core.py

from inspect import Arguments
from itertools import chain, tee
from mimetypes import guess_type, add_type
from os.path import splitext
import logging
import operator
import sys
import types

import six

from webob import (Request as WebObRequest, Response as WebObResponse, exc,
                   acceptparse)
from webob.multidict import NestedMultiDict

from .compat import urlparse, izip
from .jsonify import encode as dumps
from .secure import handle_security
from .templating import RendererFactory
from .routing import lookup_controller, NonCanonicalPath
from .util import _cfg, encode_if_needed, getargspec
from .middleware.recursive import ForwardRequestException

if six.PY3:
    from .compat import is_bound_method as ismethod
else:
    from inspect import ismethod

# make sure that json is defined in mimetypes
add_type('application/json', '.json', True)

state = None
logger = logging.getLogger(__name__)


class RoutingState(object):

    def __init__(self, request, response, app, hooks=[], controller=None,
                 arguments=None):
        self.request = request
        self.response = response
        self.app = app
        self.hooks = hooks
        self.controller = controller
        self.arguments = arguments


class Request(WebObRequest):

    def __getattribute__(self, name):
        try:
            return WebObRequest.__getattribute__(self, name)
        except UnicodeDecodeError as e:
            logger.exception(e)
            abort(400)


class Response(WebObResponse):
    pass


def proxy(key):
    class ObjectProxy(object):

        explanation_ = AttributeError(
            "`pecan.state` is not bound to a context-local context.\n"
            "Ensure that you're accessing `pecan.request` or `pecan.response` "
            "from within the context of a WSGI `__call__` and that "
            "`use_context_locals` = True."
        )

        def __getattr__(self, attr):
            try:
                obj = getattr(state, key)
            except AttributeError:
                raise self.explanation_
            return getattr(obj, attr)

        def __setattr__(self, attr, value):
            obj = getattr(state, key)
            return setattr(obj, attr, value)

        def __delattr__(self, attr):
            obj = getattr(state, key)
            return delattr(obj, attr)

        def __dir__(self):
            obj = getattr(state, key)
            return dir(obj)

    return ObjectProxy()


request = proxy('request')
response = proxy('response')


def override_template(template, content_type=None):
    '''
    Call within a controller to override the template that is used in
    your response.

    :param template: a valid path to a template file, just as you would specify
                     in an ``@expose``.
    :param content_type: a valid MIME type to use for the response.func_closure
    '''

    request.pecan['override_template'] = template
    if content_type:
        request.pecan['override_content_type'] = content_type


def abort(status_code, detail='', headers=None, comment=None, **kw):
    '''
    Raise an HTTP status code, as specified. Useful for returning status
    codes like 401 Unauthorized or 403 Forbidden.

    :param status_code: The HTTP status code as an integer.
    :param detail: The message to send along, as a string.
    :param headers: A dictionary of headers to send along with the response.
    :param comment: A comment to include in the response.
    '''

    # If there is a traceback, we need to catch it for a re-raise
    try:
        _, _, traceback = sys.exc_info()
        webob_exception = exc.status_map[status_code](
            detail=detail,
            headers=headers,
            comment=comment,
            **kw
        )

        if six.PY3:
            raise webob_exception.with_traceback(traceback)
        else:
            # Using exec to avoid python 3 parsers from crashing
            exec('raise webob_exception, None, traceback')
    finally:
        # Per the suggestion of the Python docs, delete the traceback object
        del traceback


def redirect(location=None, internal=False, code=None, headers={},
             add_slash=False, request=None):
    '''
    Perform a redirect, either internal or external. An internal redirect
    performs the redirect server-side, while the external redirect utilizes
    an HTTP 302 status code.

