File upload and revamped documentation.

This commit is contained in:
Guido van Rossum 1996-03-06 07:20:06 +00:00
parent 911ad6b067
commit 7275561d34
1 changed files with 564 additions and 149 deletions

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@ -1,65 +1,369 @@
#!/usr/local/bin/python
# XXX TODO
# - proper doc strings instead of this rambling dialogue style
# - more utilities, e.g.
# - print_header(type="test/html", blankline=1) -- print MIME header
# - utility to format a nice error message in HTML
# - utility to format a Location: ... response, including HTML
# - utility to catch errors and display traceback
"""Support module for CGI (Common Gateway Interface) scripts.
#
# A class for wrapping the WWW Forms Common Gateway Interface (CGI)
# Michael McLay, NIST mclay@eeel.nist.gov 6/14/94
#
# modified by Steve Majewski <sdm7g@Virginia.EDU> 12/5/94
#
# now maintained as part of the Python distribution
# Several classes to parse the name/value pairs that are passed to
# a server's CGI by GET, POST or PUT methods by a WWW FORM. This
# module is based on Mike McLay's original cgi.py after discussing
# changes with him and others on the comp.lang.python newsgroup, and
# at the NIST Python workshop.
#
# The rationale for changes was:
# The original FormContent class was almost, but not quite like
# a dictionary object. Besides adding some extra access methods,
# it had a values() method with different arguments and semantics
# from the standard values() method of a mapping object. Also,
# it provided several different access methods that may be necessary
# or useful, but made it a little more confusing to figure out how
# to use. Also, we wanted to make the most typical cases the simplest
# and most convenient access methods. ( Most form fields just return
# a single value, and in practice, a lot of code was just assuming
# a single value and ignoring all others. On the other hand, the
# protocol allows multiple values to be returned.
#
# The new base class (FormContentDict) is just like a dictionary.
# In fact, if you just want a dictionary, all of the stuff that was
# in __init__ has been extracted into a cgi.parse() function that will
# return the "raw" dictionary, but having a class allows you to customize
# it further.
# Mike McLay's original FormContent class is reimplemented as a
# subclass of FormContentDict.
# There are two additional sub-classes, but I'm not yet too sure
# whether they are what I want.
#
import string,regsub,sys,os,urllib
# since os.environ may often be used in cgi code, we name it in this module.
from os import environ
This module defines a number of utilities for use by CGI scripts written in
Python.
def parse():
"""Parse the query passed in the environment or on stdin"""
Introduction
------------
A CGI script is invoked by an HTTP server, usually to process user input
submitted through an HTML <FORM> or <ISINPUT> element.
Most often, CGI scripts live in the server's special cgi-bin directory.
The HTTP server places all sorts of information about the request (such as
the client's hostname, the requested URL, the query string, and lots of
other goodies) in the script's shell environment, executes the script, and
sends the script's output back to the client.
The script's input is connected to the client too, and sometimes the form
data is read this way; at other times the form data is passed via the
"query string" part of the URL. This module (cgi.py) is intended to take
care of the different cases and provide a simpler interface to the Python
script. It also provides a number of utilities that help in debugging
scripts, and the latest addition is support for file uploads from a form
(if your browser supports it -- Grail 0.3 and Netscape 2.0 do).
The output of a CGI script should consist of two sections, separated by a
blank line. The first section contains a number of headers, telling the
client what kind of data is following. Python code to generate a minimal
header section looks like this:
print "Content-type: text/html" # HTML is following
print # blank line, end of headers
The second section is usually HTML, which allows the client software to
display nicely formatted text with header, in-line images, etc. Here's
Python code that prints a simple piece of HTML:
print "<TITLE>CGI script output</TITLE>"
print "<H1>This is my first CGI script</H1>"
print "Hello, world!"
(It may not be fully legal HTML according to the letter of the standard,
but any browser will understand it.)
