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Creating a SleekXMPP Plugin

Andrea Condoluci edited this page Mar 18, 2016 · 2 revisions

Creating a SleekXMPP Plugin

One of the goals of SleekXMPP is to provide support for every draft or final XMPP extension (XEP). To do this, SleekXMPP has a plugin mechanism for adding the functionalities required by each XEP. But even though plugins were made to quickly implement and prototype the official XMPP extensions, there is no reason you can't create your own plugin to implement your own custom XMPP-based protocol.

This guide will help walk you through the steps to implement a rudimentary version of XEP-0077 In-band Registration. In-band registration was implemented in example 14-6 (page 223) of XMPP: The Definitive Guide because there was no SleekXMPP plugin for XEP-0077 at the time of writing. We will partially fix that issue here by turning the example implementation from XMPP: The Definitive Guide into a plugin. Again, note that this will not a complete implementation, and a different, more robust, official plugin for XEP-0077 may be added to SleekXMPP in the future.

Note on a Full Client Side XEP-0077 Implementation

Note, however, that creating a full, robust implementation of XEP-0077 is not possible in an automatable sense. The specification states that it is acceptable for a registration form to contain only an instruction field that directs the user to continue registration via some other method. Thus, it is possible for the following to occur:

<iq type='result' id='reg1'>
  <query xmlns='jabber:iq:register'>
    <instructions>
      Please mail your desired username and password 
      in a self-addressed, stamped envelope to:

        Weird In-Band Registrations
        221B Baker St
        London
    </instructions>
  </query>
</iq>

Obviously, handling that situation in an automated fashion is not very feasible.

First Steps

Every plugin inherits from the class base.base_plugin, and must include a plugin_init method. While the plugins distributed with SleekXMPP must be placed in the plugins directory sleekxmpp/plugins to be loaded, custom plugins may be loaded from any module. To do so, use the following form when registering the plugin:

self.register_plugin('myplugin', module=mod_containing_my_plugin)

The plugin name must be the same as the plugin's class name.

Now, we can open our favorite text editors and create xep_0077.py in SleekXMPP/sleekxmpp/plugins. We want to do some basic house-keeping and declare the name and description of the XEP we are implementing. If you are creating your own custom plugin, you don't need to include the xep attribute.

"""
Creating a SleekXMPP Plugin

This is a minimal implementation of XEP-0077 to serve
as a tutorial for creating SleekXMPP plugins.
"""

from sleekxmpp.plugins.base import base_plugin

class xep_0077(base_plugin):
    """
    XEP-0077 In-Band Registration
    """

    def plugin_init(self):
        self.description = "In-Band Registration"
        self.xep = "0077"

Now that we have a basic plugin, we need to edit sleekxmpp/plugins/__init__.py to include our new plugin by adding 'xep_0077' to the __all__ declaration.

Interacting with Other Plugins

In-band registration is a feature that should be advertised through Service Discovery. To do that, we tell the xep_0030 plugin to add the "jabber:iq:register" feature. We put this call in a method named post_init which will be called once the plugin has been loaded; by doing so we advertise that we can do registrations only after we finish activating the plugin.

The post_init method needs to call base_plugin.post_init(self) which will mark that post_init has been called for the plugin. Once the SleekXMPP object begins processing, post_init will be called on any plugins that have not already run post_init. This allows you to register plugins and their dependencies without needing to worry about the order in which you do so.

Note: by adding this call we have introduced a dependency on the XEP-0030 plugin. Be sure to register 'xep_0030' as well as 'xep_0077'. SleekXMPP does not automatically load plugin dependencies for you.

    def post_init(self):
        base_plugin.post_init(self)
        self.xmpp['xep_0030'].add_feature("jabber:iq:register")

Creating Custom Stanza Objects

Now, the IQ stanzas needed to implement our version of XEP-0077 are not very complex, and we could just interact with the XML objects directly just like in the XMPP: The Definitive Guide example. However, creating custom stanza objects is good practice.

