The document discusses the evolution of server-side push technologies for web applications, focusing on various techniques such as event polling, long polling, and AJAX streaming. It details the challenges faced by developers in implementing real-time notifications and communications, highlighting the transition from traditional client-server models to more dynamic, real-time approaches. The document also critiques previous methods while presenting new strategies and technologies to improve user experience in web applications.

1. Server-side Push
Comes of Age
by Brian Sam-Bodden
http://www.integrallis.com

2. HTTP

3. HTTP
Unsuspecting Programmers

4. HTTP
Tim Berners-Lee
Unsuspecting Programmers

5. ... and it was good

6. ...for documents

7. it scales!

8. Web Applications
Uhmm, yeah...
Remember that client-server desktop app?
It should be easy to port it to the web, right?

9. Client Server
Request
Response
C
C
Well, hello let me make
you a page good friend
... don’t forget the images
page-by-page model
C ... hold on, I got hit the DB
C ... and cook up some HTML
C ... and all other assets

10. Client Server
Request
Response
C
C
Well, hello let me make
you a page good friend
... don’t forget the images
page-by-page model
C ... hold on, I got hit the DB
C ... and cook up some HTML
C ... and all other assets

11. Client Server
Request
Response
C
C
Well, hello let me make
you a page good friend
... don’t forget the images
page-by-page model
C ... hold on, I got hit the DB
C ... and cook up some HTML
C ... and all other assets

13. ask for it
background

14. and change the
relevant bits

15. Client Server
Load the “application”
C Here’s the initial page load
ajax model
C ... just what’s changedUser Action #1
C ... and againUser Action #2

16. The Web as a
Platform

17. So things got
better, until ...

18. Push
Uhmm, yeah...
Remember that cool web app I underpaid you to build?
It should be easy to notify the user when something
important happens, right?

19. PUSH

20. Why?

21. Collaboration

22. Chat

23. Comments

24. Notifications

25. Bidding Platforms

26. Monitoring

27. Stocks

28. Scores

29. Games

31. Bi-directional

32. Asynchronous

33. Near Real-Time

34. Server Initiated*

35. Communications

36. But...

37. until fairly recently

38. Browsers Sucked!

39. So we had (have)
to Hack it

40. Java
Applets
Polling
iFrame
Streaming
Long
Polling
Flash
Streaming
XHR
Streaming

41. Java
Applets
Polling
iFrame
Streaming
Long
Polling
Flash
Streaming
XHR
Streaming

42. Java
Applets

43. Java
Applets

45. Polling
Java
Applets
iFrame
Streaming
Long
Polling
Flash
Streaming
XHR
Streaming

46. Polling

47. Polling

48. are we there yet?

49. setInterval(function() {
areWeThereYet();
}, 1000);

50. setInterval(function() {
areWeThereYet();
}, 1000);

51. setInterval(function() {
areWeThereYet();
}, 1000);

52. setInterval(function() {
areWeThereYet();
}, 1000);

53. Client Server
Request
Response
Request
Response
C
C
No Soup for you!
Ok, here you go
Event
polling

54. chatty / high traffic

55. Self-inflicted DDOS Attack!

56. iFrame
Streaming
Java
Applets
Polling
Long
Polling
Flash
Streaming
XHR
Streaming

57. iFrame
Streaming

58. iFrame
Streaming

59. Oh yes, it involves
an iFrame
#sadpanda

60. iFrame
Streaming
Demo

61. first you embed an
invisible iFrame

62. $('<iframe />', {
name: 'hidden-iframe',
id: 'hidden-iframe',
src: '/long-running',
css: { 'display': 'none' }
}).appendTo('body');

63. $('<iframe />', {
name: 'hidden-iframe',
id: 'hidden-iframe',
src: '/long-running',
css: { 'display': 'none' }
}).appendTo('body');

64. $('<iframe />', {
name: 'hidden-iframe',
id: 'hidden-iframe',
src: '/long-running',
css: { 'display': 'none' }
}).appendTo('body');

65. $('<iframe />', {
name: 'hidden-iframe',
id: 'hidden-iframe',
src: '/long-running',
css: { 'display': 'none' }
}).appendTo('body');

66. $('<iframe />', {
name: 'hidden-iframe',
id: 'hidden-iframe',
src: '/long-running',
css: { 'display': 'none' }
}).appendTo('body');

67. $('<iframe />', {
name: 'hidden-iframe',
id: 'hidden-iframe',
src: '/long-running',
css: { 'display': 'none' }
}).appendTo('body');

