HttpRequestException -- Is this a client or server issue?

Question

Awhile ago I implemented some code to consume a REST Api using the HttpClient class.

using (var client = new HttpClient() { BaseAddress = new Uri(@"https://thirdparty.com") }) {     client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(...);      var uri = new Uri(@"rest/api/foo", UriKind.Relative);     var content = new StringContent(json.ToString());      using (var response = await client.PostAsync(uri, content))     {         // etc ...     } } 

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This code seemed to work perfectly fine against both the test and production environments (each of which access a test/production uri). Recently, we started to get an HttpRequestException in the production environment only: System.Net.Http.HttpRequestException: Error while copying content to a stream.

This seemed a bit strange, so I used Postman to send the same message and it worked just fine. I wasn't sure why our code was failing and Postman was working. I changed a parameter in the json data (the state from "NY" to "NV") and our .NET code worked fine -- of course we can't just send the wrong json data, so this isn't a solution; this was more of an observation that the exact same code worked fine with different content.

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What's interesting is that there are two code changes we could make that will resolve this. Firstly, Postman is able to generate working C# code using the RestSharp package. Alternatively, I found an answer from another question pointing to using HttpVersion 1.0:

using (var request = new HttpRequestMessage(HttpMethod.Post, uri)) {     request.Version = HttpVersion.Version10;     request.Content = new StringContent(json.ToString());      using (var response = await client.SendAsync(request))     {         // etc ...     } } 

The confusing part is that Postman uses the HTTP/1.1 version. So, in summary:

• If we change the json data (US State from "NY" to "NV"), the code works.
• The same exact json and code works against the test uri.
• Changing the code to use the RestSharp package works.
• Changing the code to use HTTP/1.0 instead of HTTP/1.1 works.

Why on earth is Postman able to work using HTTP/1.1 but HttpClient fails? Is this a problem with our client (the code works for other US States)? Is this a bug in the .NET Framework? Is there something wrong with the implementation/hosting of the REST Api from the third party?

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Postman headers:

POST rest/api/foo HTTP/1.1 Host: thirdparty.com Content-Type: application/json Authorization: Basic SOME_ENCRYPTED_USER_PASS Cache-Control: no-cache Postman-Token: 2fa5b5a0-b5d3-bd4c-40f0-d2b55b60316b 

Sample Json:

{     "stateCode": "NY",     "packageID": "58330",     "name": "58330-PRI-1",     "documents": [         {             "type": "SPECIAL",             "name": "Sample Document",             "documentID": "3569976"         }     ],     "descriptions": [         {             "city": "New York",             "state": "NY"         }     ] } 

Stacktrace:

AggregateException: One or more errors occured. HttpRequestException: Error while copying content to a stream. IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. SocketException: An existing connection was forcibly closed by the remote host. 

Answer 1

Due to the fact that you can change the data slightly and have it succeed, I would say your issues has nothing to do with any of your code. What if their server has cached a bad value and will continue sending you that value until their cache clears?

Try implicitly telling the server not to use cached values...

using (var client = new HttpClient() { BaseAddress = new Uri(@"https://thirdparty.com") }) {     client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(...);      var uri = new Uri(@"rest/api/foo", UriKind.Relative);     var content = new StringContent(json.ToString());      client.DefaultRequestHeaders.CacheControl = CacheControlHeaderValue.Parse("no-cache");      using (var response = await client.PostAsync(uri, content))     {         // etc ...     } } 

and see if you get a valid response stream.