hgweb: refactor 304 handling code

We had generic code in wsgirequest for handling HTTP 304 responses.
We also had a special case for it in the catch all exception handler
in the WSGI application.

We only ever raise 304 in one place. So, we don't need to treat it
specially in the catch all exception handler.

But it is useful to validate behavior of 304 responses. We port the
code that sends a 304 to use the new response API. We then move the
code for screening 304 sanity into the new response API.

As part of doing so, we discovered that we would send
Content-Length: 0. This is not allowed. So, we fix our response code
to not emit that header for empty response bodies.

Differential Revision: https://phab.mercurial-scm.org/D2794

mercurial/hgweb/hgweb_mod.py

@@ -1,456 +1,455 b''
 # hgweb/hgweb_mod.py - Web interface for a repository.
 #
 # Copyright 21 May 2005 - (c) 2005 Jake Edge <[e-mail]>
 # Copyright 2005-2007 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import contextlib
 import os
 
 from .common import (
     ErrorResponse,
     HTTP_BAD_REQUEST,
     HTTP_NOT_FOUND,
-    HTTP_NOT_MODIFIED,
     HTTP_OK,
     HTTP_SERVER_ERROR,
     cspvalues,
     permhooks,
 )
 
 from .. import (
     encoding,
     error,
     formatter,
     hg,
     hook,
     profiling,
     pycompat,
     repoview,
     templatefilters,
     templater,
     ui as uimod,
     util,
     wireprotoserver,
 )
 
 from . import (
     request as requestmod,
     webcommands,
     webutil,
     wsgicgi,
 )
 
 archivespecs = util.sortdict((
     ('zip', ('application/zip', 'zip', '.zip', None)),
     ('gz', ('application/x-gzip', 'tgz', '.tar.gz', None)),
     ('bz2', ('application/x-bzip2', 'tbz2', '.tar.bz2', None)),
 ))
 
 def getstyle(req, configfn, templatepath):
     styles = (
         req.qsparams.get('style', None),
         configfn('web', 'style'),
         'paper',
     )
     return styles, templater.stylemap(styles, templatepath)
 
 def makebreadcrumb(url, prefix=''):
     '''Return a 'URL breadcrumb' list
 
     A 'URL breadcrumb' is a list of URL-name pairs,
     corresponding to each of the path items on a URL.
     This can be used to create path navigation entries.
     '''
     if url.endswith('/'):
         url = url[:-1]
     if prefix:
         url = '/' + prefix + url
     relpath = url
     if relpath.startswith('/'):
         relpath = relpath[1:]
 
     breadcrumb = []
     urlel = url
     pathitems = [''] + relpath.split('/')
     for pathel in reversed(pathitems):
         if not pathel or not urlel:
             break
         breadcrumb.append({'url': urlel, 'name': pathel})
         urlel = os.path.dirname(urlel)
     return reversed(breadcrumb)
 
 class requestcontext(object):
     """Holds state/context for an individual request.
 
     Servers can be multi-threaded. Holding state on the WSGI application
     is prone to race conditions. Instances of this class exist to hold
     mutable and race-free state for requests.
     """
     def __init__(self, app, repo, req, res):
         self.repo = repo
         self.reponame = app.reponame
         self.req = req
         self.res = res
 
         self.archivespecs = archivespecs
 
         self.maxchanges = self.configint('web', 'maxchanges')
         self.stripecount = self.configint('web', 'stripes')
         self.maxshortchanges = self.configint('web', 'maxshortchanges')
         self.maxfiles = self.configint('web', 'maxfiles')
         self.allowpull = self.configbool('web', 'allow-pull')
 
         # we use untrusted=False to prevent a repo owner from using
         # web.templates in .hg/hgrc to get access to any file readable
         # by the user running the CGI script
         self.templatepath = self.config('web', 'templates', untrusted=False)
 
         # This object is more expensive to build than simple config values.
         # It is shared across requests. The app will replace the object
         # if it is updated. Since this is a reference and nothing should
         # modify the underlying object, it should be constant for the lifetime
         # of the request.
         self.websubtable = app.websubtable
 
         self.csp, self.nonce = cspvalues(self.repo.ui)
 
     # Trust the settings from the .hg/hgrc files by default.
     def config(self, section, name, default=uimod._unset, untrusted=True):
         return self.repo.ui.config(section, name, default,
                                    untrusted=untrusted)
 
     def configbool(self, section, name, default=uimod._unset, untrusted=True):
         return self.repo.ui.configbool(section, name, default,
                                        untrusted=untrusted)
 
     def configint(self, section, name, default=uimod._unset, untrusted=True):
         return self.repo.ui.configint(section, name, default,
                                       untrusted=untrusted)
 
     def configlist(self, section, name, default=uimod._unset, untrusted=True):
         return self.repo.ui.configlist(section, name, default,
                                        untrusted=untrusted)
 
     def archivelist(self, nodeid):
         allowed = self.configlist('web', 'allow_archive')
         for typ, spec in self.archivespecs.iteritems():
             if typ in allowed or self.configbool('web', 'allow%s' % typ):
                 yield {'type': typ, 'extension': spec[2], 'node': nodeid}
 
     def templater(self, req):
         # determine scheme, port and server name
         # this is needed to create absolute urls
         logourl = self.config('web', 'logourl')
         logoimg = self.config('web', 'logoimg')
         staticurl = (self.config('web', 'staticurl')
                      or req.apppath + '/static/')
         if not staticurl.endswith('/'):
             staticurl += '/'
 
