Flask doesn't see JSON data sent by Node

Question

I am trying to send JSON data to Flask using Node, but I can't read the data in Flask. I tried printing request.data in Flask but it didn't output anything. I also tried printing request.json, but it returned a 400 response. Why doesn't Flask see the JSON data sent by Node?

from flask import Flask
from flask import request

app = Flask(__name__)

@app.route("/", methods=['GET', 'POST'])
def hello():
    if request.method == "POST":
        print "POST";
        print "get_json: ", request.get_json();
        # print "get_json: ", request.get_json(force = True);
        print "data: ", request.data;
        return 'POST';
    else:
        print "GET";
        return "GET";

if __name__ == "__main__":
    app.run()

var async = require('async'),
    http = require('http'),
    util = require('util');

var server = {
        hostname: '127.0.0.1',
        port: 5000
    };

function request(method, path, headers, body, callback) {
    var req = {};

    if(!headers) {
        headers = {};
    }

    headers['Content-Type'] = 'application/json';

    console.log(method + ' ' + path);
    console.log(' Req:');
    console.log('  headers: ' + JSON.stringify(headers));
    if(body) {
        console.log('  body   : ' + JSON.stringify(body));
    } else {
        console.log('  no body');
    }

    req = http.request({
            hostname: server.hostname,
            port: server.port,
            path: path,
            method: method,
            headers: headers
        }, (res) => {
            var resbody = '';

            res.on('data', (chunk) => {
                resbody = resbody + chunk;
            });

            res.on('end', () => {
                console.log(' Res:');
                console.log('  headers: ' + JSON.stringify(res.headers));
                if(body) {
                    console.log('  body   : ' + JSON.stringify(resbody));
                } else {
                    console.log('  no body');
                }               
                callback(resbody);
            });
        }
    );

    req.on('error', (err) => {
        console.log(method + ' ' + path + ' ERR: ' + util.inspect(err));
        callback(err);
    });

    if(body) {
        req.write(JSON.stringify(body));
    }

    req.end();
}

request('POST', '/', null, {foo: 'bar'}, (res) => {});

Output from JavaScript:

POST /
 Req:
  headers: {"Content-Type":"application/json"}
  body   : {"foo":"bar"}
 Res:
  headers: {"content-type":"text/html","content-length":"192","server":"Werkzeug/0.11.11 Python/2.7.11","date":"Fri, 09 Sep 2016 10:29:58 GMT"}
  body   : "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 3.2 Final//EN\">\n<title>400 Bad Request</title>\n<h1>Bad Request</h1>\n<p>The browser (or proxy) sent a request that this server could not understand.</p>\n"

Output from Python:

POST
get_json: 127.0.0.1 - - [09/Sep/2016 12:29:58] "POST / HTTP/1.1" 400 -

Edited to update all codes.

curl:

> curl.exe 127.0.0.1:5000 --header "Content-Type: application/json" --data {\"foo\":\"bar\"}
POST

If you were to use `http://httpbin.org/post` you'd get a JSON response back which echoes what you sent; you'll get the same results (nothing sent in the POST body). — Martijn Pieters, Sep 08 '16 at 16:22
Ah, I see where it is writing the JSONified body. I don't see any Content-Length header being set however; looking over the [node.js `http.request()` documentation](https://nodejs.org/api/http.html#http_http_request_options_callback) they set that header explicitly in their code. — Martijn Pieters, Sep 08 '16 at 16:24
@MartijnPieters: Setting or not the `Content-Length` doesn't change anything, and are you sure about the url of `http://httpbin.org/post`? I get `ADDRNOTFOUND` — DrakaSAN, Sep 08 '16 at 16:50
@hjpotter92: Same error than the node.js version. POSTMan do work however. — DrakaSAN, Sep 09 '16 at 11:25
@hjpotter92: Okay, I was just issuing the wrong command, curl do work, so it is something in my node.js code — DrakaSAN, Sep 09 '16 at 12:28

score 1 · Accepted Answer · answered Sep 09 '16 at 12:57

The Python Server is fine, and run correctly, the problem lies in the handcrafted http request, which for some reason is malformed.

Using the request module works:

var request = require('request');

request({
    method: 'POST',
    url: 'http://127.0.0.1:5000',
    // body: '{"foo": "bar"}'
    json: {"foo": "bar"}
}, (error, response, body) => {
    console.log(error);
    // console.log(response);
    console.log(body);
});

Flask doesn't see JSON data sent by Node

1 Answers1