/src/mailman/rest/wsgiapp.py

# Copyright (C) 2010-2016 by the Free Software Foundation, Inc.
#
# This file is part of GNU Mailman.
#
# GNU Mailman is free software: you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# GNU Mailman is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along with
# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.

"""Basic WSGI Application object for REST server."""

import re
import logging

from base64 import b64decode
from falcon import API, HTTPUnauthorized
from falcon.routing import create_http_method_map
from mailman import public
from mailman.config import config
from mailman.database.transaction import transactional
from mailman.rest.root import Root
from wsgiref.simple_server import (
    WSGIRequestHandler, WSGIServer, make_server as wsgi_server)


log = logging.getLogger('mailman.http')

MISSING = object()
SLASH = '/'
EMPTYSTRING = ''
REALM = 'mailman3-rest'


class AdminWSGIServer(WSGIServer):
    """Server class that integrates error handling with our log files."""

    def handle_error(self, request, client_address):
        # Interpose base class method so that the exception gets printed to
        # our log file rather than stderr.
        log.exception('REST server exception during request from %s',
                      client_address)


class StderrLogger:
    def __init__(self):
        self._buffer = []

    def write(self, message):
        self._buffer.append(message)

    def flush(self):
        self._buffer.insert(0, 'REST request handler error:\n')
        log.error(EMPTYSTRING.join(self._buffer))
        self._buffer = []


class AdminWebServiceWSGIRequestHandler(WSGIRequestHandler):
    """Handler class which just logs output to the right place."""

    def log_message(self, format, *args):
        """See `BaseHTTPRequestHandler`."""
        log.info('%s - - %s', self.address_string(), format % args)

    def get_stderr(self):
        # Return a fake stderr object that will actually write its output to
        # the log file.
        return StderrLogger()


class Middleware:
    """Falcon middleware object for Mailman's REST API.

    This does two things.  It sets the API version on the resource
    object, and it verifies that the proper authentication has been
    performed.
    """
    def process_resource(self, request, response, resource, params):
        # Set this attribute on the resource right before it is dispatched to.
        # This can be used by the resource to provide different responses
        # based on the API version, and for path_to() to provide an API
        # version-specific path.
        resource.api = params.pop('api')
        # Check the authorization credentials.
        authorized = False
        if request.auth is not None and request.auth.startswith('Basic '):
            # b64decode() returns bytes, but we require a str.
            credentials = b64decode(request.auth[6:]).decode('utf-8')
            username, password = credentials.split(':', 1)
            if (username == config.webservice.admin_user and
                    password == config.webservice.admin_pass):
                authorized = True
        if not authorized:
            # Not authorized.
            raise HTTPUnauthorized(
                '401 Unauthorized',
                'REST API authorization failed',
                challenges=['Basic realm=Mailman3'])


class ObjectRouter:
    def __init__(self, root):
        self._root = root

    def add_route(self, uri_template, method_map, resource):
        # We don't need this method for object-based routing.
        raise NotImplementedError

    def find(self, uri):
        segments = uri.split(SLASH)
        # Since the path is always rooted at /, skip the first segment, which
        # will always be the empty string.
        segments.pop(0)
        this_segment = segments.pop(0)
        resource = self._root
        context = {}
        while True:
            # See if any of the resource's child links match the next segment.
            for name in dir(resource):
                if name.startswith('__') and name.endswith('__'):
                    continue
                attribute = getattr(resource, name, MISSING)
                assert attribute is not MISSING, name
                matcher = getattr(attribute, '__matcher__', MISSING)
                if matcher is MISSING:
                    continue
                result = None
                if isinstance(matcher, str):
                    # Is the matcher string a regular expression or plain
                    # string?  If it starts with a caret, it's a regexp.
                    if matcher.startswith('^'):
                        cre = re.compile(matcher)
                        # Search against the entire remaining path.
                        tmp_segments = segments[:]
                        tmp_segments.insert(0, this_segment)
                        remaining_path = SLASH.join(tmp_segments)
                        mo = cre.match(remaining_path)
                        if mo:
                            result = attribute(
                                context, segments, **mo.groupdict())
                    elif matcher == this_segment:
                        result = attribute(context, segments)
                else:
                    # The matcher is a callable.  It returns None if it
                    # doesn't match, and if it does, it returns a 3-tuple
                    # containing the positional arguments, the keyword
                    # arguments, and the remaining segments.  The attribute is
                    # then called with these arguments.  Note that the matcher
                    # wants to see the full remaining path components, which
                    # includes the current hop.
                    tmp_segments = segments[:]
                    tmp_segments.insert(0, this_segment)
                    matcher_result = matcher(tmp_segments)
                    if matcher_result is not None:
                        positional, keyword, segments = matcher_result
                        result = attribute(
                            context, segments, *positional, **keyword)
                # The attribute could return a 2-tuple giving the resource and
                # remaining path segments, or it could just return the result.
                # Of course, if the result is None, then the matcher did not
                # match.
                if result is None:
                    continue
                elif isinstance(result, tuple):
                    resource, segments = result
                else:
                    resource = result
                # The method could have truncated the remaining segments,
                # meaning, it's consumed all the path segments, or this is the
                # last path segment.  In that case the resource we're left at
                # is the responder.
                if len(segments) == 0:
                    # We're at the end of the path, so the root must be the
                    # responder.
                    method_map = create_http_method_map(resource)
                    return resource, method_map, context
                this_segment = segments.pop(0)
                break
            else:
                # None of the attributes matched this path component, so the
                # response is a 404.
                return None, None, None


class RootedAPI(API):
    def __init__(self, root, *args, **kws):
        super().__init__(
            *args,
            middleware=Middleware(),
            router=ObjectRouter(root),
            **kws)
        # Let Falcon parse the form data into the request object's
        # .params attribute.
        self.req_options.auto_parse_form_urlencoded = True

    # Override the base class implementation to wrap a transactional
    # handler around the call, so that the current transaction is
    # committed if no errors occur, and aborted otherwise.
    @transactional
    def __call__(self, environ, start_response):
        return super().__call__(environ, start_response)


@public
def make_application():
    """Create the WSGI application.

    Use this if you want to integrate Mailman's REST server with your own WSGI
    server.
    """
    return RootedAPI(Root())


@public
def make_server():
    """Create the Mailman REST server.

    Use this if you just want to run Mailman's wsgiref-based REST server.
    """
    host = config.webservice.hostname
    port = int(config.webservice.port)
    server = wsgi_server(
        host, port, make_application(),
        server_class=AdminWSGIServer,
        handler_class=AdminWebServiceWSGIRequestHandler)
    return server