PappyProxy/docs/build/html/_sources/pappyplugins.txt

Writing Plugins for the Pappy Proxy
***********************************

.. contents:: Table of Contents
   :local:

Introduction
============

Are macros not powerful enough? Want to make something reusable? Want to add console commands?! Then you might want to write yourself a plugin. Some quick highlights about plugins:

* Python scripts stored in ``~/.pappy/plugins``
* Can add console commands
* For actions which aren't specific to one project
* Harder to write than macros

Since macros can also use the plugin API, plugins aren't any more powerful than macros (besides adding console commands). However, if you find yourself copying a useful macro to more than one project, it may be worth it to just bind it to some commands, put the script in one place, and stop worrying about copying it around. Plus then you can put it on GitHub for some sweet sweet nerd cred.

Should I Write a Plugin or a Macro?
-----------------------------------
A lot of the time, you can get away with writing a macro. However, you may consider writing a plugin if:

* You find yourself copying one macro to multiple projects
* You want to write a general tool that can be applied to any website
* You need to maintain state during the Pappy session

My guess is that if you need one quick thing for a project, you're better off writing a macro first and seeing if you end up using it in future projects. Then if you find yourself needing it a lot, write a plugin for it. You may also consider keeping a ``mine.py`` plugin where you can write out commands that you use regularly but may not be worth creating a dedicated plugin for.

Plugins Get Merged
------------------
If you write a useful plugin, as long as it isn't uber niche, I'll try and merge it into the core project.

Creating a Plugin
=================
Whenever you make a macro, you'll have to bind some functions to some console commands. To do this, you'll have to define a ``load_cmds`` function in your plugin. This function should take one argument. When the plugin is loaded, this function will be called and the console object will be passed to this function. You can then use ``set_cmds`` and ``add_aliases`` to bind functions to console commands.

Writing a Hello World Plugin
----------------------------
It's probably easiest to explain how to write a plugin by writing one. Here is a simple plugin that defines a ``hello`` command and gives an alias ``hlo`` (we'll go over all the parts in a second)::
    
    ## hello.py

    def hello_world(line):
        print "Hello, world!"
    
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'hello': (hello_world, None),
        })
        cmd.add_aliases([
            ('hello', 'hlo'),
        ])

Save this as ``~/.pappy/plugins/hello.py`` and run Pappy. You should have a new ``hello`` command that prints your message::

    $ cp hello.py ~/.pappy/plugins/
    $ pappy -l
    Temporary datafile is /tmp/tmp1Myw6q
    Proxy is listening on port 8000
    pappy> hello
    Hello, world!
    pappy> hlo
    Hello, world!
    pappy>
  
Awesome! So let's go over the code. Here are the important parts of the code:

* We define a function that we want to call
* We define ``load_cmds(cmd)`` to be called when our plugin is loaded to bind our function to a command
* We use ``cmd.set_cmds`` to set all our commands
* We use ``cmd.add_aliases`` to add aliases for commands

Now let's go over it in detail

Passing Arguments to Your Function
----------------------------------

Each command gets bound to one function which takes one argument. That argument is all the text that was entered after the name of the command in the console. For example if we run ``hello foo bar``, in our function line would be "foo bar". **I suggest using shlex.split(line) to parse multiple arguments**. So let's update our script to take some arguments::

    ## hello.py
    import shlex

    def hello_world(line):
        if line:
            args = shlex.split(line)
            print 'Hello, %s!' % (', '.join(args))
        else:
            print "Hello, world!"
    
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'hello': (hello_world, None),
        })
        cmd.add_aliases([
            ('hello', 'hlo'),
        ])

Save your changes and restart pappy to reload the plugin::
        
    $ pappy -l
    Temporary datafile is /tmp/tmpBOXyJ3
    Proxy is listening on port 8000
    pappy> hello
    Hello, world!
    pappy> hello foo bar baz
    Hello, foo, bar, baz!
    pappy> hello foo bar "baz lihtyur"
    Hello, foo, bar, baz lihtyur!
    pappy>

Adding More Aliases
-------------------

So now let's add some more aliases to our command. If we want to add a new alias, we just add another tuple to the list passed into ``cmd.add_aliases``. The first element is the real name of the command (what you set with ``set_cmds``) and the second value is the alias you want to type. So let's make it so we can just type ``ho`` to say hello::

    ## hello.py
    import shlex

    def hello_world(line):
        if line:
            args = shlex.split(line)
            print 'Hello, %s!' % (', '.join(args))
        else:
            print "Hello, world!"
    
