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C# Post Variables can't be read on Website - HttpClient PostAsync()

I have a web server on which I'm hosting my own api for one of my projects.
This is the php-code of the api-website:
$user = $_POST['username'];
$password = $_POST['password'];
if(strcmp($user, "username") == 0 && strcmp($password, "password") == 0) {
...
} else {
die("No Permissions");
}
I want to send the two variables username and password with a HttpClient and the postAsync-method to this website and if the right log in data is detected, it returns the data I want.
For this I have the following code in C#:
Task<HttpResponseMessage> response;
var url = "www.url.de"; //not the url I'm actually calling!
var vars = "[{\"username\":\"username\", \"password\":\"password\"}]";
using (var client = new HttpClient())
{
client.BaseAddress = new Uri(url);
client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
response = client.PostAsync(url, new StringContent(vars, Encoding.UTF8));
Console.WriteLine(response.Result.Content.ReadAsStringAsync().Result);
if (response.IsCompleted)
{
Console.WriteLine(response.Result.Content.ReadAsStringAsync().Result);
}
}
But the problem is that no matter what I have tried the output from this code is, that i have no permissions. And I have changed the php-code, so that I can see which data is stored in $username and $password, but they are empty and I don't know why. I hope somebody can help me with this.

Your PHP code is expecting the data sent as application/x-www-form-urlencoded, but your C# code is sending it as JSON.
As mentioned in the comment by M. Eriksson, you either need to change your PHP to accept JSON, or change your C# to send as form data.
This answer shows how to use HTTPClient to send data like that.
Here's my modification of your code based on the above code (I did test it):
public static async Task DoSomething()
{
string url = "http://httpbin.org/post"; //not the url I'm actually calling!
Dictionary<string, string> postData = new();
postData["username"] = "username";
postData["password"] = "password";
using HttpClient client = new();
client.DefaultRequestHeaders.Accept.Add(new("application/json"));
HttpRequestMessage request = new(HttpMethod.Post, url);
request.Content = new FormUrlEncodedContent(postData);
HttpResponseMessage response = await client.SendAsync(request);
Console.WriteLine(response.Content.ReadAsStringAsync().Result);
}

Send a string in body via SendRequestAsync

I need to send a Patch request to a backend API via SendRequestAsync func. This is regarding a UWP C# app.
Backend expected to like this:
On the app this is the code I wrote. But doesn't work
if (requestMehtod == ApplicationConstants.RequestType.PATCH)
{
Uri uri = new Uri(requestUrl);
HttpRequestMessage requestMessage = null;
if (postData != null)
{
var itemAsJson = JsonConvert.SerializeObject(postData);
requestMessage = new HttpRequestMessage(HttpMethod.Patch, uri)
{
Content = new HttpStringContent(itemAsJson, Windows.Storage.Streams.UnicodeEncoding.Utf8, "application/json-patch+json")
};
}
else
{
requestMessage = new HttpRequestMessage(HttpMethod.Patch, uri);
}
response = await httpClient.SendRequestAsync(requestMessage).AsTask(cancellationTokenSource.Token);
var rdModel = ProcessResponseData(response);
return await Handle401Error(rdModel, response, postData, url, requestMehtod, isDownloadSite, OnSendRequestProgress, requestData);
}
The above code fine to send JSON data to the same API and works fine. But I need to know how to send just a string in the body. Thank for the consideration
NOTE: App uses HttpClient from Windows.Web.Http and will not be able to use anything inside System.Net.Http namespace.

The answer is given by the #gusman and #Simon Wilson. Just to amend to their answer, in order to be able to send a string in the request body, the string needs to be within double-quotes.
var requestData = "\"hello world\"";
var request = new HttpRequestMessage(HttpMethod.Post, uri)
{
Content = new HttpStringContent(requestData, Windows.Storage.Streams.UnicodeEncoding.Utf8, "application/json")
};
response = await httpClient.SendRequestAsync(request);
This worked in my scenario.

