Flask abort() with custom http code

Question

I use Flask framework in my project with pure json api. It renders only json responses without html or static files.

I am trying to achieve abort() function with custom http code, in my case 204 (No Content) which isn't defined by default. I have currently code like:

# Error define
class NoContent(HTTPException):
    code = 204
    description = ('No Content')

abort.mapping[204] = NoContent

def make_json_error(ex):
    response = jsonify(error=str(ex))
    response.status_code = (ex.code
                        if isinstance(ex, HTTPException)
                        else 500)
    return response

custom_exceptions = {}
custom_exceptions[NoContent.code] = NoContent

for code in custom_exceptions.iterkeys():
    app.error_handler_spec[None][code] = make_json_error

# Route
@app.route("/results/<name>")
def results(name=None):
    return jsonify(data=results) if results else abort(204)

It works well I get response like:

127.0.0.1 - - [02/Dec/2014 10:51:09] "GET /results/test HTTP/1.1" 204 -

But without any content. It renders nothing, not even blank white page in browser.

I can use errorhandler

@app.errorhandler(204)
def error204(e):
    response = jsonify(data=[])
    return response

But it returns 200 http code. In need 204 here. When I add in error204() line like:

response.status_code = 204

It renders nothing once again.

I am stuck and I have no idea where there is an error with this approach. Please help.

If my approach is wrong from design perspective please propose something else.

Thanks in advance.

Have you tried running the app in debug mode and checking if any exceptions are raised. I'll take a stab in the dark and say that something is throwing an exception somewhere. — extols, Dec 02 '14 at 12:20

score 5 · Accepted Answer · edited Oct 07 '21 at 05:54

Remember, HTTP 204 is "No Content". RFC 7231 (and RFC 2616 before it) requires that user-agents ignore everything after the last header line:

The 204 (No Content) status code indicates that the server has successfully fulfilled the request and that there is no additional content to send in the response payload body ... A 204 response is terminated by the first empty line after the header fields because it cannot contain a message body.

~ RFC 7231 (emphasis mine)

The 204 response MUST NOT include a message-body, and thus is always terminated by the first empty line after the header fields.

~ RFC 2616

score 2 · Answer 2 · answered Dec 02 '14 at 13:42

2

You need to return the status code in the error handler.

@app.errorhandler(204)
def error204(e):
    response = jsonify(data=[])
    return response, 204

Leaving off the status code is interpreted as 200 by Flask.

answered Dec 02 '14 at 13:42

davidism

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Flask abort() with custom http code

2 Answers2