How to handle "413: Request Entity Too Large" in python flask server

Question

I'm using Flask-uploads to upload files to my Flask server. The max size allowed is set by using flaskext.uploads.patch_request_class(app, 16 * 1024 * 1024).

My client application (A unit test) uses requests to post a file that is to large.

I can see that my server returnes a HTTP response with status 413: Request Entity Too Large. But the client raises an exception in the requests code

ConnectionError: HTTPConnectionPool(host='api.example.se', port=80): Max retries exceeded with url: /images (Caused by <class 'socket.error'>: [Errno 32] Broken pipe)

My guess is that the server disconnect the receving socket and sends the reponse back to the client. But when the client gets a broken sending socket, it raises an exception and skips the response.

Questions:

• Are my guess about Flask-Uploads and requests correct?
• Does Flask-Uploads and request handle the 413 error correct?
• Should I expect that my client code gets back some html when the post are to large?

Update

Here is a simple example reproducing my problem.

server.py

from flask import Flask, request
app = Flask(__name__)
app.config['MAX_CONTENT_LENGTH'] = 1024

@app.route('/post', methods=('POST',))
def view_post():
    return request.data

app.run(debug=True)

client.py

from tempfile import NamedTemporaryFile
import requests

def post(size):
    print "Post with size %s" % size,
    f = NamedTemporaryFile(delete=False, suffix=".jpg")
    for i in range(0, size):
        f.write("CoDe")
    f.close()

    # Post
    files = {'file': ("tempfile.jpg", open(f.name, 'rb'))}
    r = requests.post("http://127.0.0.1:5000/post", files=files)
    print "gives status code = %s" % r.status_code

post(16)
post(40845)
post(40846)

result from client

Post with size 16 gives status code = 200
Post with size 40845 gives status code = 413
Post with size 40846
Traceback (most recent call last):
  File "client.py", line 18, in <module>
    post(40846)
  File "client.py", line 13, in post
    r = requests.post("http://127.0.0.1:5000/post", files=files)
  File "/opt/python_env/renter/lib/python2.7/site-packages/requests/api.py", line 88, in post
    return request('post', url, data=data, **kwargs)
  File "/opt/python_env/renter/lib/python2.7/site-packages/requests/api.py", line 44, in request
    return session.request(method=method, url=url, **kwargs)
  File "/opt/python_env/renter/lib/python2.7/site-packages/requests/sessions.py", line 357, in request
    resp = self.send(prep, **send_kwargs)
  File "/opt/python_env/renter/lib/python2.7/site-packages/requests/sessions.py", line 460, in send
    r = adapter.send(request, **kwargs)
  File "/opt/python_env/renter/lib/python2.7/site-packages/requests/adapters.py", line 354, in send
    raise ConnectionError(e)
requests.exceptions.ConnectionError: HTTPConnectionPool(host='127.0.0.1', port=5000): Max retries exceeded with url: /post (Caused by <class 'socket.error'>: [Errno 32] Broken pipe)

my versions

$ pip freeze
Flask==0.10.1
Flask-Mail==0.9.0
Flask-SQLAlchemy==1.0
Flask-Uploads==0.1.3
Jinja2==2.7.1
MarkupSafe==0.18
MySQL-python==1.2.4
Pillow==2.1.0
SQLAlchemy==0.8.2
Werkzeug==0.9.4
blinker==1.3
itsdangerous==0.23
passlib==1.6.1
python-dateutil==2.1
requests==2.0.0
simplejson==3.3.0
six==1.4.1
virtualenv==1.10.1
voluptuous==0.8.1
wsgiref==0.1.2

Answer 1

Flask is closing the connection, you can set an error handler for the 413 error:

@app.errorhandler(413)
def request_entity_too_large(error):
    return 'File Too Large', 413

Now the client should get a 413 error, note that I didn't test this code.

Update:

I tried recreating the 413 error, and I didn't get a ConnectionError exception.

Here's a quick example:

from flask import Flask, request

app = Flask(__name__)

app.config['MAX_CONTENT_LENGTH'] = 1024


@app.route('/post', methods=('POST',))
def view_post():
    return request.data


app.run(debug=True)

After running the file, I used the terminal to test requests and sending large data:

>>> import requests
>>> r = requests.post('http://127.0.0.1:5000/post', data={'foo': 'a'})
>>> r
<Response [200]>
>>> r = requests.post('http://127.0.0.1:5000/post', data={'foo': 'a'*10000})
>>> r
<Response [413]>
>>> r.status_code
413
>>> r.content
'<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">\n<title>413 Request Entity Too Large</title
>\n<h1>Request Entity Too Large</h1>\n<p>The data value transmitted exceeds the capacity limit.</p>\n'

As you can see, we got a response from flask 413 error and requests didn't raise an exception.

By the way I'm using:

• Flask: 0.10.1
• Requests: 2.0.0