         # some functions for the templater
 
         def motd(**map):
             yield self.config('web', 'motd')
 
         # figure out which style to use
 
         vars = {}
         styles, (style, mapfile) = getstyle(req, self.config,
                                             self.templatepath)
         if style == styles[0]:
             vars['style'] = style
 
         sessionvars = webutil.sessionvars(vars, '?')
 
         if not self.reponame:
             self.reponame = (self.config('web', 'name', '')
                              or req.reponame
                              or req.apppath
                              or self.repo.root)
 
         def websubfilter(text):
             return templatefilters.websub(text, self.websubtable)
 
         # create the templater
         # TODO: export all keywords: defaults = templatekw.keywords.copy()
         defaults = {
             'url': req.apppath + '/',
             'logourl': logourl,
             'logoimg': logoimg,
             'staticurl': staticurl,
             'urlbase': req.advertisedbaseurl,
             'repo': self.reponame,
             'encoding': encoding.encoding,
             'motd': motd,
             'sessionvars': sessionvars,
             'pathdef': makebreadcrumb(req.apppath),
             'style': style,
             'nonce': self.nonce,
         }
         tres = formatter.templateresources(self.repo.ui, self.repo)
         tmpl = templater.templater.frommapfile(mapfile,
                                                filters={'websub': websubfilter},
                                                defaults=defaults,
                                                resources=tres)
         return tmpl
 
 
 class hgweb(object):
     """HTTP server for individual repositories.
 
     Instances of this class serve HTTP responses for a particular
     repository.
 
     Instances are typically used as WSGI applications.
 
     Some servers are multi-threaded. On these servers, there may
     be multiple active threads inside __call__.
     """
     def __init__(self, repo, name=None, baseui=None):
         if isinstance(repo, str):
             if baseui:
                 u = baseui.copy()
             else:
                 u = uimod.ui.load()
             r = hg.repository(u, repo)
         else:
             # we trust caller to give us a private copy
             r = repo
 
         r.ui.setconfig('ui', 'report_untrusted', 'off', 'hgweb')
         r.baseui.setconfig('ui', 'report_untrusted', 'off', 'hgweb')
         r.ui.setconfig('ui', 'nontty', 'true', 'hgweb')
         r.baseui.setconfig('ui', 'nontty', 'true', 'hgweb')
         # resolve file patterns relative to repo root
         r.ui.setconfig('ui', 'forcecwd', r.root, 'hgweb')
         r.baseui.setconfig('ui', 'forcecwd', r.root, 'hgweb')
         # displaying bundling progress bar while serving feel wrong and may
         # break some wsgi implementation.
         r.ui.setconfig('progress', 'disable', 'true', 'hgweb')
         r.baseui.setconfig('progress', 'disable', 'true', 'hgweb')
         self._repos = [hg.cachedlocalrepo(self._webifyrepo(r))]
         self._lastrepo = self._repos[0]
         hook.redirect(True)
         self.reponame = name
 
     def _webifyrepo(self, repo):
         repo = getwebview(repo)
         self.websubtable = webutil.getwebsubs(repo)
         return repo
 
     @contextlib.contextmanager
     def _obtainrepo(self):
         """Obtain a repo unique to the caller.
 
         Internally we maintain a stack of cachedlocalrepo instances
         to be handed out. If one is available, we pop it and return it,
         ensuring it is up to date in the process. If one is not available,
         we clone the most recently used repo instance and return it.
 
         It is currently possible for the stack to grow without bounds
         if the server allows infinite threads. However, servers should
         have a thread limit, thus establishing our limit.
         """
         if self._repos:
             cached = self._repos.pop()
             r, created = cached.fetch()
         else:
             cached = self._lastrepo.copy()
             r, created = cached.fetch()
         if created:
             r = self._webifyrepo(r)
 
         self._lastrepo = cached
         self.mtime = cached.mtime
         try:
             yield r
         finally:
             self._repos.append(cached)
 
     def run(self):
         """Start a server from CGI environment.
 
         Modern servers should be using WSGI and should avoid this
         method, if possible.
         """
         if not encoding.environ.get('GATEWAY_INTERFACE',
                                     '').startswith("CGI/1."):
             raise RuntimeError("This function is only intended to be "
                                "called while running as a CGI script.")
         wsgicgi.launch(self)
 
     def __call__(self, env, respond):
         """Run the WSGI application.
 
