客戶端和服務器端 (Reacr/Node.js) 之間的 Socket.io 連接失敗

Question

我正在嘗試獲得基本的套接字連接。

服務器看起來像這樣：

    const express = require("express");
    const app = express();
    const port = 4000;
    const server = require("http").createServer(app);
    let io = require("socket.io")(server);

    app.get("/", (req, res) => res.send("Server up"));

    io.on("connection", socket => {
      console.log("a user connected");
    });

    app.get("/", (req, res) => res.send("Hello World!"));

    app.listen(port, () => console.log(`Example app listening on port ${port}!`));

React 組件如下所示：

    import React, { useState, useEffect } from "react";
    import io from "socket.io-client";

    const ChatScreen = () => {

      const socket = io('localhost:4000');


      useEffect(() => {
      }, []);

      return (
        <div className="chatScreen">HI</div>
      );
    };

    export default ChatScreen;

正如我從閱讀中得到的那樣，我應該在服務器中得到一個 console.log“一個用戶連接”。 但是我收到了這兩個錯誤：

Access to XMLHttpRequest at 'http://localhost:4000/socket.io/?EIO=3&transport=polling&t=N2xxl7i' 
from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-
Origin' header is present on the requested resource.

和

polling-xhr.js:267 GET http://localhost:4000/socket.io/?EIO=3&transport=polling&t=N2xy65_ 
net::ERR_FAILED

我該怎么做？

Answer 1

在你的 node js 應用程序中，你可以嘗試在var app = express();之后添加以下內容var app = express(); ：

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "X-Requested-With");
  res.header("Access-Control-Allow-Headers", "Content-Type");
  res.header("Access-Control-Allow-Methods", "PUT, GET, POST, DELETE, OPTIONS");
  next();
});

Answer 2

此錯誤意味着您的 Express 服務器不允許任何外部請求。 您的 React 服務器是外部服務器，這就是此錯誤的原因。

要修復此錯誤，只需將cors 中間件用作：

const express = require("express");
const cors= require("cors");
const app = express();
const port = 4000;
const server = require("http").createServer(app);
let io = require("socket.io")(server);

app.use(cors());

app.get("/", (req, res) => res.send("Server up"));

io.on("connection", socket => {
  console.log("a user connected");
});

app.get("/", (req, res) => res.send("Hello World!"));

app.listen(port, () => console.log(`Example app listening on port ${port}!`));

文檔： https : //expressjs.com/en/resources/middleware/cors.html