Twisted Web serves python objects that implement the interface IResource.
HTTPChannel instances to parse the HTTP request, and begin the object lookup process. They contain the root Resource, the resource which represents the URL / on the site.IResource interface describes the methods a Resource object must implement in order to participate in the object publishing process.Site objects serve as the glue between a port to listen for HTTP requests on, and a root Resource object.
When using mktap web --path /foo/bar/baz, a Site object is created with a root Resource that serves files out of the given path.
You can also create a Site instance by hand, passing it a
Resource object which will serve as the root of the site:
from twisted.web import server, resource
from twisted.internet import reactor
class Simple(resource.Resource):
isLeaf = True
def render_GET(self, request):
return "<html>Hello, world!</html>"
site = server.Site(Simple())
reactor.listenTCP(8080, site)
reactor.run()
Resource objects represent a single URL segment of a site. During URL parsing, getChild is called on the current Resource to produce the next Resource object.
When the leaf Resource is reached, either because there were no more URL segments or a Resource had isLeaf set to True, the leaf Resource is rendered by calling render(request). See Resource Rendering
below for more about this.
During the Resource location process, the URL segments which have already been processed and those which have not yet been processed are available in request.prepath and request.postpath.
A Resource can know where it is in the URL tree by looking at request.prepath, a list of URL segment strings.
A Resource can know which path segments will be processed after it by looking at request.postpath.
If the URL ends in a slash, for example http://example.com/foo/bar/, the final URL segment will be an empty string. Resources can thus know if they were requested with or without a final slash.
Here is a simple Resource object:
from twisted.web.resource import Resource
class Hello(Resource):
def getChild(self, name, request):
if name == '':
return self
return Resource.getChild(
self, name, request)
def render_GET(self, request):
return """<html>
Hello, world! I am located at %r.
</html>""" % (request.prepath)
resource = Hello()
Resources can be arranged in trees using putChild. putChild puts a Resource instance into another Resource instance, making it available at the given path segment name:
root = Hello()
root.putChild('fred', Hello())
root.putChild('bob', Hello())
If this root resource is served as the root of a Site instance, the following URLs will all be valid:
http://example.com/http://example.com/fredhttp://example.com/bobhttp://example.com/fred/http://example.com/bob/Files with the extension .rpy are python scripts which, when placed in a directory served by Twisted Web, will be executed when visited through the web.
An .rpy script must define a variable, resource, which is the Resource object that will render the request.
.rpy files are very convenient for rapid development and prototyping. Since they are executed on every web request, defining a Resource subclass in an .rpy will make viewing the results of changes to your class visible simply by refreshing the page:
from twisted.web.resource import Resource
class MyResource(Resource):
def render_GET(self, request):
return "<html>Hello, world!</html>"
resource = MyResource()
However, it is often a better idea to define Resource subclasses in Python modules. In order for changes in modules to be visible, you must either restart the Python process, or reload the module:
import myresource ## Comment out this line when finished debugging reload(myresource) resource = myresource.MyResource()
Creating a Twisted Web server which serves a directory is easy:
% mktap web --path /Users/dsp/Sites % twistd -nf web.tap
Resource rendering occurs when Twisted Web locates a leaf Resource object to handle a web request. A Resource's render method may do various things to produce output which will be sent back to the browser:
request.write("stuff") as many times as desired, then call request.finish() and return server.NOT_DONE_YET (This is deceptive, since you are in fact done with the request, but is the correct way to do this)Deferred, return server.NOT_DONE_YET, and call request.write("stuff") and request.finish() later, in a callback on the Deferred.
The Resource
class, which is usually what one's Resource classes subclass, has a
convenient default implementation of render. It will call a method named self.render_METHOD where METHOD
is
whatever HTTP method was used to request this resource. Examples:
request_GET, request_POST, request_HEAD, and so on. It is recommended
that you have your resource classes subclass Resource and implement render_METHOD methods as opposed to render itself. Note that for certain resources,
request_POST = request_GET may be
desirable in case one wants to process arguments passed to the
resource regardless of whether they used GET
(?foo=bar&baz=quux, and so forth) or POST.