68. on the server
you need
streaming
capabilities

69. get '/long-running' do
stream do |out|
(10..100).step(10) do |n|
word = gimme_funny_word
out << update_progress(n, word.keys.first,
word.values.first)
sleep 1.5
end
end
end

70. get '/long-running' do
stream do |out|
(10..100).step(10) do |n|
word = gimme_funny_word
out << update_progress(n, word.keys.first,
word.values.first)
sleep 1.5
end
end
end

71. get '/long-running' do
stream do |out|
(10..100).step(10) do |n|
word = gimme_funny_word
out << update_progress(n, word.keys.first,
word.values.first)
sleep 1.5
end
end
end

72. get '/long-running' do
stream do |out|
(10..100).step(10) do |n|
word = gimme_funny_word
out << update_progress(n, word.keys.first,
word.values.first)
sleep 1.5
end
end
end

73. get '/long-running' do
stream do |out|
(10..100).step(10) do |n|
word = gimme_funny_word
out << update_progress(n, word.keys.first,
word.values.first)
sleep 1.5
end
end
end

74. get '/long-running' do
stream do |out|
(10..100).step(10) do |n|
word = gimme_funny_word
out << update_progress(n, word.keys.first,
word.values.first)
sleep 1.5
end
end
end

75. def update_progress(percent, word, meaning)
%[<script type="text/javascript">
parent.updatePage(#{percent}, '#{word}', '#{meaning}');
</script>]
end

76. def update_progress(percent, word, meaning)
%[<script type="text/javascript">
parent.updatePage(#{percent}, '#{word}', '#{meaning}');
</script>]
end

77. // called by the streamed server-sent script
function updatePage(percent, word, meaning) {
$kickItButton.text(percent + '%');
$theWord.text(word);
$theMeaning.text(meaning);
if (percent == 100) {
$kickItButton.attr('disabled', false);
$kickItButton.text('Kick it again!');
}
}

78. // called by the streamed server-sent script
function updatePage(percent, word, meaning) {
$kickItButton.text(percent + '%');
$theWord.text(word);
$theMeaning.text(meaning);
if (percent == 100) {
$kickItButton.attr('disabled', false);
$kickItButton.text('Kick it again!');
}
}

79. // called by the streamed server-sent script
function updatePage(percent, word, meaning) {
$kickItButton.text(percent + '%');
$theWord.text(word);
$theMeaning.text(meaning);
if (percent == 100) {
$kickItButton.attr('disabled', false);
$kickItButton.text('Kick it again!');
}
}

80. // called by the streamed server-sent script
function updatePage(percent, word, meaning) {
$kickItButton.text(percent + '%');
$theWord.text(word);
$theMeaning.text(meaning);
if (percent == 100) {
$kickItButton.attr('disabled', false);
$kickItButton.text('Kick it again!');
}
}

81. // called by the streamed server-sent script
function updatePage(percent, word, meaning) {
$kickItButton.text(percent + '%');
$theWord.text(word);
$theMeaning.text(meaning);
if (percent == 100) {
$kickItButton.attr('disabled', false);
$kickItButton.text('Kick it again!');
}
}

82. Drawback:
Page is ‘forever’
loading

83. iFrame
Streaming
Java
Applets
Polling
Long
Polling
Flash
Streaming
XHR
Streaming

84. XHR
Streaming

85. XHR
Streaming

86. XHR
Streaming
Demo

87. better than iframes

88. use AJAX call

89. send JSON

90. get '/stream' do
stream do |out|
(10..100).step(2) do |n|
out << gimme_funny_word.as_json
sleep 1.5
end
end
end

91. get '/stream' do
stream do |out|
(10..100).step(2) do |n|
out << gimme_funny_word.as_json
sleep 1.5
end
end
end

92. get '/stream' do
stream do |out|
(10..100).step(2) do |n|
out << gimme_funny_word.as_json
sleep 1.5
end
end
end

93. polling the stream

94. parse = function() {
// parse the xhr.responseText and update the UI
};
xhr = new XMLHttpRequest();
url = "/stream";
xhr.open("GET", url, true);
xhr.send();
last_index = 0;
interval = setInterval(parse, 500);
setTimeout((function() {
clearInterval(interval);
parse();
xhr.abort();
}), 20000);

95. parse = function() {
// parse the xhr.responseText and update the UI
};
xhr = new XMLHttpRequest();
url = "/stream";
xhr.open("GET", url, true);
xhr.send();
last_index = 0;
interval = setInterval(parse, 500);
setTimeout((function() {
clearInterval(interval);
parse();
xhr.abort();
}), 20000);