    :param location: The HTTP location to redirect to.
    :param internal: A boolean indicating whether the redirect should be
                     internal.
    :param code: The HTTP status code to use for the redirect. Defaults to 302.
    :param headers: Any HTTP headers to send with the response, as a
                    dictionary.
    :param request: The :class:`pecan.Request` instance to use.
    '''
    request = request or state.request

    if add_slash:
        if location is None:
            split_url = list(urlparse.urlsplit(request.url))
            new_proto = request.environ.get(
                'HTTP_X_FORWARDED_PROTO', split_url[0]
            )
            split_url[0] = new_proto
        else:
            split_url = urlparse.urlsplit(location)

        split_url[2] = split_url[2].rstrip('/') + '/'
        location = urlparse.urlunsplit(split_url)

    if not headers:
        headers = {}
    if internal:
        if code is not None:
            raise ValueError('Cannot specify a code for internal redirects')
        request.environ['pecan.recursive.context'] = request.context
        raise ForwardRequestException(location)
    if code is None:
        code = 302
    raise exc.status_map[code](location=location, headers=headers)


def render(template, namespace, app=None):
    '''
    Render the specified template using the Pecan rendering framework
    with the specified template namespace as a dictionary. Useful in a
    controller where you have no template specified in the ``@expose``.

    :param template: The path to your template, as you would specify in
                     ``@expose``.
    :param namespace: The namespace to use for rendering the template, as a
                      dictionary.
    :param app: The instance of :class:`pecan.Pecan` to use
    '''
    app = app or state.app
    return app.render(template, namespace)


def load_app(config, **kwargs):
    '''
    Used to load a ``Pecan`` application and its environment based on passed
    configuration.

    :param config: Can be a dictionary containing configuration, a string which
                    represents a (relative) configuration filename

    returns a pecan.Pecan object
    '''
    from .configuration import _runtime_conf, set_config
    set_config(config, overwrite=True)

    for package_name in getattr(_runtime_conf.app, 'modules', []):
        module = __import__(package_name, fromlist=['app'])
        if hasattr(module, 'app') and hasattr(module.app, 'setup_app'):
            app = module.app.setup_app(_runtime_conf, **kwargs)
            app.config = _runtime_conf
            return app
    raise RuntimeError(
        'No app.setup_app found in any of the configured app.modules'
    )


class PecanBase(object):

    SIMPLEST_CONTENT_TYPES = (
        ['text/html'],
        ['text/plain']
    )

    def __init__(self, root, default_renderer='mako',
                 template_path='templates', hooks=lambda: [],
                 custom_renderers={}, extra_template_vars={},
                 force_canonical=True, guess_content_type_from_ext=True,
                 context_local_factory=None, request_cls=Request,
                 response_cls=Response, **kw):
        if isinstance(root, six.string_types):
            root = self.__translate_root__(root)

        self.root = root
        self.request_cls = request_cls
        self.response_cls = response_cls
        self.renderers = RendererFactory(custom_renderers, extra_template_vars)
        self.default_renderer = default_renderer

        # pre-sort these so we don't have to do it per-request
        if six.callable(hooks):
            hooks = hooks()

        self.hooks = list(sorted(
            hooks,
            key=operator.attrgetter('priority')
        ))
        self.template_path = template_path
        self.force_canonical = force_canonical
        self.guess_content_type_from_ext = guess_content_type_from_ext

    def __translate_root__(self, item):
        '''
        Creates a root controller instance from a string root, e.g.,

        > __translate_root__("myproject.controllers.RootController")
        myproject.controllers.RootController()

        :param item: The string to the item
        '''

        if '.' in item:
            parts = item.split('.')
            name = '.'.join(parts[:-1])
            fromlist = parts[-1:]

            module = __import__(name, fromlist=fromlist)
            kallable = getattr(module, parts[-1])
            msg = "%s does not represent a callable class or function."
            if not six.callable(kallable):
                raise TypeError(msg % item)
            return kallable()

        raise ImportError('No item named %s' % item)

    def route(self, req, node, path):
        '''
        Looks up a controller from a node based upon the specified path.

        :param node: The node, such as a root controller object.
        :param path: The path to look up on this node.
        '''
        path = path.split('/')[1:]
        try:
            node, remainder = lookup_controller(node, path, req)
            return node, remainder
        except NonCanonicalPath as e:
            if self.force_canonical and \
                    not _cfg(e.controller).get('accept_noncanonical', False):
                if req.method == 'POST':
                    raise RuntimeError(
                        "You have POSTed to a URL '%s' which "
                        "requires a slash. Most browsers will not maintain "
                        "POST data when redirected. Please update your code "
                        "to POST to '%s/' or set force_canonical to False" %
                        (req.pecan['routing_path'],
                            req.pecan['routing_path'])
                    )
                redirect(code=302, add_slash=True, request=req)
            return e.controller, e.remainder

    def determine_hooks(self, controller=None):
        '''
        Determines the hooks to be run, in which order.

