Advanced Interactive Programming Componentbased Internet Programming

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Advanced Interactive Programming
Component-based Internet Programming
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Outline

• Fundamental concepts about computer networks
• Architecture
• Communication
• Protocols
• ActiveX controls for Internet programming
• WebBrowser control
• Internet transfer control
• Winsock control
• VBScript Visual Basic Script

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The Internet and WWW

• The Internet
• A massive network of networks, a networking
  infrastructure that connects millions of
  computers together globally and any computer
  communicates with others using a variety of
  protocols
• The World Wide Web (WWW)
• An information-sharing model and an information
  space on top of the Internet
• A way of accessing information over the Internet
• Hypertext, HTML, HTTP, URI, Browser, etc.
• The Internet Vs. WWW
• The Web is just a portion of the Internet, albeit
  a large portion, but the two terms are not
  synonymous and should not be confused
• The Internet supports other services, such as
  Email, online chat, VoIP, etc.

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Network Architectures

• An architecture refers to a model or structure of
  a complex system and also the relationships among
  the system components
• Client-server architecture
• Computers are either clients or servers
• Clients are less powerful, requesting services
• Servers are powerful, dedicated, serving clients
  
• Peer to peer architecture (P2P)
• Each computer has equivalent capabilities and
  responsibilities

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Client-server Architecture Characteristics

• Server properties
• Passive (Slave)
• Waiting for requests
• On requests serves them and send a reply
• Client properties
• Active (Master)
• Sending requests
• Waits until reply arrives
• Servers can be stateless or stateful

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Peer to Peer Architecture Characteristics

• Pure P2P
• Peers act as either clients or servers
• No central server managing the network
• No central router
• Hybrid P2P
• A central server for peer information
• Peers are responsible for hosting, advertising
  and delivering information
• Mixed P2P
• Has both pure and hybrid characteristics

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Socket-based Communication

• A socket refers to the combination of a network
  address (IP address) and a port
• Socket based communication enables applications
  to view networking as stream of bytes similar to
  file input/output - a program can read from
  /write to a socket as simply as reading from /
  writing to a file.
• Socket based communication is similar to a
  telephone call the telephone handset represents
  the socket.
• The mouthpiece as the output
• The earpiece as the input
• The call, i.e. the connection, terminates by
  hanging up the phone

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Socket-based Communication

• Referred to as connection-based or
  connection-oriented service
• A connection must be established in advance but
  can guarantee data flows between processes in
  continuous stream
• Suitable for transmitting large amount of data
  and reliability is imperative
• Use TCP protocol

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Packet-based Communication

• Packet-based communication enables applications
  to transmit datagrams, i.e. individual packet of
  information, between processes without persistent
  connections.
• It is similar to sending a mail via the postal
  service, i.e. a datagram is created, addressed
  and sent over the network.
• Large data will be broken down into many
  datagrams, then sent, and finally reassembled at
  the receiving end.
• Datagrams may get lost, out of sequence,
  duplicate, etc.

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Packet-based Communication

• Referred to as connectionless communication
• Need significant extra programming on the users
  part to deal with missing, out-of-sequences, etc.
  
• Use the User Datagram Protocol (UDP)
• Suitable for transmitting small amount of data or
  intermittent data
• Usually used for streaming technologies such as
  accessing audio and video over the Internet.

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A Typical Process for Socket-based Communication

• A client attempts to establish a connection to a
  server.
• The server can accept or deny the connection.
• Once connected, socket-based communication begins
  to perform business processing.
• Both the client and the server need to close the
  connection if not needed.

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Some Internet Protocols

• Protocol is a set of rule governing communication
  within or between computer endpoints
• Internet protocol (IP)
• Used for communicating data across computer
  networks
• Provide globally unique addresses for networked
  computers
• Transmission Control Protocol (TCP)
• Create connections between networked computers
• Guarantee reliable and in-order delivery of data
• Distinguish data for multiple concurrent
  applications

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Some Internet Protocols

• User Datagram Protocol (UDP)
• Send datagram among networked computers
• Faster and more efficient for lightweight or time
  sensitive purpose
• Not provide reliable and ordering guarantee as
  TCP
• HyperText Transfer Protocol (HTTP)
• A method to transfer or convey information on the
  WWW, i.e. publish and receive HML pages
• a request/response protocol between clients and
  servers
• File Transfer Protocol (FTP)
• Used to exchange files over any networks that
  support TCP/IP
• Involve a FTP client and a FTP server
• Upload, download, rename, delete, change
  directories, etc.