         This may be called by multiple threads.
         """
         req = requestmod.wsgirequest(env, respond)
         return self.run_wsgi(req)
 
     def run_wsgi(self, wsgireq):
         """Internal method to run the WSGI application.
 
         This is typically only called by Mercurial. External consumers
         should be using instances of this class as the WSGI application.
         """
         with self._obtainrepo() as repo:
             profile = repo.ui.configbool('profiling', 'enabled')
             with profiling.profile(repo.ui, enabled=profile):
                 for r in self._runwsgi(wsgireq, repo):
                     yield r
 
     def _runwsgi(self, wsgireq, repo):
         req = wsgireq.req
         res = wsgireq.res
         rctx = requestcontext(self, repo, req, res)
 
         # This state is global across all threads.
         encoding.encoding = rctx.config('web', 'encoding')
         rctx.repo.ui.environ = wsgireq.env
 
         if rctx.csp:
             # hgwebdir may have added CSP header. Since we generate our own,
             # replace it.
             wsgireq.headers = [h for h in wsgireq.headers
                                if h[0] != 'Content-Security-Policy']
             wsgireq.headers.append(('Content-Security-Policy', rctx.csp))
             res.headers['Content-Security-Policy'] = rctx.csp
 
         handled = wireprotoserver.handlewsgirequest(
             rctx, req, res, self.check_perm)
         if handled:
             return res.sendresponse()
 
         if req.havepathinfo:
             query = req.dispatchpath
         else:
             query = req.querystring.partition('&')[0].partition(';')[0]
 
         # translate user-visible url structure to internal structure
 
         args = query.split('/', 2)
         if 'cmd' not in req.qsparams and args and args[0]:
             cmd = args.pop(0)
             style = cmd.rfind('-')
             if style != -1:
                 req.qsparams['style'] = cmd[:style]
                 cmd = cmd[style + 1:]
 
             # avoid accepting e.g. style parameter as command
             if util.safehasattr(webcommands, cmd):
                 req.qsparams['cmd'] = cmd
 
             if cmd == 'static':
                 req.qsparams['file'] = '/'.join(args)
             else:
                 if args and args[0]:
                     node = args.pop(0).replace('%2F', '/')
                     req.qsparams['node'] = node
                 if args:
                     if 'file' in req.qsparams:
                         del req.qsparams['file']
                     for a in args:
                         req.qsparams.add('file', a)
 
             ua = req.headers.get('User-Agent', '')
             if cmd == 'rev' and 'mercurial' in ua:
                 req.qsparams['style'] = 'raw'
 
             if cmd == 'archive':
                 fn = req.qsparams['node']
                 for type_, spec in rctx.archivespecs.iteritems():
                     ext = spec[2]
                     if fn.endswith(ext):
                         req.qsparams['node'] = fn[:-len(ext)]
                         req.qsparams['type'] = type_
         else:
             cmd = req.qsparams.get('cmd', '')
 
         # process the web interface request
 
         try:
             tmpl = rctx.templater(req)
             ctype = tmpl('mimetype', encoding=encoding.encoding)
             ctype = templater.stringify(ctype)
 
             # check read permissions non-static content
             if cmd != 'static':
                 self.check_perm(rctx, req, None)
 
             if cmd == '':
                 req.qsparams['cmd'] = tmpl.cache['default']
                 cmd = req.qsparams['cmd']
 
             # Don't enable caching if using a CSP nonce because then it wouldn't
             # be a nonce.
             if rctx.configbool('web', 'cache') and not rctx.nonce:
                 tag = 'W/"%d"' % self.mtime
                 if req.headers.get('If-None-Match') == tag:
-                    raise ErrorResponse(HTTP_NOT_MODIFIED)
+                    res.status = '304 Not Modified'
+                    # Response body not allowed on 304.
+                    res.setbodybytes('')
+                    return res.sendresponse()
 
                 wsgireq.headers.append((r'ETag', pycompat.sysstr(tag)))
                 res.headers['ETag'] = tag
 
             if cmd not in webcommands.__all__:
                 msg = 'no such method: %s' % cmd
                 raise ErrorResponse(HTTP_BAD_REQUEST, msg)
             else:
                 # Set some globals appropriate for web handlers. Commands can
                 # override easily enough.
                 res.status = '200 Script output follows'
                 res.headers['Content-Type'] = ctype
                 content = getattr(webcommands, cmd)(rctx, wsgireq, tmpl)
 
                 if content is res:
                     return res.sendresponse()
                 elif content is True:
                     return []
                 else:
                     wsgireq.respond(HTTP_OK, ctype)
                     return content
 
