Twisted Documentation: Handling POSTs

# Handling POSTs

All of the previous examples have focused on `GET` requests. Unlike `GET` requests, `POST` requests can have a request body - extra data after the request headers; for example, data representing the contents of an HTML form. Twisted Web makes this data available to applications via the `Request` object.

Here's an example web server which renders a static HTML form and then generates a dynamic page when that form is posted back to it. Disclaimer: While it's convenient for this example, it's often not a good idea to make a resource that `POST`s to itself; this isn't about Twisted Web, but the nature of HTTP in general; if you do this in a real application, make sure you understand the possible negative consequences.

As usual, we start with some imports. In addition to the Twisted imports, this example uses the `cgi` module to escape user-entered content for inclusion in the output.

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    from twisted.web.server import Site
    from twisted.web.resource import Resource
    from twisted.internet import reactor

    import cgi

Next, we'll define a resource which is going to do two things. First, it will respond to `GET` requests with a static HTML form:

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    class FormPage(Resource):
        def render_GET(self, request):
            return '<html><body><form method="POST"><input name="the-field" type="text" /></form></body></html>'

This is similar to the resource used in a previous installment. However, we'll now add one more method to give it a second behavior; this `render_POST` method will allow it to accept `POST` requests:

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    ...
        def render_POST(self, request):
            return '<html><body>You submitted: %s</body></html>' % (cgi.escape(request.args["the-field"][0]),)

The main thing to note here is the use of `request.args`. This is a dictionary-like object that provides access to the contents of the form. The keys in this dictionary are the names of inputs in the form. Each value is a list containing strings (since there can be multiple inputs with the same name), which is why we had to extract the first element to pass to `cgi.escape`. `request.args` will be populated from form contents whenever a `POST` request is made with a content type of `application/x-www-form-urlencoded` or `multipart/form-data` (it's also populated by query arguments for any type of request).

Finally, the example just needs the usual site creation and port setup:

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    root = Resource()
    root.putChild("form", FormPage())
    factory = Site(root)
    reactor.listenTCP(8880, factory)
    reactor.run()

Run the server and visit http://localhost:8880/form, submit the form, and watch it generate a page including the value you entered into the single field.

Here's the complete source for the example:

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    from twisted.web.server import Site
    from twisted.web.resource import Resource
    from twisted.internet import reactor

    import cgi

    class FormPage(Resource):
        def render_GET(self, request):
            return '<html><body><form method="POST"><input name="the-field" type="text" /></form></body></html>'

        def render_POST(self, request):
            return '<html><body>You submitted: %s</body></html>' % (cgi.escape(request.args["the-field"][0]),)

    root = Resource()
    root.putChild("form", FormPage())
    factory = Site(root)
    reactor.listenTCP(8880, factory)
    reactor.run()

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Version: 13.2.0