Programming Python (169 page)

Because the encryption schemes used by PyMailCGI are
reversible, it is possible to reconstruct my email account’s
password if you happen to see its encrypted form in a screenshot,
unless the private key listed in
secret.py
was different when the tests
shown were run. To sidestep this issue, the email account used in
all of this book’s examples is temporary and will be deleted by the
time you read these words. Please use an email account of your own
to test-drive the system.

#!/usr/bin/python
"""
##################################################################################
generate standard page header, list, and footer HTML;  isolates HTML generation
related details in this file;  text printed here goes over a socket to the client,
to create parts of a new web page in the web browser;  uses one print per line,
instead of string blocks;  uses urllib to escape params in URL links auto from a
dict, but cgi.escape to put them in HTML hidden fields;  some tools here may be
useful outside pymailcgi;  could also return the HTML generated here instead of
printing it, so it could be included in other pages;  could also structure as a
single CGI script that gets and tests a next action name as a hidden form field;
caveat: this system works, but was largely written during a two-hour layover at
the Chicago O'Hare airport: there is much room for improvement and optimization;
##################################################################################
"""
import cgi, urllib.parse, sys, os
# 3.0: Python 3.1 has issues printing some decoded str as text to stdout
import builtins
bstdout = open(sys.stdout.fileno(), 'wb')
def print(*args, end='\n'):
try:
builtins.print(*args, end=end)
sys.stdout.flush()
except:
for arg in args:
bstdout.write(str(arg).encode('utf-8'))
if end: bstdout.write(end.encode('utf-8'))
bstdout.flush()
sys.stderr = sys.stdout           # show error messages in browser
from externs import mailconfig    # from a package somewhere on server
from externs import mailtools     # need parser for header decoding
parser = mailtools.MailParser()   # one per process in this module
# my cgi address root
#urlroot = 'http://starship.python.net/~lutz/PyMailCgi/'
#urlroot = 'http://localhost:8000/cgi-bin/'
urlroot  = ''  # use minimal, relative paths
def pageheader(app='PyMailCGI', color='#FFFFFF', kind='main', info=''):
print('Content-type: text/html\n')
print('' % (app, kind))
print('%s %s
' % (color, app, (info or kind)))
def pagefooter(root='pymailcgi.html'):
print('
')
print('print('align=left alt="[Python Logo]" border=0 hspace=15>')
print('Back to root page' % root)
print('')
def formatlink(cgiurl, parmdict):
"""
make "%url?key=val&key=val" query link from a dictionary;
escapes str() of all key and val with %xx, changes ' ' to +
note that URL escapes are different from HTML (cgi.escape)
"""
parmtext = urllib.parse.urlencode(parmdict)     # calls parse.quote_plus
return '%s?%s' % (cgiurl, parmtext)             # urllib does all the work
def pagelistsimple(linklist):                       # show simple ordered list
print('
')
for (text, cgiurl, parmdict) in linklist:
link = formatlink(cgiurl, parmdict)
text = cgi.escape(text)
print('
\n    %s' % (link, text))
print('
')
def pagelisttable(linklist):                        # show list in a table
print('
')                      # escape text to be safe
for (text, cgiurl, parmdict) in linklist:
link = formatlink(cgiurl, parmdict)
text = cgi.escape(text)
print('
View
\n %s' % (link, text))
print('
')
def listpage(linkslist, kind='selection list'):
pageheader(kind=kind)
pagelisttable(linkslist)         # [('text', 'cgiurl', {'parm':'value'})]
pagefooter()
def messagearea(headers, text, extra=''):               # extra for readonly
addrhdrs = ('From', 'To', 'Cc', 'Bcc')              # decode names only
print('')
for hdr in ('From', 'To', 'Cc', 'Subject'):
rawhdr = headers.get(hdr, '?')
if hdr not in addrhdrs:
dechdr = parser.decodeHeader(rawhdr)        # 3.0: decode for display
else:                                           # encoded on sends
dechdr = parser.decodeAddrHeader(rawhdr)    # email names only
val = cgi.escape(dechdr, quote=1)
print('
%s:' % hdr)
print('    
print('    name=%s value="%s" %s size=60>' % (hdr, val, extra))
print('
Text:')
print('
' % extra)<br/>print('%s\n
' % (cgi.escape(text) or '?'))  # if has s
def viewattachmentlinks(partnames):
"""
create hyperlinks to locally saved part/attachment files
when clicked, user's web browser will handle opening
assumes just one user, only valid while viewing 1 msg
"""
print('
Parts:')
for filename in partnames:
basename = os.path.basename(filename)
filename  = filename.replace('\\', '/') # Windows hack
print('
%s' % (filename, basename))
print('
')
def viewpage(msgnum, headers, text, form, parts=[]):
"""
on View + select (generated link click)
very subtle thing: at this point, pswd was URL encoded in the
link, and then unencoded by CGI input parser; it's being embedded
in HTML here, so we use cgi.escape; this usually sends nonprintable
chars in the hidden field's HTML, but works on ie and ns anyhow:
in url:  ?user=lutz&mnum=3&pswd=%8cg%c2P%1e%f0%5b%c5J%1c%f3&...
