Developing TCP/IP-based Server Applications using Indy Components  Christian Wilkerson

What is Indy? (A User’s Perspective)  Indy is short for Internet Direct  Project founded by Chad Z. Hower, aka Kudzu  Originally called WinShoes  Comes with Delphi or freely downloaded at  This presentation focuses on Indy.Sockets Server components

Our company chose Indy because…  Actually I chose Indy based on usage with pet projects dating back to when it was called WinShoes  I originally liked these components because they were FREE!  The company that I worked for basically did an RFP among its developers based around a need for networking ideas  Using Indy I was the only one who developed a viable solution  Now on with the show…

Indy.Sockets Version 10  Ships with Delphi 2005  Contains 45 different server components  Implements many standard protocols

Using TidHTTPServer  Does the world really need another WebServer?  Thinking of rewriting Apache? Or IIS? Why bother?  What about configuring software remotely?  Network administrators could resolve server issues from the comfort of their office…or home.  Or turn your desktop application into a browser based application without having to master a technology outside of Delphi?  You may still have to learn HTML or AJAX, but you would not have to rely on IIS

Example 1 – TidHTTPServer  This application will have an embedded web server that allows for it to be configured remotely  Let’s look at the code…

Using TidQOTDServer  Here’s another example of the many Servers Indy provides  Quote Of The Day (QOTD) – Provides a way for a server program to provide a message to clients

Example 2 - QOTDServerExample  This application will run a QOTD server and allow entering in any quote  But wait! We also need a client application for this.

Example 2 – The client application  This is the application we will use to test the server application  Now let’s take a look at the code for both applications…

TidTCPServer – The mother of all TCP based servers  The server components used in previous examples are from the Indy.Sockets collection and are derived from TidTCPServer  TidTCPServer is the counterpart to TidTCPClient  Gives the developer the ability to implement powerful TCP based applications  Enterprise level  Peer-to-peer  Implement standards that do not yet exist

Before getting started…  Socket Blocking is the way Indy operates  No other code executes during communication  Every Server connection runs in its own thread  This eliminates any obstacles blocking introduces  Designed properly Indy servers scale very well

Multi-Threaded Programming  It is NOT evil  Indy 10 helps Multi-Threaded beginners by introducing support for fibers  Fibers are NOT threads  They must be synchronized with a scheduler  Multi-Threaded servers will run faster than Fiber servers  By default, Indy uses threads

Do you need to develop a server?  Remember, servers do not initiate connections  Clients initiate connections  If you are developing the next great peer-to-peer program you need both a server and a client

What are ports?  A port is a number that is used to identify connections using your protocol  Be careful choosing a port number as it may be used by another application  To get more information on port numbers go to the Internet Assigned Numbers Authority or

One Last Question…  Will clients remain connected to the server?  Under Windows, connections have a nasty habit of going stale  Sometimes this fools Indy  A Heartbeat mechanism can help to maintain connections over long periods of time  Send routine messages every few seconds  Immediately know when a connection goes down

Command Handlers – A Quick Overview  Previous to Indy 10, TidTCPServer allowed for the use of an OnExecute event OR using Command Handlers  OnExecute – Event that handles ALL client communication  CommandHandlers – Custom event handlers for specific TCP messages  TidCmdTCPServer is now the component to descend from for using Command Handlers  Set CommandHandlersEnabled to TRUE – As of 2/1/05 This is no longer needed or allowed  At some point our new component can be placed on the palette and dropped on a form, but we will not be doing that today

Designing Your Protocol  The developer needs to decide on the necessary commands  Cryptic or Verbose – It is up to the developer  The example that follows is a variation of the original webserver example  Allows for remote configuration of software  Uses a single command “COLOR” with different parameters for setting our form color  To maintain connections with the client, it implements a heartbeat mechanism

High Speed Command Handling Using PostMessage  Command Handlers are event handling objects that run in their own connection thread  Every TidCommandHandler object has an OnCommand event that needs to have a Try…Except surrounding its code  PostMessage is used to get commands to the GUI  This is a multi-threaded program, therefore special care must be taken  Whenever the application writes to a client a TThreadList is accessed

Example 3 - TCPServerExample  The main form…

Example 3 – The Client Application  The main form…  Now let’s see the code…

Congratulations!  If everything worked out, you just ran the server and the client much like the earlier HTTP Server demonstration  Any questions?

Conclusion  This is only the beginning  For Standard Protocols or custom protocols Indy is a solid way to go  Indy is Free  Source Code is included  Newsgroup Support  You can buy technical support

Thank You Thank You so much for your time!