how to conceptually make a post request to web api from c# program as if the it's coming from html form

Question

I have been banging my head against the wall for the past 1 week now but without any success. Actually I'm writing a C# code(a web api controller action) to call another web api to make a post request with some json data payload in the request body. Syntax-wise there is nothing wrong with the code. But when I directly call the service(web api service) from web browser I get an Html form that has a multiline text box in it, rollback property (as radio button for true and false value for this property), drop down box with 2 options such as html and json (to get response in either format) and a button(for sending request to the server and making edits in the database). Now when I manually put json data inside text box and click the button on that html form edits are done successfully in the database but when programmatically(from my C# code) I send the same json data payload and make a post request edits are never done successfully rather I get an html response body through Fiddler that says status code success 200 but unable to complete operation,some parameters couldn't be recognized. Here is my code

private static async Task<HttpResponseMessage> GeometryUpdateAsync(Feature updatedFeature, FeatureType featureType, int? objectid = null)
{
    var jsonObject = new JObject();
    dynamic esriId = jsonObject;
    if (objectid == null)
    {
        objectid = updatedFeature.OBJECTID;
    }
    esriId.OBJECTID = objectid;
    var mergedJsonString = JsonConvert.SerializeObject(new
    {
        geometry = JObject.Parse(updatedFeature.Geometry.ToString()),
        attributes = JObject.Parse(esriId.ToString())
    });
    mergedJsonString = String.Format("[{0}]", mergedJsonString);
    HttpResponseMessage response = null;
    using (var client = new HttpClient())
    {
        //string arguments = "rollbackOnFailure=true&f=pjson&features=";
        client.BaseAddress = new Uri("somebaseaddress");
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        client.Timeout = TimeSpan.FromSeconds(500.00);
        //response = await client.PostAsJsonAsync("someuri", arguments + mergedJsonString);
        response = await client.PostAsync("someuri", mergedJsonString, new     System.Net.Http.Formatting.JsonMediaTypeFormatter());
        if (response.IsSuccessStatusCode)
        {
            var v = response.Content.ReadAsStringAsync().Result;
        }
    }
}

When I look at the request body (through fiddler while making a post request through Html form) request body looks like

features=%5B%7B%22geometry%22%3A%7B%22paths%22%3A%5B%5B%5B-91.3888577181506%2C39.703158271352621%5D%91.381838690201192%2C39.690323806398723%5D%2C%5B-91.383241723424632%2C39.689645139311914%5D%2C%5B-91.3849700567206%2C39.6888078408094%5D%2C%5B-91.3861256828518%2C39.688248198995353%5D%5D%5D%7D%2C%22attributes%22%3A%7B%22OBJECTID%22%3A21%7D%5D&gdbVersion=&rollbackOnFailure=true&f=pjson

and the request body for the post request made programmatically looks likes

"[{\"geometry\":{\"paths\":[[[-91.3888577181506,39.703158271352621],[-91.381838690201192,39.690323806398723],[-91.383241723424632,39.689645139311914],[-91.3849700567206,39.6888078408094],[-91.3861256828518,39.688248198995353]]]},\"attributes\":{\"OBJECTID\":21}}]"

Even I tried appending this

string arguments = "rollbackOnFailure=true&f=pjson&features=";

in my commented out code above (where I'm using PostAsJsonAsync) to make the request body look like as if it's coming from Html form. But no success, even I'm not sure whether the JSonFormatter takes this arguments string in to account or just leaves it while serializing/deserializing during the run time. And the post request body that I get after appending "arguments" string to Json string looks like this

"rollbackOnFailure=true&f=pjson&features=[{\"geometry\":{\"paths\":[[[-91.3877577181506,39.703158271352621],[-91.36047320856953,39.702616420911333],[-91.383241723424632,39.689645139311914],[-91.3849700567206,39.6888078408094],[-91.3861256828518,39.688248198995353]]]},\"attributes\":{\"OBJECTID\":21}}]"

But still no success, Now I'm totally running out of ideas as to how to call web api service from my C# code so that web api thinks it's coming from that Html form and end up successfully doing edits in the database programmatically. All suggestions and ideas will be highly appreciated.

Answer 1

The trick lies somewhere else, I was using HttpClient to simulate browser post request and get result in c#. But in this particular scenario HttpClient is of no use. I changed to HttpWebRequest after seeing a code at How to make a post call to a Web Api Action? from utlimate_programmer_BR and it did the trick, again HttpClient was a bad choice by me to get this particular thing done.