How do I read a request's POST data in a simple JavaScript server

Question

I'm writing a simple REST server as part of a javascript tutorial, but I don't know how to read POST data, and I don't even know how to get the length of the POST data. (I have no trouble processing a GET command.) Here's what I'm doing:

const http = require('http');
const URL = require('url').URL;

const book = {title:"Dune", author:"Frank Herbert"}

const app = http.createServer((req, res) => {
    console.log("Headers:", req.headers);
    accept = req.headers.accept;
    console.log("Accept:", accept);
    // contentLength = req.headers.contentLength;
    // console.log("content length:", contentLength);
    data = req.read(61);
    console.log("req.read(61):", data);

    let path=req.url;
    if (req.method === 'GET') {
        doGet(req, res, path);
    } else if (req.method === 'POST') {
        doPost(req, res, path);
    }
})

function doGet(req, res, path) {
    if (path === "/basic") {
        console.log("Basic path")
        res.writeHead(200, {"Content-Type": "text/json","Access-Control-Allow-Origin":"*"});
        res.write(JSON.stringify(book));
        res.end();
    } else {
        console.log("error path");
        res.writeHead(404, {"Content-Type": "text/json","Access-Control-Allow-Origin":"*"});
        // res.write(asHtml("Not Found"));
        res.write(JSON.stringify("{Not Found: " + path + "}"));
        res.end();
    }
}

// to test this method, I use this curl call:
// curl --data "{title:'Stranger In a Strange Land',author:'Robert Heinlein'}" localhost:4000/add
function doPost(req, res, path) {
    if (path === "/add") {
        res.writeHead(200);
        var data = '';
        req.on("data", function(chunk) {
            data += chunk;
        })
        console.log("req.on():", data);

        var postData = req.body;
        console.log("req.body:", postData);

        var readData = req.read();
        console.log("POST data by read:", readData);

        res.end();
    } else {
        res.writeHead(400);
        res.write('');
        res.end();
    }
}

app.listen(4000);

So I can get the value of the accept header with this expression: req.headers.accept But if I say req.headers.content-length it will throw an error, and if I say req.headers.'content-length', it won't even compile.

How can I read the value of the content-length, and how can I read the POST data?

Addendum: I should have been more clear about my results. The value of req.body is undefined.

Here is the output of the code above: (I modified it a bit for clarity.)

Headers: {
  host: 'localhost:4000',
  'user-agent': 'curl/7.79.1',
  accept: '*/*',
  'content-length': '61',
  'content-type': 'application/x-www-form-urlencoded'
}
Accept: */*
req.read(61): null     
req.on(): 
req.body: undefined    
POST data by read: null

As you can see, the content-length, at 61, is correct. But req.body, which is where I expected to find the data, is undefined.

I should have clarified. req.body returns undefined. I have modified the question to show my results. — MiguelMunoz
– MiguelMunoz, Commented Apr 24, 2022 at 1:13

Arky Asmal · Accepted Answer · 2022-04-24 00:51:18Z

1

The post data should be in req.body but try parsing the body first. Try using body-parser middleware on your app, and checking req.body again

Here's the documentation for this middleware and how to have your app automatically decode your request bodies for you, especially if you're using express, which is how you should be implementing a node server. The second link also walks through how to set up a simple JavaScript server, without needing body parser or express if you don't want to use it, and it comes directly from node.js documentation. It does require more setup, which is why express is recommended, but its up to you. Let me know if this helps !

edited Apr 24, 2022 at 0:51

answered Apr 23, 2022 at 23:30

Arky Asmal

1,3516 silver badges11 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

MiguelMunoz Over a year ago

Unfortunately, the value of req.body is undefined. If it had held anything useful, I would have been happy with it.

Arky Asmal Over a year ago

I think you may have forgotten the req.on("end") portion. You have req.on("data") but not "end". Since receiving a request is asynchronous and occurs in a stream, you may have to add that portion, and on the req.on("end") you can parse your json data.

MiguelMunoz Over a year ago

Actually, your 'node server' link explained it. I had never used javascript streams before so I didn't use the code correctly. I fixed it by changing the code that called res.on(). I posted the new code in a separate answer.

MiguelMunoz · Accepted Answer · 2022-04-24 01:46:02Z

Here's the solution, which comes from the node server link provided in Arky Asmal's answer. First, when I process the valid POST request, I removed the call to res.end(). This looks all wrong, because without this call, the server never returns a result. But I fixed the code to read the stream using res.on(). Here's what it my doPost() method looks like now.

function doPost(req, res, path) {
    if (path === "/add") {
        res.writeHead(200);
        var postValue = '';
        // Read the stream.
        req.on("data", function(chunk) {
            postValue += chunk; // chunk is a buffer, but this still works.
        })
        req.on("end", () => {
            console.log('PostData:', postValue);
            console.log('req.body:', req.body); // still empty
            res.end(); // Don't send the reply till we're done reading the stream.
        })
    } else {
        res.writeHead(400);
        res.write('');
        res.end();
    }

Collectives™ on Stack Overflow

How do I read a request's POST data in a simple JavaScript server

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related