EventMachine Server Design With XMPP

EventMachine Server Design With XMPP @davidgraham 17 April 2012

gem install vines

gem install couchproxy

XMPP is not HTTP

Long Lived Connections

Connections Mostly Idle

Stateful

Requires Asynchronous IO

EventMachine

You do not block the event loop.

# test.ru app = proc do |env| sleep 20 [
200, {'Content-Type' => 'text/html'}, ['Hello World'] ] end run app $ thin --rackup test.ru start $ curl http://localhost:3000 $ curl http://localhost:3000

# test.ru app = proc do |env| sleep 20 [
200, {'Content-Type' => 'text/html'}, ['Hello World'] ] end run app $ thin --rackup test.ru --threaded start $ curl http://localhost:3000 $ curl http://localhost:3000

require 'eventmachine' module EchoServer def post_init puts "-- someone connected
to the echo server!" end def receive_data data send_data ">>> you sent: #{data}" end end EventMachine::run do EventMachine::start_server "127.0.0.1", 8081, EchoServer puts 'running echo server on 8081' end Easy!

IO Read Parser Queue State Machine IO Write

require 'eventmachine' module EchoServer def post_init puts "-- someone connected
to the echo server!" end def receive_data data send_data ">>> you sent: #{data}" end end EventMachine::run do EventMachine::start_server "127.0.0.1", 8081, EchoServer puts 'running echo server on 8081' end Easy! Maybe Not

Stream Negotiation

<stream:stream from='[email protected]' to='im.example.com' version='1.0' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'>

<stream:stream from='[email protected]' to='im.example.com' version='1.0' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'> <stream:stream from='im.example.com' id='t7AMCin9zjMNwQKDnplntZPIDEI=' to='[email protected]'
version='1.0' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'>

version='1.0' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'> <stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'> <required/> </starttls> </stream:features>

version='1.0' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'> <stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'> <required/> </starttls> </stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>

version='1.0' xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams'> <stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'> <required/> </starttls> </stream:features> <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/> <proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>

Stanzas

<message from='[email protected]/balcony' to='[email protected]'> <body>Wherefore art thou, Romeo?</body> </message>

<message from='[email protected]/balcony' to='[email protected]'> <body>Wherefore art thou, Romeo?</body> </message> <presence from='[email protected]/balcony'>
<show>away</show> <status>I’m not here!</status> </presence>

<message from='[email protected]/balcony' to='[email protected]'> <body>Wherefore art thou, Romeo?</body> </message> <presence from='[email protected]/balcony'>
<show>away</show> <status>I’m not here!</status> </presence> <iq from='[email protected]/balcony' id='hu2bac18' type='get'> <query xmlns='jabber:iq:roster'/> </iq>

Parsers

Line Separated def post_init @parser = BufferedTokenizer.new end def receive_data(data)
@parser.extract(data).each do |line| receive_line(line) end end

XML def post_init @parser = Nokogiri::XML::SAX::PushParser.new(self) end def receive_data(data) @parser
<< data end

HTTP def post_init @parser = HTTP::Parser.new end def receive_data(data) @parser
<< data end

JSON::Stream def post_init @parser = JSON::Stream::Parser.new end def receive_data(data) @parser
<< data end

YAJL-JSON def post_init @parser = YAJL::Parser.new end def receive_data(data) @parser
<< data end

@parser << data

Queues

10.1. In-Order Processing An XMPP server MUST ensure in-order processing
of the stanzas and other XML elements it receives over a given input stream from a connected client or remote server. XMPP RFC 6120

Blocking Queue def post_init @nodes = Queue.new end def process_node_queue
node = @nodes.pop # blocks process_node(node) process_node_queue end

Asynchronous Queue def post_init @nodes = EM::Queue.new end def process_node_queue
@nodes.pop do |node| process_node(node) process_node_queue end end

