Xamarin Forms - simple PostAsync() returns error 400 bad request

Question

I have checked out every one of these similar questions and although they are similar, no solutions have been found.

The Problem:

I have implemented a very simple post request from my Xamarin mobile application to a PHP server, using HttpClient(). The PHP server simply prints out any post request it is given, for now.

When I use Postman to send my web server post requests, the PHP works perfectly, however attempting to send post requests from my mobile application results in an error:

{StatusCode: 400, ReasonPhrase: 'Bad Request', Version: 1.1, Content: System.Net.Http.StreamContent, Headers: { Date: Fri, 03 Aug 2018 08:52:36 GMT Transfer-Encoding: chunked Connection: keep-alive Set-Cookie: __cfduid=d54d4c18d07eeae5179fde8e4533dd6881533286355; expires=Sat, 03-Aug-19 08:52:35 GMT; path=/; domain=.braz.io; HttpOnly; Secure Expect-CT: max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct" Server: cloudflare CF-RAY: 44478c8b9d0c1d68-MEL Content-Type: text/html }}

public class RestService
{
    HttpClient client;
    private const string URL = "https://braz.io/mobile.php";

    public RestService()
    {
        client = new HttpClient();
        client.MaxResponseContentBufferSize = 256000;
    }

    public async Task<string> getUserInformation(string username, string password)
    {
        var uri = new Uri(string.Format(URL, string.Empty));
        try
        {
            StringContent s = new StringContent("HELLO WORLD");
            var response = await client.PostAsync(uri, s);
        }
        catch (Exception ex)
        {Console.WriteLine(ex);}
        return null;
    }
}

It seems like I am missing a nuance with the PostAsync(); function. Why can I successfully do Post requests from Postman but fail when using PostAsync() on my mobile application?

After some discussion on SO:

I added string body = await response.Content.ReadAsStringAsync(); to see if the web server was sending any useful information about the error, back to my mobile application. Unfortunately it just sent back a simple ERROR 400 webpage

   <html>\r\n<head><title>400 Bad Request</title></head>\r\n<body bgcolor=\"white\">\r\n<center><h1>400 Bad Request</h1></center>\r\n<hr><center>openresty/1.11.2.4</center>\r\n</body>\r\n</html>\r\n"

Could be for many reasons. I would suggest first checking the body of the response to see if it provides details about why the request is bad. — Nkosi, Aug 03 '18 at 11:05
No you need to read the body of the response `string body = await response.Content.ReadAsStringAsync();` to see if it has any important details. Sometime servers will provide the details in the response. — Nkosi, Aug 03 '18 at 11:09
It seems that the above function you described has just returned me a simple `400 Bad Request` html page, I will add it into the question — Barney Chambers, Aug 03 '18 at 11:11
What is the right content type? The php back end file only dumps the post command with the `var_dump($_POST);` command and that's it — Barney Chambers, Aug 03 '18 at 11:15

score 0 · Answer 1 · answered Aug 03 '18 at 11:40

Here is the solution I somehow stumbled upon (if someone could write in the comments / edit this answer for why this is the solution that'd be great!)

Right Click Android Project -> Android Options -> Advanced -> Change HttpClient implementation from Default to Android

Xamarin Forms - simple PostAsync() returns error 400 bad request

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