Retrieve content from 404 error using HttpWebRequest

Question

This is similar to a question asked here: httpWebRequest - get error content but I'm hoping to provide some more information in hope of an answer.

I am integrating with the LinkedIn API using C#. When I make an invalid call to the API, it can return a HTTP response like such (from Fiddler):

HTTP/1.1 404 Not Found
Server: Apache-Coyote/1.1
x-li-request-id: VL2EER2ROJ
Date: Tue, 16 Oct 2012 08:52:59 GMT
Vary: *
x-li-format: xml
Content-Type: text/xml;charset=UTF-8
Content-Length: 266

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<error>
  <status>404</status>
  <timestamp>1350377580000</timestamp>
  <request-id>VL2EER2ROJ</request-id>
  <error-code>0</error-code>
  <message>Could not find member {/people/XXXXXX}</message>
</error>

I would specifically like to get at the error xml, however HttpWebRequest seems to simply throw the exception and then has nothing to do with the content. In my debugger, I can see that the content length is 266, but any attempt to call (System.Net.WebException).Response.GetResponseStream() results in a stream was not readable exception.

This method of returning error messages within a non 200 HTTP status response seems quite popular in web APIs - I'm hoping there is a way to get at these responses...

What version of .NEt is this? This sounds like a bug. Get a system.net trace log and use that to create a bug report on msdn community site. BTW can you show your code? Maybe there is something there that can be changed to make this work? — feroze
Read the manual: "Note: If a WebException is thrown, use the Response and Status properties of the exception to determine the response from the server." See also this duplicate. — CodeCaster
@CodeCaster : As stated in the question an attempt to access the Response stream results in a "Cannot read from stream" exception. The answer supplied in the referenced duplicate is not correct — GrantDG
@feroze This is happening in .NET 4.0 (and I assume for all earlier versions). I tend to agree with you that this is a bug in the framework — GrantDG
@GrantDG please show your code. If you use catch (WebException wex) { var resp = new StreamReader(wex.Response.GetResponseStream()).ReadToEnd(); } it should work. This is most probably not a bug in the framework but one in your code, otherwise lots of people would've encountered it. — CodeCaster

mobese46 mobese46 · Accepted Answer · 2015-03-21T17:36:58

You'll probably need to hit the socket connection directly to get the response xml.

See this answer: https://stackoverflow.com/a/6755142

I'm running into the same thing while trying to implement Amazon's Off Amazon Payments API. If I pass an invalid transaction id, they return a 404 error...not what I was expecting.

Also of note: I'm using async when sending the http post and this 404 throws a WebException on the BeginGetResponse method; not while trying to read the response in the callback. Conversely, 400 Bad Request WebException's, are raised while reading the response stream in the callback.

Retrieve content from 404 error using HttpWebRequest

1 Answers