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'hello': (hello_world, None),
        })
        cmd.add_aliases([
            ('hello', 'hlo'),
            ('hello', 'ho'),
        ])

.. note::

   You must use the actual name of the command that you used in ``set_cmds``. You can't "chain" alieases. As a result, in our example we couldn't add the alias ``('hlo', 'ho')`` to add ``ho`` as our alias.

Then reload the plugin::

    $ pappy -l
    Temporary datafile is /tmp/tmpBOXyJ3
    Proxy is listening on port 8000
    pappy> ho
    Hello, world!
    pappy> ho foo bar baz
    Hello, foo, bar, baz!
    pappy> ho foo bar "baz lihtyur"
    Hello, foo, bar, baz lihtyur!
    pappy>

Adding Another Command
----------------------
So now let's add a ``robe_and_wizard_hat`` command. To do this, we will define another function, then add another entry in the dict that is passed to ``set_cmds``. The second value in the tuple is the autocomplete function, but we'll get to that later. For now, just put in ``None`` to say we don't have one. We will also add a ``wh`` alias to it::

    $ pappy -l
    Temporary datafile is /tmp/tmpyl2cEZ
    Proxy is listening on port 8000
    pappy> wh
    I put on my robe and wizard hat
    pappy>
    
Adding Autocompletion
---------------------
You can also define a function to handle autocompletion for your command. In order to do this, you define a function that takes 4 arguments: ``text``, ``line``, ``begidx``, and ``endidx``. From the `Cmd docs <https://docs.python.org/2/library/cmd.html>`_, this is what the arguments mean:

  ``text`` is the string prefix we are attempting to match: all returned matches must begin with it. ``line`` is the current input line with leading whitespace removed, ``begidx`` and ``endidx`` are the beginning and ending indexes of the prefix text, which could be used to provide different completion depending upon which position the argument is in.

Let's let the user to autocomplete some names in our plugin::

    import shlex
    
    _AUTOCOMPLETE_NAMES = ['alice', 'allie', 'sarah', 'mallory', 'slagathor']
    
    def hello_world(line):
        if line:
            args = shlex.split(line)
            print 'Hello, %s!' % (', '.join(args))
        else:
            print "Hello, world!"
            
    def put_on_rope_and_wizard_hat(line):
        if line:
            print '%s puts on their robe and wizard hat' % line
        else:
            print 'I put on my robe and wizard hat'
    
    def complete_hello_world(text, line, begidx, endidx):
        return [n for n in _AUTOCOMPLETE_NAMES if n.startswith(text)]
            
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'hello': (hello_world, complete_hello_world),
            'wizard_hat': (put_on_rope_and_wizard_hat, None),
        })
        cmd.add_aliases([
            ('hello', 'hlo'),
            ('wizard_hat', 'wh'),
        ])

Then restart and run::

    $ pappy -l
    Temporary datafile is /tmp/tmp3J97rE
    Proxy is listening on port 8000
    pappy> hello
    alice      allie      mallory    sarah      slagathor
    pappy> hello allie
    Hello, allie!
    pappy>

You can't see it, but I hit tab twice after typing hello to get the completions to appear.

Adding Help
-----------
Now let's say we want to add some help to the command so that when the user runs ``help hello`` they get something useful. To do that, just add a docstring to your function::

    import shlex
    
    _AUTOCOMPLETE_NAMES = ['alice', 'allie', 'sarah', 'mallory', 'slagathor']
    
    def hello_world(line):
        """
        Say hello to the world. Usage: hello [name]
        """

        if line:
            args = shlex.split(line)
            print 'Hello, %s!' % (', '.join(args))
        else:
            print "Hello, world!"
            
    def put_on_rope_and_wizard_hat(line):
        if line:
            print '%s puts on their robe and wizard hat' % line
        else:
            print 'I put on my robe and wizard hat'
    
    def complete_hello_world(text, line, begidx, endidx):
        return [n for n in _AUTOCOMPLETE_NAMES if n.startswith(text)]
            
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'hello': (hello_world, complete_hello_world),
            'wizard_hat': (put_on_rope_and_wizard_hat, None),
        })
        cmd.add_aliases([
            ('hello', 'hlo'),
            ('wizard_hat', 'wh'),
        ])
Using defer.inlineCallbacks With a Command
------------------------------------------

.. note::
   If you are using inlineCallbacks, you can't use any functions which are blocking versions of async functions. For example, you cannot use :func:`pappyproxy.http.Request.save` and must instead use :func:`pappyproxy.http.Request.async_deep_save`.