State Machines

Security

Sanity

Easy to Test

it 'rejects invalid elements' do state = Stream::Client::Auth.new assert_raises(StreamErrors::NotAuthorized) do
state.node('<bogus/>') end end Authentication Fails

it 'accepts valid plain auth passwords' do state = Stream::Client::Auth.new
next_state = Stream::Client::BindRestart.new stream = MiniTest::Mock.new stream.expect(:write, nil, ['<success/>']) stream.expect(:advance, nil, [next_state]) node = "<auth mechanism='PLAIN'>#{@password}</auth>" state.node(node) assert stream.verify end Authentication Passes

Case Statement

case @state when :start_document then start_document when :start_object then start_object
when :start_string then start_string when :unicode_escape then unicode_escape when :start_surrogate_pair then start_surrogate when :start_negative_number then start_negative when :start_zero then start_zero when :start_float then start_float when :start_exponent then start_exponent when :start_int then start_int when :start_true then start_true when :start_false then start_false when :start_null then start_null when :end_key then end_key when :start_array then start_array when :end_value then end_value when :end_document then end_document end JSON::Stream

case @state when :start_document case ch when "{" @state =
:start_object @stack.push(:object) notify_start_document notify_start_object when "[" @state = :start_array @stack.push(:array) notify_start_document notify_start_array when WS # ignore else error("Expected object or array start") end when :start_object case ch JSON::Stream

case @state when :start_document case ch when LEFT_BRACE @state =
:start_object @stack.push(:object) notify_start_document notify_start_object when LEFT_BRACKET @state = :start_array @stack.push(:array) notify_start_document notify_start_array when WS # ignore else error("Expected object or array start") end when :start_object case ch when RIGHT_BRACE end_container(:object) when QUOTE @state = :start_string @stack.push(:key) when WS # ignore else error("Expected object key start") end when :start_string case ch when QUOTE if @stack.pop == :string @state = :end_value notify_value(@buf) else # :key @state = :end_key notify_key(@buf) end @buf = "" when BACKSLASH @state = :start_escape when CONTROL error('Control characters must be escaped') else @buf << ch end when :start_escape case ch when QUOTE, BACKSLASH, SLASH @buf << ch @state = :start_string when B @buf << "\b" @state = :start_string when F @buf << "\f" @state = :start_string when N @buf << "\n" @state = :start_string when R @buf << "\r" @state = :start_string when T @buf << "\t" @state = :start_string when U @state = :unicode_escape else error("Expected escaped character") end when :unicode_escape case ch when HEX @unicode << ch if @unicode.size == 4 codepoint = @unicode.slice!(0, 4).hex if codepoint >= 0xD800 && codepoint <= 0xDBFF error('Expected low surrogate pair half') if @stack[-1].is_a?(Fixnum) @state = :start_surrogate_pair @stack.push(codepoint) elsif codepoint >= 0xDC00 && codepoint <= 0xDFFF high = @stack.pop error('Expected high surrogate pair half') unless high.is_a?(Fixnum) pair = ((high - 0xD800) * 0x400) + (codepoint - 0xDC00) + 0x10000 @buf << pair @state = :start_string else @buf << codepoint @state = :start_string end end else error('Expected unicode escape hex digit') end when :start_surrogate_pair case ch when BACKSLASH @state = :start_surrogate_pair_u else error('Expected low surrogate pair half') end when :start_surrogate_pair_u case ch when U @state = :unicode_escape else error('Expected low surrogate pair half') end when :start_negative_number case ch when ZERO @state = :start_zero @buf << ch when DIGIT_1_9 @state = :start_int @buf << ch else error('Expected 0-9 digit') end when :start_zero case ch when POINT @state = :start_float @buf << ch when EXPONENT @state = :start_exponent @buf << ch else @state = :end_value notify_value(@buf.to_i) @buf = "" @pos -= 1 redo end when :start_float case ch when DIGIT @state = :in_float @buf << ch else error('Expected 0-9 digit') end when :in_float case ch when DIGIT @buf << ch when EXPONENT @state = :start_exponent @buf << ch else @state = :end_value notify_value(@buf.to_f) @buf = "" @pos -= 1 redo end when :start_exponent case ch when MINUS, PLUS, DIGIT @state = :in_exponent @buf << ch else error('Expected +, -, or 0-9 digit') end when :in_exponent case ch when DIGIT @buf << ch else error('Expected 0-9 digit') unless @buf =~ DIGIT_END @state = :end_value num = @buf.include?('.') ? @buf.to_f : @buf.to_i notify_value(num) @buf = "" @pos -= 1 redo end when :start_int case ch when DIGIT @buf << ch when POINT @state = :start_float @buf << ch when EXPONENT @state = :start_exponent @buf << ch else @state = :end_value notify_value(@buf.to_i) @buf = "" @pos -= 1 redo end when :start_true keyword(TRUE_KEYWORD, true, TRUE_RE, ch) when :start_false keyword(FALSE_KEYWORD, false, FALSE_RE, ch) when :start_null keyword(NULL_KEYWORD, nil, NULL_RE, ch)