         except (error.LookupError, error.RepoLookupError) as err:
             wsgireq.respond(HTTP_NOT_FOUND, ctype)
             msg = pycompat.bytestr(err)
             if (util.safehasattr(err, 'name') and
                 not isinstance(err,  error.ManifestLookupError)):
                 msg = 'revision not found: %s' % err.name
             return tmpl('error', error=msg)
         except (error.RepoError, error.RevlogError) as inst:
             wsgireq.respond(HTTP_SERVER_ERROR, ctype)
             return tmpl('error', error=pycompat.bytestr(inst))
         except ErrorResponse as inst:
             wsgireq.respond(inst, ctype)
-            if inst.code == HTTP_NOT_MODIFIED:
-                # Not allowed to return a body on a 304
-                return ['']
             return tmpl('error', error=pycompat.bytestr(inst))
 
     def check_perm(self, rctx, req, op):
         for permhook in permhooks:
             permhook(rctx, req, op)
 
 def getwebview(repo):
     """The 'web.view' config controls changeset filter to hgweb. Possible
     values are ``served``, ``visible`` and ``all``. Default is ``served``.
     The ``served`` filter only shows changesets that can be pulled from the
     hgweb instance.  The``visible`` filter includes secret changesets but
     still excludes "hidden" one.
 
     See the repoview module for details.
 
     The option has been around undocumented since Mercurial 2.5, but no
     user ever asked about it. So we better keep it undocumented for now."""
     # experimental config: web.view
     viewconfig = repo.ui.config('web', 'view', untrusted=True)
     if viewconfig == 'all':
         return repo.unfiltered()
     elif viewconfig in repoview.filtertable:
         return repo.filtered(viewconfig)
     else:
         return repo.filtered('served')

mercurial/hgweb/request.py

@@ -1,627 +1,651 b''
 # hgweb/request.py - An http request from either CGI or the standalone server.
 #
 # Copyright 21 May 2005 - (c) 2005 Jake Edge <[e-mail]>
 # Copyright 2005, 2006 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import errno
 import socket
 import wsgiref.headers as wsgiheaders
 #import wsgiref.validate
 
 from .common import (
     ErrorResponse,
-    HTTP_NOT_MODIFIED,
     statusmessage,
 )
 
 from ..thirdparty import (
     attr,
 )
 from .. import (
     error,
     pycompat,
     util,
 )
 
 class multidict(object):
     """A dict like object that can store multiple values for a key.
 
     Used to store parsed request parameters.
 
     This is inspired by WebOb's class of the same name.
     """
     def __init__(self):
         # Stores (key, value) 2-tuples. This isn't the most efficient. But we
         # don't rely on parameters that much, so it shouldn't be a perf issue.
         # we can always add dict for fast lookups.
         self._items = []
 
     def __getitem__(self, key):
         """Returns the last set value for a key."""
         for k, v in reversed(self._items):
             if k == key:
                 return v
 
         raise KeyError(key)
 
     def __setitem__(self, key, value):
         """Replace a values for a key with a new value."""
         try:
             del self[key]
         except KeyError:
             pass
 
         self._items.append((key, value))
 
     def __delitem__(self, key):
         """Delete all values for a key."""
         oldlen = len(self._items)
 
         self._items[:] = [(k, v) for k, v in self._items if k != key]
 
         if oldlen == len(self._items):
             raise KeyError(key)
 
     def __contains__(self, key):
         return any(k == key for k, v in self._items)
 
     def __len__(self):
         return len(self._items)
 
     def get(self, key, default=None):
         try:
             return self.__getitem__(key)
         except KeyError:
             return default
 
     def add(self, key, value):
         """Add a new value for a key. Does not replace existing values."""
         self._items.append((key, value))
 
     def getall(self, key):
         """Obtains all values for a key."""
         return [v for k, v in self._items if k == key]
 
     def getone(self, key):
         """Obtain a single value for a key.
 
         Raises KeyError if key not defined or it has multiple values set.
         """
         vals = self.getall(key)
 
         if not vals:
             raise KeyError(key)
 
         if len(vals) > 1:
             raise KeyError('multiple values for %r' % key)
 
         return vals[0]
 
     def asdictoflists(self):
         d = {}
         for k, v in self._items:
             if k in d:
                 d[k].append(v)
             else:
                 d[k] = [v]
 
         return d
 
 @attr.s(frozen=True)
 class parsedrequest(object):
     """Represents a parsed WSGI request.
 
