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COMP3241 E-Business Technologies Richard Henson University of Worcester October 2012 Week 2 – Early Web Applications, ActiveX controls, and .net Objectives: Compare and contrast embedded code for client-only applications & server scripting Explain how client-side VBScript evolved into run-time ActiveX, which itself evolved into secure server-script Use a client-server .net development environment for development and testing of .net master pages and code behind Interpreted and Compiled Languages Programming (source) code must be converted into “machine code” before it can be understood and acted on by the CPU This can be done in two ways: convert whole program (using a compiler) and save it in a file leave program as it is, and convert it (using an interpreter) one line at a time when it is needed Compiled code generally occupies much more space than source code so of more limited use on the Internet (esp. early days)... How do Browsers cope with source code? Designed to use interpretation on HTML code reads one line of HTML key words and their parameters and uses HTML interpreter to convert (or interpret) that line into CPU instructions reads & interprets next line… and so on… CPU does further processing and sends commands to the video card which creates the visual display Embedded programming code in HTML Files Still .html and executed on the Browser Browser needs to have interpreter for that programming language e.g. » VB Script » Java Script For the Browser to call the right interpreter, an appropriate declaration statement needs to be included in the <HTML> start line Request and responses Organisation of application processing across a client-server network… Client: requests services or information from another computer (e.g. the server) Server: responds to the client's request by sending the results of the request back to the client computer Request and responses client requests information server processes the request, sends a response back to the client CLIENT Client Program SERVER REQUEST RESPONSE Send Request Read Results Server Program Process Request Send Back Results Internet Communications Based on principles of client/server networking EITHER Internet computer can “play” the role of client or the role of server e.g.(1) A user in one university sends an email to a user in another university: » “A” client sends email to “B” server (2) When a reply comes back… » “B” client sends email to “A” server Client-Server web applications & Server Scripts Client-server web applications usually require: 1. a web server, for interpreting or compiling then processing the scripts 2. a server-end database to provide and store data 3. physical & logical connections between serverscripts, client-end input forms and server-end database 4. clearly defined locations for gathering input data at client-end, for server scripts, and for database(s) Writing Server Scripts NOT saved as .html! Server code can be embedded directly into HTML code… Command is needed to inform the web server » (1) that non-HTML code is about to be used » (2) when next code reverts to HTML With .asp scripts… (no longer used) the command to start the script was <% to end the script… %> With .php scripts… <?php starts the script ?> ends the script Server Scripts and “Localhost” No matter which scripting type is used, the code can be tested locally on a computer running a web server that can understand that type of script how? use “localhost” in the URL at the Browser end (localhost = path to the server scripting root folder) A typical URL for testing such a script locally could then be (depending on script type): http://localhost/scriptname.aspx http://localhost/scriptname.php Web Dynamic Client-Server Model (1) Server-Side Processing in a typical web-based client-server application: 1. HTML form on web browser collects data at the client end 2. HTTP enables the form data to be sent to a web server Web Dynamic Client-Server Model (2) 3. web server processes the form data according to instructions on a server script called at the client end 4. output from processing stored temporarily on web server Web Dynamic Client-Server model (3) 5. server script sends output back to browser with HTML code to create a structure to display the data (e.g. HTML table) 6. This gets even more complex when a database, and database programming, are also involved at the server end… Introduction to Server-scripting The following apply to ALL types of scripting… real programming code is essential » note: HTML is a FORMATTING language, NOT a programming language both client and server ends need to have links to programming code: » client end…embedded within a HTML page » server end… could be embedded or separate Languages used for Server Scripting Much has been tried since HTML became interactive in the early 1990s: Can use an existing language in a completely separate file, which is already compiled and ready to go: » the original approach: .cgi » any language could in theory be used » in practice “C” was usually favoured Can use an existing language embedded in a HTML file » The Microsoft .asp approach, using embedded VB source code » The Sun .jsp approach, using embedded Java (Script) source Can utilise/invent a scripting language that is “HTML-like” and easily embeds with HTML » PERL » Cold Fusion .cf » Preprocessor Hypertext processing .php Microsoft’s first attempt at server scripting… In 1996, Microsoft introduced active server pages (asp) hugely successful soon became more popular than .cgi However, in spite of the great success of asp, big problems were emerging… by 2000, hackers were attacking Microsoft servers and finding many security holes in IIS » Microsoft only coped by offering hotfixes further problem: used VB source code » if server not secure, code could be copied or compromised » Scripts could not be truly “object oriented” ASP becomes ASP.NET Microsoft’s new approach to server scripting