Need help converting my RestSharp code to use HttpClient instead

Due to the fact that I need to convert this C# dll into a tlp file to be called from Visual Basic 6, I need avoid using external dependencies. I have used RestSharp to consume a WebAPI by doing the following (working):
using RestSharp;
using Newtonsoft.Json;
..
public string GetToken (string Key, string Password) {
var client = new RestClient (BaseUrl + "auth/GetToken");
var request = new RestRequest (Method.POST);
request.AddHeader ("cache-control", "no-cache");
request.AddHeader ("Content-Type", "application/json");
Dictionary<string, string> data = new Dictionary<string, string> {
{ "APIKey", Key },
{ "APIPassword", Password }
};
var dataJSON = JsonConvert.SerializeObject (data);
request.AddParameter ("undefined", dataJSON, ParameterType.RequestBody);
IRestResponse response = client.Execute (request);
GetTokenResults g = JsonConvert.DeserializeObject<GetTokenResults> (response.Content);
return g.Token;
}
where GetTokenResults was a struct that contained a declaration for the string Token. I want to achieve this same functionality without using RestSharp. Here is my unsuccessful attempt:
using System.Net.Http;
using System.Net.Http.Headers;
..
public async void GetToken (string Key, string Password) {
var client = new HttpClient ( );
client.DefaultRequestHeaders.Accept.Clear ( );
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue ("application/json"));
client.BaseAddress = new Uri (BaseUrl + "auth/GetToken");
Dictionary<string, string> data = new Dictionary<string, string> {
{ "APIKey", Key },
{ "APIPassword", Password }
};
var dataJSON = JsonConvert.SerializeObject (data);
var content = new StringContent (dataJSON, Encoding.UTF8, "application/json");
var response = await client.PostAsync ("", content);
}
I am unclear on how to achieve the same results (send API key and password, return token as string) using HttpClient as I did using RestSharp earlier. Anything that can point me in the right direction is greatly appreciated!

I think you got stung by this issue. In short, the URI in client.BaseAddress needs a slash at the end of it.
However, I wouldn't simply add it, I'd consider doing it a little different. Presumably your BaseUrl already has a trailing slash, given you're appending "auth/GetToken" to it. I'd do it this way:
client.BaseAddress = new Uri(BaseUrl);
...
var response = await client.PostAsync("auth/GetToken", content);
As you can see, HttpClient fits very cleanly with how your code is already set up, i.e. you have a "base" address with a trailing slash and you want to append to it for a specific call.
That should get you un-stuck to this point. The next thing you'll need to tackle is deserializing the JSON response so you can get the token out of it. It's similar to how you did it in RestSharp, except that response.Content is not a string in the HttpClient world, so you need one more step to get that:
var json = await response.Content.ReadAsStringAsync();
GetTokenResults g = JsonConvert.DeserializeObject<GetTokenResults>(json);
return g.Token;
Last thing you'll need to do to get this to compile is change the method signature to:
public async Task<string> GetTokenAsync
One final note: you are now in the async world, and that's a good thing, but you need to know how to use it correctly or you could end up with deadlocks and other mysterious bugs. In short, don't block on async code by calling .Result or .Wait() anywhere up the call stack. That's by far most common mistake people make. Use async/await all the way down.

I think you are missing first parameter in the method PostAsync i.e. requestUri=Client.BaseAddress (see my implementation below).
Try with this first, if did not work, read below. I have a little different implementation where I passed client.BaseAddress as first parameter and I am passing my content as ByteArrayContent. In my case I have to pass my content as "application/x-www-form-urlencoded" excerpt of my code:
var buffer = Encoding.UTF8.GetBytes(content);
var byteContent = new ByteArrayContent(buffer);
//as I can't send JSON, probably, you can skip as it's already JSON
byteContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/x-www-form-urlencoded");
//requestUri=client.BaseAddress
await client.PostAsync(requestUri, byteContent).ConfigureAwait(false);
We have somewhat different need but I think you are pretty close. If it does not help, write me I will share my code. After reading the comment, I would like to share how I have made my HttpClient. The code is as it is:
using (var client = CreateMailClientForPOST($"{BaseUrl}/"))
{
//removed code, you can call above code as method like
var response= await client.DoThingAsAsync($"{client.BaseAddress}, content").ConfigureAwait(false);
}
protected HttpClient CreateMailClientForPOST(string resource)
{
var handler = new HttpClientHandler();
if (handler.SupportsAutomaticDecompression)
{
handler.AutomaticDecompression = System.Net.DecompressionMethods.GZip | System.Net.DecompressionMethods.Deflate;
}
var client = new HttpClient(handler)
{
BaseAddress = new Uri($"https://api.address.com/rest/{resource}")
};
return client;
}

