Messing with JavaScript and the DOM to measure network characteristics

Messing with JS & the DOM to analyse the
Network

Philip Tellis / philip@bluesmoon.info

JSConf.eu / 2011-10-01

JSConf.eu / 2011-10-01 Messing with JS & the DOM to analyse the Network 1

HTTP/TCP/IP

Developed by three guys with one beard between them


JavaScript: The good parts

Discovered by one guy with one beard on him


Let’s play with the nasty parts


1
Latency


1 Blinkenlichten

It takes about 23ms for light to get from Berlin to NY
(35ms through ﬁbre)
Image from http://cablemap.info


1 HTTP


So to measure latency, we need to send 1 packet each way, and
time it


1 Network latency in JavaScript

var ts, rtt, img = new Image;
img.onload=function() { rtt=(+new Date - ts) };
ts = +new Date;
img.src="/1x1.gif";


TCP handshake
2

2 ACK-ACK-ACK


2 Connection: keep-alive


2 Network latency & TCP handshake in JavaScript
var t=[], n=2, tcp, rtt;
var ld = function() {
t.push(+new Date);
if(t.length > n)
done();
else {
var img = new Image;
img.onload = ld;
img.src="/1x1.gif?" + Math.random()
+ ’=’ + new Date;
}
};
var done = function() {
rtt=t[2]-t[1];
tcp=t[1]-t[0]-rtt;
};
ld();

The astute reader will notice that we’ve ignored DNS lookup
time here... how would you measure it?


1 Notes

• 1x1 gif is 35 bytes
• including HTTP headers, is smaller than a TCP packet
• Fires onload on all browsers
• 0 byte image ﬁres onerror
• which is indistinguishable from network error


Network Throughput
3

3 Measuring Network Throughput

size
download_time


3 Network Throughput in JavaScript

// Assume global object
// image={ url: ..., size: ... }
var ts, rtt, bw, img = new Image;
img.onload=function() {
rtt=(+new Date - ts);
bw = image.size*1000/rtt; // rtt is in ms
};
ts = +new Date;
img.src=image.url;



If it were that simple, I wouldn’t be doing a talk at @jsconfeu


3 TCP Slow Start



So to make the best use of bandwidth, we need resources that ﬁt
in a TCP window


3 There is no single size that will tax all available networks

http://www.yuiblog.com/blog/2010/04/08/analyzing-bandwidth-and-latency/


3 Network Throughput in JavaScript – Take 2

// image object is now an array of multiple images
var i=0;
if(i>0)
image[i-1].end = +new Date;
if(i >= image.length)
done();
else {
img.onload = ld;
image[i].start = +new Date;
img.src=image[i].url;
}
i++;
};



Slow network connection, meet really huge image



img.onload = ld;
image[i].start = +new Date;
image[i].timer =
setTimeout(function() {
image[i].expired=true
},
image[i].timeout);
img.src=image[i].url;



if(i>0) {
image[i-1].end = +new Date;
clearTimeout(image[i-1].timer);
}



if(i >= image.length
|| (i > 0 && image[i-1].expired)) {
done();
}



Are we done yet?



Are we done yet?
sure...



Except network throughput is different every time you test it


Statistics to the Rescue

ﬂickr/sophistechate/4264466015/


The code for that is NOT gonna ﬁt on a slide


4 DNS


4 Measuring DNS

time_with_dns − time_without_dns


4 Measuring DNS in JavaScript
var t=[], dns, ip, hosts=[’http://hostname.com/’,
’http://ip.ad.dr.ess/’];
t.push(+new Date);
if(t.length > hosts.length)
done();
else {
img.onload = ld;
img.src=hosts[t.length-1] + "/1x1.gif";
}
};
var done = function() {
ip=t[2]-t[1];
dns=t[1]-t[0]-ip;
};
ld();

4 Measuring DNS

What if DNS were already cached?


4 Measuring DNS

What if DNS were already cached?
Use a wildcard DNS entry


4 Measuring DNS

What if you map DNS based on geo location?


4 Measuring DNS

What if you map DNS based on geo location?
A little more complicated, but doable


4 Measuring DNS

Full code in boomerang’s DNS plugin


5 IPv6


5 Measuring IPv6 support and latency

1 Try to load image from IPv6 host
• If timeout or error, then no IPv6 support
• If successful, then calculate latency and proceed
2 Try to load image from hostname that resolves only to IPv6
host
• If timeout or error, then DNS server doesn’t support IPv6
• If successful, calculate latency


5 Measuring IPv6 support and latency

Full code in boomerang’s IPv6 plugin


6
Private Network Scanning


6 Private Network Scanning

JavaScript in the browser runs with the User’s Security
Privileges


6 Private Network Scanning

This means you can see the user’s private LAN


6 Private Network Scanning – Gateways

1 Look at common gateway IPs: 192.168.1.1, 10.0.0.1, etc.
2 When found, look for common image URLs assuming
various routers/DSL modems
3 When found, try to log in with default username/password
if you’re lucky, the user is already logged in


6 Private Network Scanning – Services

1 Scan host range on private network for common ports (80,
22, 3306, etc.)
2 Measure how long it takes to onerror
• Short timeout: connection refused
• Long timeout: something listening, but it isn’t HTTP
• Longer timeout: probably HTTP, but not an image
3 Try an iframe instead of an image


–
.done()


Code/References

• http://github.com/bluesmoon/boomerang
• http://samy.pl/mapxss/


• Philip Tellis
• LogNormal.com
• philip@bluesmoon.info
• @bluesmoon
• geek paranoid speedfreak
• http://bluesmoon.info/


Thank you


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