96. parse = function() {
// parse the xhr.responseText and update the UI
};
xhr = new XMLHttpRequest();
url = "/stream";
xhr.open("GET", url, true);
xhr.send();
last_index = 0;
interval = setInterval(parse, 500);
setTimeout((function() {
clearInterval(interval);
parse();
xhr.abort();
}), 20000);

97. parse = function() {
// parse the xhr.responseText and update the UI
};
xhr = new XMLHttpRequest();
url = "/stream";
xhr.open("GET", url, true);
xhr.send();
last_index = 0;
interval = setInterval(parse, 500);
setTimeout((function() {
clearInterval(interval);
parse();
xhr.abort();
}), 20000);

98. parse = function() {
// parse the xhr.responseText and update the UI
};
xhr = new XMLHttpRequest();
url = "/stream";
xhr.open("GET", url, true);
xhr.send();
last_index = 0;
interval = setInterval(parse, 500);
setTimeout((function() {
clearInterval(interval);
parse();
xhr.abort();
}), 20000);

99. frequency of polling the stream
>=
server serving rate

100. No Throbber
Freakout

101. Long
Polling
iFrame
Streaming
Java
Applets
Polling
Flash
Streaming
XHR
Streaming

102. Long
Polling

103. Long
Polling

104. most commonly
used

105. response is
blocked...

106. ...until server event
occurs

107. Client Server
Request
Response
C
C
Nothing here, but hang on...
... and there you go, good day!
Event
polling

108. Long
Polling
Demo

109. get '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
not_changed_or_emtpy = true
while (not_changed_or_emtpy) do
sleep 0.1
not_changed_or_emtpy = File.zero?(filename) || (current <= last)
current = last_modification(filename)
end
{ :messages => File.read(filename), :timestamp => current }.to_json
end

110. get '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
not_changed_or_emtpy = true
while (not_changed_or_emtpy) do
sleep 0.1
not_changed_or_emtpy = File.zero?(filename) || (current <= last)
current = last_modification(filename)
end
{ :messages => File.read(filename), :timestamp => current }.to_json
end

111. get '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
not_changed_or_emtpy = true
while (not_changed_or_emtpy) do
sleep 0.1
not_changed_or_emtpy = File.zero?(filename) || (current <= last)
current = last_modification(filename)
end
{ :messages => File.read(filename), :timestamp => current }.to_json
end

112. get '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
not_changed_or_emtpy = true
while (not_changed_or_emtpy) do
sleep 0.1
not_changed_or_emtpy = File.zero?(filename) || (current <= last)
current = last_modification(filename)
end
{ :messages => File.read(filename), :timestamp => current }.to_json
end

113. get '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
not_changed_or_emtpy = true
while (not_changed_or_emtpy) do
sleep 0.1
not_changed_or_emtpy = File.zero?(filename) || (current <= last)
current = last_modification(filename)
end
{ :messages => File.read(filename), :timestamp => current }.to_json
end

114. get '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
not_changed_or_emtpy = true
while (not_changed_or_emtpy) do
sleep 0.1
not_changed_or_emtpy = File.zero?(filename) || (current <= last)
current = last_modification(filename)
end
{ :messages => File.read(filename), :timestamp => current }.to_json
end

115. get '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
not_changed_or_emtpy = true
while (not_changed_or_emtpy) do
sleep 0.1
not_changed_or_emtpy = File.zero?(filename) || (current <= last)
current = last_modification(filename)
end
{ :messages => File.read(filename), :timestamp => current }.to_json
end

116. function longPoll() {
$.ajax({
type : 'get',
url : '/read?timestamp=' + timestamp,
async : true,
cache : false,
timeout : 10000,
success : function(json) {
var messages = json['messages'].split("n")
var last = messages[messages.length-1];
if (last) {
$('#msg').append('<div>'+last+'</div>');
timestamp = json['timestamp'];
}
setTimeout(longPoll, 1000);
},
error : function(xhr, textStatus, error) {
setTimeout(longPoll, 2000);
}
});
}

117. function longPoll() {
$.ajax({
type : 'get',
url : '/read?timestamp=' + timestamp,
async : true,
cache : false,
timeout : 10000,
success : function(json) {
var messages = json['messages'].split("n")
var last = messages[messages.length-1];
if (last) {
$('#msg').append('<div>'+last+'</div>');
timestamp = json['timestamp'];
}
setTimeout(longPoll, 1000);
},
error : function(xhr, textStatus, error) {
setTimeout(longPoll, 2000);
}
});
}

