrong on the server. By default, WebAPI will
not send error details to remote clients and will provide these additional error details to clients
on the local machine. Returning to our first example, whereas a local client would see this:
{
“Message”: “No HTTP resource was found that matches the request
URI ‘http: //localhost/Foo’.”,
“Message Detail”: “No type was found that matches the controller
named ‘Foo’.”
}
A remote client would only see this:
{
“Message”: “No HTTP resource was found that matches the request
URI ‘http: //localhost/Foo’.”
}

The difference between Message and Message Detail above is that MessageDetail contains error
information that is WebAPI-specific that remote clients should not have to see in most cases.
The exact meaning of error detail depends on the case. For exceptions, error detail includes the

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