We will create a new Registration stanza. Following the XMPP: The Definitive Guide example, we will add support for a username and password field. We also need two flags: registered and remove. The registered flag is sent when an already registered user attempts to register, along with their registration data. The remove flag is a request to unregister a user's account.

Adding additional fields specified in XEP-0077 will not be difficult and is left as an exercise for the reader.

Our Registration class needs to start with a few descriptions of its behaviour:

  • namespace The namespace our stanza object lives in. In this case, "jabber:iq:register".

  • name The name of the root XML element. In this case, the query element.

  • plugin_attrib The name to access this type of stanza. In particular, given a registration stanza, the Registration object can be found using: iq_object['register'].

  • interfaces A list of dictionary-like keys that can be used with the stanza object. When using "key", if there exists a method of the form getKey, setKey, ordelKey (depending on context) then the result of calling that method will be returned. Otherwise, the value of the attribute key of the main stanza element is returned if one exists.

    Note: The accessor methods currently use title case, and not camel case. Thus if you need to access an item named "methodName" you will need to use getMethodname. This naming convention might change to full camel case in a future version of SleekXMPP.

  • sub_interfaces A subset of interfaces, but these keys map to the text of any subelements that are direct children of the main stanza element. Thus, referencing iq_object['register']['username'] will either execute getUsername or return the value in the username element of the query.

    If you need to access an element, say elem, that is not a direct child of the main stanza element, you will need to add getElem, setElem, and delElem. See the note above about naming conventions.

from sleekxmpp.xmlstream import ElementBase, ET, JID, register_stanza_plugin
from sleekxmpp import Iq

class Registration(ElementBase):
    namespace = 'jabber:iq:register'
    name = 'query'
    plugin_attrib = 'register'
    interfaces = set(('username', 'password', 'registered', 'remove'))
    sub_interfaces = interfaces

    def getRegistered(self):
        present = self.xml.find('{%s}registered' % self.namespace)
        return present is not None

    def getRemove(self):
        present = self.xml.find('{%s}remove' % self.namespace)
        return present is not None

    def setRegistered(self, registered):
        if registered:
            self.addField('registered')
        else:
            del self['registered']

    def setRemove(self, remove):
        if remove:
            self.addField('remove')
        else:
            del self['remove']

    def addField(self, name):
        itemXML = ET.Element('{%s}%s' % (self.namespace, name))
        self.xml.append(itemXML)

Setting a sub_interface attribute to "" will remove that subelement. Since we want to include empty registration fields in our form, we need the addField method to add the empty elements.

Since the registered and remove elements are just flags, we need to add custom logic to enforce the binary behavior.

Extracting Stanzas from the XML Stream

Now that we have a custom stanza object, we need to be able to detect when we receive one. To do this, we register a stream handler that will pattern match stanzas off of the XML stream against our stanza object's element name and namespace. To do so, we need to create a Callback object which contains an XML fragment that can identify our stanza type. We can add this handler registration to our plugin_init method.

Also, we need to associate our Registration class with IQ stanzas; that requires the use of the register_stanza_plugin function (in sleekxmpp.xmlstream.stanzabase) which takes the class of a parent stanza type followed by the substanza type. In our case, the parent stanza is an IQ stanza, and the substanza is our registration query.

The __handleRegistration method referenced in the callback will be our handler function to process registration requests.

    def plugin_init(self):
        self.description = "In-Band Registration"
        self.xep = "0077"

        self.xmpp.registerHandler(
          Callback('In-Band Registration',
            MatchXPath('{%s}iq/{jabber:iq:register}query' % self.xmpp.default_ns),
            self.__handleRegistration))
        register_stanza_plugin(Iq, Registration)

Handling Incoming Stanzas and Triggering Events

There are six situations that we need to handle to finish our implementation of XEP-0077.

