I am facing an error with node/express. I am assuming the issue is with my asynchronous code design.

Output: Success in container

Expected Output: Success in container.. Success in Uploading...

Error: (node:18364) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch()

DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Code:

const express = require("express");
const multer = require("multer");
const AuthReq = require("../middleWare/AuthReq");
require("dotenv").config();
const Azure_Storage_Connection_String = process.env.Azure_Connection_String;
const { BlobServiceClient } = require("@azure/storage-blob");

const Router = express.Router();

const storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, "uploads");
  },
  filename: function (req, file, cb) {
    cb(null, Date.now()   "-"   file.originalname);
  },
});

const upload = multer({ storage: storage });

Router.post("/profile", AuthReq, upload.single("profile"), async (req, res) => {
  const file = req.file;

  const blobServiceClient = BlobServiceClient.fromConnectionString(
    Azure_Storage_Connection_String
  );

  const containerName = req.user._id;

  const ContainerClient = blobServiceClient.getContainerClient(containerName);

  try {
    const containerResponse = await ContainerClient.create();
  } catch (err) {
    return res.status(400).send("Error while sending image");
  }

  res.send("Success in container");

  const contentType = file.mimetype;

  const filePath = file.path;

  const blobName = file.filename   contentType;

  const blockBlobClient = ContainerClient.getBlockBlobClient(blobName);

  try {
    const uploadBlobResponse = await blockBlobClient.uploadFile(filePath);
  } catch (err) {
    return res.status(400).send("Error while sending image");
  }

  res.send("Success in Uploading...");
});

module.exports = Router;

CodePudding user response：

You cannot use res.send more than once per request, because one request has only one response. I assume that you want to send a "two-part" response, so that the user first sees "Success in container" and then (a few seconds later) "Success in Uploading ...".

Node.js will send the response in two "chunks" if you use

res.write("Success in container");
...
res.end("Success in Uploading...");

(See also the explanation in this answer.)