node.js - 間違ったパスワードでログインしようとした後、/api/users/login を localhost:3000 から http://localhost:5000/ にプロキシ要求しようとしているときにエラーが発生しました

Question

MERN アプリケーションをローカルで実行していますが、間違ったパスワードでログインしようとすると常にエラーが発生します。エラーなしで正しい資格情報でログインできました。

クライアントの package.jsonファイルは次のとおりです。

{
  "name": "client",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@testing-library/jest-dom": "^4.2.4",
    "@testing-library/react": "^9.3.2",
    "@testing-library/user-event": "^7.1.2",
    "axios": "^0.19.2",
    "materialize-css": "^1.0.0-rc.2",
    "react": "^16.12.0",
    "react-dom": "^16.12.0",
    "react-redux": "^7.2.0",
    "react-router-dom": "^5.1.2",
    "react-scripts": "3.4.0",
    "redux": "^4.0.5",
    "redux-promise": "^0.6.0",
    "redux-thunk": "^2.3.0"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },
  "eslintConfig": {
    "extends": "react-app"
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  },
  "devDependencies": {
    "http-proxy-middleware": "^0.19.1"
  }
}

内部のsetupProxy.jsファイル:

const proxy = require("http-proxy-middleware");

// module.exports = function(app) {
//   app.use(proxy("/api", { target: "http://localhost:5000/" }));
// };

module.exports = function(app) {
  app.use(
    proxy("/api", {
      target: "http://localhost:5000/",
      headers: {
        Connection: "keep-alive"
      }
    })
  );
};

サーバー の package.jsonファイル:

{
  "name": "simple-dentfx-app",
  "version": "1.0.0",
  "description": "MERN dentfx app",
  "main": "index.js",
  "engine": {
    "node": "10.13.0",
    "npm": "6.13.4"
  },
  "scripts": {
    "start": "node server/index.js",
    "backend": "nodemon server/index.js",
    "frontend": "npm run start --prefix client",
    "dev": "concurrently \"npm run backend\" \"npm run start --prefix client\""
  },
  "author": "Enes Tatli",
  "license": "ISC",
  "dependencies": {
    "bcrypt": "^3.0.8",
    "body-parser": "^1.18.3",
    "cookie-parser": "^1.4.3",
    "express": "^4.17.1",
    "jsonwebtoken": "^8.5.1",
    "mongoose": "^5.4.20"
  },
  "devDependencies": {
    "concurrently": "^5.1.0",
    "nodemon": "^2.0.2"
  }
}

サーバー *index.jsファイル:

const express = require("express");
const app = express();
const mongoose = require("mongoose");
const bodyParser = require("body-parser");
const cookieParser = require("cookie-parser");

const { User } = require("./models/user");
const config = require("./config/key");
const { auth } = require("./middleware/auth");

mongoose
  .connect(
    config.mongoURI,
    { useNewUrlParser: true }
  )
  .then(() => console.log("DB connected"))
  .catch(err => console.log(err));

app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());
app.use(cookieParser());

app.get("/", (req, res) => {
  res.json({ Hello: "I am happy to deploy our application" });
});

app.get("/api/users/auth", auth, (req, res) => {
  res.status(200).json({
    _id: req._id,
    isAuth: true,
    email: req.user.email,
    name: req.user.name,
    lastName: req.user.lastName,
    role: req.user.role
  });
});

app.post("/api/users/register", (req, res) => {
  const user = new User(req.body);

  user.save((err, userData) => {
    if (err) return res.json({ success: false, err });
    return res.status(200).json({
      success: true
    });
  });
});

app.post("/api/users/login", (req, res) => {
  //find the email
  User.findOne({ email: req.body.email }, (err, user) => {
    if (!user)
      return res.json({
        loginSuccess: false,
        message: "Auth failed, email not found"
      });
    //comparePassword
    user.comparePassword(req.body.password, (err, isMatch) => {
      if (!isMatch) {
        return res.json({ loginSuccess: false, message: "Wrong Password" });
      }
    });
    //generateToken
    user.generateToken((err, user) => {
      if (err) return res.status(400).send(err);
      res
        .cookie("x_auth", user.token)
        .status(200)
        .json({
          loginSuccess: true
        });
    });
  });
});

app.get("/api/users/logout", auth, (req, res) => {
  User.findOneAndUpdate({ _id: req.user._id }, { token: "" }, (err, doc) => {
    if (err) return res.json({ success: false, err });
    return res.status(200).send({
      success: true
    });
  });
});

const port = process.env.PORT || 5000;

app.listen(port, () => {
  console.log(`Server Running at ${port}`);
});

最後に、エラー メッセージの出力を次に示します。

Server Running at 5000
[0] (node:15816) DeprecationWarning: collection.ensureIndex is deprecated. Use createIndexes instead.
[0] DB connected
[0] _http_outgoing.js:470
[0]     throw new ERR_HTTP_HEADERS_SENT('set');
[0]     ^
[0]
[0] Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
[0]     at ServerResponse.setHeader (_http_outgoing.js:470:11)
...
[0] [nodemon] app crashed - waiting for file changes before starting...
[1] [HPM] Error occurred while trying to proxy request /api/users/login from localhost:3000 to http://localhost:5000/ (ECONNREFUSED) (https://nodejs.org/api/errors.html#errors_common_system_errors)```