Flask not getting any data from jQuery request data

Question

I\'ve a handler for a URL,

@app.route(\"/\", methods=[\'POST\'])
@crossdomain(origin=\'*\')
def hello():
    ss=str(request.data)
    print ss
    return ss
         


        

Answer 1

I have been working with similar functionality and after a bit of messing around with the ajax and python, this is what I came up with for python reading the ajax data

JavaScript:

var data = {
      data: JSON.stringify({
                        "value":'asdf'
                    })
   }
};

$.ajax({
   url:"/",
   type: 'POST',
   data: data,
   success: function(msg){
              alert(msg);
            }
})

Python:

from flask import json
@app.route("/", methods=['POST'])
def get_data():
    data = json.loads(request.form.get('data'))
    ss = data['value']
    return str(ss)

Answer 2

Hmm, I get AJAX requests via request.form. I'm using DataTables and specify it like this:

<script type="text/javascript">
$(document).ready( function() {
        $('#mgmtdata').dataTable( {
                "bServerSide": true,
                "sAjaxSource": "{{url_for('.xhr')|safe}}",
                "sServerMethod": "POST",
                "bDeferRender": true,  
                "bFilter": {{ info.filter if info.filter else "false" }},
                "aoColumnDefs": [ {{ info.columndefs|safe if info.columndefs }} ],
        } );
} );

The xhr() function is simple:

@usersview.route('/xhr', methods=["POST"])
def xhr():
    if not 'usersview' in g:   
        g.usersview = UsersDatatableView()
    return g.usersview.render()

usersview is an instance of the my Grid() object. In this case, it's only interesting on how it get's to the ajax data that DataTables sent in:

def render(self):
    q = self.getQuery()

    # add filtering
    if 'sSearch' in request.form and request.form['sSearch']:
        q = self.applyFilter(q, request.form['sSearch'])

    # add sorting
    if 'iSortingCols' in request.form:
       # and so on

Answer 3

interesting, as it turns out you can only use request.data if the data was posted with a mimetype that flask can't handle, otherwise its an empty string "" I think, the docs weren't very clear, I did some tests and that seems to be the case, you can take a look at the console output the flask generates when you run my tests.

Incoming Request Data

data
  Contains the incoming request data as string in case it came with a mimetype Flask does not handle.

taken from http://flask.pocoo.org/docs/api/

but since we are doing a standard POST using json flask can handle this quite well as such you can access the data from the standard request.form this ss=str(request.form) should do the trick as I've tested it.

As a side note @crossdomain(origin='*') this seems dangerous, theres a reason why we don't allow cross site ajax requests, though Im sure you have your reasons.

this is the complete code I used for testing:

from flask import Flask
app = Flask(__name__)

from datetime import timedelta
from flask import make_response, request, current_app
from functools import update_wrapper


def crossdomain(origin=None, methods=None, headers=None,
                max_age=21600, attach_to_all=True,
                automatic_options=True):
    if methods is not None:
        methods = ', '.join(sorted(x.upper() for x in methods))
    if headers is not None and not isinstance(headers, basestring):
        headers = ', '.join(x.upper() for x in headers)
    if not isinstance(origin, basestring):
        origin = ', '.join(origin)
    if isinstance(max_age, timedelta):
        max_age = max_age.total_seconds()

    def get_methods():
        if methods is not None:
            return methods

        options_resp = current_app.make_default_options_response()
        return options_resp.headers['allow']

    def decorator(f):
        def wrapped_function(*args, **kwargs):
            if automatic_options and request.method == 'OPTIONS':
                resp = current_app.make_default_options_response()
            else:
                resp = make_response(f(*args, **kwargs))
            if not attach_to_all and request.method != 'OPTIONS':
                return resp

            h = resp.headers

            h['Access-Control-Allow-Origin'] = origin
            h['Access-Control-Allow-Methods'] = get_methods()
            h['Access-Control-Max-Age'] = str(max_age)
            if headers is not None:
                h['Access-Control-Allow-Headers'] = headers
            return resp

        f.provide_automatic_options = False
        return update_wrapper(wrapped_function, f)
    return decorator



@app.route("/", methods=['POST'])
@crossdomain(origin='*')
def hello():
    ss=str(request.form)

    print 'ss: ' + ss + ' request.data: ' + str(request.data)
    return ss


@app.route("/test/")
def t():
    return """
<html><head></head><body>
<script src="http://code.jquery.com/jquery.min.js" type="text/javascript"></script>
<script type='text/javascript'>
jQuery.ajax(
   {
      type: "POST",
      dataType: "json",
      data: "adasdasd",
    url: 'http://127.0.0.1:5000/',
complete: function(xhr, statusText)
      {  alert(xhr.responseText) }})

var oReq = new XMLHttpRequest();
oReq.open("POST", "/", false);
oReq.setRequestHeader("Content-Type", "unknown");
oReq.send('sync call');
alert(oReq.responseXML);
</script></body></html>
"""

if __name__ == '__main__':
    app.run()

output:

$ python test.py 
 * Running on http://127.0.0.1:5000/
127.0.0.1 - - [07/Aug/2012 02:45:28] "GET /test/ HTTP/1.1" 200 -
ss: ImmutableMultiDict([('adasdasd', u'')]) request.data: 
127.0.0.1 - - [07/Aug/2012 02:45:28] "POST / HTTP/1.1" 200 -
ss: ImmutableMultiDict([]) request.data: sync call
127.0.0.1 - - [07/Aug/2012 02:45:28] "POST / HTTP/1.1" 200 -
127.0.0.1 - - [07/Aug/2012 02:45:29] "GET /favicon.ico HTTP/1.1" 404 -

and my system:

$ python --version
Python 2.6.1

$ python -c 'import flask; print flask.__version__;'
0.8

$ uname -a
Darwin 10.8.0 Darwin Kernel Version 10.8.0: Tue Jun  7 16:33:36 PDT 2011; root:xnu-1504.15.3~1/RELEASE_I386 i386

using google chrome Version 20.0.1132.57

Answer 4

This worked for me.

In Javascript:

$.ajax({
  type: 'POST',
  url: "enter your correct url",
  contentType: "application/json; charset=utf-8",
  data: JSON.stringify({title: 'My Title', article: 'My article'}),
  success: function(result){
    console.log(result)
  }
});

In Python (flask):

 from flask import request
 import json

 @app.route("/", methods=['POST'])
 def home():
   json_data = json.loads(request.data)
   print(json_data)
   return json_data

NOTE: The points are;

• JSON.stringify()
• contentType: "application/json; charset=utf-8"
• json.loads
• request.data