render.com example REACT

different files

App.jsx (client side):

import { useState, useRef } from 'react';

const SERVER_URL = 'https://netserver-dkf4.onrender.com/send';

function App() {
    const [inputValue, setInputValue] = useState('5');
    const [isSending, setIsSending] = useState(false);
    const [messages, setMessages] = useState([]);
    const resultRef = useRef(null);
    const inputRef = useRef(null);

    const appendResult = (message, type) => {
        setMessages((prev) => [...prev, { message, type }]);
        setTimeout(() => {
            if (resultRef.current) {
                resultRef.current.scrollTop = resultRef.current.scrollHeight;
            }
        }, 0);
    };

    const sendNumber = async () => {
        if (isSending) return;
        const input = inputValue.trim();
        if (!input) {
            appendResult('Пожалуйста, введите число или "exit".', 'error');
            return;
        }

        if (input.toLowerCase() === 'exit') {
            stopSending();
            return;
        }

        setIsSending(true);
        appendResult('Отправка...', 'success');

        try {
            const response = await fetch(SERVER_URL, {
                method: 'POST',
                headers: {
                    'Content-Type': 'text/plain',
                    'Accept': 'text/plain',
                },
                body: input,
            });

            if (!response.ok) {
                const errorText = await response.text();
                throw new Error(`Ошибка ${response.status}: ${errorText}`);
            }

            const result = await response.text();
            document.title = `Сервер ответил: ${result}`;
            appendResult(`Сервер ответил: ${result}`, 'success');
        } catch (error) {
            appendResult(`Ошибка отправки: ${error.message}`, 'error');
        } finally {
            setIsSending(false);
            setInputValue('');
            inputRef.current?.focus();
        }
    };

    const stopSending = () => {
        setIsSending(false);
        appendResult('Отправка остановлена.', 'success');
        document.title = 'Отправка числа на сервер';
    };

    const handleKeyPress = (e) => {
        if (e.key === 'Enter') {
            sendNumber();
        }
    };

    const styles = {
        body: {
            fontFamily: 'Arial, sans-serif',
            backgroundColor: '#121212',
            color: '#ffffff',
            padding: '2rem',
            margin: 0,
            minHeight: '100vh',
        },
        container: {
            maxWidth: '600px',
            margin: '0 auto',
            backgroundColor: '#1e1e1e',
            padding: '20px',
            borderRadius: '10px',
        },
        input: {
            padding: '8px',
            borderRadius: '5px',
            border: 'none',
            backgroundColor: '#2a2a2a',
            color: '#ffffff',
            width: '100%',
            boxSizing: 'border-box',
            marginBottom: '10px',
        },
        button: {
            padding: '0.5rem 1rem',
            margin: '5px',
            borderRadius: '5px',
            border: 'none',
            backgroundColor: '#1db954',
            color: '#ffffff',
            cursor: 'pointer',
            fontSize: '16px',
        },
        buttonHover: {
            backgroundColor: '#1ed760',
        },
        buttonDisabled: {
            backgroundColor: '#555',
            cursor: 'not-allowed',
        },
        resultBox: {
            margin: '20px 0',
            padding: '10px',
            border: '1px solid #444',
            borderRadius: '5px',
            textAlign: 'left',
            maxHeight: '300px',
            overflowY: 'auto',
        },
        success: {
            color: '#00FF00',
        },
        error: {
            color: '#FF5555',
        },
        h2: {
            textAlign: 'center',
        },
    };

    return (
        <div style={styles.body}>
            <div style={styles.container}>
                <h2 style={styles.h2}>Отправка числа на сервер</h2>
                <input
                    type="text"
                    placeholder="Введите число или 'exit'"
                    value={inputValue}
                    onChange={(e) => setInputValue(e.target.value)}
                    onKeyPress={handleKeyPress}
                    style={styles.input}
                    ref={inputRef}
                />
                <button
                    style={{ ...styles.button, ...(isSending ? styles.buttonDisabled : {}) }}
                    onMouseOver={(e) => !isSending && (e.currentTarget.style.backgroundColor = styles.buttonHover.backgroundColor)}
                    onMouseOut={(e) => !isSending && (e.currentTarget.style.backgroundColor = styles.button.backgroundColor)}
                    onClick={sendNumber}
                    disabled={isSending}
                >
                    Отправить
                </button>
                <button
                    style={{ ...styles.button, ...(!isSending ? styles.buttonDisabled : {}) }}
                    onMouseOver={(e) => isSending && (e.currentTarget.style.backgroundColor = styles.buttonHover.backgroundColor)}
                    onMouseOut={(e) => isSending && (e.currentTarget.style.backgroundColor = styles.button.backgroundColor)}
                    onClick={stopSending}
                    disabled={!isSending}
                >
                    Остановить
                </button>
                <div style={styles.resultBox} ref={resultRef}>
                    {messages.map((msg, index) => (
                        <div key={index} style={styles[msg.type]}>
                            {msg.message}
                        </div>
                    ))}
                </div>
            </div>
        </div>
    );
}

export default App;

=====================================================================================================

https://github.com/sunmeat/NetServer/blob/master/Program.cs (server side):

using System;
using System.Net;
using System.Text;
using System.IO;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        string port = Environment.GetEnvironmentVariable("PORT") ?? "5000";
        string url = $"http://+:{port}/send/";
        
        HttpListener listener = new HttpListener();
        listener.Prefixes.Add(url);
        listener.Start();
        Console.WriteLine($"Сервер запущен на {url}");

        while (true)
        {
            var context = await listener.GetContextAsync();
            _ = Task.Run(() => ProcessRequest(context));
        }
    }

    static async Task ProcessRequest(HttpListenerContext context)
    {
        HttpListenerRequest request = context.Request;
        HttpListenerResponse response = context.Response;

        // add CORS headers to all responses (for JavaScript example)
        response.AddHeader("Access-Control-Allow-Origin", "*");
        response.AddHeader("Access-Control-Allow-Methods", "POST, OPTIONS");
        response.AddHeader("Access-Control-Allow-Headers", "Content-Type");

        // handle preflight OPTIONS request (for JavaScript example)
        if (request.HttpMethod == "OPTIONS")
        {
            response.StatusCode = 200;
            response.Close();
            return;
        }

        if (request.HttpMethod != "POST")
        {
            response.StatusCode = 405;
            await response.OutputStream.WriteAsync(Encoding.UTF8.GetBytes("Только POST-запросы"));
            response.Close();
            return;
        }

        using var reader = new StreamReader(request.InputStream, Encoding.UTF8);
        string numberStr = await reader.ReadToEndAsync();

        if (int.TryParse(numberStr, out int number))
        {
            int result = number + 1;
            byte[] buffer = Encoding.UTF8.GetBytes(result.ToString());

            response.ContentType = "text/plain";
            response.ContentLength64 = buffer.Length;
            await response.OutputStream.WriteAsync(buffer, 0, buffer.Length);
            Console.WriteLine($"Получено: {number}, отправлено: {result}");
        }
        else
        {
            response.StatusCode = 400;
            await response.OutputStream.WriteAsync(Encoding.UTF8.GetBytes("Ошибка: ожидалось число."));
        }

        response.Close();
    }
}