30. Long Polling – 1 server function poll_server () { new Ajax. Request ( this .urlPolling, { method: 'post' , parameters: data, onSuccess: this .successHandler, onFailure: this .handleFailure, onException: this .handleException }); } document. observe ( 'dom:loaded' , poll_server);
31. Long Polling – 1 server function successHandler (trans, messages_div) { if (trans.responseText) { var json = trans.responseText. evalJSON (); if (json.message) { var msg = json.message + '<br />' ; $(messages_div). insert (msg); } } poll_server (); }
32. Long Polling – 1 server <?php $query = 'SELECT message FROM messages WHERE dateadded > ?' ; $stmt = $pdo -> prepare ( $query ); while (true) { $message = $stmt -> execute ( $cursor_date ); if (! empty ( $message )) { echo json_encode ( $message ); break ; } } ?>
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36. Long Polling – 2 servers web server polling server HTTP XHR over HTTP
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39. Long Polling – 2 servers function poll_server () { new Ajax. Request ( this .urlPolling, { method: 'post' , parameters: data, onSuccess: this .successHandler, onFailure: this .handleFailure, onException: this .handleException }); } document. observe ( 'dom:loaded' , poll_server);
40. Long Polling – 2 servers function successHandler (trans, messages_div) { if (trans.responseText) { var json = trans.responseText. evalJSON (); if (json.message) { var msg = json.message + '<br />' ; $(messages_div). insert (msg); } } poll_server (); }
41. Long Polling – 2 servers Main Web Server Polling Server <?php $query = 'INSERT INTO messages VALUES (?, ?)' ; $stmt = $pdo -> prepare ( $query ); $stmt -> prepare ( $message , $date ); $polling_server -> send ( $message ); ?> <?php foreach ( $this ->waiting as $connection ){ $connection -> respond ( $message ); } ?>
50. WebSockets function poll_server () { var socket = new WebSocket ( 'ws://example.com/' ); socket.onmessage = function (response) { successHandler (response, 'message_errors' ); } } document. observe ( 'dom:loaded' , poll_server);
51. WebSockets function successHandler (trans, messages_div) { if (trans.data) { var json = trans.data. evalJSON (); if (json.message) { var msg = json.message + '<br />' ; $(messages_div). insert (msg); } } }
52. WebSockets Main Web Server WebSocket Server <?php $query = 'INSERT INTO messages VALUES (?, ?)' ; $stmt = $pdo -> prepare ( $query ); $stmt -> prepare ( $message , $date ); $polling_server -> send ( $message ); ?> <?php foreach ( $this ->waiting as $connection ){ $connection -> respond ( $message ); } ?>
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58. WaterSpout - Listeners <?php public function listen () { // Handle cursor for long polling fall back. // ... $this ->dispatcher-> add_listener ( $this ); } ?>
59. WaterSpout - Dispatcher <?php /* Called every .25 seconds on all waiting listeners */ public function process_event (Controller $mover = null) { $key = array_search (( int ) $this ->_cursor, array_keys (self:: $_commands )); if ( $key === false && ! is_null ( $this ->_cursor)) { return ; } $commands = array_slice (self:: $_commands , $key ); if ( empty ( $commands )) { return ; } $response = new HTTPResponse ( 200 ); $body = array ( '__URI__' => $this ->uri, 'commands' => $commands, 'cursor' => end ( array_keys (self:: $_commands )) + 1 ); $response -> set_body ( $body , true); $this -> write ( $response ); $this ->_cursor = ( int ) end ( array_keys (self:: $_commands )) + 1 ; } ?>
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Editor's Notes
- Once upon a time, the internet was flat. Users asked for content and web servers gave it to them. - XMLHttpRequest came along and change all of that. - Google said “well, we know they are going to ask for their new messages soon anyway, so why not give them the new messages before they ask?”
- Unless you are Facebook, the database is your bottle neck. - Solutions that consume database resources are not very scalable - Timeliness is often sacrificed for scalability
Basically the same as refresh but with less data transfered
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