How to pass long string in HttpClient.PostAsync request

Trying to send a rather long string to a REST web api (youtrack). I get the following exception:
Invalid URI: The Uri string is too long.
My code:
var encodedMessage = HttpUtility.UrlEncode(message);
var requestUri = string.Format("{0}{1}issue/{2}/execute?comment={3}", url, YoutrackRestUrl, issue.Id, encodedMessage);
var response = await httpClient.PostAsync(requestUri, null).ConfigureAwait(false);
So I took my chances with a FormUrlEncodedContent
var requestUri = string.Format("{0}{1}issue/{2}/execute", url, YoutrackRestUrl, issue.Id);
var postData = new List<KeyValuePair<string, string>>();
postData.Add(new KeyValuePair<string, string>("comment", message));
var content = new FormUrlEncodedContent(postData);
var response = await httpClient.PostAsync(requestUri, content).ConfigureAwait(false);
Which results in the exact same issue.
The string (comment) I am sending, is the changed file set of a commit into SVN. Which can be really long, so I don't really have a way to get around that. Is there a way to post content without the string length restriction?
Read the following topics, but didn't find an answer there:
.NET HttpClient. How to POST string value?
How do I set up HttpContent for my HttpClient PostAsync second parameter?
https://psycodedeveloper.wordpress.com/2014/06/30/how-to-call-httpclient-postasync-with-a-query-string/
http://forums.asp.net/t/2057125.aspx?Invalid+URI+The+Uri+string+is+too+long+HttpClient

Well the short answer to it - just put it into the Body, instead of trying to push all the data via the URL
But as the work on the ticket showed - the answer was here How to set large string inside HttpContent when using HttpClient?
The actual problem beeing in the FormUrlEncodedContent

Try this..Will be helpful for uwp..
Uri uri = new Uri("your uri string");
Windows.Web.Http.HttpClient client = new Windows.Web.Http.HttpClient();
var value1 = new System.Collections.Generic.List<System.Collections.Generic.KeyValuePair<string,string>>
{
// your key value pairs
};
var response = await client.PostAsync(uri,new HttpFormUrlEncodedContent(value1));
var result = await response.Content.ReadAsStringAsync();

Call and consume Web API in winform using C#.net

I am beginner and creating winform application. In which i have to use API for Simple CRUD operation. My client had shared API with me and asked to send data in form of JSON.
API : http://blabla.com/blabla/api/login-valida
KEY : "HelloWorld"
Value : { "email": "user#gmail.com","password": "123456","time": "2015-09-22 10:15:20"}
Response : Login_id
How can i convert data to JSON, call API using POST method and get response?
EDIT
Somewhere on stackoverflow i found this solution
public static void POST(string url, string jsonContent)
{
url="blabla.com/api/blala" + url;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(baseURL);
request.Method = "POST";
System.Text.UTF8Encoding encoding = new System.Text.UTF8Encoding();
Byte[] byteArray = encoding.GetBytes(jsonContent);
request.ContentLength = byteArray.Length;
request.ContentType = #"application/json";
using (Stream dataStream = request.GetRequestStream())
{
dataStream.Write(byteArray, 0, byteArray.Length);
}
long length = 0;
try
{
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
length = response.ContentLength;
}
}
catch
{
throw;
}
}
//on my login button click
private void btnLogin_Click(object sender, EventArgs e)
{
CallAPI.POST("login-validate", "{ \"email\":" + txtUserName.Text + " ,\"password\":" + txtPassword.Text + ",\"time\": " + DateTime.Now.ToString("yyyy-MM-dd h:mm tt") + "}");
}
I got exception that says "The remote server returned an error: (404) Not Found."