Using the cgi module
--------------------
Begin by writing "import cgi". Don't use "from cgi import *" -- the module
defines all sorts of names for its own use that you don't want in your
namespace.
If you have a standard form, it's best to use the SvFormContentDict class.
Instantiate the SvFormContentDict class exactly once: it consumes any input
on standard input, which can't be wound back (it's a network connection,
not a disk file).
The SvFormContentDict instance can be accessed as if it were a Python
dictionary. For instance, the following code checks that the fields
"name" and "addr" are both set to a non-empty string:
form = SvFormContentDict()
form_ok = 0
if form.has_key("name") and form.has_key("addr"):
if form["name"] != "" and form["addr"] != "":
form_ok = 1
if not form_ok:
print "<H1>Error</H1>"
print "Please fill in the name and addr fields."
return
...actual form processing here...
If you have an input item of type "file" in your form and the client
supports file uploads, the value for that field, if present in the form,
is not a string but a tuple of (filename, content-type, data).
Overview of classes
-------------------
SvFormContentDict: single value form content as dictionary; described
above.
FormContentDict: multiple value form content as dictionary (the form items
are lists of values). Useful if your form contains multiple fields with
the same name.
Other classes (FormContent, InterpFormContentDict) are present for
backwards compatibility only.
Overview of functions
---------------------
These are useful if you want more control, or if you want to employ some
of the algorithms implemented in this module in other circumstances.
parse(): parse a form into a Python dictionary.
parse_qs(qs): parse a query string.
parse_multipart(...): parse input of type multipart/form-data (for file
uploads).
parse_header(string): parse a header like Content-type into a main value
and a dictionary of parameters.
test(): complete test program.
print_environ(): format the shell environment in HTML.
print_form(form): format a form in HTML.
print_environ_usage(): print a list of useful environment variables in HTML.
escape(): convert the characters "&", "<" and ">" to HTML-safe sequences.
Caring about security
---------------------
There's one important rule: if you invoke an external program (e.g. via
the os.system() or os.popen() functions), make very sure you don't pass
arbitrary strings received from the client to the shell. This is a
well-known security hole whereby clever hackers anywhere on the web can
exploit a gullible CGI script to invoke arbitrary shell commands. Even
parts of the URL or field names cannot be trusted, since the request
doesn't have to come from your form!
To be on the safe side, if you must pass a string gotten from a form to a
shell command, you should make sure the string contains only alphanumeric
characters, dashes, underscores, and periods.
Installing your CGI script on a Unix system
-------------------------------------------
Read the documentation for your HTTP server and check with your local
system administrator to find the directory where CGI scripts should be
installed; usually this is in a directory cgi-bin in the server tree.
Make sure that your script is readable and executable by "others"; the Unix
file mode should be 755 (use "chmod 755 filename"). Make sure that the
first line of the script contains "#!" starting in column 1 followed by the
pathname of the Python interpreter, for instance:
#!/usr/local/bin/python
Make sure the Python interpreter exists and is executable by "others".
Make sure that any files your script needs to read or write are readable or
writable, respectively, by "others" -- their mode should be 644 for
readable and 666 for writable. This is because, for security reasons, the
HTTP server executes your script as user "nobody", without any special
privileges. It can only read (write, execute) files that everybody can
read (write, execute). The current directory at execution time is also
different (it is usually the server's cgi-bin directory) and the set of
environment variables is also different from what you get at login. in
particular, don't count on the shell's search path for executables ($PATH)
or the Python module search path ($PYTHONPATH) to be set to anything
interesting.
If you need to load modules from a directory which is not on Python's
default module search path, you can change the path in your script, before
importing other modules, e.g.:
import sys
sys.path.insert(0, "/usr/home/joe/lib/python")
sys.path.insert(0, "/usr/local/lib/python")
(This way, the directory inserted last will be searched first!)
Instructions for non-Unix systems will vary; check your HTTP server's
documentation (it will usually have a section on CGI scripts).
