Among the most important things to master for a mobile application developer is network programming. Every mobile application I have developed has involved some kind of network communication. During the year I have learned a thing or two. Read on to get some tips & trick from me.
Quite often the server is developed alongside the client. This means that you as a client developer have to wait for those awfully slow server programmers. Not every server programmer is slow, but most likely you have to wait for some server functionality. In situations like these, it is handy to roll your own server. But as a client developer, you do not want to spend an massive amount of time to setup a server. In fact, if it takes longer than a couple of minutes most client developers give up. What you need is a server that is very quick and easy to setup. Also it needs to be simple, yet powerful. Many server programmers would recommend you setting up a Tomcat server. The advantage of using a Tomcat server is that it is very versatile. But I do not really like
Tomcat. It is to advanced for me. Another solution is to use a
Jetty server. This is simpler to setup than Tomcat, but yet rather powerful. It could be executed from
Maven. As such is is convenient to use for automated tests. Maven takes cares most of the work, including starting and stopping your Jetty server. But there is a new and rising star, the
Sinatra server. The Sinatra server is actually a
Ruby library. You use Ruby to program the behavior of your server.
A simple “Hello World” implementation for Sinatra looks like the one below (from the
Sinatra Book).
require 'rubygems'require 'sinatra'get '/' do "Hello world, it's #{Time.now} at the server!"end
The file is saved as a file with
.rb extension, in our example we save it as “
hello.rb”. Then you start your server as simple as this:
ruby hello.rb
You get a nice line saying that Sinatra has taken the stage and that your server uses port 4567. This could of course be changed, if you want to mimic another server without changing your code. It is very easy to extend your server functionality. Ruby is easy to learn and powerful for making your own server without any big hazzle. Take a look at the
“Sinatra Book” if you want to master Sinatra.
Another common scenario is that you need to figure out what happens when you make a certain URL request, for example if you do a REST request. Before even writing a single of code, you could use the
cURL command line tool. Its available on most platforms, like Unix, Linux, Mac OS, Windows etc. For a matter of discussion, let us assume that you want to check that you programmed your Sinatra web server correctly. Then you the following command:
curl http://127.0.0.1:4567/
The response should look like this:
Hello world, it's Mon Oct 25 20:44:19 +0200 2010 at the server!
So now you know how to implement your own simple server, as well as how to debug your server request using curl. But wait, there is even more tricks I want to share with you. I hope that you feel like reading a little bit more.
I think that XML is a rather misused technologies around. It is used for many things, ranging from describing your builds (Ant, Maven, etc) to describing serialized objects traveling through cyberspace (SOAP, REST etc). When SOAP was introduced, one main argument for XML is that it human readable. What? Have you ever seen a SOAP request that is human readable? If you are about to send and/or receive objects there are much more suitable technologies than XML. Especially when making a mobile client, where XML parsing could take to much time and memory, it is important to understand that there are good alternatives. One good old technology is
ASN.1, that is hugely underestimated. It was designed for communicating data between different architectures and CPUs. It is fast even on a 8-bit CPU. The biggest drawback is that it is not widely supported and it requires an ASN.1 compiler. However you could implement your own ASN.1 encoder/decoder quite easy. Another solution that is easier to use, but building on the same principles as ASN.1 is the Hessian protocol. It is a binary web service protocol. The specification is originally designed by Caucho, who did the Resin web server. The specification is open and implemented in many languages, including .NET, Flash, Ruby, Python, Objective-C etc. I have primarily used it for Java ME, where only a subset is implemented. If you use it in Java ME, I would recommend considering using it to store object data in the record store. But now it is more relevant for me to use it on Android or iPhone. The Objective-C variant for iPhone is called
HessianKit. It is open source and released under Apache 2.0 license. Thus it is not a viral open source license, which I think is great. I will not describe how to use it, since there already is a good article on the subject “HessianKit Released”. I hope that you will consider using Hessian if you are in the position to decide what web service protocol to use. If you feel the urge to use XML for your web services, you could use
Burlap which is the XML version of Hessian. The communication is as simple as it could get using XML.
Another useful tool is a network analyzer. This is good for finding out what happens between the client and server. For example, if you want to take a look at the headers are many times auto generated. I have used
Wireshark with great success. It would not say it is easy to use, but when you need to use it is priceless.
These are the tools that I think I use the most for network programming. What are your best tools when doing network programming?
