addingviews.html

As discussed in [the Flow View section of the mitmproxy overview](@!urlTo("mitmproxy.html")!@), mitmproxy allows you to inspect and manipulate flows.  When inspecting a single flow, mitmproxy uses a number of heuristics to show a friendly view of various content types; if mitmproxy cannot show a friendly view, mitmproxy defaults to a __raw__ view.

By default, mitmproxy has support for displaying the following content types in a friendly view:

- __1__: Hex
- __2__: HTML
- __3__: Image
- __4__: JavaScript
- __5__: JSON
- __6__: URL-encoded data
- __7__: XML
- __8__: AMF (requires PyAMF)
- __9__: Protobuf (requires protobuf library)

Each content type invokes a different flow viewer to parse the data and display the friendly view.  Users can add custom content viewers by adding a view class to contentview.py, discussed below.

## Adding a new View class to contentview.py

The content viewers used by mitmproxy to present a friendly view of various content types are stored in contentview.py.  Reviewing this file shows a number of classes named ViewSomeDataType, each with the properties: __name__, __prompt__, and __content\_types__ and a function named __\_\_call\_\___.

Adding a new content viewer to parse a data type is as simple as writing a new View class.  Your new content viewer View class should have the same properties as the other View classes: __name__, __prompt__, and __content\_types__ and a __\_\_call\_\___ function to parse the content of the request/response. 

* The __name__ property should be a string describing the contents and new content viewer; 
* The __prompt__ property should be a two item tuple:

  - __1__: A string that will be used to display the new content viewer's type; and
  - __2__: A one character string that will be the hotkey used to select the new content viewer from the Flow View screen; 

* The __content\_types__ property should be a list of strings of HTTP Content\-Types that the new content viewer can parse.  
  * Note that mitmproxy will use the content\_types to try and heuristically show a friendly view of content and that you can override the built-in views by populating content\_types with values for content\_types that are already parsed -- e.g. "image/png".

After defining the __name__, __prompt__, and __content\_types__ properties of the class, you should write the __\_\_call\_\___ function, which will parse the request/response data and provide a friendly view of the data.  The __\_\_call\_\___ function should take the following arguments: __self__, __hdrs__, __content__, __limit__; __hdrs__ is a ODictCaseless object containing the headers of the request/response; __content__ is the content of the request/response, and __limit__ is an integer representing the amount of data to display in the view window.

The __\_\_call\_\___ function returns two values: (1) a string describing the parsed data; and (2) the parsed data for friendly display.  The parsed data to be displayed should be a list of strings formatted for display.  You can use the __\_view\_text__ function in contentview.py to format text for display.  Alternatively, you can display content as a series of key-value pairs; to do so, prepare a list of lists, where each list item is a two item list -- a key that describes the data, and then the data itself; after preparing the list of lists, use the __common.format\_keyvals__ function on it to prepare it as text for display.  

If the new content viewer fails or throws an exception, mitmproxy will default to a __raw__ view.