     Contains both parsed parameters as well as a handle on the input stream.
     """
 
     # Request method.
     method = attr.ib()
     # Full URL for this request.
     url = attr.ib()
     # URL without any path components. Just <proto>://<host><port>.
     baseurl = attr.ib()
     # Advertised URL. Like ``url`` and ``baseurl`` but uses SERVER_NAME instead
     # of HTTP: Host header for hostname. This is likely what clients used.
     advertisedurl = attr.ib()
     advertisedbaseurl = attr.ib()
     # URL scheme (part before ``://``). e.g. ``http`` or ``https``.
     urlscheme = attr.ib()
     # Value of REMOTE_USER, if set, or None.
     remoteuser = attr.ib()
     # Value of REMOTE_HOST, if set, or None.
     remotehost = attr.ib()
     # WSGI application path.
     apppath = attr.ib()
     # List of path parts to be used for dispatch.
     dispatchparts = attr.ib()
     # URL path component (no query string) used for dispatch.
     dispatchpath = attr.ib()
     # Whether there is a path component to this request. This can be true
     # when ``dispatchpath`` is empty due to REPO_NAME muckery.
     havepathinfo = attr.ib()
     # The name of the repository being accessed.
     reponame = attr.ib()
     # Raw query string (part after "?" in URL).
     querystring = attr.ib()
     # multidict of query string parameters.
     qsparams = attr.ib()
     # wsgiref.headers.Headers instance. Operates like a dict with case
     # insensitive keys.
     headers = attr.ib()
     # Request body input stream.
     bodyfh = attr.ib()
 
 def parserequestfromenv(env, bodyfh):
     """Parse URL components from environment variables.
 
     WSGI defines request attributes via environment variables. This function
     parses the environment variables into a data structure.
     """
     # PEP-0333 defines the WSGI spec and is a useful reference for this code.
 
     # We first validate that the incoming object conforms with the WSGI spec.
     # We only want to be dealing with spec-conforming WSGI implementations.
     # TODO enable this once we fix internal violations.
     #wsgiref.validate.check_environ(env)
 
     # PEP-0333 states that environment keys and values are native strings
     # (bytes on Python 2 and str on Python 3). The code points for the Unicode
     # strings on Python 3 must be between \00000-\000FF. We deal with bytes
     # in Mercurial, so mass convert string keys and values to bytes.
     if pycompat.ispy3:
         env = {k.encode('latin-1'): v for k, v in env.iteritems()}
         env = {k: v.encode('latin-1') if isinstance(v, str) else v
                for k, v in env.iteritems()}
 
     # https://www.python.org/dev/peps/pep-0333/#environ-variables defines
     # the environment variables.
     # https://www.python.org/dev/peps/pep-0333/#url-reconstruction defines
     # how URLs are reconstructed.
     fullurl = env['wsgi.url_scheme'] + '://'
     advertisedfullurl = fullurl
 
     def addport(s):
         if env['wsgi.url_scheme'] == 'https':
             if env['SERVER_PORT'] != '443':
                 s += ':' + env['SERVER_PORT']
         else:
             if env['SERVER_PORT'] != '80':
                 s += ':' + env['SERVER_PORT']
 
         return s
 
     if env.get('HTTP_HOST'):
         fullurl += env['HTTP_HOST']
     else:
         fullurl += env['SERVER_NAME']
         fullurl = addport(fullurl)
 
     advertisedfullurl += env['SERVER_NAME']
     advertisedfullurl = addport(advertisedfullurl)
 
     baseurl = fullurl
     advertisedbaseurl = advertisedfullurl
 
     fullurl += util.urlreq.quote(env.get('SCRIPT_NAME', ''))
     advertisedfullurl += util.urlreq.quote(env.get('SCRIPT_NAME', ''))
     fullurl += util.urlreq.quote(env.get('PATH_INFO', ''))
     advertisedfullurl += util.urlreq.quote(env.get('PATH_INFO', ''))
 
     if env.get('QUERY_STRING'):
         fullurl += '?' + env['QUERY_STRING']
         advertisedfullurl += '?' + env['QUERY_STRING']
 
     # When dispatching requests, we look at the URL components (PATH_INFO
     # and QUERY_STRING) after the application root (SCRIPT_NAME). But hgwebdir
     # has the concept of "virtual" repositories. This is defined via REPO_NAME.
     # If REPO_NAME is defined, we append it to SCRIPT_NAME to form a new app
     # root. We also exclude its path components from PATH_INFO when resolving
     # the dispatch path.
 
     apppath = env['SCRIPT_NAME']
 
     if env.get('REPO_NAME'):
         if not apppath.endswith('/'):
             apppath += '/'
 
         apppath += env.get('REPO_NAME')
 
     if 'PATH_INFO' in env:
         dispatchparts = env['PATH_INFO'].strip('/').split('/')
 
         # Strip out repo parts.
         repoparts = env.get('REPO_NAME', '').split('/')
         if dispatchparts[:len(repoparts)] == repoparts:
             dispatchparts = dispatchparts[len(repoparts):]
     else:
         dispatchparts = []
 
     dispatchpath = '/'.join(dispatchparts)
 
     querystring = env.get('QUERY_STRING', '')
 
     # We store as a list so we have ordering information. We also store as
     # a dict to facilitate fast lookup.
     qsparams = multidict()
     for k, v in util.urlreq.parseqsl(querystring, keep_blank_values=True):
         qsparams.add(k, v)
 
