How to submit a file and some other form content to Web API using C# HttpClient

Question

I am trying to submit a file with some KeyValuePairs.(which is id in this case) using HttpClient in C#. the File is being submitted but i cannot read the KeyValuePairs

This is my controller.

    [HttpPost]
        public async Task<ActionResult> Index(HttpPostedFileBase File)
        {
            HttpClient client = new HttpClient();
            client.BaseAddress = new Uri("http://localhost:65211/");
            MultipartFormDataContent form = new MultipartFormDataContent();
    //Here I am adding a file to a form
            HttpContent content = new StringContent("fileToUpload");
            form.Add(content, "fileToUpload");
            var stream = File.InputStream;
            content = new StreamContent(stream);
            content.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data")
            {
                Name = "fileToUpload",
                FileName = File.FileName
            };
            form.Add(content);
    // and here i am adding a dictionary with one keyvaluepair 
            Dictionary<string, string> Parameters = new Dictionary<string, string>();
            Parameters.Add("id", "3");
            form.Add(new FormUrlEncodedContent(Parameters));
    //this will hit the api         
   var response = await client.PostAsync("/api/Upload", form);
            var k = response.Content.ReadAsStringAsync().Result;
            return View();
        }

This is the Api Code

[Route("api/Upload")]
        [HttpPost]
       // i have tested public async Task<HttpResponseMessage> Upload(string id) <= giving parameters. the api doesnt hit if i give any
        public async Task<HttpResponseMessage> Upload()
        {
            var request = HttpContext.Current.Request;
            HttpResponseMessage result = null;    
            if (request.Files.Count == 0)
            {
                result = Request.CreateResponse(HttpStatusCode.OK, "Ok");;
            }
            var postedFile = request.Files[0];
            return Request.CreateResponse(HttpStatusCode.OK, "Ok");
        }

I am able to read the file. It gets submitted to the API. the problem is the "id" that i submitted as a keyvaluepair. I don't know how to read it. If i pass parameters to the Api. client returns the error "Not Found".

Try adding a parameter to your route and pass it through the call URL [Route("api/Upload/{id}")], public async Task<HttpResponseMessage> Upload(string id), var response = await client.PostAsync($"/api/Upload/{id}", form); — Vidmantas Blazevicius
– Vidmantas Blazevicius, Commented Feb 6, 2018 at 13:13
that does not work. breakpoint never hits on api and the response is 404 not found. — zetawars
– zetawars, Commented Feb 7, 2018 at 5:27

zetawars · Accepted Answer · 2018-02-18 21:10:30Z

I finally was able to read both the file and the parameters I sent to the Web API. It was a simple implimentation with HttpContext.Current.Request

This is how i modified the API code.

[Route("api/Upload")]
    [HttpPost]
   // i have tested public async Task<HttpResponseMessage> Upload(string id) <= giving parameters. the api doesnt hit if i give any
    public async Task<HttpResponseMessage> Upload()
    {
        var request = HttpContext.Current.Request;
        var key = Request.Params["key"]; // **<- LOOK AT THIS HERE**
        HttpResponseMessage result = null;    
        if (request.Files.Count == 0)
        {
            result = Request.CreateResponse(HttpStatusCode.OK, "Ok");;
        }
        var postedFile = request.Files[0];
        return Request.CreateResponse(HttpStatusCode.OK, "Ok");
    }

By using HttpContext.Current.Request.Params, I was able to read the other values from the api. Request.Files contains all the files and Request.Params contains all string parameters.

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