Review: High Performance Web Sites

This is a review of “High Performance Web Sites” by Steve Souders

First off this book is written by someone who knows just a tad about front end client web interfaces and their performance, being the performance chief at Yahoo he has quite a bit of experience under his belt. Myself having done a fair amount of Javascript learned quite a bit by reading this book and I highly recommend it to anyone who is responsible for creating fast loading client web interfaces built with HTML and Javascript.

Some of the tips will be very familiar to folks out there such as minifying Javascript libraries, using a CDN and tinkering with your server’s expires headers, however some of the other tips are a bit less well known, such as putting JS library calls at the bottom of your page… why? Because all other resources, except JS files are downloaded in parallel, however a JS download by itself and nothing else will continue downloading until it is finished. The author does a great job of explaining several very helpful “under the hood” performance issues with browsers that you may have otherwise not known about. Get this book as it is a short read with a big bang for the buck.

Recommended? YES
Skill Level – Beginner to Advanced, however the advanced folks will get more out of the low-level HTTP and browser performance issues than beginners.

Advanced HTTP operations in Flex outside of AIR

I am currently pretty deep into a Flex/AS3 RIA desktop app project whereby I have several advanced needs. Such as to download partial files to the desktop (byte-range requests), execute HEAD requests to get remote file sizes, execute multipart POSTs, talk to some REST apis, and finally be able to read any write HTTP headers….. outside of AIR? Good luck with URLStream, URLRequest, URLRequestMethod and URLRequestHeader

Due to security sandbox restrictions, unless your application is running within Adobe AIR you are restricted to simple GETs and POSTs. You are also NOT allowed to touch the following headers:

Accept-Charset, Accept-Encoding, Accept-Ranges, Age, Allow, Allowed, Authorization, Charge-To, Connect, Connection, Content-Length, Content-Location, Content-Range, Cookie, Date, Delete, ETag, Expect, Get, Head, Host, Keep-Alive, Last-Modified, Location, Max-Forwards, Options, Origin, Post, Proxy-Authenticate, Proxy-Authorization, Proxy-Connection, Public, Put, Range, Referer, Request-Range, Retry-After, Server, TE, Trace, Trailer, Transfer-Encoding, Upgrade, URI, User-Agent, Vary, Via, Warning, WWW-Authenticate, x-flash-version.

That’s basically all of the ones I needed to touch…..so what to do? In my case I was developing some file management functionality that runs in both Adobe AIR as well as MDM Zinc. Amongst other protocols such as FTP, I needed to be able to pull file updates over HTTP as well (+authentication, HEAD checks etc). So I had to create an generic IHttpClient interface abstraction which then allowed me to implement runtime specific clients. So for the AIR side of things I was good to go by using all of Adobe’s URL* classes right out of the box and they work great for the AirHttpClient implementation of my interface. However for my Zinc client I was still stuck, until I ran across a fantastic little HTTP library out there that provides a custom HTTP library built on top of the Flex socket stack.

The AS3 library that ended up being used in my ZincHttpClient was: as3httpclientlib. as3httpclientlib solved all of my problems when running outside of the AIR environment. With as3httpclientlib you can do all of the following and more:

* GET, HEAD, PUT, POST, DELETE
* multipart/form-data (PUT and POST)
* HTTPS support using AS3Crypto TLS
* Post with application/x-www-form-urlencoded
* Reading chunked (Transfer-Encoding)

If you have the need to access a bit more advanced HTTP functionality and need to do it outside of the AIR runtime. I HIGHLY recommend as3httpclientlib. I have put this library through the works doing byte range requests, HEAD requests, header manipulation and downloading and posting all sorts of file sizes, the library works great. My only note is that it is a tad slower than URLStream based HTTP downloads under Adobe AIR, regardless, this little HTTP library is worth it. Kudos to the AS3HttpClientLib team!