CODEWITHSUNDEEP
pythonrestnginxpostmanhttp-status-code-400
Matthew Moisen
Matthew Moisen

Reputation: 18299

How to intentionally cause a 400 Bad Request in Python/Flask?

A consumer of my REST API says that on occasion I am returning a 400 Bad Request - The request sent by the client was syntactically incorrect. error.

My application (Python/Flask) logs don't seem to be capturing this, and neither do my webserver/Nginx logs.

Edit: I would like to try to cause a 400 bad request in Flask for debugging purposes. How can I do this?

Following James advice, I added something similar to the following:

@app.route('/badrequest400')
def bad_request():
    return abort(400)

When I call this, flask returns the following HTML, which doesn't use the "The request sent by the client was syntactically incorrect" line:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<title>400 Bad Request</title>
<h1>Bad Request</h1>
<p>The browser (or proxy) sent a request that this server could not understand.</p>

(I'm not sure why it isn't including the <body> tags.

It appears to me that there are different variations of the 400 error message. For example, if I set a cookie to a value of length 50,000 (using Interceptor with Postman), I'll get the following error from Flask instead:

<html>
<head>
    <title>Bad Request</title>
</head>
<body>
    <h1>
        <p>Bad Request</p>
    </h1>
Error parsing headers: 'limit request headers fields size'

</body>
</html>

Is there a way to get Flask to through the different variations of 400 errors?

Upvotes: 21

Views: 23144

Answers (4)

hernan
hernan

Reputation: 393

Also, You can use jsonify

from flask import jsonify

class SomeView(MethodView):
    def post(self, *args, **kwargs):
        if "csv_file" not in request.files:
            return jsonify({'errors': 'No csv_file key in request.files.'}), 400

Upvotes: 3

Xtonev
Xtonev

Reputation: 141

You can also use abort with custom message error:

from flask import abort
abort(400, 'My custom message')

See https://flask-restplus.readthedocs.io/en/stable/errors.html

Upvotes: 14

James Scholes
James Scholes

Reputation: 7926

You can use abort to raise an HTTP error by status code.

from flask import abort
@app.route('/badrequest400')
def bad_request():
    abort(400)

Upvotes: 18

John
John

Reputation: 5364

you can return the status code as a second parameter of the return, see example below

@app.route('/my400')
def my400():
    code = 400
    msg = 'my message'
    return msg, code

Upvotes: 25

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