HTTP is a stateless protocol; every request-response is treated as an individual unit, distinguishable from any other request only by the URL requested. With the advent of Cookies in the mid nineties, dynamic web servers gained the ability to distinguish between requests coming from different browser sessions by sending a Cookie to a browser. The browser then sends this cookie whenever it makes a request to a web server, allowing the server to track which requests come from which browser session.
Twisted Web provides an abstraction of this browser-tracking behavior called the Session object. Calling request.getSession() checks to see if a session cookie has been set; if not, it creates a unique session id, creates a Session object, stores it in the Site, and returns it. If a session object already exists, the same session object is returned. In this way, you can store data specific to the session in the session object.
Non-trivial configurations of Twisted Web are achieved with Python
configuration files. This is a Python snippet which builds up a variable
called application. Usually, a twisted.application.internet.TCPServer instance will
be used to make the application listen on a TCP port (80, in case direct
web serving is desired), with the listener being a
twisted.web.server.Site. The resulting file can then
be run with twistd -y. Alternatively a reactor
object can be used directly to make a runnable script.
The Site will wrap a Resource object -- the
root.
from twisted.application import internet, service
from twisted.web import static, server
root = static.File("/var/www/htdocs")
application = service.Application('web')
site = server.Site(root)
sc = service.IServiceCollection(application)
i = internet.TCPServer(80, site)
i.setServiceParent(sc)
Most advanced configurations will be in the form of tweaking the root resource object.
Usually, the root's children will be based on the filesystem's contents.
It is possible to override the filesystem by explicit putChild
methods.
Here are two examples. The first one adds a /doc child
to serve the documentation of the installed packages, while the second
one adds a cgi-bin directory for CGI scripts.
from twisted.internet import reactor
from twisted.web import static, server
root = static.File("/var/www/htdocs")
root.putChild("doc", static.File("/usr/share/doc"))
reactor.listenTCP(80, server.Site(root))
reactor.run()
from twisted.internet import reactor
from twisted.web import static, server, twcgi
root = static.File("/var/www/htdocs")
root.putChild("cgi-bin", twcgi.CGIDirectory("/var/www/cgi-bin"))
reactor.listenTCP(80, server.Site(root))
reactor.run()
File resources, be they root object or children thereof,
have two important attributes that often need to be modified:
indexNames and processors. indexNames
determines which files are treated as index files
-- served
up when a directory is rendered. processors determine how
certain file extensions are treated.
Here is an example for both, creating a site where all .rpy
extensions are Resource Scripts, and which renders directories by
searching for a index.rpy file.
from twisted.application import internet, service
from twisted.web import static, server, script
root = static.File("/var/www/htdocs")
root.indexNames=['index.rpy']
root.processors = {'.rpy': script.ResourceScript}
application = service.Application('web')
sc = service.IServiceCollection(application)
site = server.Site(root)
i = internet.TCPServer(80, site)
i.setServiceParent(sc)
File objects also have a method called ignoreExt.
This method can be used to give extension-less URLs to users, so that
implementation is hidden. Here is an example:
from twisted.application import internet, service
from twisted.web import static, server, script
root = static.File("/var/www/htdocs")
root.ignoreExt(".rpy")
root.processors = {'.rpy': script.ResourceScript}
application = service.Application('web')
sc = service.IServiceCollection(application)
site = server.Site(root)
i = internet.TCPServer(80, site)
i.setServiceParent(sc)
Now, a URL such as /foo might be served from a Resource
Script called foo.rpy, if no file by the name of foo
exists.
Virtual hosting is done via a special resource, that should be
used as the root resource -- NameVirtualHost.
NameVirtualHost has an attribute named default,
which holds the default website. If a different root for some other
name is desired, the addHost method should be called.
