python3.7 flask2.2.3 webapi can be connected by Postman and browser but not c# Net6 HttpClient.PostAsync

[superdavid0816]

Hi,
I build a very simple web api by flask2.2.3 using python3.7.
I can use Postman and browser to connect this webapi but not working in c# Net6 by HttpClient.PostAsync.
Please help me to pass this error.
Thank you.

error message in c#:

---

{System.Net.Sockets.SocketException (111): Connection refused
at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)
at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.System.Threading.Tasks.Sources.IValueTaskSource.GetResult(Int16 token)
at System.Net.Sockets.Socket.g__WaitForConnectWithCancellation|277_0(AwaitableSocketAsyncEventArgs saea, ValueTask connectTask, CancellationToken cancellationToken)
at System.Net.Http.HttpConnectionPool.ConnectToTcpHostAsync(String host, Int32 port, HttpRequestMessage initialRequest, Boolean async, CancellationToken cancellationToken)}

---

here is the code:

---

from flask import Flask, jsonify, redirect, url_for, render_template,request, Response
import json
from flask_cors import CORS

app = Flask(name)
CORS(app)

@app.route('/qryData/', methods=['POST', 'GET'])
def qryData():

return jsonify(True);

if name == 'main':
app.run(host='0.0.0.0',port=58080,debug=True)

---

Thanks for your help.

[akshayamadhuri]

@superdavid0816
The error message you're encountering indicates that the connection is being refused when trying to access your Flask API from C# using HttpClient.PostAsync. There could be a few reasons for this issue. Here are some steps you can follow to troubleshoot and resolve the problem:

Check if the Flask API is running: Ensure that your Flask API is running and accessible. You mentioned that you can successfully connect to the API using Postman and a web browser, so make sure the API is still running when you try to access it from C#.

Verify the API endpoint: Double-check the URL you are using to access the Flask API in your C# code. Ensure that the URL is correct, including the host, port, and any additional path or query parameters.

Verify the network connectivity: Check if there are any network-related issues that could prevent the C# application from connecting to the Flask API. Make sure there are no firewalls or network configurations blocking the connection.

Verify the Flask API's host and port: In your Flask code, you specified host='0.0.0.0' and port=58080. Confirm that these values match the host and port you are using in your C# code.

Check if CORS is causing the issue: Since you have enabled CORS in your Flask API using the flask_cors package, ensure that it is configured correctly and allows requests from the domain or origin where your C# application is hosted. You may need to specify the allowed origins explicitly.

Update C# code for HttpClient: Make sure you have the correct C# code to send the request using HttpClient.PostAsync. Here's an example:

csharp
Copy code
using System;
using System.Net.Http;
using System.Threading.Tasks;

class Program
{
static async Task Main(string[] args)
{
using (var httpClient = new HttpClient())
{
var url = "http://localhost:58080/qryData/";
var content = new StringContent("");
var response = await httpClient.PostAsync(url, content);

        if (response.IsSuccessStatusCode)
        {
            // Handle successful response
            var result = await response.Content.ReadAsStringAsync();
            Console.WriteLine(result);
        }
        else
        {
            // Handle unsuccessful response
            Console.WriteLine($"Request failed with status code: {response.StatusCode}");
        }
    }
}

}
Make sure to replace the url variable with the correct URL for your Flask API.

By following these steps, you should be able to troubleshoot the connection issue and successfully access your Flask API from your C# application.