f1260f1f1f
Error handlers may now raise instances of HTTPError and expect them to be converted to a proper HTTP response, as they would be when raised from within a regular resource responder or hook. Also added examples to the README of using the error handler feature.
279 lines
10 KiB
Python
279 lines
10 KiB
Python
"""Defines the API class.
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Copyright 2013 by Rackspace Hosting, Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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"""
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from falcon.request import Request
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from falcon.response import Response
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import falcon.responders
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from falcon.status_codes import HTTP_416
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from falcon import api_helpers as helpers
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from falcon.http_error import HTTPError
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from falcon import DEFAULT_MEDIA_TYPE
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class API(object):
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"""Provides routing and such for building a web service application
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This class is the main entry point into a Falcon-based app. It provides a
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callable WSGI interface and a simple routing engine based on URI templates.
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"""
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__slots__ = ('_after', '_before', '_error_handlers', '_media_type',
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'_routes', '_default_route')
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def __init__(self, media_type=DEFAULT_MEDIA_TYPE, before=None, after=None):
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"""Initialize a new Falcon API instances
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Args:
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media_type: Default media type to use as the value for the
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Content-Type header on responses. (default 'application/json')
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before: A global action hook (or list of hooks) to call before
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each on_* responder, for all resources. Similar to the
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'falcon.before' decorator, but applies to the entire API. When
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more than one action function is given, they will be executed
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in natural order (starting with the first in the list).
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after: A global action hook (or list of hooks) to call after each
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on_* responder, for all resources. Similar to the 'after'
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decorator, but applies to the entire API.
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"""
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self._routes = []
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self._default_route = None
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self._media_type = media_type
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self._before = helpers.prepare_global_hooks(before)
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self._after = helpers.prepare_global_hooks(after)
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self._error_handlers = []
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def __call__(self, env, start_response):
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"""WSGI "app" method
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Makes instances of API callable by any WSGI server. See also PEP 333.
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Args:
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env: A WSGI environment dictionary
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start_response: A WSGI helper method for setting status and headers
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on a response.
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"""
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req = Request(env)
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resp = Response()
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responder, params, na_responder = self._get_responder(
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req.path, req.method)
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try:
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# NOTE(kgriffs): Using an inner try..except in order to
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# address the case when err_handler raises HTTPError.
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#
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# NOTE(kgriffs): Coverage is giving false negatives,
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# so disabled on relevant lines. All paths are tested
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# afaict.
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try:
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responder(req, resp, **params) # pragma: no cover
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except Exception as ex:
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for err_type, err_handler in self._error_handlers:
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if isinstance(ex, err_type):
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err_handler(ex, req, resp, params)
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break # pragma: no cover
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else:
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# PERF(kgriffs): This will propagate HTTPError to
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# the handler below. It makes handling HTTPError
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# less efficient, but that is OK since error cases
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# don't need to be as fast as the happy path, and
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# indeed, should perhaps be slower to create
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# backpressure on clients that are issuing bad
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# requests.
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raise
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except HTTPError as ex:
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resp.status = ex.status
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if ex.headers is not None:
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resp.set_headers(ex.headers)
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if req.client_accepts('application/json'):
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resp.body = ex.json()
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#
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# Set status and headers
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#
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use_body = not helpers.should_ignore_body(resp.status, req.method)
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if use_body:
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helpers.set_content_length(resp)
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body = helpers.get_body(resp)
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else:
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# Default: return an empty body
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body = []
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# Set content type if needed
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use_content_type = (body or
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req.method == 'HEAD' or
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resp.status == HTTP_416)
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if use_content_type:
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media_type = self._media_type
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else:
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media_type = None
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headers = resp._wsgi_headers(media_type)
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# Return the response per the WSGI spec
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start_response(resp.status, headers)
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return body
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def add_route(self, uri_template, resource):
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"""Associate a URI path with a resource
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A resource is an instance of a class that defines various on_*
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"responder" methods, one for each HTTP method the resource
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allows. For example, to support GET, simply define an "on_get"
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responder. If a client requests an unsupported method, Falcon
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will respond with "405 Method not allowed".
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Responders must always define at least two arguments to receive
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request and response objects, respectively. For example:
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def on_post(self, req, resp):
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pass
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In addition, if the route's uri template contains field
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expressions, any responders that desires to receive requests
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for that route must accept arguments named after the respective
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field names defined in the template. For example, given the
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following uri template:
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/das/{thing}
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A PUT request to "/das/code" would be routed to:
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def on_put(self, req, resp, thing):
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pass
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If, on the other hand, the responder had been defined thus:
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def on_put(self, req, resp):
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pass
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Falcon would respond to the client's request with "405 Method
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not allowed." This allows you to define multiple routes to the
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same resource, e.g., in order to support GET for "/widget/1234"
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and POST to "/widgets". In this last example, a POST to
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"/widget/5000" would result in a 405 response.
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Args:
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uri_template: Relative URI template. Currently only Level 1
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templates are supported. See also RFC 6570.
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resource: Object which represents an HTTP/REST "resource". Falcon
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will pass "GET" requests to on_get, "PUT" requests to on_put,
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etc. If any HTTP methods are not supported by your resource,
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simply don't define the corresponding request handlers, and
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Falcon will do the right thing.
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"""
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uri_fields, path_template = helpers.compile_uri_template(uri_template)
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method_map, na_responder = helpers.create_http_method_map(
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resource, uri_fields, self._before, self._after)
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# Insert at the head of the list in case we get duplicate
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# adds (will cause the last one to win).
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self._routes.insert(0, (path_template, method_map, na_responder))
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def set_default_route(self, default_resource):
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"""Route all the unrouted requests to a default resource
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Args:
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default_resource: Object which works like an HTTP/REST resource.
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Falcon will pass "GET" requests to on_get, "PUT" requests to
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on_put, etc. If you want to exclude some HTTP method from the
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default routing, just simply don't define the corresponding
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request handlers.
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"""
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self._default_route = helpers.create_http_method_map(
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default_resource, set(), self._before, self._after)
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def add_error_handler(self, exception, handler):
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"""Adds a handler for a given exception type
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Args:
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exception: Whenever an exception occurs when handling a request
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that is an instance of this exception class, the given handler
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callable will be used to handle the exception.
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handler: Callable that gets called with (ex, req, resp, params)
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when there is a matching exception when handling a request.
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"""
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# Insert at the head of the list in case we get duplicate
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# adds (will cause the last one to win).
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self._error_handlers.insert(0, (exception, handler))
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#----------------------------------------------------------------------------
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# Helpers
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#----------------------------------------------------------------------------
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def _get_responder(self, path, method):
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"""Searches routes for a matching responder
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Args:
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path: URI path to search (without query string)
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method: HTTP method (uppercase) requested
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Returns:
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A 3-member tuple, containing a responder callable, a dict
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containing parsed path fields (if any were specified in
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the matching route's URI template), and a reference to
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the "method not allowed" responder for the resource.
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"""
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for route in self._routes:
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path_template, method_map, na_responder = route
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m = path_template.match(path)
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if m:
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params = m.groupdict()
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try:
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responder = method_map[method]
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except KeyError:
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responder = falcon.responders.bad_request
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break
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else:
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params = {}
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if self._default_route is not None:
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method_map, na_responder = self._default_route
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try:
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responder = method_map[method]
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except KeyError:
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responder = falcon.responders.bad_request
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else:
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responder = falcon.responders.path_not_found
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na_responder = falcon.responders.create_method_not_allowed([])
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return (responder, params, na_responder)
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