Testing your CGI script
-----------------------
Unfortunately, a CGI script will generally not run when you try it from the
command line, and a script that works perfectly from the command line may
fail mysteriously when run from the server. There's one reason why you
should still test your script from the command line: if it contains a
syntax error, the python interpreter won't execute it at all, and the HTTP
server will most likely send a cryptic error to the client.
Assuming your script has no syntax errors, yet it does not work, you have
no choice but to read the next section:
Debugging CGI scripts
---------------------
First of all, check for trivial installation errors -- reading the section
above on installing your CGI script carefully can save you a lot of time.
If you wonder whether you have understood the installation procedure
correctly, try installing a copy of this module file (cgi.py) as a CGI
script. When invoked as a script, the file will dump its environment and
the contents of the form in HTML form. Give it the right mode etc, and
send it a request. If it's installed in the standard cgi-bin directory, it
should be possible to send it a request by entering a URL into your browser
of the form:
http://yourhostname/cgi-bin/cgi.py?name=Joe+Blow&addr=At+Home
If this gives an error of type 404, the server cannot find the script --
perhaps you need to install it in a different directory. If it gives
another error (e.g. 500), there's an installation problem that you should
fix before trying to go any further. If you get a nicely formatted listing
of the environment and form content (in this example, the fields should be
listed as "addr" with value "At Home" and "name" with value "Joe Blow"),
the cgi.py script has been installed correctly. If you follow the same
procedure for your own script, you should now be able to debug it.
The next step could be to call the cgi module's test() function from your
script: replace its main code with the single statement
cgi.test()
This should produce the same results as those gotten from installing the
cgi.py file itself.
When an ordinary Python script raises an unhandled exception (e.g. because
of a typo in a module name, a file that can't be opened, etc.), the Python
interpreter prints a nice traceback and exits. While the Python
interpreter will still do this when your CGI script raises an exception,
most likely the traceback will end up in one of the HTTP server's log
file, or be discarded altogether.
Fortunately, once you have managed to get your script to execute *some*
code, it is easy to catch exceptions and cause a traceback to be printed.
The test() function below in this module is an example. Here are the
rules:
1. Import the traceback module (before entering the try-except!)
2. Make sure you finish printing the headers and the blank line early
3. Assign sys.stderr to sys.stdout
3. Wrap all remaining code in a try-except statement
4. In the except clause, call traceback.print_exc()
For example:
import sys
import traceback
print "Content-type: text/html"
print
sys.stderr = sys.stdout
try:
...your code here...
except:
print "\n\n<PRE>"
traceback.print_exc()
Notes: The assignment to sys.stderr is needed because the traceback prints
to sys.stderr. The print "\n\n<PRE>" statement is necessary to disable the
word wrapping in HTML.
If you suspect that there may be a problem in importing the traceback
module, you can use an even more robust approach (which only uses built-in
modules):
import sys
sys.stderr = sys.stdout
print "Content-type: text/plain"
print
...your code here...
This relies on the Python interpreter to print the traceback. The content
type of the output is set to plain text, which disables all HTML
processing. If your script works, the raw HTML will be displayed by your
client. If it raises an exception, most likely after the first two lines
have been printed, a traceback will be displayed. Because no HTML
interpretation is going on, the traceback will readable.
Good luck!
Common problems and solutions
-----------------------------
- Most HTTP servers buffer the output from CGI scripts until the script is
completed. This means that it is not possible to display a progress report
on the client's display while the script is running.
- Check the installation instructions above.
- Check the HTTP server's log files. ("tail -f logfile" in a separate
window may be useful!)
- Always check a script for syntax errors first, by doing something like
"python script.py".
- When using any of the debugging techniques, don't forget to add
"import sys" to the top of the script.
- When invoking external programs, make sure they can be found. Usually,
this means using absolute path names -- $PATH is usually not set to a
very useful value in a CGI script.
