chiark / gitweb /
cgi.py (cookie): Exclude attribute keys whose value is false.
[chopwood] / cgi.py
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1### -*-python-*-
2###
3### CGI machinery
4###
5### (c) 2013 Mark Wooding
6###
7
8###----- Licensing notice ---------------------------------------------------
9###
10### This file is part of Chopwood: a password-changing service.
11###
12### Chopwood is free software; you can redistribute it and/or modify
13### it under the terms of the GNU Affero General Public License as
14### published by the Free Software Foundation; either version 3 of the
15### License, or (at your option) any later version.
16###
17### Chopwood is distributed in the hope that it will be useful,
18### but WITHOUT ANY WARRANTY; without even the implied warranty of
19### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20### GNU Affero General Public License for more details.
21###
22### You should have received a copy of the GNU Affero General Public
23### License along with Chopwood; if not, see
24### <http://www.gnu.org/licenses/>.
25
26from __future__ import with_statement
27
28import contextlib as CTX
29import os as OS; ENV = OS.environ
30import re as RX
31import sys as SYS
32import time as T
33import traceback as TB
34
35from auto import HOME, PACKAGE, VERSION
36import config as CONF; CFG = CONF.CFG
37import format as F
38import output as O; OUT = O.OUT; PRINT = O.PRINT
39import subcommand as SC
40import util as U
41
42###--------------------------------------------------------------------------
43### Configuration tweaks.
44
45_script_name = ENV.get('SCRIPT_NAME', '/cgi-bin/chpwd')
46
47CONF.DEFAULTS.update(
48
49 ## The URL of this program, when it's run through CGI.
50 SCRIPT_NAME = _script_name,
51
52 ## A (maybe relative) URL for static content. By default this comes from
53 ## the main script, but we hope that user agents cache it.
54 STATIC = _script_name + '/static')
55
56###--------------------------------------------------------------------------
57### Escaping and encoding.
58
59## Some handy regular expressions.
60R_URLESC = RX.compile('%([0-9a-fA-F]{2})')
61R_URLBAD = RX.compile('[^-\\w,.!]')
62R_HTMLBAD = RX.compile('[&<>]')
63
64def urldecode(s):
65 """Decode a single form-url-encoded string S."""
66 return R_URLESC.sub(lambda m: chr(int(m.group(1), 16)),
67 s.replace('+', ' '))
68 return s
69
70def urlencode(s):
71 """Encode a single string S using form-url-encoding."""
72 return R_URLBAD.sub(lambda m: '%%%02x' % ord(m.group(0)), s)
73
74def htmlescape(s):
75 """Escape a literal string S so that HTML doesn't misinterpret it."""
76 return R_HTMLBAD.sub(lambda m: '&#x%02x;' % ord(m.group(0)), s)
77
78## Some standard character sequences, and HTML entity names for prettier
79## versions.
80_quotify = U.StringSubst({
81 "`": '&lsquo;',
82 "'": '&rsquo;',
83 "``": '&ldquo;',
84 "''": '&rdquo;',
85 "--": '&ndash;',
86 "---": '&mdash;'
87})
88def html_quotify(s):
89 """Return a pretty HTML version of S."""
90 return _quotify(htmlescape(s))
91
92###--------------------------------------------------------------------------
93### Output machinery.
94
95class HTTPOutput (O.FileOutput):
96 """
97 Output driver providing an automatic HTTP header.
98
99 The `headerp' attribute is true if we've written a header. The `header'
100 method will print a custom header if this is wanted.
101 """
102
103 def __init__(me, *args, **kw):
104 """Constructor: initialize `headerp' flag."""
105 super(HTTPOutput, me).__init__(*args, **kw)
106 me.headerp = False
107
108 def write(me, msg):
109 """Output protocol: print a header if we've not written one already."""
110 if not me.headerp: me.header('text/plain')
111 super(HTTPOutput, me).write(msg)
112
113 def header(me, content_type = 'text/plain', **kw):
114 """
115 Print a header, if none has yet been printed.
116
117 Keyword arguments can be passed to emit HTTP headers: see `http_header'
118 for the formatting rules.
