Python CGI script only printing partial data

Question

I have a simple web form that sends the contents of a div (an SVG document) to the following Python script. The script takes the SVG data and prints it to the browser. The client then saves it as a file:

#!/usr/bin/python

import cgi, cgitb, urllib

form = cgi.FieldStorage()
try:
    data = urllib.unquote(form.getvalue('output-data'))
    fn = urllib.unquote(form.getvalue('output-fn'))
except AttributeError:
    data = None
    fn = None

print "Content-Type: application/x-gzip"
print "Content-Disposition: attachment; filename=" + str(fn) 
print "Content-Description: File to download\n"
print data;

Here is the form:

<form id="form-figure-export-svg" action="assets/src/exportSvg.py" method="POST" style="display:none;" enctype="multipart/form-data">
    <input type="text" id="form-figure-svg-data" name="output-data" style="">
    <input type="text" id="form-figure-svg-fn" name="output-fn" style="">
</form>

The problem is that if the form contains a lot of data (around about 450-500 KB — actually 524288 bytes; see update below) then the data that the Python script prints is truncated. This corrupts the SVG output. Chrome and Safari browsers truncate at different points — the latest version of Firefox appears to work okay.

I verified that the data in the form is correct (e.g., console.log($('#form-figure-svg-data').val())) before it is submitted to the Python script.

Is there some parameter I need to add to the Python script, to ensure that the complete contents of data are printed?

Other things I have tried:

Replacing the Content-Type directive with the MIME type image/svg+xml
Adding the Content-Transfer-Encoding directive setting of binary
Using the Python StringIO and gzip libraries to manually compress the SVG data before printing

Update

On inspection of output from Webkit browsers (Chrome and Safari) this might be due to a limit on the maximum length of an input field (524288 bytes). I'm investigating to see if there is a way to remove this limit, or use some other means for sending my data through the form without an artificial limit.

Alex Reynolds · Accepted Answer · 2014-02-07 21:06:02Z

1

So it looks like this issue is related to the maximum length allowed by an input div in Chrome and Safari (Webkit browsers). Namely, a limitation of 524288 bytes.

To solve this, I replaced the data field in my form with a textarea div, which removes this limitation:

<form id="form-figure-export-svg" action="assets/src/exportSvg.py" method="POST" style="display:none;" enctype="multipart/form-data">
    <textarea id="form-figure-svg-data" name="output-data" style=""></textarea>
    <input type="text" id="form-figure-svg-fn" name="output-fn" style="">
</form>

When I submit this form, there is no longer any client-side limitation on the data sent through the form via Chrome and Safari. I could, however, still implement a web server-based limitation on the allowed size of the form data (for security or other testing purposes).

answered Feb 7, 2014 at 21:06

Alex Reynolds

97.3k59 gold badges251 silver badges356 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Python CGI script only printing partial data

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related