        :param controller: If specified, includes hooks for a specific
                           controller.
        '''

        controller_hooks = []
        if controller:
            controller_hooks = _cfg(controller).get('hooks', [])
            if controller_hooks:
                return list(
                    sorted(
                        chain(controller_hooks, self.hooks),
                        key=operator.attrgetter('priority')
                    )
                )
        return self.hooks

    def handle_hooks(self, hooks, hook_type, *args):
        '''
        Processes hooks of the specified type.

        :param hook_type: The type of hook, including ``before``, ``after``,
                          ``on_error``, and ``on_route``.
        :param \*args: Arguments to pass to the hooks.
        '''
        if hook_type not in ['before', 'on_route']:
            hooks = reversed(hooks)

        for hook in hooks:
            result = getattr(hook, hook_type)(*args)
            # on_error hooks can choose to return a Response, which will
            # be used instead of the standard error pages.
            if hook_type == 'on_error' and isinstance(result, WebObResponse):
                return result

    def get_args(self, state, all_params, remainder, argspec, im_self):
        '''
        Determines the arguments for a controller based upon parameters
        passed the argument specification for the controller.
        '''
        args = []
        varargs = []
        kwargs = dict()
        valid_args = argspec.args[:]
        if ismethod(state.controller) or im_self:
            valid_args.pop(0)  # pop off `self`
        pecan_state = state.request.pecan

        remainder = [x for x in remainder if x]

        if im_self is not None:
            args.append(im_self)

        # grab the routing args from nested REST controllers
        if 'routing_args' in pecan_state:
            remainder = pecan_state['routing_args'] + list(remainder)
            del pecan_state['routing_args']

        # handle positional arguments
        if valid_args and remainder:
            args.extend(remainder[:len(valid_args)])
            remainder = remainder[len(valid_args):]
            valid_args = valid_args[len(args):]

        # handle wildcard arguments
        if [i for i in remainder if i]:
            if not argspec[1]:
                abort(404)
            varargs.extend(remainder)

        # get the default positional arguments
        if argspec[3]:
            defaults = dict(izip(argspec[0][-len(argspec[3]):], argspec[3]))
        else:
            defaults = dict()

        # handle positional GET/POST params
        for name in valid_args:
            if name in all_params:
                args.append(all_params.pop(name))
            elif name in defaults:
                args.append(defaults[name])
            else:
                break

        # handle wildcard GET/POST params
        if argspec[2]:
            for name, value in six.iteritems(all_params):
                if name not in argspec[0]:
                    kwargs[encode_if_needed(name)] = value

        return args, varargs, kwargs

    def render(self, template, namespace):
        if template == 'json':
            renderer = self.renderers.get('json', self.template_path)
        elif ':' in template:
            renderer_name, template = template.split(':', 1)
            renderer = self.renderers.get(
                renderer_name,
                self.template_path
            )
            if renderer is None:
                raise RuntimeError(
                    'support for "%s" was not found; ' % renderer_name +
                    'supported template engines are %s' % self.renderers.keys()
                )
        else:
            renderer = self.renderers.get(
                self.default_renderer,
                self.template_path
            )
        if namespace is None:
            return None
        return renderer.render(template, namespace)

    def find_controller(self, state):
        '''
        The main request handler for Pecan applications.
        '''
        # get a sorted list of hooks, by priority (no controller hooks yet)
        req = state.request
        pecan_state = req.pecan

        # store the routing path for the current application to allow hooks to
        # modify it
        pecan_state['routing_path'] = path = req.path_info

        # handle "on_route" hooks
        self.handle_hooks(self.hooks, 'on_route', state)

        # lookup the controller, respecting content-type as requested
        # by the file extension on the URI
        pecan_state['extension'] = None