119 """
120 if me.headerp: return
121 me.headerp = True
122 for h in O.http_headers(content_type = content_type, **kw):
123 me.writeln(h)
124 me.writeln('')
125
126def cookie(name, value, **kw):
127 """
128 Return a HTTP `Set-Cookie' header.
129
130 The NAME and VALUE give the name and value of the cookie; both are
131 form-url-encoded to prevent misinterpretation (fortunately, `cgiparse'
132 knows to undo this transformation). The KW are other attributes to
133 declare: the names are forced to lower-case and underscores `_' are
134 replaced by hyphens `-'; a `True' value is assumed to indicate that the
135 attribute is boolean, and omitted.
136 """
137 attr = {}
138 for k, v in kw.iteritems():
139 k = '-'.join(i.lower() for i in k.split('_'))
140 attr[k] = v
141 try: maxage = int(attr['max-age'])
142 except KeyError: pass
143 else:
144 attr['expires'] = T.strftime('%a, %d %b %Y %H:%M:%S GMT',
145 T.gmtime(U.NOW + maxage))
146 return '; '.join(['%s=%s' % (urlencode(name), urlencode(value))] +
147 [v is not True and '%s=%s' % (k, v) or k
623103db 148 for k, v in attr.iteritems() if v])
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149
150def action(*v, **kw):
151 """
152 Build a URL invoking this script.
153
154 The positional arguments V are used to construct a path which is appended
155 to the (deduced or configured) script name (and presumably will be read
156 back as `PATH_INFO'). The keyword arguments are (form-url-encoded and)
157 appended as a query string, if present.
158 """
159 url = '/'.join([CFG.SCRIPT_NAME] + list(v))
160 if kw:
161 url += '?' + ';'.join('%s=%s' % (urlencode(k), urlencode(kw[k]))
162 for k in sorted(kw))
163 return htmlescape(url)
164
165def static(name):
166 """Build a URL for the static file NAME."""
167 return htmlescape(CFG.STATIC + '/' + name)
168
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169def redirect(where, **kw):
170 """
171 Write a complete redirection to some other URL.
172 """
173 OUT.header(content_type = 'text/html',
174 status = 302, location = where,
175 **kw)
176 PRINT("""\
177<html>
178<head><title>No, sorry, it's moved again.</title></head>
179<body><p>I'm <a href="%s">over here</a> now.<body>
180</html>""" % htmlescape(where))
181
182###--------------------------------------------------------------------------
183### Templates.
184
185## Where we find our templates.
186TMPLDIR = HOME
187
188## Keyword arguments for templates.
189STATE = U.Fluid()
190STATE.kw = {}
191
192## Set some basic keyword arguments.
193@CONF.hook
194def set_template_keywords():
195 STATE.kw.update(
196 package = PACKAGE,
197 version = VERSION,
198 script = CFG.SCRIPT_NAME,
199 static = CFG.STATIC)
200
201class TemplateFinder (object):
202 """
203 A magical fake dictionary whose keys are templates.
204 """
205 def __init__(me, dir):
206 me._cache = {}
207 me._dir = dir
208 def __getitem__(me, key):
209 try: return me._cache[key]
210 except KeyError: pass
211 with open(OS.path.join(me._dir, key)) as f: tmpl = f.read()
212 me._cache[key] = tmpl
213 return tmpl
214TMPL = TemplateFinder(TMPLDIR)
215
216@CTX.contextmanager
217def tmplkw(**kw):
218 """
219 Context manager: execute the body with additional keyword arguments
220 """
221 d = dict()
222 d.update(STATE.kw)
223 d.update(kw)
224 with STATE.bind(kw = d): yield
225
226FORMATOPS = {}
227
228class FormatHTML (F.SimpleFormatOperation):
229 """
230 ~H: escape output suitable for inclusion in HTML.
231
232 With `:', instead apply form-urlencoding.
233 """
234 def _convert(me, arg):
235 if me.colonp: return html_quotify(arg)
236 else: return htmlescape(arg)
237FORMATOPS['H'] = FormatHTML
238
239def format_tmpl(control, **kw):
240 with F.COMPILE.bind(opmaps = [FORMATOPS, F.BASEOPS]):
241 with tmplkw(**kw):
242 F.format(OUT, control, **STATE.kw)
243
244def page(template, header = {}, title = 'Chopwood', **kw):
245 header = dict(header, content_type = 'text/html')
246 OUT.header(**header)
247 format_tmpl(TMPL['wrapper.fhtml'],
248 title = title, payload = TMPL[template], **kw)
249
250###--------------------------------------------------------------------------
251### Error reporting.