from twisted.application import internet, service
from twisted.web import static, server, vhost, script
root = vhost.NameVirtualHost()
# Add a default -- htdocs
root.default=static.File("/var/www/htdocs")
# Add a simple virtual host -- foo.com
root.addHost("foo.com", static.File("/var/www/foo"))
# Add a simple virtual host -- bar.com
root.addHost("bar.com", static.File("/var/www/bar"))
# The "baz" people want to use Resource Scripts in their web site
baz = static.File("/var/www/baz")
baz.processors = {'.rpy': script.ResourceScript}
baz.ignoreExt('.rpy')
root.addHost('baz', baz)
application = service.Application('web')
sc = service.IServiceCollection(application)
site = server.Site(root)
i = internet.TCPServer(80, site)
i.setServiceParent(sc)
Since the configuration is a Python snippet, it is possible to use the full power of Python. Here are some simple examples:
# No need for configuration of virtual hosts -- just make sure
# a directory /var/vhosts/<vhost name> exists:
from twisted.web import vhost, static, server
from twisted.application import internet, service
root = vhost.NameVirtualHost()
root.default = static.File("/var/www/htdocs")
for dir in os.listdir("/var/vhosts"):
root.addHost(dir, static.File(os.path.join("/var/vhosts", dir)))
application = service.Application('web')
sc = service.IServiceCollection(application)
site = server.Site(root)
i = internet.TCPServer(80, site)
i.setServiceParent(sc)
# Determine ports we listen on based on a file with numbers:
from twisted.web import vhost, static, server
from twisted.application import internet, service
root = static.File("/var/www/htdocs")
site = server.Site(root)
application = service.Application('web')
serviceCollection = service.IServiceCollection(application)
for num in map(int, open("/etc/web/ports").read().split()):
serviceCollection.addCollection(internet.TCPServer(num, site))
In many cases, you'll end up repeating common usage patterns of twisted.web. In those cases you'll probably want to use Twisted's pre-configured web server setup.
To install the Twisted.Web server, you'll need to have installed Twisted.
Pre-configured Twisted servers, like the web server, do not have configuration files. Instead, you instantiate the server and store it into a 'Pickle' file, web.tap. This file will then be loaded by the Twisted Daemon.
% mktap web --path /path/to/web/content
If you just want to serve content from your own home directory, the following will do:
% mktap web --path ~/public_html/
Some other configuration options are available as well:
--port: Specify the port for the web
server to listen on. This defaults to 8080. --logfile: Specify the path to the
log file. The full set of options that are available can be seen with:
% mktap web --help
Once you've created your web.tap file and done any configuration, you can start the server:
% twistd -f web.tap
You can stop the server at any time by going back to the directory you started it in and running the command:
% kill `cat twistd.pid`
Twisted.Web serves flat HTML files just as it does any other flat file.
A Resource script is a Python file ending with the extension .rpy, which is required to create an instance of a (subclass of a) twisted.web.resource.Resource.
Resource scripts have 3 special variables:
__file__: The name of the .rpy file, including the full path. This variable is automatically defined and present within the namespace. registry: An object of class static.Registry. It can be used to access and set persistent data keyed by a class.resource: The variable which must be defined by the script and set to the resource instance that will be used to render the page. A very simple Resource Script might look like:
from twisted.web import resource
class MyGreatResource(resource.Resource):
def render_GET(self, request):
return "<html>foo</html>"
resource = MyGreatResource()
A slightly more complicated resource script, which accesses some persistent data, might look like:
from twisted.web import resource
from SillyWeb import Counter
counter = registry.getComponent(Counter)
if not counter:
registry.setComponent(Counter, Counter())
counter = registry.getComponent(Counter)
class MyResource(resource.Resource):
def render_GET(self, request):
counter.increment()
return "you are visitor %d" % counter.getValue()
resource = MyResource()
This is assuming you have the SillyWeb.Counter module,
implemented something like the following:
class Counter:
def __init__(self):
self.value = 0
def increment(self):
self.value += 1
def getValue(self):
return self.value
The Nevow framework, available as part of the Quotient project, is an advanced system for giving Web UIs to your application. Nevow uses Twisted Web but is not itself part of Twisted.
One of the most interesting applications of Twisted.Web is the distributed webserver; multiple servers can all answer requests on the same port, using the twisted.spread package for spreadable
computing. In two different directories, run the commands:
% mktap web --user % mktap web --personal [other options, if you desire]
Both of these create a web.tap; you need to run both at the same time. Once you have, go to http://localhost:8080/your_username.twistd/ -- you will see the front page from the server you created with the --personal option. What's happening here is that the request you've sent is being relayed from the central (User) server to your own (Personal) server, over a PB connection. This technique can be highly useful for small community
sites; using the code that makes this demo work, you can connect one HTTP port to multiple resources running with different permissions on the same machine, on different local machines, or even over the internet to a remote site.
