This document discusses Node.js and how it enables event-driven and non-blocking programming in JavaScript. It provides examples of how Node.js allows for handling a large number of concurrent connections efficiently. It then discusses different techniques for asynchronous communication between a client and server, including AJAX polling, Comet, and websockets. Finally, it provides a specific example of implementing a long polling system on the server-side using a custom buffer and on the client-side by periodically requesting updates from the server.

1. Current
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2. What is Node.js?
_ non-blocking
_ evented
_ javascript
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3. Why is node useful?
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4. Why is node useful?
It can handle a ton of
concurrent connections
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5. A Gross
Oversimplification
of HTTP
Give me a page
Sure
Connection Closed
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6. AJAX Polling
Got any updates?
No
Connection Closed
Got any updates?
No
Connection Closed
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7. Comet
Got any updates?
...wait
Yes
Connection Closed
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8. Websocket
asyncronous updates
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9. Evented Programming
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10. Non-Evented Example
mysql_select_db("example", $con);
$result = mysql_query("SELECT * FROM user WHERE fname='Bill'");
while($row = mysql_fetch_array($result)){
echo $row['fname'];
}
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11. Evented Example
fs.readFile("./file", function (err, data) {
if (err) throw err;
sys.puts(data);
});
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12. An Example
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13. Server Side
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14. Setup the Data Source
var rb = new lpb.LongPollingBuffer(70);
var dump = process.createChildProcess("tcpdump",["-i","en1","-A","-n","port", "80"]);
var ignorelist = ['localhost','foxnews.com'];
//Setup the listener to handle the flow of data from the dump
dump.addListener("output", function (data) {
var hosts = data.match(/Host: (.*)/g);
if(hosts){
_.each(hosts, function(item){
var out = item.slice(6);
sys.puts(out);
if(!_.detect(ignorelist, function(s){ return (item.indexOf(s) > -1); })){
rb.push(out);
}
});
}
});
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15. LongPollingBuffer
DATA ARRAY
DATA: 1 1 1 0 1 0 0 1 1 0
OFFSET: 0 2 3 4 5 6 7 8 9 10
CLIENT ONE CLIENT TWO
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16. Setup the Updater
fu.get("/update", function (req, res) {
//Send the HTTP Headers
res.sendHeader(200,{"Content-Type": "text/html"});
//Parse out the since from the query string
var thesince;
if(url.parse(req.url,true).hasOwnProperty('query') &&
url.parse(req.url,true).query.hasOwnProperty('since')){
thesince = parseInt(url.parse(req.url,true)['query']['since']);
}
else {
thesince = -1;
}
//Setup the datalistener (note why this works so well with JS scoping)
rb.addListenerForUpdateSince(thesince, function(data){
var body = '['+_.map(data,JSON.stringify).join(',n')+']';
res.write( body );
res.close();
});
});
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17. Client Side
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18. Long Polling Request
var url = “/update?since=” + lastrecieved;
$.getJSON(url, function(data){
var itemstoadd = _.map(data.reverse(),function(item){
lastrecieved = item["offset"];
return domainmarkup(item['value']);
});
var uc = $("#updatedcontent");
_.map(itemstoadd, function(item){
if(!interrupt){
uc.prepend(item);
}
});
setTimeout('getupdate(lastrecieved)', 1000);
});
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19. Questions?
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