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Internet Protocol Suite
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VB Internet Controls
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WebBrowser Control

• Enable applications to
• Browse Web sites, view Web pages and download
  data located on the Internet, which provides an
  application with many features of an Internet
  browser
• Open any ActiveX document, including Microsoft
  Office documents
• Open folders on a local hard disk and on a local
  area network
• Manage navigation, hyperlinking, history lists,
  favourites and security

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Example A Simple Web Browser
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Code Example
The same way as creating standard exe applications
Add the WebBrowser control and call correspondent
methods
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Internet Transfer Control

• Enable applications to use HTTP and FTP for
  Internet-based applications
• That is, applications can retrieve files from and
  send files to any site that uses one of these
  protocols
• Possible uses
• To parse a World Wide Web site for application
  specific uses
• To present a customized display of dynamic data
  retrieved from a Web page.
• To add FTP capabilities to any application
• To create an application that automatically
  downloads files from a public FTP site

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HTTP Connection Application

• Connect to a Web server using HTTP
• Different from WebBrowser in that it simply
  provides the text of the document being retrieved
  
• Synchronous transfer the program waits for the
  transfer to complete

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HTTP Connection Example

• Use Internet Transfer control to download the
  content of a file

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HTTP Connection Example

• Create a standard application with the GUI
• Add the Internet Transfer Control to the
  application and configure its protocol as HTTP
• Call the OpenURL method to download the URL

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FTP Connection Application

• Download files from or upload files to FTP
  servers
• Support asynchronous transfer, i.e. keep
  executing while the server responds to the
  requests
• Support a number of FTP commands such as get,
  push, cd, cdup,, rename, rmdir, quit, etc.

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FTP Connection Example

• Create a standard application with the GUI with
  server name, retrieved file name, user name and
  password
• Add the Internet Transfer Control to the
  application and configure its protocol as FTP
• Click Get the File to download the specified
  file

Download a text file
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Example Code
Set the controls properties
Call the Execute method to download the file
Support asynchronous transfer through the event
procedure StateChanges
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Properties and Methods
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Basic Operations

• The functionality of the Internet Transfer
  control depends on the protocol you wish to use.
• Set the AccessType property to a valid proxy
  server
• Invoke the OpenURL method with a valid URL
• Invoke the Execute method with a valid URL and
  command appropriate to the protocol
• Use the GetChunk method to retrieve data from the
  buffer

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The Winsock Control

• Enable applications to connect to a remote
  machine and exchange data using either TCP or UDP
• Both protocols can be used to create client and
  server applications
• Possible uses
• Create a client application that collects user
  information before sending it to a central server
• Create a server application that functions as a
  central collection point for data from several
  users
• Create a server application that provides
  services for users
• Create a "chat" application

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Establishing a TCP Server

• Step1 create an object of Winsock control in the
  application, e.g. tcpServer
• Step2 set up the port number of the controls
  LocalPort property to listen for connections from
  clients
• tcpServer.LocalPort 5000
• Step3 tell the server to listen indefinitely for
  an attempt of connection
• call tcpServer.Listen

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Establishing a TCP Server

• Step4 accept the request for connection from a
  client when a connection request is received
• Execute event procedure ConnectionRequest
• call tcpServer.Accept(requestID)
• Step5 the processing phase in which the client
  and server communicate via the connection
• Execute DataArrival event when data arrives at
  the server
• To retrieve data, use tcpServer.GetData(message
  )
• To send data, use tcpServer.SendData(message)
• Step6 once transmission is complete and the
  client closes the connection, the server also
  closes the connection
• tcpServer.Close