252
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253@CTX.contextmanager
254def cgi_errors(hook = None):
255 """
256 Context manager: report errors in the body as useful HTML.
257
258 If HOOK is given, then call it before reporting errors. It may have set up
259 useful stuff.
260 """
261 try:
262 yield None
263 except Exception, e:
264 if hook: hook()
265 if isinstance(e, U.ExpectedError) and not OUT.headerp:
266 page('error.fhtml',
b569edae 267 header = dict(status = e.code),
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268 title = 'Chopwood: error', error = e)
269 else:
270 exty, exval, extb = SYS.exc_info()
271 with tmplkw(exception = TB.format_exception_only(exty, exval),
272 traceback = TB.extract_tb(extb),
273 PARAM = sorted(PARAM),
274 COOKIE = sorted(COOKIE.items()),
275 PATH = PATH,
276 ENV = sorted(ENV.items())):
277 if OUT.headerp:
278 format_tmpl(TMPL['exception.fhtml'], toplevel = False)
279 else:
280 page('exception.fhtml',
b569edae 281 header = dict(status = 500),
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282 title = 'Chopwood: internal error',
283 toplevel = True)
284
285###--------------------------------------------------------------------------
286### CGI input.
287
288## Lots of global variables to be filled in by `cgiparse'.
289COOKIE = {}
290SPECIAL = {}
291PARAM = []
292PARAMDICT = {}
293PATH = []
294
295## Regular expressions for splitting apart query and cookie strings.
296R_QSPLIT = RX.compile('[;&]')
297R_CSPLIT = RX.compile(';')
298
299def split_keyvalue(string, delim, default):
300 """
301 Split a STRING, and generate the resulting KEY=VALUE pairs.
302
303 The string is split at DELIM; the components are parsed into KEY[=VALUE]
304 pairs. The KEYs and VALUEs are stripped of leading and trailing
305 whitespace, and form-url-decoded. If the VALUE is omitted, then the
306 DEFAULT is used unless the DEFAULT is `None' in which case the component is
307 simply ignored.
308 """
309 for kv in delim.split(string):
310 try:
311 k, v = kv.split('=', 1)
312 except ValueError:
313 if default is None: continue
314 else: k, v = kv, default
315 k, v = k.strip(), v.strip()
316 if not k: continue
317 k, v = urldecode(k), urldecode(v)
318 yield k, v
319
320def cgiparse():
321 """
322 Process all of the various exciting CGI environment variables.
323
324 We read environment variables and populate some tables left in global
325 variables: it's all rather old-school. Variables set are as follows.
326
327 `COOKIE'
328 A dictionary mapping cookie names to the values provided by the user
329 agent.
330
331 `SPECIAL'
332 A dictionary holding some special query parameters which are of
333 interest at a global level, and should not be passed to a subcommand
334 handler. No new entries will be added to this dictionary, though
335 values will be modified to reflect the query parameters discovered.
336 Conventionally, such parameters have names beginning with `%'.
337
338 `PARAM'
339 The query parameters as a list of (KEY, VALUE) pairs. Special
340 parameters are omitted.
341
342 `PARAMDICT'
343 The query parameters as a dictionary. Special parameters, and
344 parameters which appear more than once, are omitted.
345
346 `PATH'
347 The trailing `PATH_INFO' path, split at `/' markers, with any
348 trailing empty component removed.
349 """
350
351 def getenv(var):
352 try: return ENV[var]
353 except KeyError: raise U.ExpectedError, (500, "No `%s' supplied" % var)
354
355 ## Yes, we want the request method.
356 method = getenv('REQUEST_METHOD')
357
358 ## Acquire the query string.
359 if method == 'GET':
360 q = getenv('QUERY_STRING')
361
362 elif method == 'POST':
363
364 ## We must read the query string from stdin.
365 n = getenv('CONTENT_LENGTH')
366 if not n.isdigit():
367 raise U.ExpectedError, (500, "Invalid CONTENT_LENGTH")
368 n = int(n, 10)
369 if getenv('CONTENT_TYPE') != 'application/x-www-form-urlencoded':
370 raise U.ExpectedError, (500, "Unexpected content type `%s'" % ct)
371 q = SYS.stdin.read(n)
372 if len(q) != n:
373 raise U.ExpectedError, (500, "Failed to read correct length")
374
375 else:
376 raise U.ExpectedError, (500, "Unexpected request method `%s'" % method)
377
378 ## Populate the `SPECIAL', `PARAM' and `PARAMDICT' tables.