- When reading or writing external files, make sure they can be read or
written by every user on the system.
- Don't try to give a CGI script a set-uid mode. This doesn't work on most
systems, and is a security liability as well.
History
-------
Michael McLay started this module. Steve Majewski changed the interface to
SvFormContentDict and FormContentDict. The multipart parsing was inspired
by code submitted by Andreas Paepcke. Guido van Rossum rewrote,
reformatted and documented the module and is currently responsible for its
maintenance.
"""
# Imports
# =======
import string
import regsub
import sys
import os
import urllib
# A shorthand for os.environ
environ = os.environ
# Parsing functions
# =================
def parse(fp=None):
"""Parse a query in the environment or from a file (default stdin)"""
if not fp:
fp = sys.stdin
if not environ.has_key('REQUEST_METHOD'):
environ['REQUEST_METHOD'] = 'GET' # For testing
if environ['REQUEST_METHOD'] == 'POST':
qs = sys.stdin.read(string.atoi(environ['CONTENT_LENGTH']))
ctype, pdict = parse_header(environ['CONTENT_TYPE'])
if ctype == 'multipart/form-data':
return parse_multipart(fp, ctype, pdict)
elif ctype == 'application/x-www-form-urlencoded':
clength = string.atoi(environ['CONTENT_LENGTH'])
qs = fp.read(clength)
else:
qs = '' # Bad content-type
environ['QUERY_STRING'] = qs
elif environ.has_key('QUERY_STRING'):
qs = environ['QUERY_STRING']
else:
environ['QUERY_STRING'] = qs = ''
if sys.argv[1:]:
qs = sys.argv[1]
else:
qs = ""
environ['QUERY_STRING'] = qs
return parse_qs(qs)
@ -81,21 +385,129 @@ def parse_qs(qs):
return dict
def parse_multipart(fp, ctype, pdict):
"""Parse multipart input.
# The FormContent constructor creates a dictionary from the name/value pairs
# passed through the CGI interface.
Arguments:
fp : input file
ctype: content-type
pdict: dictionary containing other parameters of conten-type header
Returns a dictionary just like parse_qs() (keys are the field
names, each value is a list of values for that field) except
that if the value was an uploaded file, it is a tuple of the
form (filename, content-type, data). Note that content-type
is the raw, unparsed contents of the content-type header.
XXX Should we parse further when the content-type is
multipart/*?
"""
import mimetools
if pdict.has_key('boundary'):
boundary = pdict['boundary']
else:
boundary = ""
nextpart = "--" + boundary
lastpart = "--" + boundary + "--"
partdict = {}
terminator = ""
while terminator != lastpart:
bytes = -1
data = None
if terminator:
# At start of next part. Read headers first.
headers = mimetools.Message(fp)
clength = headers.getheader('content-length')
if clength:
try:
bytes = string.atoi(clength)
except string.atoi_error:
pass
if bytes > 0:
data = fp.read(bytes)
else:
data = ""
# Read lines until end of part.
lines = []
while 1:
line = fp.readline()
if not line:
terminator = lastpart # End outer loop
break
if line[:2] == "--":
terminator = string.strip(line)
if terminator in (nextpart, lastpart):
break
if line[-2:] == '\r\n':
line = line[:-2]
elif line[-1:] == '\n':
line = line[:-1]
lines.append(line)
# Done with part.
if data is None:
continue
if bytes < 0:
data = string.joinfields(lines, "\n")
line = headers['content-disposition']
if not line:
continue
key, params = parse_header(line)
if key != 'form-data':
continue
if params.has_key('name'):
name = params['name']
else:
continue
if params.has_key('filename'):
data = (params['filename'],
headers.getheader('content-type'), data)
if partdict.has_key(name):
partdict[name].append(data)
else:
partdict[name] = [data]
return partdict
#
# form['key']
# form.__getitem__('key')
# form.has_key('key')
# form.keys()
# form.values()
# form.items()
# form.dict
def parse_header(line):
"""Parse a Content-type like header.
