3100 Developing TCPIPbased Server Applications using Indy Components

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3100 - Developing TCP/IP-based Server
Applications using Indy Components

• Christian Wilkerson

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What is Indy? (A Users 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
  www.indyproject.org
• This presentation focuses on Indy.Sockets Server
  components

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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

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Indy.Sockets Version 10

• Ships with Delphi 2005
• Contains 45 different server components
• Implements many standard protocols

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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 officeor 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

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Example 1 TidHTTPServer

• This application will have an embedded web server
  that allows for it to be configured remotely
• Lets look at the code

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Using TidQOTDServer

• Heres 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

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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.

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Example 2 The client application

• This is the application we will use to test the
  server application
• Now lets take a look at the code for both
  applications

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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

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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

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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

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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

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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
  www.iana.org

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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

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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

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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

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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 TryExcept 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

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Example 3 - TCPServerExample

• The main form

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Example 3 The Client Application

• The main form
• Now lets see the code

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Congratulations!

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

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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

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Thank You

• Thank You so much for your time!