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//lib/python2.7/site-packages/werkzeug/middleware/shared_data.py

"""
Serve Shared Static Files
=========================

.. autoclass:: SharedDataMiddleware
    :members: is_allowed

:copyright: 2007 Pallets
:license: BSD-3-Clause
"""
import mimetypes
import os
import posixpath
from datetime import datetime
from io import BytesIO
from time import mktime
from time import time
from zlib import adler32

from .._compat import PY2
from .._compat import string_types
from ..filesystem import get_filesystem_encoding
from ..http import http_date
from ..http import is_resource_modified
from ..security import safe_join
from ..wsgi import get_path_info
from ..wsgi import wrap_file

class SharedDataMiddleware(object):

"""A WSGI middleware that provides static content for development
    environments or simple server setups. Usage is quite simple::

import os
        from werkzeug.wsgi import SharedDataMiddleware

app = SharedDataMiddleware(app, {
            '/static': os.path.join(os.path.dirname(__file__), 'static')
        })

The contents of the folder ``./shared`` will now be available on
    ``http://example.com/shared/``.  This is pretty useful during development
    because a standalone media server is not required.  One can also mount
    files on the root folder and still continue to use the application because
    the shared data middleware forwards all unhandled requests to the
    application, even if the requests are below one of the shared folders.

If `pkg_resources` is available you can also tell the middleware to serve
    files from package data::

app = SharedDataMiddleware(app, {
            '/static': ('myapplication', 'static')
        })

This will then serve the ``static`` folder in the `myapplication`
    Python package.

The optional `disallow` parameter can be a list of :func:`~fnmatch.fnmatch`
    rules for files that are not accessible from the web.  If `cache` is set to
    `False` no caching headers are sent.

Currently the middleware does not support non ASCII filenames.  If the
    encoding on the file system happens to be the encoding of the URI it may
    work but this could also be by accident.  We strongly suggest using ASCII
    only file names for static files.

The middleware will guess the mimetype using the Python `mimetype`
    module.  If it's unable to figure out the charset it will fall back
    to `fallback_mimetype`.

.. versionchanged:: 0.5
       The cache timeout is configurable now.

.. versionadded:: 0.6
       The `fallback_mimetype` parameter was added.

:param app: the application to wrap.  If you don't want to wrap an
                application you can pass it :exc:`NotFound`.
    :param exports: a list or dict of exported files and folders.
    :param disallow: a list of :func:`~fnmatch.fnmatch` rules.
    :param fallback_mimetype: the fallback mimetype for unknown files.
    :param cache: enable or disable caching headers.
    :param cache_timeout: the cache timeout in seconds for the headers.
    """

def __init__(
        self,
        app,
        exports,
        disallow=None,
        cache=True,
        cache_timeout=60 * 60 * 12,
        fallback_mimetype="text/plain",
    ):
        self.app = app
        self.exports = []
        self.cache = cache
        self.cache_timeout = cache_timeout

if hasattr(exports, "items"):
            exports = exports.items()

for key, value in exports:
            if isinstance(value, tuple):
                loader = self.get_package_loader(*value)
            elif isinstance(value, string_types):
                if os.path.isfile(value):
                    loader = self.get_file_loader(value)
                else:
                    loader = self.get_directory_loader(value)
            else:
                raise TypeError("unknown def %r" % value)

self.exports.append((key, loader))

if disallow is not None:
            from fnmatch import fnmatch

self.is_allowed = lambda x: not fnmatch(x, disallow)

self.fallback_mimetype = fallback_mimetype

def is_allowed(self, filename):
        """Subclasses can override this method to disallow the access to
        certain files.  However by providing `disallow` in the constructor
        this method is overwritten.
        """
        return True

def _opener(self, filename):
        return lambda: (
            open(filename, "rb"),
            datetime.utcfromtimestamp(os.path.getmtime(filename)),
            int(os.path.getsize(filename)),
        )

def get_file_loader(self, filename):
        return lambda x: (os.path.basename(filename), self._opener(filename))

def get_package_loader(self, package, package_path):
        from pkg_resources import DefaultProvider, ResourceManager, get_provider

loadtime = datetime.utcnow()
        provider = get_provider(package)
        manager = ResourceManager()
        filesystem_bound = isinstance(provider, DefaultProvider)

def loader(path):
            if path is None:
                return None, None

path = safe_join(package_path, path)

if not provider.has_resource(path):
                return None, None

basename = posixpath.basename(path)

if filesystem_bound:
                return (
                    basename,
                    self._opener(provider.get_resource_filename(manager, path)),
                )

s = provider.get_resource_string(manager, path)
            return basename, lambda: (BytesIO(s), loadtime, len(s))

return loader

def get_directory_loader(self, directory):
        def loader(path):
            if path is not None:
                path = safe_join(directory, path)
            else:
                path = directory

if os.path.isfile(path):
                return os.path.basename(path), self._opener(path)

return None, None

return loader

def generate_etag(self, mtime, file_size, real_filename):
        if not isinstance(real_filename, bytes):
            real_filename = real_filename.encode(get_filesystem_encoding())

return "wzsdm-%d-%s-%s" % (
            mktime(mtime.timetuple()),
            file_size,
            adler32(real_filename) & 0xFFFFFFFF,
        )

def __call__(self, environ, start_response):
        path = get_path_info(environ)

if PY2:
            path = path.encode(get_filesystem_encoding())

file_loader = None

for search_path, loader in self.exports:
            if search_path == path:
                real_filename, file_loader = loader(None)

if file_loader is not None:
                    break

if not search_path.endswith("/"):
                search_path += "/"

if path.startswith(search_path):
                real_filename, file_loader = loader(path[len(search_path) :])

if file_loader is not None:
                    break

if file_loader is None or not self.is_allowed(real_filename):
            return self.app(environ, start_response)

guessed_type = mimetypes.guess_type(real_filename)
        mime_type = guessed_type[0] or self.fallback_mimetype
        f, mtime, file_size = file_loader()

headers = [("Date", http_date())]

if self.cache:
            timeout = self.cache_timeout
            etag = self.generate_etag(mtime, file_size, real_filename)
            headers += [
                ("Etag", '"%s"' % etag),
                ("Cache-Control", "max-age=%d, public" % timeout),
            ]

if not is_resource_modified(environ, etag, last_modified=mtime):
                f.close()
                start_response("304 Not Modified", headers)
                return []

headers.append(("Expires", http_date(time() + timeout)))
        else:
            headers.append(("Cache-Control", "public"))

headers.extend(
            (
                ("Content-Type", mime_type),
                ("Content-Length", str(file_size)),
                ("Last-Modified", http_date(mtime)),
            )
        )
        start_response("200 OK", headers)
        return wrap_file(environ, f)