        # attempt to guess the content type based on the file extension
        if self.guess_content_type_from_ext \
                and not pecan_state['content_type'] \
                and '.' in path:
            _, extension = splitext(path.rstrip('/'))

            # preface with a letter to ensure compat for 2.5
            potential_type = guess_type('x' + extension)[0]

            if extension and potential_type is not None:
                path = ''.join(path.rsplit(extension, 1))
                pecan_state['extension'] = extension
                pecan_state['content_type'] = potential_type

        controller, remainder = self.route(req, self.root, path)
        cfg = _cfg(controller)

        if cfg.get('generic_handler'):
            raise exc.HTTPNotFound

        # handle generic controllers
        im_self = None
        if cfg.get('generic'):
            im_self = six.get_method_self(controller)
            handlers = cfg['generic_handlers']
            controller = handlers.get(req.method, handlers['DEFAULT'])
            handle_security(controller, im_self)
            cfg = _cfg(controller)

        # add the controller to the state so that hooks can use it
        state.controller = controller

        # if unsure ask the controller for the default content type
        content_types = cfg.get('content_types', {})
        if not pecan_state['content_type']:
            # attempt to find a best match based on accept headers (if they
            # exist)
            accept = getattr(req.accept, 'header_value', '*/*')
            if accept == '*/*' or (
                    accept.startswith('text/html,') and
                    list(content_types.keys()) in self.SIMPLEST_CONTENT_TYPES):
                pecan_state['content_type'] = cfg.get(
                    'content_type',
                    'text/html'
                )
            else:
                best_default = acceptparse.MIMEAccept(
                    accept
                ).best_match(
                    content_types.keys()
                )

                if best_default is None:
                    msg = "Controller '%s' defined does not support " + \
                          "content_type '%s'. Supported type(s): %s"
                    logger.error(
                        msg % (
                            controller.__name__,
                            pecan_state['content_type'],
                            content_types.keys()
                        )
                    )
                    raise exc.HTTPNotAcceptable()

                pecan_state['content_type'] = best_default
        elif cfg.get('content_type') is not None and \
                pecan_state['content_type'] not in content_types:

            msg = "Controller '%s' defined does not support content_type " + \
                  "'%s'. Supported type(s): %s"
            logger.error(
                msg % (
                    controller.__name__,
                    pecan_state['content_type'],
                    content_types.keys()
                )
            )
            raise exc.HTTPNotFound

        # fetch any parameters
        if req.method == 'GET':
            params = req.GET
        elif req.content_type in ('application/json',
                                  'application/javascript'):
            try:
                if not isinstance(req.json, dict):
                    raise TypeError('%s is not a dict' % req.json)
                params = NestedMultiDict(req.GET, req.json)
            except (TypeError, ValueError):
                params = req.params
        else:
            params = req.params

        # fetch the arguments for the controller
        args, varargs, kwargs = self.get_args(
            state,
            params.mixed(),
            remainder,
            cfg['argspec'],
            im_self
        )
        state.arguments = Arguments(args, varargs, kwargs)

        # handle "before" hooks
        self.handle_hooks(self.determine_hooks(controller), 'before', state)

        return controller, args + varargs, kwargs

    def invoke_controller(self, controller, args, kwargs, state):
        '''
        The main request handler for Pecan applications.
        '''
        cfg = _cfg(controller)
        content_types = cfg.get('content_types', {})
        req = state.request
        resp = state.response
        pecan_state = req.pecan

        # If a keyword is supplied via HTTP GET or POST arguments, but the
        # function signature does not allow it, just drop it (rather than
        # generating a TypeError).
        argspec = getargspec(controller)
        keys = kwargs.keys()
        for key in keys:
            if key not in argspec.args and not argspec.keywords:
                kwargs.pop(key)

        # get the result from the controller
        result = controller(*args, **kwargs)

        # a controller can return the response object which means they've taken
        # care of filling it out
        if result is response:
            return
        elif isinstance(result, WebObResponse):
            state.response = result
            return

        raw_namespace = result

        # pull the template out based upon content type and handle overrides
        template = content_types.get(pecan_state['content_type'])