.. note::
   This tutorial won't tell you how to use inlineCallbacks in general. Type "twisted inline callbacks" into google to figure out what they are. This is mainly just a reminder to use the ``crochet`` wrapper for console commands and warning you that some functions may return deferreds that you may have to deal with.

Since you're writing a plugin, you'll probably be using functions which return a deferred. And to keep things readable, you'll want to use the ``defer.inlineCallbacks`` function wrapper. Unfortunately, you can't bind async functions to commands. Luckily, there's a library called `crochet <https://pypi.python.org/pypi/crochet>`_ which lets you add another wrapper to the function that lets it be used like a blocking function. Rather than talking about it, let's write a plugin to call :func:`pappyproxy.console.load_reqlist` to print out some requests' hosts. Let's start by pretending it's a normal function::

    import shlex
    from pappyproxy.console import load_reqlist
    
    def print_hosts(line):
        args = shlex.split(line)
        reqs = load_reqlist(args[0]) # It's supposed to return a list of requests, right?
        for r in reqs:
            print 'The host for request %s is: %s' % (r.reqid, r.host)
    
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'print_hosts': (print_hosts, None),
        })
        cmd.add_aliases([
        ])

And we run it::

    pappy> print_hosts 1
    Traceback (most recent call last):
      File "/usr/local/lib/python2.7/dist-packages/cmd2.py", line 788, in onecmd_plus_hooks
        stop = self.onecmd(statement)
      File "/usr/local/lib/python2.7/dist-packages/cmd2.py", line 871, in onecmd
        stop = func(statement)
      File "/home/supahacker/pappy/pappyproxy/console.py", line 15, in catch
        func(*args, **kwargs)
      File "/home/supahacker/.pappy/plugins/hosts.py", line 7, in print_hosts
        for r in reqs:
    TypeError: iteration over non-sequence
    iteration over non-sequence
    pappy>
  
Iteration over a non-sequence? what? Well, :func:`pappyproxy.console.load_reqlist` doesn't actually return a list of requests. It returns a deferred which returns a list of requests. I'm not going into the details (look up some stuff on using inline callbacks with Twisted if you want more info), but the way to fix it is to slap an ``inlineCallbacks`` wrapper on the function and ``yield`` the result of the function. Now it looks like this::

    import shlex
    from pappyproxy.console import load_reqlist
    from twisted.internet import defer
    
    @defer.inlineCallbacks
    def print_hosts(line):
        args = shlex.split(line)
        reqs = yield load_reqlist(args[0])
        for r in reqs:
            print 'The host for request %s is: %s' % (r.reqid, r.host)
    
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'print_hosts': (print_hosts, None),
        })
        cmd.add_aliases([
        ])

However, the console assumes that any functions it calls will be blocking. As a result, we need to add the ``crochet.wait_for`` wrapper::

    import shlex
    import crochet
    from pappyproxy.console import load_reqlist
    from twisted.internet import defer
    
    @crochet.wait_for(timeout=None)
    @defer.inlineCallbacks
    def print_hosts(line):
        args = shlex.split(line)
        reqs = yield load_reqlist(args[0])
        for r in reqs:
            print 'The host for request %s is: %s' % (r.reqid, r.host)
    
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'print_hosts': (print_hosts, None),
        })
        cmd.add_aliases([
        ])

And now we're good! If you run it without the crochet wrapper, it may still work. However, since the console assumes any functions it calls will be blocking, not having the wrapper could lead to weird errors.
    
Plugin API
==========
There are also some useful functions that you can use to interact with the request history and the context. It's somewhat limited for now, but for now you can at least look through history and create/send new requests. Hopefully the API will expand as people find themselves wanting to do new things. That means **if you're writing a plugin, let me know and I'll add any APIs you need**. For now at least, plugins will let you maintain state over the course of the session and let you define commands.