118. function longPoll() {
$.ajax({
type : 'get',
url : '/read?timestamp=' + timestamp,
async : true,
cache : false,
timeout : 10000,
success : function(json) {
var messages = json['messages'].split("n")
var last = messages[messages.length-1];
if (last) {
$('#msg').append('<div>'+last+'</div>');
timestamp = json['timestamp'];
}
setTimeout(longPoll, 1000);
},
error : function(xhr, textStatus, error) {
setTimeout(longPoll, 2000);
}
});
}

119. function longPoll() {
$.ajax({
type : 'get',
url : '/read?timestamp=' + timestamp,
async : true,
cache : false,
timeout : 10000,
success : function(json) {
var messages = json['messages'].split("n")
var last = messages[messages.length-1];
if (last) {
$('#msg').append('<div>'+last+'</div>');
timestamp = json['timestamp'];
}
setTimeout(longPoll, 1000);
},
error : function(xhr, textStatus, error) {
setTimeout(longPoll, 2000);
}
});
}

120. Naive Long polling w/ 10sec timeout
{
Requests that
returned data
Current polling
request
Requests in RED
are timed out
long polls

121. There is a big issue with
the previous example...

122. There is a big issue with
the previous example...
Besides using a Text
File as a database

123. The server doesn’t support
async responses...

124. The busy IO checking loop
will block

125. aget '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
EM.defer do
check_file_changes = proc do
if File.zero?(filename) || (current <= last)
current = last_modification(filename)
EM.next_tick(&check_file_changes)
else
body({ :messages => File.read(filename),
:timestamp => current }.to_json)
end
end
EM.next_tick(&check_file_changes)
end
end

126. aget '/read' do
content_type :json
filename = 'data.txt'
last = params[:timestamp] == 'null' ? 0 : params[:timestamp].to_i
current = last_modification(filename)
EM.defer do
check_file_changes = proc do
if File.zero?(filename) || (current <= last)
current = last_modification(filename)
EM.next_tick(&check_file_changes)
else
body({ :messages => File.read(filename),
:timestamp => current }.to_json)
end
end
EM.next_tick(&check_file_changes)
end
end

127. Difficult to
Implement

128. Flash
Streaming
Long
Polling
iFrame
Streaming
Java
Applets
Polling
XHR
Streaming

129. Flash
Streaming

130. Flash
Streaming

131. XML Socket

132. Single Pixel
Flash Movie

133. Go Away
Flash!

134. Push
Frameworks

135. Comet
!=
Just Long Polling

136. Amalgamation of
Techniques

137. Provide both Client
and Server
Components

138. Many use a
Pub-Sub Protocol

139. Bayeaux

140. Comet
Demo
with
http://faye.jcoglan.com

141. var client = new Faye.Client('/faye');
var subscription = client.subscribe('/<%= room %>', function(message) {
$messages = $('#messages');
$message = $('<div>' + message['user'] + ' : ' + message['text'] +'</div>')
$messages.append($message);
});
$("#chat-form").submit(function(e){
e.preventDefault();
var message = $('#message').val();
client.publish('/<%= room %>', {user: '<%= username %>', text: message});
$('#message').val('');
});

142. var client = new Faye.Client('/faye');
var subscription = client.subscribe('/<%= room %>', function(message) {
$messages = $('#messages');
$message = $('<div>' + message['user'] + ' : ' + message['text'] +'</div>')
$messages.append($message);
});
$("#chat-form").submit(function(e){
e.preventDefault();
var message = $('#message').val();
client.publish('/<%= room %>', {user: '<%= username %>', text: message});
$('#message').val('');
});

143. var client = new Faye.Client('/faye');
var subscription = client.subscribe('/<%= room %>', function(message) {
$messages = $('#messages');
$message = $('<div>' + message['user'] + ' : ' + message['text'] +'</div>')
$messages.append($message);
});
$("#chat-form").submit(function(e){
e.preventDefault();
var message = $('#message').val();
client.publish('/<%= room %>', {user: '<%= username %>', text: message});
$('#message').val('');
});

144. var client = new Faye.Client('/faye');
var subscription = client.subscribe('/<%= room %>', function(message) {
$messages = $('#messages');
$message = $('<div>' + message['user'] + ' : ' + message['text'] +'</div>')
$messages.append($message);
});
$("#chat-form").submit(function(e){
e.preventDefault();
var message = $('#message').val();
client.publish('/<%= room %>', {user: '<%= username %>', text: message});
$('#message').val('');
});

