@use_kwargs 更改响应内容

Question

I notice that @use_kwargs in flask-apispec changes the response content-type. In the following "hello world" example, The use of @use_kwargs changes the response content-type from text/html to application/json . I find it a bit surprising since the flask-apispec doc doesn't mention it and I wouldn't expect injecting args also changes the response type:

from flask import Flask
from flask_apispec import use_kwargs
from marshmallow import fields

app = Flask(__name__)

@app.route('/')
@use_kwargs({'email': fields.Str()}, location="query")
def hello_world(**kwargs):
    return 'Hello, World!

curl -v http://127.0.0.1:5000/\?email\=abc shows the response

> GET /?email=abc HTTP/1.1
> Host: 127.0.0.1:5000
> User-Agent: curl/7.64.1
> Accept: */*
>
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Content-Type: application/json
< Content-Length: 16
< Server: Werkzeug/1.0.1 Python/3.8.2
< Date: Tue, 12 Jan 2021 06:09:25 GMT
<
"Hello, World!"

Note that the Content-Type: application/json and value hello world is quoted. However, without the line of @use_kwargs , the response is of Content-Type: text/html and the content hello world is not quoted:

~ curl -v http://127.0.0.1:5000/\?email\=abc
*   Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to 127.0.0.1 (127.0.0.1) port 5000 (#0)
> GET /?email=abc HTTP/1.1
> Host: 127.0.0.1:5000
> User-Agent: curl/7.64.1
> Accept: */*
>
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Content-Type: text/html; charset=utf-8
< Content-Length: 13
< Server: Werkzeug/1.0.1 Python/3.8.2
< Date: Tue, 12 Jan 2021 06:09:42 GMT
<
* Closing connection 0
Hello, World!%

What is the rationale of changing the response? How can I set the response content type of "text/html" even with the use of @use_kwargs ? Thank you !

Update:

Just add a bit more details on the answer given by @Diego Miguel: The effect of changing content is caused by the logic in Wrapper. call

    def __call__(self, *args, **kwargs):
        response = self.call_view(*args, **kwargs)
        if isinstance(response, werkzeug.Response):
            return response
        rv, status_code, headers = unpack(response)
        mv = self.marshal_result(rv, status_code)
        response = packed(mv, status_code, headers)
        return flask.current_app.make_response(response)

marshal_result calls flask.jsonify which makes a Response object with "application/json" mimetype and also introduces an extra level of quotation of the "hello world" example above.

Answer 1

I'm not entirely sure why using @use_kwargs changes the content-type. By looking at the source code , it seems to return a dict , judging by this function (that is called by activate ). So my best guess is that Flask when executing app.route jsonifys that dict , as that the default behaviour . At that point, the content-type is changed to application/json . However, hello_world is executed after use_kwargs , finally returning a string, that is, "Hello World.".

In any case, I don't think this behaviour is actually intended by flask-apispec .

You can change the content-type of your response (and any other field), creating a Flask.Response object with make_reponse and then setting its content-type to "text/html" (however, this is set by default when passing a string to make_response so it's not necessary):

from flask import Flask, make_response
from flask_apispec import use_kwargs
from marshmallow import fields

app = Flask(__name__)

@app.route('/')
@use_kwargs({'email': fields.Str()}, location="query")
def hello_world(**kwargs):
    response = make_response("Hello World!")
    response.content_type = 'text/html'  # can be omitted
    return response

Output of curl -v http://127.0.0.1:5000/\?email\=abc :

> GET /?email=abc HTTP/1.1
> Host: 127.0.0.1:5000
> User-Agent: curl/7.74.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Content-Type: text/html
< Content-Length: 13
< Server: Werkzeug/1.0.1 Python/3.9.1
< Date: Tue, 12 Jan 2021 19:08:05 GMT
< 
Hello World!