     # HTTP_* keys contain HTTP request headers. The Headers structure should
     # perform case normalization for us. We just rewrite underscore to dash
     # so keys match what likely went over the wire.
     headers = []
     for k, v in env.iteritems():
         if k.startswith('HTTP_'):
             headers.append((k[len('HTTP_'):].replace('_', '-'), v))
 
     headers = wsgiheaders.Headers(headers)
 
     # This is kind of a lie because the HTTP header wasn't explicitly
     # sent. But for all intents and purposes it should be OK to lie about
     # this, since a consumer will either either value to determine how many
     # bytes are available to read.
     if 'CONTENT_LENGTH' in env and 'HTTP_CONTENT_LENGTH' not in env:
         headers['Content-Length'] = env['CONTENT_LENGTH']
 
     # TODO do this once we remove wsgirequest.inp, otherwise we could have
     # multiple readers from the underlying input stream.
     #bodyfh = env['wsgi.input']
     #if 'Content-Length' in headers:
     #    bodyfh = util.cappedreader(bodyfh, int(headers['Content-Length']))
 
     return parsedrequest(method=env['REQUEST_METHOD'],
                          url=fullurl, baseurl=baseurl,
                          advertisedurl=advertisedfullurl,
                          advertisedbaseurl=advertisedbaseurl,
                          urlscheme=env['wsgi.url_scheme'],
                          remoteuser=env.get('REMOTE_USER'),
                          remotehost=env.get('REMOTE_HOST'),
                          apppath=apppath,
                          dispatchparts=dispatchparts, dispatchpath=dispatchpath,
                          havepathinfo='PATH_INFO' in env,
                          reponame=env.get('REPO_NAME'),
                          querystring=querystring,
                          qsparams=qsparams,
                          headers=headers,
                          bodyfh=bodyfh)
 
 class offsettrackingwriter(object):
     """A file object like object that is append only and tracks write count.
 
     Instances are bound to a callable. This callable is called with data
     whenever a ``write()`` is attempted.
 
     Instances track the amount of written data so they can answer ``tell()``
     requests.
 
     The intent of this class is to wrap the ``write()`` function returned by
     a WSGI ``start_response()`` function. Since ``write()`` is a callable and
     not a file object, it doesn't implement other file object methods.
     """
     def __init__(self, writefn):
         self._write = writefn
         self._offset = 0
 
     def write(self, s):
         res = self._write(s)
         # Some Python objects don't report the number of bytes written.
         if res is None:
             self._offset += len(s)
         else:
             self._offset += res
 
     def flush(self):
         pass
 
     def tell(self):
         return self._offset
 
 class wsgiresponse(object):
     """Represents a response to a WSGI request.
 
     A response consists of a status line, headers, and a body.
 
     Consumers must populate the ``status`` and ``headers`` fields and
     make a call to a ``setbody*()`` method before the response can be
     issued.
 
     When it is time to start sending the response over the wire,
     ``sendresponse()`` is called. It handles emitting the header portion
     of the response message. It then yields chunks of body data to be
     written to the peer. Typically, the WSGI application itself calls
     and returns the value from ``sendresponse()``.
     """
 
     def __init__(self, req, startresponse):
         """Create an empty response tied to a specific request.
 
         ``req`` is a ``parsedrequest``. ``startresponse`` is the
         ``start_response`` function passed to the WSGI application.
         """
         self._req = req
         self._startresponse = startresponse
 
         self.status = None
         self.headers = wsgiheaders.Headers([])
 
         self._bodybytes = None
         self._bodygen = None
         self._bodywillwrite = False
         self._started = False
         self._bodywritefn = None
 
     def _verifybody(self):
         if (self._bodybytes is not None or self._bodygen is not None
             or self._bodywillwrite):
             raise error.ProgrammingError('cannot define body multiple times')
 
     def setbodybytes(self, b):
-        """Define the response body as static bytes."""
+        """Define the response body as static bytes.
+
+        The empty string signals that there is no response body.
+        """
         self._verifybody()
         self._bodybytes = b
         self.headers['Content-Length'] = '%d' % len(b)
 
     def setbodygen(self, gen):
         """Define the response body as a generator of bytes."""
         self._verifybody()
         self._bodygen = gen
 
     def setbodywillwrite(self):
         """Signal an intent to use write() to emit the response body.
 
         **This is the least preferred way to send a body.**
 
         It is preferred for WSGI applications to emit a generator of chunks
         constituting the response body. However, some consumers can't emit
         data this way. So, WSGI provides a way to obtain a ``write(data)``
         function that can be used to synchronously perform an unbuffered
         write.
 
         Calling this function signals an intent to produce the body in this
         manner.
         """
         self._verifybody()
         self._bodywillwrite = True
 
     def sendresponse(self):
         """Send the generated response to the client.
 
         Before this is called, ``status`` must be set and one of
         ``setbodybytes()`` or ``setbodygen()`` must be called.
 