145. Now we can create a room ... and have a conversation

147. Web Sockets

148. Two Way
Communications

149. Over a dedicated
socket

150. in simple way

151. with security,
proxies & firewalls
in mind

152. Web
Sockets
Demo

153. EventMachine.run do
EventMachine::WebSocket.start(:host => "0.0.0.0", :port => 8080) do |ws|
ws.onopen do
end
ws.onmessage do |msg|
end
ws.onclose do
end
end
end
em-websocket provides an
easy to use WebSocket class
On the server
we’ll implement
some WebSocket
event handlers

154. EventMachine.run do
@channel = EM::Channel.new
@users = {}
@messages = []
...
ws.onopen do
new_user = @channel.subscribe { |msg| ws.send msg }
@users[ws.object_id] = new_user
@messages.each do |message|
ws.send message
end
end
subscribe a new user to the channel
passing the callback to our push action
we’ll keep a list of users in a Hash keyed by
the object_id of the incoming ws connection
push the last batch of
messages to the user

155. ws.onmessage do |msg|
@messages << msg
@messages.shift if @messages.length > 10
@channel.push msg
end
add the new message to the end of the
queue
broadcast the message to all users
connected to the channel
we’ll keep the last 10 messages

156. ws.onclose do
@channel.unsubscribe(@users[ws.object_id])
@users.delete(ws.object_id)
end
we unsubscribe them from the channel
remove them from the Hash of users

157. EventMachine.run do
EventMachine::WebSocket.start(...) do |ws|
...
end
class App < Sinatra::Base
get '/' do
erb :index
end
end
App.run!
end
our single page
application is contained in
/public/views/index.erb
The Sinatra app runs as part
of the EV “Reactor Loop”

158. <div class="container">
<h1 class="visible-desktop">WebSockets Sinatra Draw</h1>
<legend>Draw Something</legend>
<div id="whiteboard" class="well well-small">
<canvas id="draw-canvas"></canvas>
</div>
</div>
We’ll nest the canvas in
a div in order to resize it
correctly
$(document).ready(function() {
var $canvas = $('#draw-canvas');
var ws = new WebSocket("ws://" + location.hostname + ":8080");
When the document is ready we’ll
connect to the EM Websocket server
running on :8080

159. var currentX = 0;
var currentY = 0;
var lastX, lastY, lastReceivedX, lastReceivedY;
var drawing = false;
var ctx = $('#draw-canvas')[0].getContext('2d');
We’ll grab the 2D canvas
context in order to draw on it
$canvas.bind('mousemove',function(ev){
ev = ev || window.event;
currentX = ev.pageX - $canvas.offset().left;
currentY = ev.pageY - $canvas.offset().top;
});
$canvas.bind('touchmove',function(ev){
var touch = ev.originalEvent.touches[0] || ev.originalEvent.changedTouches[0];
currentX = touch.pageX - $canvas.offset().left;
currentY = touch.pageY - $canvas.offset().top;
});
We’ll update the currentX and currentY
coordinates of the mouse over the canvas both for
desktop and mobile browsers
touchmove is provided by
jQuery-Mobile-Events
plugin

160. $canvas.bind('tapstart',function(ev) {
drawing = true
});
$canvas.bind('tapend',function(ev) {
drawing = false
});
tapstart and tapend are also provided
by the jQuery-Mobile-Events

161. ws.onopen = function(event) {
setInterval(function() {
if ((currentX !== lastX || currentY !== lastY) && drawing) {
lastX = currentX;
lastY = currentY;
ws.send(JSON.stringify({ x: currentX, y: currentY}));
}
}, 30);
}

162. ws.onmessage = function(event) {
var msg = $.parseJSON(event.data);
ctx.beginPath();
ctx.moveTo(lastReceivedX, lastReceivedY);
ctx.lineTo(msg.x, msg.y);
ctx.closePath();
ctx.stroke();
lastReceivedX = msg.x;
lastReceivedY = msg.y;
};
We’ll only draw indirectly when we
receive a message (even when we
are the ones doing the drawing)

163. On Firefox
On Safari Desktop
... and on my almost out of
batteries iPhone

164. What are we
missing?

165. Server-sent
Events

166. BOSH

167. WebRTC

168. What should
you do?

169. Use a
Framework!

170. That plays well
with your
framework

171. Thanks
All example code available at:
https://github.com/integrallis/server-side-push
Watch out for an upcoming article at http://integrallis.com
by Brian Sam-Bodden
http://www.integrallis.com
http://www.slideshare.net/bsbodden/ssp-oscon