Send JSON-Request to Flask via Curl

Question

I setup a very simple post route in flask like this:

from flask import Flask, request

app = Flask(__name__)

@app.route('/post', methods=['POST'])
def post_route():
    if request.method == 'POST':

        data = request.get_json()

        print('Data Received: "{data}"'.format(data=data))
        return "Request Processed.\n"

app.run()

This is the curl request I am trying to send from the command-line:

curl localhost:5000/post -d '{"foo": "bar"}'

But still, it prints out 'Data Received: "None"'. So, it doesn't recognize the JSON I passed it.

Is it necessary to specify the json format in this case?

Solution

According to the get_json docs:

[..] function will return None if the mimetype is not application/json but this can be overridden by the force parameter.

So, either specify the mimetype of the incoming request to be application/json:

curl localhost:5000/post -d '{"foo": "bar"}' -H 'Content-Type: application/json'

or force JSON decoding with force=True:

data = request.get_json(force=True)

---

If running this on Windows (cmd.exe, not PowerShell), you'll also need to change the quoting of your JSON data, from single quotes to double quotes:

curl localhost:5000/post -d "{\"foo\": \"bar\"}" -H 'Content-Type: application/json'

Comments

[OhMad]

Still not working, unfortunately.

[randomir]

Have you seen the edit of question? I thought you had a typo, but maybe that was also an error in your code. Check your print line uses format: print('Data Received: "{data}"'.format(data=data)).

[OhMad]

Oh, I am just using the new Python 3.6 feature instead of the format method where you put an 'f' in front of your string and can use the variable directly inside of it :)

[randomir]

In case you wanted to use the new interpolated strings, you missed the f prefix..

[OhMad]

Guess I removed it from the code above, but I have it on my machine. Still, it's not functioning with the f, nor with the format method. So, I guess that's not the problem in this case :)

[randomir]

What version of flask/curl do you use? On what platform?

[OhMad]

I use curl 7.56.1 and Flask 0.12.2 on Windows

[OhMad]

I fixed it. I guess it's a Windows specific problem with the double quotes. curl localhost:5000/post -d "{\"foo\": \"bar\"}" -H "Content-Type: application/json" works just fine.

[randomir]

Glad to hear that. So it works even without the tips I gave you in my answer?

[OhMad]

Nope, had to add the content type as well. So, thank you!

[randomir]

That makes sense. You're welcome!

[user305883]

for me it was a combination of things: I was printing request.form : that was read as a string, need to include content type on curl, and instead of reading fields and values like : fields = [k for k in request.form] I've got to use request.get_json(). But why fields = [k for k in request.form] was not parsed properly, despite content type application/json ?

[randomir]

@user305883, request.form contains form values. When you use JSON body encoding, that's not form. See an intro to forms here.