         Calling this method multiple times is not allowed.
         """
         if self._started:
             raise error.ProgrammingError('sendresponse() called multiple times')
 
         self._started = True
 
         if not self.status:
             raise error.ProgrammingError('status line not defined')
 
         if (self._bodybytes is None and self._bodygen is None
             and not self._bodywillwrite):
             raise error.ProgrammingError('response body not defined')
 
+        # RFC 7232 Section 4.1 states that a 304 MUST generate one of
+        # {Cache-Control, Content-Location, Date, ETag, Expires, Vary}
+        # and SHOULD NOT generate other headers unless they could be used
+        # to guide cache updates. Furthermore, RFC 7230 Section 3.3.2
+        # states that no response body can be issued. Content-Length can
+        # be sent. But if it is present, it should be the size of the response
+        # that wasn't transferred.
+        if self.status.startswith('304 '):
+            # setbodybytes('') will set C-L to 0. This doesn't conform with the
+            # spec. So remove it.
+            if self.headers.get('Content-Length') == '0':
+                del self.headers['Content-Length']
+
+            # Strictly speaking, this is too strict. But until it causes
+            # problems, let's be strict.
+            badheaders = {k for k in self.headers.keys()
+                          if k.lower() not in ('date', 'etag', 'expires',
+                                               'cache-control',
+                                               'content-location',
+                                               'vary')}
+            if badheaders:
+                raise error.ProgrammingError(
+                    'illegal header on 304 response: %s' %
+                    ', '.join(sorted(badheaders)))
+
+            if self._bodygen is not None or self._bodywillwrite:
+                raise error.ProgrammingError("must use setbodybytes('') with "
+                                             "304 responses")
+
         # Various HTTP clients (notably httplib) won't read the HTTP response
         # until the HTTP request has been sent in full. If servers (us) send a
         # response before the HTTP request has been fully sent, the connection
         # may deadlock because neither end is reading.
         #
         # We work around this by "draining" the request data before
         # sending any response in some conditions.
         drain = False
         close = False
 
         # If the client sent Expect: 100-continue, we assume it is smart enough
         # to deal with the server sending a response before reading the request.
         # (httplib doesn't do this.)
         if self._req.headers.get('Expect', '').lower() == '100-continue':
             pass
         # Only tend to request methods that have bodies. Strictly speaking,
         # we should sniff for a body. But this is fine for our existing
         # WSGI applications.
         elif self._req.method not in ('POST', 'PUT'):
             pass
         else:
             # If we don't know how much data to read, there's no guarantee
             # that we can drain the request responsibly. The WSGI
             # specification only says that servers *should* ensure the
             # input stream doesn't overrun the actual request. So there's
             # no guarantee that reading until EOF won't corrupt the stream
             # state.
             if not isinstance(self._req.bodyfh, util.cappedreader):
                 close = True
             else:
                 # We /could/ only drain certain HTTP response codes. But 200 and
                 # non-200 wire protocol responses both require draining. Since
                 # we have a capped reader in place for all situations where we
                 # drain, it is safe to read from that stream. We'll either do
                 # a drain or no-op if we're already at EOF.
                 drain = True
 
         if close:
             self.headers['Connection'] = 'Close'
 
         if drain:
             assert isinstance(self._req.bodyfh, util.cappedreader)
             while True:
                 chunk = self._req.bodyfh.read(32768)
                 if not chunk:
                     break
 
         write = self._startresponse(pycompat.sysstr(self.status),
                                     self.headers.items())
 
         if self._bodybytes:
             yield self._bodybytes
         elif self._bodygen:
             for chunk in self._bodygen:
                 yield chunk
         elif self._bodywillwrite:
             self._bodywritefn = write
         else:
             error.ProgrammingError('do not know how to send body')
 
     def getbodyfile(self):
         """Obtain a file object like object representing the response body.
 
         For this to work, you must call ``setbodywillwrite()`` and then
         ``sendresponse()`` first. ``sendresponse()`` is a generator and the
         function won't run to completion unless the generator is advanced. The
         generator yields not items. The easiest way to consume it is with
         ``list(res.sendresponse())``, which should resolve to an empty list -
         ``[]``.
         """
         if not self._bodywillwrite:
             raise error.ProgrammingError('must call setbodywillwrite() first')
 
         if not self._started:
             raise error.ProgrammingError('must call sendresponse() first; did '
                                          'you remember to consume it since it '
                                          'is a generator?')
 
         assert self._bodywritefn
         return offsettrackingwriter(self._bodywritefn)
 
 class wsgirequest(object):
     """Higher-level API for a WSGI request.
 