Return the main content-type and a dictionary of options.
"""
plist = map(string.strip, string.splitfields(line, ';'))
key = string.lower(plist[0])
del plist[0]
pdict = {}
for p in plist:
i = string.find(p, '=')
if i >= 0:
name = string.lower(string.strip(p[:i]))
value = string.strip(p[i+1:])
if len(value) >= 2 and value[0] == value[-1] == '"':
value = value[1:-1]
pdict[name] = value
return key, pdict
# Main classes
# ============
class FormContentDict:
"""Basic (multiple values per field) form content as dictionary.
form = FormContentDict()
form[key] -> [value, value, ...]
form.has_key(key) -> Boolean
form.keys() -> [key, key, ...]
form.values() -> [[val, val, ...], [val, val, ...], ...]
form.items() -> [(key, [val, val, ...]), (key, [val, val, ...]), ...]
form.dict == {key: [val, val, ...], ...}
"""
def __init__( self ):
self.dict = parse()
self.query_string = environ['QUERY_STRING']
@ -113,45 +525,42 @@ class FormContentDict:
return len(self.dict)
# This is the "strict" single-value expecting version.
# IF you only expect a single value for each field, then form[key]
# will return that single value ( the [0]-th ), and raise an
# IndexError if that expectation is not true.
# IF you expect a field to have possible multiple values, than you
# can use form.getlist( key ) to get all of the values.
# values() and items() are a compromise: they return single strings
# where there is a single value, and lists of strings otherwise.
class SvFormContentDict(FormContentDict):
def __getitem__( self, key ):
if len( self.dict[key] ) > 1 :
"""Strict single-value expecting form content as dictionary.
IF you only expect a single value for each field, then form[key]
will return that single value.
It will raise an IndexError if that expectation is not true.
IF you expect a field to have possible multiple values, than you
can use form.getlist(key) to get all of the values.
values() and items() are a compromise: they return single strings
where there is a single value, and lists of strings otherwise.
"""
def __getitem__(self, key):
if len(self.dict[key]) > 1:
raise IndexError, 'expecting a single value'
return self.dict[key][0]
def getlist( self, key ):
def getlist(self, key):
return self.dict[key]
def values( self ):
def values(self):
lis = []
for each in self.dict.values() :
for each in self.dict.values():
if len( each ) == 1 :
lis.append( each[0] )
else: lis.append( each )
lis.append(each[0])
else: lis.append(each)
return lis
def items( self ):
def items(self):
lis = []
for key,value in self.dict.items():
if len(value) == 1 :
lis.append( (key,value[0]) )
else: lis.append( (key,value) )
lis.append((key, value[0]))
else: lis.append((key, value))
return lis
# And this sub-class is similar to the above, but it will attempt to
# interpret numerical values. This is here as mostly as an example,
# but I think the real way to handle typed-data from a form may be
# to make an additional table driver parsing stage that has a table
# of allowed input patterns and the output conversion types - it
# would signal type-errors on parse, not on access.
class InterpFormContentDict(SvFormContentDict):
"""This class is present for backwards compatibility only."""
def __getitem__( self, key ):
v = SvFormContentDict.__getitem__( self, key )
if v[0] in string.digits+'+-.' :
@ -178,28 +587,8 @@ class InterpFormContentDict(SvFormContentDict):
return lis
# class FormContent parses the name/value pairs that are passed to a
# server's CGI by GET, POST, or PUT methods by a WWW FORM. several
# specialized FormContent dictionary access methods have been added
# for convenience.
# function return value
#
# form.keys() all keys in dictionary
# form.has_key('key') test keys existance
# form[key] returns list associated with key
# form.values('key') key's list (same as form.[key])
# form.indexed_value('key' index) nth element in key's value list
# form.value(key) key's unstripped value
# form.length(key) number of elements in key's list
# form.stripped(key) key's value with whitespace stripped
# form.pars() full dictionary
class FormContent(FormContentDict):
# This is the original FormContent semantics of values,
# not the dictionary like semantics.
"""This class is present for backwards compatibility only."""
def values(self,key):
if self.dict.has_key(key):return self.dict[key]
else: return None
@ -221,14 +610,66 @@ class FormContent(FormContentDict):
return self.dict
# Test/debug code
# ===============
def test():
"""Robust test CGI script.