379 seen = set()
380 for k, v in split_keyvalue(q, R_QSPLIT, 't'):
381 if k in SPECIAL:
382 SPECIAL[k] = v
383 else:
384 PARAM.append((k, v))
385 if k in seen:
386 del PARAMDICT[k]
387 else:
388 PARAMDICT[k] = v
389 seen.add(k)
390
391 ## Parse out the cookies, if any.
392 try: c = ENV['HTTP_COOKIE']
393 except KeyError: pass
394 else:
395 for k, v in split_keyvalue(c, R_CSPLIT, None): COOKIE[k] = v
396
397 ## Set up the `PATH'.
398 try: p = ENV['PATH_INFO']
399 except KeyError: pass
400 else:
401 pp = p.lstrip('/').split('/')
402 if pp and not pp[-1]: pp.pop()
403 PATH[:] = pp
404
405###--------------------------------------------------------------------------
406### CGI subcommands.
407
408class Subcommand (SC.Subcommand):
409 """
410 A CGI subcommand object.
411
412 As for `subcommand.Subcommand', but with additional protocol for processing
413 CGI parameters.
414 """
415
416 def cgi(me, param, path):
417 """
418 Invoke the subcommand given a collection of CGI parameters.
419
420 PARAM is a list of (KEY, VALUE) pairs from the CGI query. The CGI query
421 parameters are checked against the subcommand's parameters (making sure
422 that mandatory parameters are supplied, that any switches are given
423 boolean values, and that only the `rest' parameter, if any, is
424 duplicated).
425
426 PATH is a list of trailing path components. They are used to satisfy the
427 `rest' parameter if there is one and there are no query parameters which
428 satisfy the `rest' parameter; otherwise, an `ExpectedError' is raised if
429 the list of path elements is non-empty.
430 """
431
432 ## We're going to make a pass over the supplied parameters, and we'll
433 ## check them off against the formal parameters as we go; so we'll need
434 ## to be able to look them up. We'll also keep track of the ones we've
435 ## seen so that we can make sure that all of the mandatory parameters
436 ## were actually supplied.
437 ##
438 ## To that end: `want' is a dictionary mapping parameter names to
439 ## functions which will do something useful with the value; `seen' is a
440 ## set of the parameters which have been assigned; and `kw' is going to
441 ## be the keyword-argument dictionary we pass to the handler function.
442 want = {}
443 kw = {}
444
445 def set_value(k, v):
446 """Set a simple value: we shouldn't see multiple values."""
447 if k in kw:
448 raise U.ExpectedError, (400, "Repeated parameter `%s'" % k)
449 kw[k] = v
450 def set_bool(k, v):
451 """Set a simple boolean value: for switches."""
452 set_value(k, v.lower() in ['true', 't', 'yes', 'y'])
453 def set_list(k, v):
454 """Append the value to a list: for the `rest' parameter."""
455 kw.setdefault(k, []).append(v)
456
457 ## Set up the `want' map.
458 for o in me.opts:
459 if o.argname: want[o.name] = set_value
460 else: want[o.name] = set_bool
461 for p in me.params: want[p.name] = set_value
462 for p in me.oparams: want[p.name] = set_value
463 if me.rparam: want[me.rparam.name] = set_list
464
465 ## Work through the list of supplied parameters.
466 for k, v in param:
467 try:
468 f = want[k]
469 except KeyError:
470 if v:
471 raise U.ExpectedError, (400, "Unexpected parameter `%s'" % k)
472 else:
473 f(k, v)
474
475 ## Deal with a path, if there is one.
476 if path:
477 if me.rparam and me.rparam.name not in kw:
478 kw[me.rparam.name] = path
479 else:
480 raise U.ExpectedError, (404, "Superfluous path elements")
481
482 ## Make sure we saw all of the mandatory parameters.
483 for p in me.params:
484 if p.name not in kw:
485 raise U.ExpectedError, (400, "Missing parameter `%s'" % p.name)
486
487 ## Invoke the subcommand.
488 me.func(**kw)
489
490def subcommand(name, contexts, desc, cls = Subcommand, *args, **kw):
491 """Decorator for defining CGI subcommands."""
492 return SC.subcommand(name, contexts, desc, cls = cls, *args, **kw)
493
494###----- That's all, folks --------------------------------------------------