     WSGI applications are invoked with 2 arguments. They are used to
     instantiate instances of this class, which provides higher-level APIs
     for obtaining request parameters, writing HTTP output, etc.
     """
     def __init__(self, wsgienv, start_response):
         version = wsgienv[r'wsgi.version']
         if (version < (1, 0)) or (version >= (2, 0)):
             raise RuntimeError("Unknown and unsupported WSGI version %d.%d"
                                % version)
 
         inp = wsgienv[r'wsgi.input']
 
         if r'HTTP_CONTENT_LENGTH' in wsgienv:
             inp = util.cappedreader(inp, int(wsgienv[r'HTTP_CONTENT_LENGTH']))
         elif r'CONTENT_LENGTH' in wsgienv:
             inp = util.cappedreader(inp, int(wsgienv[r'CONTENT_LENGTH']))
 
         self.err = wsgienv[r'wsgi.errors']
         self.threaded = wsgienv[r'wsgi.multithread']
         self.multiprocess = wsgienv[r'wsgi.multiprocess']
         self.run_once = wsgienv[r'wsgi.run_once']
         self.env = wsgienv
         self.req = parserequestfromenv(wsgienv, inp)
         self.res = wsgiresponse(self.req, start_response)
         self._start_response = start_response
         self.server_write = None
         self.headers = []
 
     def respond(self, status, type, filename=None, body=None):
         if not isinstance(type, str):
             type = pycompat.sysstr(type)
         if self._start_response is not None:
             self.headers.append((r'Content-Type', type))
             if filename:
                 filename = (filename.rpartition('/')[-1]
                             .replace('\\', '\\\\').replace('"', '\\"'))
                 self.headers.append(('Content-Disposition',
                                      'inline; filename="%s"' % filename))
             if body is not None:
                 self.headers.append((r'Content-Length', str(len(body))))
 
             for k, v in self.headers:
                 if not isinstance(v, str):
                     raise TypeError('header value must be string: %r' % (v,))
 
             if isinstance(status, ErrorResponse):
                 self.headers.extend(status.headers)
-                if status.code == HTTP_NOT_MODIFIED:
-                    # RFC 2616 Section 10.3.5: 304 Not Modified has cases where
-                    # it MUST NOT include any headers other than these and no
-                    # body
-                    self.headers = [(k, v) for (k, v) in self.headers if
-                                    k in ('Date', 'ETag', 'Expires',
-                                          'Cache-Control', 'Vary')]
                 status = statusmessage(status.code, pycompat.bytestr(status))
             elif status == 200:
                 status = '200 Script output follows'
             elif isinstance(status, int):
                 status = statusmessage(status)
 
             # Various HTTP clients (notably httplib) won't read the HTTP
             # response until the HTTP request has been sent in full. If servers
             # (us) send a response before the HTTP request has been fully sent,
             # the connection may deadlock because neither end is reading.
             #
             # We work around this by "draining" the request data before
             # sending any response in some conditions.
             drain = False
             close = False
 
             # If the client sent Expect: 100-continue, we assume it is smart
             # enough to deal with the server sending a response before reading
             # the request. (httplib doesn't do this.)
             if self.env.get(r'HTTP_EXPECT', r'').lower() == r'100-continue':
                 pass
             # Only tend to request methods that have bodies. Strictly speaking,
             # we should sniff for a body. But this is fine for our existing
             # WSGI applications.
             elif self.env[r'REQUEST_METHOD'] not in (r'POST', r'PUT'):
                 pass
             else:
                 # If we don't know how much data to read, there's no guarantee
                 # that we can drain the request responsibly. The WSGI
                 # specification only says that servers *should* ensure the
                 # input stream doesn't overrun the actual request. So there's
                 # no guarantee that reading until EOF won't corrupt the stream
                 # state.
                 if not isinstance(self.req.bodyfh, util.cappedreader):
                     close = True
                 else:
                     # We /could/ only drain certain HTTP response codes. But 200
                     # and non-200 wire protocol responses both require draining.
                     # Since we have a capped reader in place for all situations
                     # where we drain, it is safe to read from that stream. We'll
                     # either do a drain or no-op if we're already at EOF.
                     drain = True
 
             if close:
                 self.headers.append((r'Connection', r'Close'))
 
             if drain:
                 assert isinstance(self.req.bodyfh, util.cappedreader)
                 while True:
                     chunk = self.req.bodyfh.read(32768)
                     if not chunk:
                         break
 
             self.server_write = self._start_response(
                 pycompat.sysstr(status), self.headers)
             self._start_response = None
             self.headers = []
         if body is not None:
             self.write(body)
             self.server_write = None
 
     def write(self, thing):
         if thing:
             try:
                 self.server_write(thing)
             except socket.error as inst:
                 if inst[0] != errno.ECONNRESET:
                     raise
 
     def flush(self):
         return None
 
 def wsgiapplication(app_maker):
     '''For compatibility with old CGI scripts. A plain hgweb() or hgwebdir()
     can and should now be used as a WSGI application.'''
     application = app_maker()
     def run_wsgi(env, respond):
         return application(env, respond)
     return run_wsgi