        # check if for controller override of template
        template = pecan_state.get('override_template', template)
        if template is None and cfg['explicit_content_type'] is False:
            if self.default_renderer == 'json':
                template = 'json'

        pecan_state['content_type'] = pecan_state.get(
            'override_content_type',
            pecan_state['content_type']
        )

        # if there is a template, render it
        if template:
            if template == 'json':
                pecan_state['content_type'] = 'application/json'
            result = self.render(template, result)

        # If we are in a test request put the namespace where it can be
        # accessed directly
        if req.environ.get('paste.testing'):
            testing_variables = req.environ['paste.testing_variables']
            testing_variables['namespace'] = raw_namespace
            testing_variables['template_name'] = template
            testing_variables['controller_output'] = result

        # set the body content
        if result and isinstance(result, six.text_type):
            resp.text = result
        elif result:
            resp.body = result

        if pecan_state['content_type']:
            # set the content type
            resp.content_type = pecan_state['content_type']

    def _handle_empty_response_body(self, state):
        # Enforce HTTP 204 for responses which contain no body
        if state.response.status_int == 200:
            # If the response is a generator...
            if isinstance(state.response.app_iter, types.GeneratorType):
                # Split the generator into two so we can peek at one of them
                # and determine if there is any response body content
                a, b = tee(state.response.app_iter)
                try:
                    next(a)
                except StopIteration:
                    # If we hit StopIteration, the body is empty
                    state.response.status = 204
                finally:
                    state.response.app_iter = b
            else:
                text = None
                if state.response.charset:
                    # `response.text` cannot be accessed without a valid
                    # charset (because we don't know which encoding to use)
                    try:
                        text = state.response.text
                    except UnicodeDecodeError:
                        # If a valid charset is not specified, don't bother
                        # trying to guess it (because there's obviously
                        # content, so we know this shouldn't be a 204)
                        pass
                if not any((state.response.body, text)):
                    state.response.status = 204

        if state.response.status_int in (204, 304):
            state.response.content_type = None

    def __call__(self, environ, start_response):
        '''
        Implements the WSGI specification for Pecan applications, utilizing
        ``WebOb``.
        '''

        # create the request and response object
        req = self.request_cls(environ)
        resp = self.response_cls()
        state = RoutingState(req, resp, self)
        environ['pecan.locals'] = {
            'request': req,
            'response': resp
        }
        controller = None

        # track internal redirects
        internal_redirect = False

        # handle the request
        try:
            # add context and environment to the request
            req.context = environ.get('pecan.recursive.context', {})
            req.pecan = dict(content_type=None)

            controller, args, kwargs = self.find_controller(state)
            self.invoke_controller(controller, args, kwargs, state)
        except Exception as e:
            # if this is an HTTP Exception, set it as the response
            if isinstance(e, exc.HTTPException):
                # if the client asked for JSON, do our best to provide it
                best_match = acceptparse.MIMEAccept(
                    getattr(req.accept, 'header_value', '*/*')
                ).best_match(('text/plain', 'text/html', 'application/json'))
                state.response = e
                if best_match == 'application/json':
                    json_body = dumps({
                        'code': e.status_int,
                        'title': e.title,
                        'description': e.detail
                    })
                    if isinstance(json_body, six.text_type):
                        e.text = json_body
                    else:
                        e.body = json_body
                    state.response.content_type = best_match
                environ['pecan.original_exception'] = e

            # note if this is an internal redirect
            internal_redirect = isinstance(e, ForwardRequestException)

            # if this is not an internal redirect, run error hooks
            on_error_result = None
            if not internal_redirect:
                on_error_result = self.handle_hooks(
                    self.determine_hooks(state.controller),
                    'on_error',
                    state,
                    e
                )

            # if the on_error handler returned a Response, use it.
            if isinstance(on_error_result, WebObResponse):
                state.response = on_error_result
            else:
                if not isinstance(e, exc.HTTPException):
                    raise

            # if this is an HTTP 405, attempt to specify an Allow header
            if isinstance(e, exc.HTTPMethodNotAllowed) and controller:
                allowed_methods = _cfg(controller).get('allowed_methods', [])
                if allowed_methods:
                    state.response.allow = sorted(allowed_methods)
        finally:
            # if this is not an internal redirect, run "after" hooks
            if not internal_redirect:
                self.handle_hooks(
                    self.determine_hooks(state.controller),
                    'after',
                    state
                )

        self._handle_empty_response_body(state)