for the new millennium… building on asp principles new system that used “intermediate language”, rather than source code on the server much more difficult to hack Security problems with VB… out with the old (asp) in with the new (asp.net) New environment known as the .net framework many developers accustomed to VB/.asp took awhile to catch on! Development of .NET framework for Server Scripting BASIC and VB very much a part of Microsoft’s strategy, until circa 1999/2000… use of raw source code became a security issue Gates realised that e-business and e-commerce would never be reliable without using secure (and therefore compiled) code Microsoft rejected their previous strategy which used source VB code and an interpreter program within IIS What to replace VB source code with? applied source VB -> ActiveX run-time principles server-side Server equivalent of ActiveX controls could now be used/developed Result: .net Framework & ASP.NET: VB evolved into the more object oriented (and complied) VB.NET .net framework provided the basis for » .net server-side controls » the ubiquitous use of compiled languages Advantages of ASP.NET scripts compared to ASP Compiled, not interpreted Web Controls use xml-type tags Can be written using a variety of programming languages language declared at beginning of file fully object-oriented and many controls written to respond to on-screen “events” Which Source Code Language? Source code for .net development can be written in any language that can be translated into IL VB.NET builds on existing practice from asp But… C# has proved to be most popular with developers, many of whom had previously used “C” and C++ » why use VB.net, when you can use a more powerful, compiled, and object-oriented language like C? Components of the evolving .net framework Common Language Infrastructure (CLI) at the server end (i.e. IIS) “managed execution” framework for scripts runs Intel x86 IL code » common Language run-time (CLR) for executing controls » ready to run; development language irrelevant /app_code folder for deployed “assemblies” or “controls” containing executable code, and databases web.config file » store of configuration info e.g. a path to database file from v2 onwards the following additional folders: » app_browsers, app_themes, app_localresources, app_globalresources, app_webreferences How the .net environment manages an application “Assemblies” from .aspx files added to /App_Code (usually .dll files created by compiling the assembly components) CLI executes IL assemblies as CLR (runtime) makes sure script execution is “controlled” and kept within boundaries » an earlier version of IIS used to “leak” memory until the system needed rebooting usually loaded implicitly when a .net application is run Mechanism of Loading Assemblies for processing “AppDomain” sets up a security boundary in memory for each application Code (.exe, or .dll) loaded into process “spaceperfo” JIT compilation ensures “flat out performance” cf Wallace & Grommit – latter lays out the track as the train is about to pass along it HTTP processing .net architecture designed “with failure in mind” overall control with http.sys if memory usage gets too large, .net pulled down and restarted… Each AppDomain uses a pipeline of objects to handle requests Httpapplication – oversees flow Httpcontext – tracks “per request” state Modules – generic “pluggable services Handlers – http requests Covers most (all?) eventualities and makes sure requests are correctly dealt with – no muddling of threads (!) Very Useful ASP.net components: 1. Web Controls Reusable classes used to render parts of a page Similar to Windows “forms” New control created for each request » view state/Event tracking handled automatically A typical web page may have a hierarchical structure of web controls to makes them easily manageable Very Useful ASP.net components: 2. Event Handlers HTTP is stateless (no data retention) no multi-step processes possible e.g. HTML form contents disappear once form submitted Web Controls provide scope for handling events, when triggered (or raised) e.g. Page_Load, OnClick “PostBack architecture” » allows web forms data to reappear on the screen Very Useful ASP.net components: 3. Master Pages Master Page Created as a .master file defines template for other pages » cf PowerPoint slide master Contains top <html>, <body>, <form> tags “Page” command (top of page) utilises master: » either “static” or “dynamic” “Page_init” process renders components Very Useful ASP.net components: 4. Themes Allow common styles to be applied across a series of pages Developers can still use .CSS files fully supported by the master file and page “themes” concepts .net Development and RAD tools By now, you may be thinking… “Help! I can’t program in “C”!” DON’T BE SCARED! the syntax of object-oriented C# is similar to Java RAD tools such as Dreamweaver (earlier versions) and Visual Web Developer (VWD) provide a range of web controls already written in C# Extension Managers enable other controls to be added to the RAD environment VWD also help with general file/folder management such as putting controls/assemblies into the right folder i.e. /app_code Managing C# Code, HTML code, and web controls Each has its own syntax! earlier versions of .net had all three types together! More recently “code behind” files encouraged » Standard HTML & web control file saved as .aspx » associated C# code saved as a .cs file declared through “Page” command Running .aspx, .cs, etc. pages toghether All managed within the .net run-time environment normally at server-end using IIS Visual Studio allows use of a cut-down version of IIS at client end for testing developer doesn’t need to do anything more, provided that files all in the right folders… Running controls & C# with ASP.NET Semi-compiled into “intermediate language” (MSIL) for .net framework and saved together as an “assembly” intermediate code executes very quickly when required… Now you try it… \