  • Registration Form Request from a New User:
<iq type="result">
 <query xmlns="jabber:iq:register">
  <username />
  <password />
 </query>
</iq>
  • Registration Form Request from an Existing User:
<iq type="result">
 <query xmlns="jabber:iq:register">
  <registered />
  <username>Foo</username>
  <password>hunter2</password>
 </query>
</iq>
  • Unregister Account:
<iq type="result">
 <query xmlns="jabber:iq:register" />
</iq>
  • Incomplete Registration:
<iq type="error">
  <query xmlns="jabber:iq:register">
    <username>Foo</username>
  </query>
 <error code="406" type="modify">
  <not-acceptable xmlns="urn:ietf:params:xml:ns:xmpp-stanzas" />
 </error>
</iq>
  • Conflicting Registrations:
<iq type="error">
 <query xmlns="jabber:iq:register">
  <username>Foo</username>
  <password>hunter2</password>
 </query>
 <error code="409" type="cancel">
  <conflict xmlns="urn:ietf:params:xml:ns:xmpp-stanzas" />
 </error>
</iq>
  • Successful Registration:
<iq type="result">
 <query xmlns="jabber:iq:register" />
</iq>

Cases 1 and 2: Registration Requests

Responding to registration requests depends on if the requesting user already has an account. If there is an account, the response should include the registered flag and the user's current registration information. Otherwise, we just send the fields for our registration form.

We will handle both cases by creating a sendRegistrationForm method that will create either an empty of full form depending on if we provide it with user data. Since we need to know which form fields to include (especially if we add support for the other fields specified in XEP-0077), we will also create a method setForm which will take the names of the fields we wish to include.

    def plugin_init(self):
        self.description = "In-Band Registration"
        self.xep = "0077"
        self.form_fields = ('username', 'password')
        ... remainder of plugin_init

    ...

    def __handleRegistration(self, iq):
        if iq['type'] == 'get':
            # Registration form requested
            userData = self.backend[iq['from'].bare]
            self.sendRegistrationForm(iq, userData)

    def setForm(self, *fields):
        self.form_fields = fields

    def sendRegistrationForm(self, iq, userData=None):
        reg = iq['register']
        if userData is None:
            userData = {}
        else:
            reg['registered'] = True

        for field in self.form_fields:
            data = userData.get(field, '')
            if data:
                # Add field with existing data
                reg[field] = data
            else:
                # Add a blank field
                reg.addField(field)

        iq.reply().setPayload(reg.xml)
        iq.send()

Note how we are able to access our Registration stanza object with iq['register'].

A User Backend: You might have noticed the reference to self.backend, which is an object that abstracts away storing and retrieving user information. Since it is not much more than a dictionary, we will leave the implementation details to the final, full source code example.

Case 3: Unregister an Account

The next simplest case to consider is responding to a request to remove an account. If we receive a remove flag, we instruct the backend to remove the user's account. Since your application may need to know about when users are registered or unregistered, we trigger an event using self.xmpp.event('unregister_user', iq). See the component examples below for how to respond to that event.

     def __handleRegistration(self, iq):
        if iq['type'] == 'get':
            # Registration form requested
            userData = self.backend[iq['from'].bare]
            self.sendRegistrationForm(iq, userData)
        elif iq['type'] == 'set':
            # Remove an account
            if iq['register']['remove']:
                self.backend.unregister(iq['from'].bare)
                self.xmpp.event('unregistered_user', iq)
                iq.reply().send()
                return

Case 4: Incomplete Registration

For the next case we need to check the user's registration to ensure it has all of the fields we wanted. The simple option that we will use is to loop over the field names and check each one; however, this means that all fields we send to the user are required. Adding optional fields is left to the reader.