The best way to learn what you can do is to go through the :ref:`pappyproxy-package` and look at all the available functions.

API Functions
-------------
See :mod:`pappyproxy.plugin` for docs on all the functions you can use. You can also use any of the functions provided for writing macros (and vice-versa).

Storing Data on Disk
--------------------
Unfortunately, you're on your own if you want to store plugin specific stuff on disk. It's also important that you store any data that is specific to a project in the same directory as the data file. This is to make sure that if you encrypt your project folder, you can be sure that no sensitive data about the test can be found anywhere else. The only time you should store anything outside of the current directory is to store global plugin settings, and even then it would probably be better to parse options from ``config.config_dict``. Pappy doesn't even store data outside of the project directory except for its CA certificates.

However, if your plugin is a special snowflake that needs to store unencrypted, global settings, you should create a directory for your plugin in ``{config.DATA_DIR}/plugindata`` and put your files there. But again, avoid this if you can.

.. note::
   Any project-specific data (ie anything that contains info about requests) should be stored in the project directory unless you have a really really good reason. This is because it must be possible to secure any sensitive data by encrypting the project folder and storing data outside of the directory will add complications.

.. warning::
   Do not modify the data file schema. There is a good chance the schema will break in future versions of Pappy.

Storing Custom Request Metadata
-------------------------------
:class:`pappyproxy.http.Request` objects have a ``plugin_data`` attribute. It is a dictionary that is intended to be used by plugins to give the request custom metadata. If you want to store metadata about a request, it is suggested that you add a key to this dictionary and store any metadata you want under that key. You can use :func:`pappyproxy.http.Request.get_plugin_dict` to get a dictionary for a specific name. It will create an entry for that name if it doesn't exist. I also suggest defining a function plugin-wide for getting the plugin's data dict from a specific request. Since dictionaries are always passed by reference, any modifications you make to the returned dict will be applied to the request as well.

.. note::
   You will need to save the request using something like :func:`pappyproxy.http.Request.save` or :func:`pappyproxy.http.Request.async_deep_save` in order to store the changes in the data file.

Here is an example plugin for storing the user-agent (if it exists) in the ``plugin_data`` dict of a request under the key ``agent``::

    import crochet
    import shlex
    from twisted.internet import defer
    
    from pappyproxy.console import load_reqlist
    from pappyproxy.plugin import main_context
    from pappyproxy.util import PappyException
    
    DATA_KEY = 'agent'
    
    def get_data(r):
        return r.get_plugin_dict(DATA_KEY)
    
    @crochet.wait_for(timeout=None)
    @defer.inlineCallbacks
    def update_agent_metadata(line):
        for r in main_context().active_requests:
            if 'user-agent' in r.headers:
                get_data(r)['agent'] = r.headers['user-agent']
            yield r.async_deep_save()
    
    @crochet.wait_for(timeout=None)
    @defer.inlineCallbacks
    def view_agent(line):
        args = shlex.split(line)
        reqs = yield load_reqlist(args[0])
        for r in reqs:
            if 'agent' in get_data(r):
                print 'The user agent for %s is "%s"' % (r.reqid, get_data(r)['agent'])
            else:
                print 'Request %s has no user agent data' % r.reqid
    
    ###############
    ## Plugin hooks
    
    def load_cmds(cmd):
        cmd.set_cmds({
            'agent_update': (update_agent_metadata, None),
            'view_agent': (view_agent, None),
        })
        cmd.add_aliases([
        ])

Useful Functions
----------------
* Load a request by id: :func:`pappyproxy.http.Request.load_request`
* Create a filter from a filter string: :func:`pappyproxy.context.Filter.from_filter_string`

Built In Plugins As Examples
============================

Built In Plugins
----------------
All the commands in Pappy are implemented as plugins. I have done what I could to avoid using internal functions as much as I could, but there are still some instances where I had to implement an internal function in order to get the functions I needed. However, you can still look them over to see how things are structured and see some examples of semi-complicated plugins.

Interceptor and Repeater
------------------------
Pappy's interceptor and repeater are fully implemented as a plugin. It defines an intercepting macro that handles saving then editing messages and commands that read those files and edit them. It relies on Twisted to switch between the macro handling the request and the command modifying it, so if you want to make something similar, you'll have to learn how to use deferreds.