How to get POSTed json in Flask?

Question

I'm trying to build a simple API using Flask, in which I now want to read some POSTed JSON. I do the post with the PostMan Chrome extension, and the JSON I post is simply {"text":"lalala"}. I try to read the JSON using the following method:

@app.route('/api/add_message/<uuid>', methods=['GET', 'POST'])
def add_message(uuid):
    content = request.json
    print content
    return uuid

On the browser it correctly returns the uuid I put in the GET, but on the console, it just prints out None (where I expect it to print out the {"text":"lalala"}. Does anybody know how I can get the posted JSON from within the Flask method?

Answer 1

For reference, here's complete code for how to send json from a Python client:

import requests
res = requests.post('http://localhost:5000/api/add_message/1234', json={"mytext":"lalala"})
if res.ok:
    print res.json()

The "json=" input will automatically set the content-type, as discussed here: Post JSON using Python Requests

And the above client will work with this server-side code:

from flask import Flask, request, jsonify
app = Flask(__name__)

@app.route('/api/add_message/<uuid>', methods=['GET', 'POST'])
def add_message(uuid):
    content = request.json
    print content['mytext']
    return jsonify({"uuid":uuid})

if __name__ == '__main__':
    app.run(host= '0.0.0.0',debug=True)

Answer 2

This solution works:

from flask import Flask, request, jsonify

app = Flask(__name__)


@app.route('/hello', methods=['POST'])
def hello():
   return jsonify(request.json)

Answer 3

You need to set the request content type to application/json for the .json property to work; it'll be None otherwise. See the Flask Request documentation:

If the mimetype is application/json this will contain the parsed JSON data. Otherwise this will be None.

Flask 0.10 added the request.get_json() method, and you should use that method instead of the .json property. You can tell the method to skip the content type requirement by setting force=True.

Note that if an exception is raised at this point (possibly resulting in a 400 Bad Request response), your JSON data is invalid. It is in some way malformed; you may want to check it with a JSON validator.

Answer 4

This is the way I would do it and it should be

@app.route('/api/add_message/<uuid>', methods=['GET', 'POST'])
def add_message(uuid):
    content = request.get_json(silent=True)
    # print(content) # Do your processing
    return uuid

With silent=True set, the get_json function will fail silently when trying to retrieve the json body. By default this is set to False.

Setting force=True will ignore the request.headers.get('Content-Type') == 'application/json' check that flask does for you. By default this is also set to False.

See flask documentation.

I would strongly recommend leaving force=False and make the client send the Content-Type header to make it more explicit.

Hope this helps!