Since we have received an incomplete form, we need to send an error message back to the user. We have to send a few different types of errors, so we will also create a _sendError method that will add the appropriate error element to the IQ reply.

    def __handleRegistration(self, iq):
        if iq['type'] == 'get':
            # Registration form requested
            userData = self.backend[iq['from'].bare]
            self.sendRegistrationForm(iq, userData)
        elif iq['type'] == 'set':
            if iq['register']['remove']:
                # Remove an account
                self.backend.unregister(iq['from'].bare)
                self.xmpp.event('unregistered_user', iq)
                iq.reply().send()
                return

            for field in self.form_fields:
                if not iq['register'][field]:
                    # Incomplete Registration
                    self._sendError(iq, '406', 'modify', 'not-acceptable'
                                    "Please fill in all fields.")
                    return

    ...

    def _sendError(self, iq, code, error_type, name, text=''):
        iq.reply().setPayload(iq['register'].xml)
        iq.error()
        iq['error']['code'] = code
        iq['error']['type'] = error_type
        iq['error']['condition'] = name
        iq['error']['text'] = text
        iq.send()

Cases 5 and 6: Conflicting and Successful Registration

We are down to the final decision on if we have a successful registration. We send the user's data to the backend with the self.backend.register method. If it returns True, then registration has been successful. Otherwise, there has been a conflict with usernames and registration has failed. Like with unregistering an account, we trigger an event indicating that a user has been registered by using self.xmpp.event('registered_user', iq). See the component examples below for how to respond to this event.

    def __handleRegistration(self, iq):
        if iq['type'] == 'get':
            # Registration form requested
            userData = self.backend[iq['from'].bare]
            self.sendRegistrationForm(iq, userData)
        elif iq['type'] == 'set':
            if iq['register']['remove']:
                # Remove an account
                self.backend.unregister(iq['from'].bare)
                self.xmpp.event('unregistered_user', iq)
                iq.reply().send()
                return

            for field in self.form_fields:
                if not iq['register'][field]:
                    # Incomplete Registration
                    self._sendError(iq, '406', 'modify', 'not-acceptable',
                                    "Please fill in all fields.")
                    return

            if self.backend.register(iq['from'].bare, iq['register']):
                # Successful registration
                self.xmpp.event('registered_user', iq)
                iq.reply().setPayload(iq['register'].xml)
                iq.send()
            else:
                # Conflicting registration
                self._sendError(iq, '409', 'cancel', 'conflict',
                                "That username is already taken.")

Example Component Using the XEP-0077 Plugin

Alright, the moment we've been working towards - actually using our plugin to simplify our other applications. Here is a basic component that simply manages user registrations and sends the user a welcoming message when they register, and a farewell message when they delete their account.

Note that we have to register the 'xep_0030' plugin first, and that we specified the form fields we wish to use with self.xmpp.plugin['xep_0077'].setForm('username', 'password').

import sleekxmpp.componentxmpp

class Example(sleekxmpp.componentxmpp.ComponentXMPP):

    def __init__(self, jid, password):
        sleekxmpp.componentxmpp.ComponentXMPP.__init__(self, jid, password, 'localhost', 8888)

        self.registerPlugin('xep_0030')
        self.registerPlugin('xep_0077')
        self.plugin['xep_0077'].setForm('username', 'password')

        self.add_event_handler("registered_user", self.reg)
        self.add_event_handler("unregistered_user", self.unreg)

    def reg(self, iq):
        msg = "Welcome! %s" % iq['register']['username']
        self.sendMessage(iq['from'], msg, mfrom=self.fulljid)

    def unreg(self, iq):
        msg = "Bye! %s" % iq['register']['username']
        self.sendMessage(iq['from'], msg, mfrom=self.fulljid)

Congratulations! We now have a basic, functioning implementation of XEP-0077.

Complete Source Code for XEP-0077 Plugin

Here is a copy of a more complete implementation of the plugin we created, but with some additional registration fields implemented.

