Easing the creation of REST API services in Twisted
txrestapi makes it easier to create Twisted REST API services. Normally, one would create Resource subclasses defining each segment of a path; this is cubersome to implement and results in output that isn’t very readable. txrestapi provides an APIResource class allowing complex mapping of path to callback (a la Django) with a readable decorator.
Basic URL callback registration
First, let’s create a bare API service:
>>> from txrestapi.resource import APIResource >>> api = APIResource()
and a web server to serve it:
>>> from twisted.web.server import Site >>> from twisted.internet import reactor >>> site = Site(api, timeout=None)
and a function to make it easy for us to make requests (only for doctest purposes; normally you would of course use reactor.listenTCP(site, 8080)):
>>> from twisted.web.server import Request >>> class FakeChannel(object): ... transport = None >>> def makeRequest(method, path): ... req = Request(FakeChannel(), None) ... req.prepath = req.postpath = None ... req.method = method; req.path = path ... resource = site.getChildWithDefault(path, req) ... return resource.render(req)
We can now register callbacks for paths we care about. We can provide different callbacks for different methods; they must accept request as the first argument:
>>> def get_callback(request): return 'GET callback' >>> api.register('GET', '^/path/to/method', get_callback) >>> def post_callback(request): return 'POST callback' >>> api.register('POST', '^/path/to/method', post_callback)
Then, when we make a call, the request is routed to the proper callback:
>>> print makeRequest('GET', '/path/to/method') GET callback >>> print makeRequest('POST', '/path/to/method') POST callback
We can register multiple callbacks for different requests; the first one that matches wins:
>>> def default_callback(request): ... return 'Default callback' >>> api.register('GET', '^/.*$', default_callback) # Matches everything >>> print makeRequest('GET', '/path/to/method') GET callback >>> print makeRequest('GET', '/path/to/different/method') Default callback
Our default callback, however, will only match GET requests. For a true default callback, we can either register callbacks for each method individually, or we can use ALL:
>>> api.register('ALL', '^/.*$', default_callback) >>> print makeRequest('PUT', '/path/to/method') Default callback >>> print makeRequest('DELETE', '/path/to/method') Default callback >>> print makeRequest('GET', '/path/to/method') GET callback
Let’s unregister all references to the default callback so it doesn’t interfere with later tests (default callbacks should, of course, always be registered last, so they don’t get called before other callbacks):
Since callbacks accept request, they have access to POST data or query arguments, but we can also pull arguments out of the URL by using named groups in the regular expression (similar to Django). These will be passed into the callback as keyword arguments:
>>> def get_info(request, id): ... return 'Information for id %s' % id >>> api.register('GET', '/(?P<id>[^/]+)/info$', get_info) >>> print makeRequest('GET', '/someid/info') Information for id someid
Bear in mind all arguments will come in as strings, so code should be accordingly defensive.
Registration via the register() method is somewhat awkward, so decorators are provided making it much more straightforward.
>>> from txrestapi.methods import GET, POST, PUT, ALL >>> class MyResource(APIResource): ... ... @GET('^/(?P<id>[^/]+)/info') ... def get_info(self, request, id): ... return 'Info for id %s' % id ... ... @PUT('^/(?P<id>[^/]+)/update') ... @POST('^/(?P<id>[^/]+)/update') ... def set_info(self, request, id): ... return "Setting info for id %s" % id ... ... @ALL('^/') ... def default_view(self, request): ... return "I match any URL"
Again, registrations occur top to bottom, so methods should be written from most specific to least. Also notice that one can use the decorator syntax as one would expect to register a method as the target for two URLs
>>> site = Site(MyResource(), timeout=None) >>> print makeRequest('GET', '/anid/info') Info for id anid >>> print makeRequest('PUT', '/anid/update') Setting info for id anid >>> print makeRequest('POST', '/anid/update') Setting info for id anid >>> print makeRequest('DELETE', '/anid/delete') I match any URL
Callback return values
You can return Resource objects from a callback if you wish, allowing you to have APIs that send you to other kinds of resources, or even other APIs. Normally, however, you’ll most likely want to return strings, which will be wrapped in a Resource object for convenience.
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