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Error 500 Sending JSON POST Request to API

I'm developing an app in Xamarin.Forms (Shared Project Library) that sends a list of custom types (just a document number and a file type enumeration) to a locally hosted API.
If I capture the JSON string and send it from Postman, everything works fine, but as soon as I run the httpClient.PostAsync from the app, I receive the following error:
{StatusCode: 500, ReasonPhrase: 'Internal Server Error', Version: 1.1,
Content: System.Net.Http.StreamContent, Headers: { Cache-Control:
no-cache Pragma: no-cache Server: Microsoft-IIS/7.5 X-AspNet-Version:
4.0.30319 X-Powered-By: ASP.NET Date: Thu, 25 May 2017 16:00:44 GMT Content-Type: application/json; charset=utf-8 Expires: -1
Content-Length: 36 }}
I'm at a loss a to what I'm doing wrong. Can anyone help, please?
Type:
class EmailFiles
{
public string docNumber { get; set; }
public EmailFileTypes.EmailFileType type { get; set; }
}
Request:
List<EmailFiles> files = new List<EmailFiles>();
if (chkShipping.IsToggled)
{
EmailFiles file = new EmailFiles();
file.type = EmailFileTypes.EmailFileType.CustomerFile;
file.docNumber = Helpers.GlobalVariables.gSOLookup.PackList;
files.Add(file);
}
if (chkClosed.IsToggled)
{
EmailFiles file = new EmailFiles();
file.type = EmailFileTypes.EmailFileType.ClosedFile;
file.docNumber = Helpers.GlobalVariables.gSOLookup.Invoice;
files.Add(file);
}
if (chkInvoice.IsToggled)
{
EmailFiles file = new EmailFiles();
file.type = EmailFileTypes.EmailFileType.Invoice;
file.docNumber = Helpers.GlobalVariables.gSOLookup.Invoice;
files.Add(file);
}
string url = SetUrls.urlMtApi + "/api/EmailFile/?emailAddresses=" + strEmails;
string strJson = JsonConvert.SerializeObject(files);
//Results in: "[{\"docNumber\":\"234273\",\"type\":1},{\"docNumber\":\"633007\",\"type\":2}]" - which works in Postman!!
StringContent content = new StringContent(strJson, Encoding.UTF8, "application/json");
HttpClient httpClient = new HttpClient();
HttpResponseMessage response = await httpClient.PostAsync(url, content);
Web Service:
[System.Web.Http.HttpPost]
public string EmailFile([FromBody]string jsonfiles, [FromUri] string emailAddresses)
{
List<EmailFiles> files = JsonConvert.DeserializeObject<List<EmailFiles>>(jsonfiles);
...
}

No need to manually deserialize the json body, just let the model binder do it for you by using correct parameters:
[System.Web.Http.HttpPost]
public MyModelReturnType EmailFile([FromBody] List<EmailFiles> files, [FromUri] string emailAddresses)
{
// the framework has already deserialized the json request for you
}
If you use string instead of the true model for your parameter the server will not be able to bind your request body to it, because it will expect a JSON string (surrounded by double quotes "), and this could cause a model binding exception that will lead to a 500 error in your client.
The same is for the return type, just use whatever class you want your client to receive as return type and do not use string if you want to send it Json.

Content-Length 0 when handling HEAD request in Web API 2

I want to handle HEAD requests in my Web API 2 application. I copy-pasted the code from StrathWeb's blog post Adding HTTP HEAD support to ASP.NET Web API:
public class HeadHandler : DelegatingHandler
{
private const string Head = "IsHead";
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
{
if (request.Method == HttpMethod.Head)
{
request.Method = HttpMethod.Get;
request.Properties.Add(Head, true);
}
var response = await base.SendAsync(request, cancellationToken);
object isHead;
response.RequestMessage.Properties.TryGetValue(Head, out isHead);
if (isHead != null && ((bool) isHead))
{
var oldContent = await response.Content.ReadAsByteArrayAsync();
var content = new StringContent(string.Empty);
content.Headers.Clear();
foreach (var header in response.Content.Headers)
{
content.Headers.Add(header.Key, header.Value);
}
content.Headers.ContentLength = oldContent.Length;
response.Content = content;
}
return response;
}
}
When I make a HEAD request from Fiddler:
HEAD http://localhost:54225/api/books/5 HTTP/1.1
User-Agent: Fiddler
Host: localhost:54225
I get the following response back:
HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Length: 0
Content-Type: application/json; charset=utf-8
Expires: -1
Server: Microsoft-IIS/10.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?QzpcVXNlcnNcc2ltb25lXERvY3VtZW50c1xTaW1vbnNEb2N1bWVudHNcSVRcQyNcRGVtb0NvZGVcUkVTVGZ1bFdlYlNlcnZpY2VDbGllbnRERU1PXEJvb2tTZXJ2aWNlXGFwaVxib29rc1w1?=
X-Powered-By: ASP.NET
Date: Sun, 19 Feb 2017 12:09:52 GMT
The Content-Length is 0 but it should be 104 bytes.
When I add a breakpoint to the HeadHandler and step through the code it seems to set the Content-Length header value correctly, to 104 bytes, before returning the response.
Could there be some other step in the pipeline that is running after the HeadHandler, which recognises the response has no body, and sets the Content-Length to 0? The only things in the WebApiConfig.cs that come after the HeadHandler has been added are the mapping of the HttpAttribute routes and the setting up of the default route, neither of which seem likely to me to result in the Content-Length header being reset. Alternatively, could a configuration setting somewhere possibly affect the Content-Length returned in the response?