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Establishing a TCP Client

• Step1 create an object of Winsock control in the
  application, e.g. tcpClient
• Step2 set up the server to which to connect and
  the port number on that server
• tcpClient.RemoteHost localhost
• could be server name like www.microsoft.com or
  localhost or IP addresses
• tcpClient.RemotePort 5000
• march the one assigned in the server
• Step3 connect to the specified server
• tcpClient.Connect

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Establishing a TCP Client

• Once connected successfully
• Step4 the processing phase in which the client
  and server communicate via the connection
• To retrieve data, use tcpClient.GetData(message)
  
• To send data, use tcpClient.SendData(message)
• Step5 once transmission is complete and the
  server closes the connection, the client also
  closes the connection
• tcpClient.Close

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Example a TCP-based Chat Program Using Winsock
Control
Client GUI
10 -1
Server GUI
10 - 2
Invisible WinSock object
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Setup the VB Winsock Control

• Properties can be set up in Property Pages or in
  program code
• Usually invisible

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Example Code for the Server
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Example Code for the Server
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Example Code for the Client
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Example Code for the Client
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Example a TCP-based Chat Program Using Winsock
Control
Client GUI
10 -1
Server GUI
10 - 2
Invisible WinSock object
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Example a UDP-based Chat Program Using Winsock
Control
Client GUI
Server GUI

• Each has two TextBoxes, a Button and a WinSock
  control

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Setup the VB Winsock Control

• Properties can be set up in Property Pages or in
  program code
• Usually invisible

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Example Code for the UDP Server
Specify the port for receiving packets
Close the server
NO CONNECTION
Receive data and display in text box
Send a packet of information
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Example Code for the UDP Client
NO CONNECTION
Specify the server
Specify the port
Close the client
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Example Code for the UDP Client
Receive data and display in text box
Send a packet of information
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Example a UDP-based Chat Program Using Winsock
Control
Client GUI
10 -3
Server GUI
10 -4
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Properties, Methods and Events
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VBScript Visual Basic Script

• What is VBScript?
• VBScript is a scripting language, i.e. a
  lightweight programming language
• VBScript is a light version of Visual Basic
• Used in client side to enhance the functionality
  of a web page
• When a VBScript is inserted into a HTML document,
  the Internet browser will read the HTML and
  interpret the VBScript. The VBScript can be
  executed immediately, or at a later event.
• Used in server side to enhance the functionality
  of server-side applications
• Default scripting language for ASP the
  server-side technology for dynamically-generated
  web pages, which is similar to a HTML file

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VBScript Visual Basic Script

• When a browser requests an ASP file, IIS passes
  the request to the ASP engine. The ASP engine
  reads the ASP file, line by line, and executes
  the scripts in the file. Finally, the ASP file is
  returned to the browser as plain HTML
• With VBScripts in both client side and
  server-side, it is able to dynamically edit,
  change or add any content of a Web page, respond
  to data submitted from HTML forms, access any
  data or databases and return the results to a
  browser, customize a Web page to make it more
  dynamic, interactive and more useful for
  individual users.

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VBScript Language Overview

• A subset of VB
• Use the same VB syntax
• Support many control structures, such as
  if/then/else, do/loop, for/next
• Support many operators such as arithmetic,
  logical, relational operations

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VBScript Language Overview

• Provide many predefined constants, such as color,
  date/time, file I/O, etc.
• Support user defined constants
• Enable defining variables at multi-levels
• ONLY provide one data type variant that is
  capable of storing data of many VB types

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Using VBScript in Web Pages

• VBScripts can be in either HEAD section or BODY
  section, normally in HEAD section
• Use ltSCRIPTgt with some attributes and HTML
  comment tag to mark up

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Example Code
10 -5
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Intrinsic HTML GUI Controls
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Events of HTML GUI Controls
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Tags for HTML GUI Control

• Use INPUT tag within FORM tags to specify HTML
  GUI controls in HTML files

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Summary

• Fundamental concepts about Internet programming
• Architecture
• Communication
• Protocols
• ActiveX controls for Internet programming
• WebBrowser control
• Internet transfer control
• Winsock control
• VBScript Visual Basic Script