Everything related to CGI is located in the
twisted.web.twcgi, and it's here you'll find the classes that you
need to subclass in order to support the language of your (or somebody elses)
taste. You'll also need to create your own kind of resource if you are using a
non-unix operatingsystem (such as Windows), or if the default resources has
wrong pathnames to the parsers.
The following snippet is a .rpy that serves perl-files. Look at twisted.web.twcgi
for more examples regarding twisted.web and CGI.
from twisted.web import static, twcgi
class PerlScript(twcgi.FilteredScript):
filter = '/usr/bin/perl' # Points to the perl parser
resource = static.File("/perlsite") # Points to the perl website
resource.processors = {".pl": PerlScript} # Files that end with .pl will be
# processed by PerlScript
resource.indexNames = ['index.pl']
It is common to use one server (for example, Apache) on a site with multiple
names which then uses reverse proxy (in Apache, via mod_proxy) to different
internal web servers, possibly on different machines. However, naive
configuration causes miscommunication: the internal server firmly believes it
is running on internal-name:port
, and will generate URLs to that effect,
which will be completely wrong when received by the client.
While Apache has the ProxyPassReverse directive, it is really a hack and is nowhere near comprehensive enough. Instead, the recommended practice in case the internal web server is Twisted.Web is to use VHostMonster.
From the Twisted side, using VHostMonster is easy: just drop a file named
(for example) vhost.rpy containing the following:
from twisted.web import vhost resource = vhost.VHostMonsterResource()
Of course, an equivalent .trp can also be used. Make sure
the web server is configured with the correct processors for the
rpy or trp extensions (the web server
mktap web --path generates by default is so configured).
From the Apache side, instead of using the following ProxyPass directive:
<VirtualHost ip-addr> ProxyPass / http://localhost:8538/ ServerName example.com </VirtualHost>
Use the following directive:
<VirtualHost ip-addr> ProxyPass / http://localhost:8538/vhost.rpy/http/example.com:80/ ServerName example.com </VirtualHost>
Here is an example for Twisted.Web's reverse proxy:
from twisted.application import internet, service
from twisted.web import proxy, server, vhost
vhostName = 'example.com'
reverseProxy = proxy.ReverseProxyResource('internal', 8538,
'/vhost.rpy/http/'+vhostName+'/')
root = vhost.NameVirtualHost()
root.addHost(vhostName, reverseProxy)
site = server.Site(root)
application = service.Application('web-proxy')
sc = service.IServiceCollection(application)
i = internet.TCPServer(80, site)
i.setServiceParent(sc)
Sometimes it is convenient to modify the content of the
Request object
before passing it on. Because this is most often used to rewrite
either the URL, the similarity to Apache's mod_rewrite has
inspired the twisted.web.rewrite module. Using
this module is done via wrapping a resource with a
twisted.web.rewrite.RewriterResource which
then has rewrite rules. Rewrite rules are functions which accept a request
object, and possible modify it. After all rewrite rules run, the child
resolution chain continues as if the wrapped resource, rather than
the RewriterResource,
was the child.
Here is an example, using the only rule currently supplied by Twisted itself:
default_root = rewrite.RewriterResource(default, rewrite.tildeToUsers)
This causes the URL /~foo/bar.html to be treated like
/users/foo/bar.html. If done after setting default's
users child to a
distrib.UserDirectory,
it gives a configuration similar to the classical configuration of
web server, common since the first NCSA servers.
Sometimes it is useful to know when the other side has broken the connection. Here is an example which does that:
from twisted.web.resource import Resource
from twisted.web import server
from twisted.internet import reactor
from twisted.python.util import println
class ExampleResource(Resource):
def render_GET(self, request):
request.write("hello world")
d = request.notifyFinish()
d.addCallback(lambda _: println("finished normally"))
d.addErrback(println, "error")
reactor.callLater(10, request.finish)
return server.NOT_DONE_YET
resource = ExampleResource()
This will allow us to run statistics on the log-file to see how many users are frustrated after merely 10 seconds.
Sometimes, you want to be able to send headers and status directly. While
you can do this with a
ResourceScript, an easier
way is to use AsIsProcessor.
Use it by, for example, addding it as a processor for the .asis
extension. Here is a sample file:
HTTP/1.0 200 OK Content-Type: text/html Hello world