All you need to do is set the Content-Length of the response's Content.Headers - no need to create new content for the response. The act of requesting HEAD removes the body content from the response anyway.
This may have been a change since the article you quoted was written (2013), and no longer needs to create content from scratch...
So this is all you should need:
public class HeadHandler : DelegatingHandler
{
private const string Head = "IsHead";
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
{
if (request.Method == HttpMethod.Head)
{
request.Method = HttpMethod.Get;
request.Properties.Add(Head, true);
}
var response = await base.SendAsync(request, cancellationToken);
object isHead;
response.RequestMessage.Properties.TryGetValue(Head, out isHead);
if (isHead != null && ((bool)isHead))
{
var oldContent = await response.Content.ReadAsByteArrayAsync();
response.Content.Headers.ContentLength = oldContent.Length;
return response;
}
return response;
}
}

Cache-Control headers not sent in response despite being configured on response object

I'm trying to set cache headers in ASP.NET MVC Web API, but the response from IIS suggests that the CacheControl values set are being ignored.
My original assumption was that I was using the EnableCorsAttribute in System.Web.Http.Cors, which is necessary in this use case. However, even without that attribute, the response Cache-Control header is still 'private'.
Is there something I am doing wrong here?
// GET api/<version>/content
// [EnableCors(origins: "*", headers: "*", methods: "*")]
public HttpResponseMessage Get(HttpRequestMessage request)
{
int cacheMaxAgeSeconds;
string cacheMaxAgeString = request.GetQueryString("cache-max-age") ?? request.GetQueryString("cache-max-age-seconds");
string rawUri = request.RequestUri.ToString();
try
{
cacheMaxAgeSeconds = cacheMaxAgeString == null ? Config.ApiCacheControlMaxSeconds : int.Parse(cacheMaxAgeString);
}
catch (Exception ex)
{
cacheMaxAgeSeconds = Config.ApiCacheControlMaxSeconds;
//...
}
try
{
//...
var response = new HttpResponseMessage(HttpStatusCode.OK)
{
Content = new StringContent("...", Encoding.UTF8, "application/json")
};
response.Headers.CacheControl = new CacheControlHeaderValue
{
Public = true,
MaxAge = TimeSpan.FromSeconds(cacheMaxAgeSeconds)
};
return response;
}
catch (Exception apiEx)
{
//...
}
}
Response
HTTP/1.1 200 OK
Cache-Control: private
Content-Type: application/json; charset=utf-8
Date: Thu, 23 Jul 2015 10:53:17 GMT
Server: Microsoft-IIS/7.5
Set-Cookie: ASP.NET_SessionId=knjh4pncbrhad30kjykvwxyz; path=/; HttpOnly
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Content-Length: 2367
Connection: keep-alive

Code below sets "cache-control: public, max-age=15" correctly in vanilla WebApi application (System.Web.Http 4.0.0.0). So... it's probably not the WebApi itself that causes the issue.
You may have some magic in your project that changes cache settings (think of global action filters or something similar). Or maybe you are going through proxy which rewrites HTTP headers.
public HttpResponseMessage Get()
{
var content = new JavaScriptSerializer().Serialize(new { foo = "bar" });
var response = new HttpResponseMessage(HttpStatusCode.OK)
{
Content = new StringContent(content, Encoding.UTF8, "application/json")
};
response.Headers.CacheControl = new CacheControlHeaderValue
{
Public = true,
MaxAge = TimeSpan.FromSeconds(15)
};
return response;
}
// returns in the response: "Cache-Control: public, max-age=15"

The answer, having picked this up some weeks later:
Cache-Control header appears to be set to 'private' when running debug builds. The issue goes away when I run with a release build.