Dump all information provided to the script in HTML form.
"""
import traceback
print "Content-type: text/html"
print
sys.stderr = sys.stdout
try:
print_environ()
print_form(FormContentDict())
print
print "<H3>Current Working Directory</H3>"
try:
pwd = os.getcwd()
except os.error, msg:
print "os.error:", escape(str(msg))
else:
print escape(pwd)
print
except:
print "\n\n<PRE>" # Turn of word wrap
traceback.print_exc()
def print_environ():
"""Dump the shell environment in HTML form."""
keys = environ.keys()
keys.sort()
print
print "<H3>Shell environment:</H3>"
print "<DL>"
for key in keys:
print "<DT>", escape(key), "<DD>", escape(environ[key])
print "</DL>"
print
def print_form(form):
"""Dump the contents of a form in HTML form."""
keys = form.keys()
keys.sort()
print
print "<H3>Form contents:</H3>"
print "<DL>"
for key in keys:
print "<DT>" + escape(key) + ":",
print "<i>" + escape(`type(form[key])`) + "</i>"
print "<DD>" + escape(`form[key]`)
print "</DL>"
print
def print_environ_usage():
"""Print a list of environment variables used by the CGI protocol."""
print """
<H3>These operating system environment variables could have been
set:</H3> <UL>
<H3>These environment variables could have been set:</H3>
<UL>
<LI>AUTH_TYPE
<LI>CONTENT_LENGTH
<LI>CONTENT_TYPE
@ -257,47 +698,21 @@ set:</H3> <UL>
</UL>
"""
def print_environ():
skeys = environ.keys()
skeys.sort()
print '<h3> The following environment variables ' \
'were set by the CGI script: </h3>'
print '<dl>'
for key in skeys:
print '<dt>', escape(key), '<dd>', escape(environ[key])
print '</dl>'
def print_form( form ):
skeys = form.keys()
skeys.sort()
print '<h3> The following name/value pairs ' \
'were entered in the form: </h3>'
print '<dl>'
for key in skeys:
print '<dt>', escape(key), ':',
print '<i>', escape(`type(form[key])`), '</i>',
print '<dd>', escape(`form[key]`)
print '</dl>'
# Utilities
# =========
def escape( s ):
s = regsub.gsub('&', '&amp;', s) # Must be done first
s = regsub.gsub('<', '&lt;', s)
s = regsub.gsub('>', '&gt;', s)
def escape(s):
"""Replace special characters '&', '<' and '>' by SGML entities."""
s = regsub.gsub("&", "&amp;", s) # Must be done first!
s = regsub.gsub("<", "&lt;", s)
s = regsub.gsub(">", "&gt;", s)
return s
def test( what ):
label = escape(str(what))
print 'Content-type: text/html\n\n'
print '<HEADER>\n<TITLE>' + label + '</TITLE>\n</HEADER>\n'
print '<BODY>\n'
print "<H1>" + label +"</H1>\n"
form = what()
print_form( form )
print_environ()
print_environ_usage()
print '</body>'
if __name__ == '__main__' :
test_classes = ( FormContent, FormContentDict, SvFormContentDict, InterpFormContentDict )
test( test_classes[0] ) # by default, test compatibility with
# old version, change index to test others.
# Invoke mainline
# ===============
# Call test() when this file is run as a script (not imported as a module)
if __name__ == '__main__':
test()