"""
Creating a SleekXMPP Plugin

This is a minimal implementation of XEP-0077 to serve
as a tutorial for creating SleekXMPP plugins.
"""

from sleekxmpp.plugins.base import base_plugin
from sleekxmpp.xmlstream.handler.callback import Callback
from sleekxmpp.xmlstream.matcher.xpath import MatchXPath
from sleekxmpp.xmlstream import ElementBase, ET, JID, register_stanza_plugin
from sleekxmpp import Iq
import copy


class Registration(ElementBase):
    namespace = 'jabber:iq:register'
    name = 'query'
    plugin_attrib = 'register'
    interfaces = set(('username', 'password', 'email', 'nick', 'name', 
                      'first', 'last', 'address', 'city', 'state', 'zip', 
                      'phone', 'url', 'date', 'misc', 'text', 'key', 
                      'registered', 'remove', 'instructions'))
    sub_interfaces = interfaces

    def getRegistered(self):
        present = self.xml.find('{%s}registered' % self.namespace)
        return present is not None

    def getRemove(self):
        present = self.xml.find('{%s}remove' % self.namespace)
        return present is not None

    def setRegistered(self, registered):
        if registered:
            self.addField('registered')
        else:
            del self['registered']

    def setRemove(self, remove):
        if remove:
            self.addField('remove')
        else:
            del self['remove']

    def addField(self, name):
        itemXML = ET.Element('{%s}%s' % (self.namespace, name))
        self.xml.append(itemXML)


class UserStore(object):
    def __init__(self):
        self.users = {}

    def __getitem__(self, jid):
        return self.users.get(jid, None)

    def register(self, jid, registration):
        username = registration['username']

        def filter_usernames(user):
            return user != jid and self.users[user]['username'] == username

        conflicts = filter(filter_usernames, self.users.keys())
        if conflicts:
            return False

        self.users[jid] = registration
        return True

    def unregister(self, jid):
        del self.users[jid]

class xep_0077(base_plugin):
    """
    XEP-0077 In-Band Registration
    """

    def plugin_init(self):
        self.description = "In-Band Registration"
        self.xep = "0077"
        self.form_fields = ('username', 'password')
        self.form_instructions = ""
        self.backend = UserStore()

        self.xmpp.registerHandler(
            Callback('In-Band Registration',
                     MatchXPath('{%s}iq/{jabber:iq:register}query' % self.xmpp.default_ns),
                     self.__handleRegistration))
        register_stanza_plugin(Iq, Registration)

    def post_init(self):
        base_plugin.post_init(self)
        self.xmpp['xep_0030'].add_feature("jabber:iq:register")

    def __handleRegistration(self, iq):
        if iq['type'] == 'get':
            # Registration form requested
            userData = self.backend[iq['from'].bare]
            self.sendRegistrationForm(iq, userData)
        elif iq['type'] == 'set':
            if iq['register']['remove']:
                # Remove an account
                self.backend.unregister(iq['from'].bare)
                self.xmpp.event('unregistered_user', iq)
                iq.reply().send()
                return

            for field in self.form_fields:
                if not iq['register'][field]:
                    # Incomplete Registration
                    self._sendError(iq, '406', 'modify', 'not-acceptable',
                                    "Please fill in all fields.")
                    return

            if self.backend.register(iq['from'].bare, iq['register']):
                # Successful registration
                self.xmpp.event('registered_user', iq)
                iq.reply().setPayload(iq['register'].xml)
                iq.send()
            else:
                # Conflicting registration
                self._sendError(iq, '409', 'cancel', 'conflict',
                                "That username is already taken.")

    def setForm(self, *fields):
        self.form_fields = fields

    def setInstructions(self, instructions):
        self.form_instructions = instructions

    def sendRegistrationForm(self, iq, userData=None):
        reg = iq['register']
        if userData is None:
            userData = {}
        else:
            reg['registered'] = True

        if self.form_instructions:
            reg['instructions'] = self.form_instructions

        for field in self.form_fields:
            data = userData.get(field, '')
            if data:
                # Add field with existing data
                reg[field] = data
            else:
                # Add a blank field
                reg.addField(field)

        iq.reply().setPayload(reg.xml)
        iq.send()

    def _sendError(self, iq, code, error_type, name, text=''):
        iq.reply().setPayload(iq['register'].xml)
        iq.error()
        iq['error']['code'] = code
        iq['error']['type'] = error_type
        iq['error']['condition'] = name
        iq['error']['text'] = text
        iq.send()
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