You can take a look at the following docs tutorial:
Call a Web API From a .NET Client
But as an answer, here I will share a quick and short a step by step guide about how to call and consume web API in Windows forms:
Install Package - Install the Microsoft.AspNet.WebApi.Client NuGet package (Web API Client Libraries).
Open Tools menu → NuGet Package Manager → Package Manager Console → In the Package Manager Console window, type the following command:
Install-Package Microsoft.AspNet.WebApi.Client
You can install package by right click on project and choosing Manage NuGet Packages as well.
Set up HttpClient - Create an instance of HttpClient and set up its BaseAddress and DefaultRequestHeaders. For example:
// In the class
static HttpClient client = new HttpClient();
// Put the following code where you want to initialize the class
// It can be the static constructor or a one-time initializer
client.BaseAddress = new Uri("http://localhost:4354/api/");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(
new MediaTypeWithQualityHeaderValue("application/json"));
Send Request - To send the requests, you can use the following methods of the HttpClient:
GET: GetAsync, GetStringAsync, GetByteArrayAsync, GetStreamAsync
POST: PostAsync, PostAsJsonAsync, PostAsXmlAsync
PUT: PutAsync, PutAsJsonAsync, PutAsXmlAsync
DELETE: DeleteAsync
Another HTTP method: Send
Note: To set the URL of the request for the methods, keep in mind, since you have specified the base URL when you defined the client, then here for these methods, just pass path, route values and query strings, for example:
// Assuming http://localhost:4354/api/ as BaseAddress
var response = await client.GetAsync("products");
or
// Assuming http://localhost:4354/api/ as BaseAddress
var product = new Product() { Name = "P1", Price = 100, Category = "C1" };
var response = await client.PostAsJsonAsync("products", product);
Get the Response
To get the response, if you have used methods like GetStringAsync, then you have the response as string and it's enough to parse the response. If the response is a Json content which you know, you can easily use JsonConvert class of Newtonsoft.Json package to parse it. For example:
// Assuming http://localhost:4354/api/ as BaseAddress
var response = await client.GetStringAsync("product");
var data = JsonConvert.DeserializeObject<List<Product>>(response);
this.productBindingSource.DataSource = data;
If you have used methods like GetAsync or PostAsJsonAsync and you have an HttpResponseMessage then you can use ReadAsAsync, ReadAsByteArrayAsync, ReadAsStreamAsync, `ReadAsStringAsync, for example:
// Assuming http://localhost:4354/api/ as BaseAddress
var response = await client.GetAsync("products");
var data = await response.Content.ReadAsAsync<IEnumerable<Product>>();
this.productBindingSource.DataSource = data;
Performance Tip
HttpClient is a type that is meant to be created once and then shared. So don't try to put it in a using block every time that you want to use it. Instead, create an instance of the class and share it through a static member. To read more about this, take a look at Improper Instantiation antipattern
Design Tip
Try to avoid mixing the Web API related code with your application logic. For example let's say you have a product Web API service. Then to use it, first define an IProductServieClient interface, then as an implementation put all the WEB API logic inside the ProductWebAPIClientService which you implement to contain codes to interact with WEB API. Your application should rely on IProductServieClient. (SOLID Principles, Dependency Inversion).

Just use the following library.
https://www.nuget.org/packages/RestSharp
GitHub Project: https://github.com/restsharp/RestSharp
Sample Code::
public Customer GetCustomerDetailsByCustomerId(int id)
{
var client = new RestClient("http://localhost:3000/Api/GetCustomerDetailsByCustomerId/" + id);
var request = new RestRequest(Method.GET);
request.AddHeader("X-Token-Key", "dsds-sdsdsds-swrwerfd-dfdfd");
IRestResponse response = client.Execute(request);
var content = response.Content; // raw content as string
dynamic json = JsonConvert.DeserializeObject(content);
JObject customerObjJson = json.CustomerObj;
var customerObj = customerObjJson.ToObject<Customer>();
return customerObj;
}

Use Json.Net to convert data into JSON
Use WebClient to POST data

Use This code:
var client = new HttpClient();
client.BaseAddress = new Uri("http://www.mywebsite.com");
var request = new HttpRequestMessage(HttpMethod.Post, "/path/to/post/to");
var keyValues = new List<KeyValuePair<string, string>>();
keyValues.Add(new KeyValuePair<string, string>("site", "http://www.google.com"));
keyValues.Add(new KeyValuePair<string, string>("content", "This is some content"));
request.Content = new FormUrlEncodedContent(keyValues);
var response = await client.SendAsync(request);

Here is another example using an online REST service (https://northwind.vercel.app) which allows interaction with Northwind API.
This example uses HttpClient and JsonConvert to get or post data. Here is a very quick example:
Install Newtonsoft.Json nuget package. And add the following using statements to your form:
using System.Net.Http;
using Newtonsoft.Json
Define an instance of the HttpClient, at class level:
private static HttpClient client = new HttpClient();
To send a GET request, for example getting list of all data:
var url = "https://northwind.vercel.app/api/categories";
var response = await client.GetAsync(url);
if (response.StatusCode == System.Net.HttpStatusCode.OK)
{
var content = await response.Content.ReadAsStringAsync();
var categories = JsonConvert.DeserializeObject<List<Category>>(content);
dataGridView1.DataSource = categories;
}
You can also use other overloads of Get, like GetStringAsync, GetStreamAsync, and etc. But GetAsync is a more generic method allowing you to get the status code as well.
To send a POST request, for example posting a new data:
var url = "https://northwind.vercel.app/api/categories";
var data = new Category() { Name = "Lorem", Description = "Ipsum" };
var jsonData = Newtonsoft.Json.JsonConvert.SerializeObject(data);
var requestContent = new StringContent(jsonData, Encoding.Unicode, "application/json");
var response = await client.PostAsync(url, requestContent);
if (response.StatusCode == System.Net.HttpStatusCode.Created)
{
var content = await response.Content.ReadAsStringAsync();
var createdCategory = JsonConvert.DeserializeObject<Category>(content);
MessageBox.Show(createdCategory.Id.ToString())
}
To learn more and see some best practices or see an example without JsonConvert, see my other post.