Problems setting browser cookies in Python cgi

Question

I am developing a web tool and am having some problems with setting cookies. I used to do this in Perl 20 years ago and am shocked that there doesn't seem to be a clear and clean way to handle cookies with Python in 2017! What I thought would be easy and quick has taken all day. I have experimented with manually setting cookies, using the requests module, and a multitude of partial code examples I found on Stack Overflow. Everywhere I look, the documentation is poor, there are no complete working examples, or the answers are old.

I am creating a cgi script with Python. On the login page of the script, I have print "Content-type: text/html\r\n" in order to have a text box and select menu appear on the web page. When the user clicks submit, I have a validation step that needs to print something to the page if there is an error. If there are no errors, I need the script to load a new page and set a cookie.

Here is the code I am using to set my cookies:

    #!C:\Python27\python.exe -u

    import Cookie
    c = Cookie.SimpleCookie()
    c['id'] = '12345'
    c['score'] = '8.76'
    c['page'] = '3'
    print "Content-type: text/html %s;\r\n" % (c)
    print ""
    print c

The problems are:

Only two of the three c values shown above are stored as cookies when I check "Show Cookies" in Firefox after running the above code by itself.
The page that I land on in the script shows Content-type: text/html Set-Cookie: score=8.76 Set-Cookie: id=12345 Set-Cookie: page=3 ; at the top, due to setting the cookies with a print statement and sending the Content-type again. When this happens, no cookies are stored in my browser. Cookies are only stored if isn't already a Content-type: text/html in the headers.

Is there a way to set cookies from inside my script without printing another copy of Content-type: text/html to the browser?

I also need a way to seemlessly update cookies when the user moves around in the tool. For example, when they click the next page, the cookie would update to the next page number.

I am using Python 2.7 on Windows 10 and am using Firefox as my test browser.

Chris Nielsen Chris Nielsen · Accepted Answer · 2017-08-10T00:23:12

I have managed to solve both problems.

Problem #1: Only two of the three c values shown above are stored as cookies.

Solution: I set up my cookie so that I passed three values in one cookie. For example:

import Cookie
c = Cookie.SimpleCookie()
c['id'] = '12345|score=8.76|page=3'

# Output the HTTP message containing the cookie BEFORE Content-type text/html!
print c
print "Content-type: text/html\r\n"

Problem #2: Extra Content-type: text/html header in the web page output:

Solution: Every time the server responds to a GET or POST event from the browser, setting the cookie needs to be the FIRST thing that happens in the http response. I had to reorder the logic used in my script to make sure this was always the case. With every http response, nothing gets printed to the browser via Content-type: text/html until AFTER the cookie is taken care of.

Problems setting browser cookies in Python cgi

1 Answers