To add another thing that can cause this:
You run through an Owin pipeline.
In that case, you need to set the headers in an Owin middleware defined as this:
class MiddleWare : OwinMiddleware
{
public MiddleWare(OwinMiddleware next)
: base(next)
{
}
public override async Task Invoke(IOwinContext context)
{
context.Response.Headers["Cache-Control"] = "no-cache, no-store, must-revalidate";
context.Response.Headers["Pragma"] = "no-cache";
context.Response.Headers["Expires"] = "0";
await Next.Invoke(context);
}
}

Call WebAPI method from MVC4

I have an MVC4 WebAPI project and have a controller FileController that has this Get method in it:
public HttpResponseMessage Get(string id)
{
if (String.IsNullOrEmpty(id))
return Request.CreateErrorResponse(HttpStatusCode.BadRequest, "File Name Not Specified");
HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
var stream = fileService.GetFileStream(id);
if (stream == null)
{
return Request.CreateErrorResponse(HttpStatusCode.NotFound, "File Not Found");
}
response.Content = new StreamContent(stream);
response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
response.Content.Headers.ContentDisposition = new System.Net.Http.Headers.ContentDispositionHeaderValue("attachment");
response.Content.Headers.ContentDisposition.FileName = id;
return response;
}
In the browser going to localhost:9586/File/myfile.mp3it dispatches the file correctly as an attachment and you can save it. If it is an audio file, you can stream it from the HTML5 audio tag.
Now, I need to call this WebAPI method from an MVC4 web app, basically wrapping it. Here it comes:
public HttpResponseMessage DispatchFile(string id)
{
HttpClient client = new HttpClient();
client.BaseAddress = new Uri("http://localhost:8493/");
HttpResponseMessage response = client.GetAsync("api/File/"+id).Result;
return response;
}
Going to localhost:8493/File/DispatchFile/my.mp3 returns:
StatusCode: 200, ReasonPhrase: 'OK', Version: 1.1, Content: System.Net.Http.StreamContent, Headers: { Pragma: no-cache Connection: Close Cache-Control: no-cache Date: Thu, 05 Sep 2013 15:33:23 GMT Server: ASP.NET Server: Development Server: Server/10.0.0.0 X-AspNet-Version: 4.0.30319 Content-Length: 13889 Content-Disposition: attachment; filename=horse.ogg Content-Type: application/octet-stream Expires: -1 }
So it looks like the Content is indeed StreamContent, but it doesn't return it as a saveable file. Now the question is, how to mirror the behavior when calling the API directly? Any suggestions much appreciated.

I believe the use of HttpClient.Result is not the correct approach here. I think you may need to use the 'Content' property and then call ReadAsStreamAsync to get a handle on the file stream that is returned by your WebAPI method. At that point, you should be able to just write this stream to the response stream, allowing the file to be downloaded / audio to be streamed via HTML5.
See here for an example of using HttpClient to get a file (the link shows how to handle large files, but I believe the approach used there is what you will need to do):
http://developer.greenbutton.com/downloading-large-files-with-the-net-httpclient/

Get Response with HttpClient

I'm trying to use HttpClient to read the response content from a 3rd party API (Rackspace Cloud Files). Here's what I have so far. I can't seem to get the content.
HttpClient client = new HttpClient();
client.DefaultRequestHeaders.Add("X-Auth_User", username);
client.DefaultRequestHeaders.Add("X-Auth-Key", api);
client.GetAsync("identity.api.rackspacecloud.com".ToAbsoluteUrl()).ContinueWith(
(requestTask) =>
{
HttpResponseMessage response = requestTask.Result;
response.EnsureSuccessStatusCode();
response.Content.ReadAsAsync<string>().ContinueWith(
(readTask) =>
{
var result = readTask.Result;
});
});
This gives me "No 'MediaTypeFormatter' is available to read an object of type 'String' with the media type 'text/html'." error.
I need to retrieve the response details as noted in the Rackspace docs (example):
HTTP/1.1 204 No Content
Date: Mon, 12 Nov 2007 15:32:21 GMT
X-Storage-Url: https://storage.clouddrive.com/v1/CF_xer7_34
X-CDN-Management-Url: https://cdn.clouddrive.com/v1/CF_xer7_34
X-Auth-Token: eaaafd18-0fed-4b3a-81b4-663c99ec1cbb
Content-Length: 0
Content-Type: text/plain; charset=UTF-8
How do I get the response?
When I use ReadAsStringAsync, it gives my the HTML source of my page.
Thank you.