in html: 
could urllib.parse.quote html field here too, but must urllib.parse.unquote
in next script (which precludes passing the inputs in a URL instead
of the form); can also fall back on numeric string fmt in secret.py
"""
pageheader(kind='View')
user, pswd, site = list(map(cgi.escape, getstandardpopfields(form)))
print('
' % urlroot)
print('' % msgnum)
print('' % user)    # from page|url
print('' % site)    # for deletes
print('' % pswd)    # pswd encoded
messagearea(headers, text, 'readonly')
if parts: viewattachmentlinks(parts)
# onViewPageAction.quotetext needs date passed in page
print('' % headers.get('Date','?'))
print('
Action:')
print('
')
print('    ReplyForwardDelete')
print('')
print('
')                     # no 'reset' needed here
pagefooter()
def sendattachmentwidgets(maxattach=3):
print('
Attach:
')
for i in range(1, maxattach+1):
print('
' % i)
print('
')
def editpage(kind, headers={}, text=''):
# on Send, View+select+Reply, View+select+Fwd
pageheader(kind=kind)
print('
print('action="%sonEditPageSend.py">' % urlroot)
if mailconfig.mysignature:
text = '\n%s\n%s' % (mailconfig.mysignature, text)
messagearea(headers, text)
sendattachmentwidgets()
print('')
print('')
print('
')
pagefooter()
def errorpage(message, stacktrace=True):
pageheader(kind='Error')                        # was sys.exc_type/exc_value
exc_type, exc_value, exc_tb = sys.exc_info()
print('Error Description
', message)
print('Python Exception
',  cgi.escape(str(exc_type)))
print('Exception details
', cgi.escape(str(exc_value)))
if stacktrace:
print('Exception traceback
')
import traceback
traceback.print_tb(exc_tb, None, sys.stdout)
print('
')
pagefooter()
def confirmationpage(kind):
pageheader(kind='Confirmation')
print('%s operation was successful' % kind)
print('
Press the link below to return to the main page.
')
pagefooter()
def getfield(form, field, default=''):
# emulate dictionary get method
return (field in form and form[field].value) or default
def getstandardpopfields(form):
"""
fields can arrive missing or '' or with a real value
hardcoded in a URL; default to mailconfig settings
"""
return (getfield(form, 'user', mailconfig.popusername),
getfield(form, 'pswd', '?'),
getfield(form, 'site', mailconfig.popservername))
def getstandardsmtpfields(form):
return  getfield(form, 'site', mailconfig.smtpservername)
def runsilent(func, args):
"""
run a function without writing stdout
ex: suppress print's in imported tools
else they go to the client/browser
"""
class Silent:
def write(self, line): pass
save_stdout = sys.stdout
sys.stdout  = Silent()                        # send print to dummy object
try:                                          # which has a write method
result = func(*args)                      # try to return func result
finally:                                      # but always restore stdout
sys.stdout = save_stdout
return result
def dumpstatepage(exhaustive=0):
"""
for debugging: call me at top of a CGI to
generate a new page with CGI state details
"""
if exhaustive:
cgi.test()                       # show page with form, environ, etc.
else:
pageheader(kind='state dump')
form = cgi.FieldStorage()        # show just form fields names/values
cgi.print_form(form)
pagefooter()
sys.exit()
def selftest(showastable=False):                    # make phony web page
links = [                                       # [(text, url, {parms})]
('text1', urlroot + 'page1.cgi', {'a':1}),
('text2', urlroot + 'page1.cgi', {'a':2, 'b':'3'}),
('text3', urlroot + 'page2.cgi', {'x':'a b', 'y':'a('te<>4', urlroot + 'page2.cgi', {'':'', 'y':'', 'z':None})]
pageheader(kind='View')
if showastable:
pagelisttable(links)
else:
pagelistsimple(links)
pagefooter()
if __name__ == '__main__':                          # when run, not imported
selftest(len(sys.argv) > 1)                     # HTML goes to stdout