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A Request’s Flow Through The TurboGears Stack

Content Types and Request Extensions

Content Types and Request Extensions are supported by both tg.controllers.TGController and tg.controllers.RestController.

Request Extensions

Request extensions allow the user to provide a specifier at the end of their data stream which specifies how they would like their data retrieved, using a dot operator.

For example: /users, /users.html and /users.json will all resolve to the users method from the RootController.

A Simple Json Example

TurboGears Controllers gives the developer the ability to attach common types that will be translated into mime-type to their methods to express data using different protocols. The most common usage for this is with json, a standard protocol used for Asynchronous JavaScript. Consider the following code snippet:

users = "sally", "dave", "john"

class Forum(TGController):

    def users(self):
        return {'users':users}

This allows you to map a URL like /forum/users.json

Cascading Exposes To Provide Web Services

Sometimes you want a controller to return content based on the extension provided by the user, or the lack-there-of. You can cascade multiple expose decorators to accomplish this. Consider this example: you have a page which lists the user in a table which is generated using JavaScript. JS makes an asynchronous call to your web application to fill the data. It makes sense to fetch the data for the Json call, but not for the rendering of the HTML template used to render the data. Here is the users example again which expresses this use case:

users = "sally", "dave", "john"

class Forum(TGController):

    def users(self):
        if pylons.request.response_type == 'application/json':
            return {'users':users}
        return {}

The users method will service both /forum/users/ and /forum/users.json. Simply provide the JavaScript code with a link to users.json and you are good to go. This makes providing your users with RESTful URLs much simpler. You could imagine using this capability to expose your application’s resources for SOAP, or XML-RPC.

This method is extensibly used by tgext.admin. Which provides a very clean API out of the box.

Application-Specific Mime-type Configuration

By default, only json/application and text/html are defined mimetypes. If you would like to use additional mime-types you must register them with your application’s config. You can accomplish this by adding the following code your your file:

base_config.mimetype_lookup = {'.ext':'my-mimetype'}

Setting the Content Type

Setting the Content-Type for your return data is often used to tell the web browser how to display that data to the user. For instance, if you want the browser to open an Excel file as such, you need to tell the browser that the data coming back is in Excel format.

Per Method

Sometimes we want to set the content-type for our response within the controller method.

By providing the @expose decorator with a content_type parameter we are able to accomplish this.

Here is an example of how to return a simple .csv file that the browser will treat as an attachment:

class MyController(BaseController):
    def stats(self):
        return '1,2,3'

It is also possible to set this up with a template:

class MyController(BaseController):
        def stats(self):
            return dict(data = somedata)

Per Request

Sometimes you will want to set the content type at runtime, the best example of this is when you want to restrict downloads behind auth and you will only know which file you are serving based on the request parameters.

This is done in the same way as plain old pylons.


due to bug #2378 we currently need to flag the controller as “setting the content type at runtime”

In this example we are flagging the content type:

from tg import request, response
from tg.controllers import CUSTOM_CONTENT_TYPE

class MyController(BaseController):
    def stats(self):
        response.content_type = 'text/csv'
        return '1,2,3'

Once the above bug is fixed all you will need is to set the content type at runtime by modifiying the headers:

from tg import response

class MyController(BaseController):
    def stats(self):
        response.headers['Content-type'] = 'text/csv'
        return '1,2,3'