State Design Pattern

Start TLS AuthRestart Auth BindRestart Bind Ready Closed

class Start < State def initialize(stream, success=TLS) super end def
node(node) raise StreamErrors::NotAuthorized unless stream?(node) stream.start(node) doc = Document.new features = doc.create_element('stream:features') do |el| el << doc.create_element('starttls') do |tls| tls.default_namespace = NAMESPACES[:tls] tls << doc.create_element('required') end end stream.write(features) advance end end

class Ready < State def node(node) stanza = to_stanza(node) raise
StreamErrors::UnsupportedStanzaType unless stanza stanza.validate_to stanza.validate_from stanza.process end end

EventMachine, a Lonely Island

Also, a Lonely Island

Let’s talk to a database!

gem install activerecord

gem install mongo_mapper

gem install redis

gem install couchrest

Blocking (a.k.a. Normal) IO

gem install em-redis em-hiredis em-mongo em-http-request

No problem, let’s use threads!

# runs on thread pool operation = proc do sleep
20 42 end # runs on the reactor thread callback = proc do |result| send_data(result) end EM.defer(operation, callback) Thread Pool

user = find_user('[email protected]') user.name = 'Alice' user = save_user(user) puts
user.name Callback Spaghetti find_user('[email protected]') do |user| user.name = 'Alice' save_user(user) do |user| puts user.name end end

Fibers

fiber = Fiber.new do Fiber.yield 1 Fiber.yield 2 Fiber.yield 3
end fiber.resume #=> 1 fiber.resume #=> 2 fiber.resume #=> 3 fiber.resume #=> FiberError: dead fiber called Episode IV: A New Stack

def find_user(username) User.find_by_username(username) # blocks end

def find_user(username) fiber = Fiber.current op = proc { User.find_by_username(username)
} cb = proc {|user| fiber.resume(user) } EM.defer(op, cb) Fiber.yield end Threads + Fibers

def find_user(username) fiber = Fiber.current op = proc { User.find_by_username(username)
} cb = proc {|user| fiber.resume(user) } EM.defer(op, cb) Fiber.yield end Boilerplate

def find_user(username) User.find_by_username(username) end defer :find_user Decorator

def self.defer(method) old = "_deferred_#{method}" alias_method old, method define_method method
do |*args| fiber = Fiber.current op = proc { method(old).call(*args) } cb = proc {|result| fiber.resume(result) } EM.defer(op, cb) Fiber.yield end end Metaprogramming

def find_user(username) # find user end defer :find_user def save_user(user)
# save user end defer :save_user def find_vcard(jid) # find card end defer :find_vcard def save_vcard(jid, card) # save card end defer :save_vcard DRY

def post_init @nodes = EM::Queue.new end def process_node_queue @nodes.pop do
|node| Fiber.new do process_node(node) process_node_queue end.resume end end Fiber/Stanza

The End @davidgraham [email protected]

EventMachine Server Design With XMPP

EventMachine Server Design With XMPP

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