        # get the response
        return state.response(environ, start_response)


class ExplicitPecan(PecanBase):

    def get_args(self, state, all_params, remainder, argspec, im_self):
        # When comparing the argspec of the method to GET/POST params,
        # ignore the implicit (req, resp) at the beginning of the function
        # signature
        if hasattr(state.controller, '__self__'):
            _repr = '.'.join((
                state.controller.__self__.__class__.__module__,
                state.controller.__self__.__class__.__name__,
                state.controller.__name__
            ))
        else:
            _repr = '.'.join((
                state.controller.__module__,
                state.controller.__name__
            ))

        signature_error = TypeError(
            'When `use_context_locals` is `False`, pecan passes an explicit '
            'reference to the request and response as the first two arguments '
            'to the controller.\nChange the `%s` signature to accept exactly '
            '2 initial arguments (req, resp)' % _repr
        )
        try:
            positional = argspec.args[:]
            positional.pop(1)  # req
            positional.pop(1)  # resp
            argspec = argspec._replace(args=positional)
        except IndexError:
            raise signature_error

        args, varargs, kwargs = super(ExplicitPecan, self).get_args(
            state, all_params, remainder, argspec, im_self
        )

        if ismethod(state.controller):
            args = [state.request, state.response] + args
        else:
            # generic controllers have an explicit self *first*
            # (because they're decorated functions, not instance methods)
            args[1:1] = [state.request, state.response]
        return args, varargs, kwargs


class Pecan(PecanBase):
    '''
    Pecan application object. Generally created using ``pecan.make_app``,
    rather than being created manually.

    Creates a Pecan application instance, which is a WSGI application.

    :param root: A string representing a root controller object (e.g.,
                "myapp.controller.root.RootController")
    :param default_renderer: The default template rendering engine to use.
                             Defaults to mako.
    :param template_path: A relative file system path (from the project root)
                          where template files live.  Defaults to 'templates'.
    :param hooks: A callable which returns a list of
                  :class:`pecan.hooks.PecanHook`
    :param custom_renderers: Custom renderer objects, as a dictionary keyed
                             by engine name.
    :param extra_template_vars: Any variables to inject into the template
                                namespace automatically.
    :param force_canonical: A boolean indicating if this project should
                            require canonical URLs.
    :param guess_content_type_from_ext: A boolean indicating if this project
                            should use the extension in the URL for guessing
                            the content type to return.
    :param use_context_locals: When `True`, `pecan.request` and
                               `pecan.response` will be available as
                               thread-local references.
    :param request_cls: Can be used to specify a custom `pecan.request` object.
                        Defaults to `pecan.Request`.
    :param response_cls: Can be used to specify a custom `pecan.response`
                         object.  Defaults to `pecan.Response`.
    '''

    def __new__(cls, *args, **kw):
        if kw.get('use_context_locals') is False:
            self = super(Pecan, cls).__new__(ExplicitPecan, *args, **kw)
            self.__init__(*args, **kw)
            return self
        return super(Pecan, cls).__new__(cls)

    def __init__(self, *args, **kw):
        self.init_context_local(kw.get('context_local_factory'))
        super(Pecan, self).__init__(*args, **kw)

    def __call__(self, environ, start_response):
        try:
            state.hooks = []
            state.app = self
            state.controller = None
            state.arguments = None
            return super(Pecan, self).__call__(environ, start_response)
        finally:
            del state.hooks
            del state.request
            del state.response
            del state.controller
            del state.arguments
            del state.app

    def init_context_local(self, local_factory):
        global state
        if local_factory is None:
            from threading import local as local_factory
        state = local_factory()

    def find_controller(self, _state):
        state.request = _state.request
        state.response = _state.response
        controller, args, kw = super(Pecan, self).find_controller(_state)
        state.controller = controller
        state.arguments = _state.arguments
        return controller, args, kw

    def handle_hooks(self, hooks, *args, **kw):
        state.hooks = hooks
        return super(Pecan, self).handle_hooks(hooks, *args, **kw)