Martin Kruliš by Martin Kruliš (v1.1)1

 Serving Static Pages by Martin Kruliš (v1.1)2 Web Server Client ` HTTP Request GET /myweb/index.html... HTTP Request GET /myweb/index.html... Internet HTTP Response HTTP/ OK Content-Length: 1019 Content-Type: text/html;... HTTP Response HTTP/ OK Content-Length: 1019 Content-Type: text/html;... index.html Apache configuration /var/www/myweb/

 Serving Dynamic Content by Martin Kruliš (v1.1)3 Web Server Client ` HTTP Request GET /myweb/app.cgi... HTTP Request GET /myweb/app.cgi... Internet HTTP Response HTTP/ OK Content-Length: 2049 Content-Type: text/html;... HTTP Response HTTP/ OK Content-Length: 2049 Content-Type: text/html;... /var/www/myweb/ app.cgi stdin stdout

 Common Gateway Interface ◦ One of the first standards for generating dynamic web content ◦ NSCA specification from 1993 how to invoke command line applications  Current version CGI 1.1 (RFC 3875) from 2004 ◦ Specifies only the interface  Application may be written in any language  Important information and headers are set as environ- ment variables, POST body is directed to std. input  Response is taken from the std. output by Martin Kruliš (v1.1)4 Example 1

 CGI Issues ◦ Starting a process takes some system time ◦ Each process handles exactly one request  Unable to keep session/shared data in memory  Fast CGI Improvement ◦ Fast CGI server runs independently from web server  Keeps the process pool, resources, … ◦ Communicates with web server via socket/TCP ◦ Multi-request processing may be achieved by multiplexing or multiple connections (or both) by Martin Kruliš (v1.1)5

 Integrating Scripting Modules by Martin Kruliš (v1.1)6 Web Server Client ` HTTP Request GET /myweb/index.php... HTTP Request GET /myweb/index.php... Internet HTTP Response HTTP/ OK Content-Length: 1984 Content-Type: text/html;... HTTP Response HTTP/ OK Content-Length: 1984 Content-Type: text/html;... /var/www/myweb/ mod_php index.php

 PHP: Hypertext Preprocessor ◦ Popular language originally designed for the web  The language has integrate API for handling requests  Things like URL parameters, POSTed data, headers, or server settings are presented in global variables ◦ PHP script code can be directly interleaved with HTML (or other type of generated content)  The script is embedded between marks  The PHP interpret process the script and replace its body with its output in the document by Martin Kruliš (v1.1)7 Example 2

 Web Server Gateway Interface ◦ Universal interface between web servers and web applications designed for the Python language  Interface is called WSGI middleware and it is implemented by both sides (server and application) ◦ Specific new features  Routing requests to application objects (by URL)  Multiple applications may run in one process  Content post-processing (e.g., by XSLT)  Load balancing (remote processing, forwarding, …) ◦ Similar APIs  Rack (Ruby), PSGI (Perl), JSGI (JavaScript) by Martin Kruliš (v1.1)8 Example 3

 ASP.NET ◦ Microsoft solution built on.NET platform  Supports all.NET languages (C#, VB, …) ◦ Successor to Microsoft’s Active Server Pages ◦ Requires Microsoft IIS web server  Mono version ( mod_mono and FastCGI) exists ◦ WebForms  Basic building blocks for ASP.NET web pages  Similar HTML interleaving syntax as PHP  The idea is to design web pages in the same manner as desktop applications by Martin Kruliš (v1.1)9

 ASP.NET ◦ WebForms  Event-based model, events may be processed at server  The forms automatically serializes the whole state ◦ Razor syntax  Block starts and does not require explicit closing ◦ MVC  Alternative type of ASP.NET applications  Default view engine is either Razor (.cshtml,.vbhtml), or Web Forms (.aspx)  Controllers are.NET classes, methods are actions  Routers select controller class and invoke an action by Martin Kruliš (v1.1)10

 Java Server Pages ◦ Java-based solution for dynamic web pages ◦ Requires web server with servlet container  Apache Tomcat, Jetty, … ◦ Supports both “simple” PHP-like approach and MVC  Uses marks for scriptlet-HTML interleaving  MVC usually uses JavaBeans as the model and Java servlets as the controller ◦ Java compilation  Compiler is integrated in the web server and compiles the page when first needed (or when changed) by Martin Kruliš (v1.1)11

 Ruby on Rails ◦ Ruby scripting language + Rails web framework ◦ Basic philosophy  DRY (Don’t Repeat Yourself) – avoid code duplication  Convention Over Configuration – our way is the “best” ◦ Very strict style of application development  Improves efficiency, but ties your hands ◦ Specific structure of the application  Reflects the MVC pattern  $> rails new myapp  Generates new application structure in./myapp by Martin Kruliš (v1.1)12

 Representational State Transfer (REST) ◦ Architectural abstraction for distributed systems ◦ The application is formed by resources  Resources are identified by URL ◦ Components of the application communicate over the network and exchange resource representations  Representation is typically HTML, XML, or JSON ◦ The API is built over HTTP and is hypertext driven  GET  DELETE by Martin Kruliš (v1.1)13

 JavaScript Server-side Platform ◦ Basically a Google V8 JavaScript engine compiled as CLI script interpreter  V8 is used in Chrome and it is the fastest JS interpreter ◦ Contains many pre-built packages for server-side application development (sockets, HTTP, …)  HTTP server is embedded in the application, so the programmer may tune it for specific needs ◦ Aims for fast developed single-language solutions  Using Javascript on client and server allows some level of code sharing by Martin Kruliš (v1.1)14 Example 4

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 Client-server Architectures ◦ Strict separation of two application parts  Client - data presentation, user interface  Server – business logic, data storage ◦ Both sides are connected via specific API (HTTP)  The communication latency and overhead influence the application design ◦ Three-tier architecture  Server part is overloaded, so we separate the data storage and management into separate tier ◦ Thick client  Functionality is slowly shifting to the client-side by Martin Kruliš (v1.1)16

 Specific Issues of the Server Side ◦ Traditional web applications  Work in batches – client wants to perform a large task with each HTTP request  Download a page full of formatted data  Submit a form and generate a response  Difficult state management (HTTP is stateless)  Code replication and dependency injections ◦ Modern web applications  Just a remote API for AJAX calls  Difficult to integrate AJAX API into existing applications, or create applications that work both ways by Martin Kruliš (v1.1)17

 Model-View-Controller by Martin Kruliš (v1.1)18 Database View Model Invoking actions Dataflow Controller

 Model-View-Controller ◦ A guideline how to divide code and responsibility ◦ Basis for many frameworks ◦ Model  Uniform data API for the application  Communicates with DB/file storage/…  Simplifies portability to other storage types  Transparently handles encoding, integrity checks, transactions, data pre/post-processing, … by Martin Kruliš (v1.1)19

 Model-View-Controller ◦ View  User interface, data presentation  Typically responsible for generating HTML  Automatic sanitization of presented data ( chars)  Translations for multilingual applications  Templates  Mechanisms that separate HTML coding from application programming  Allow implementing View features (mentioned above) in declarative (instead of imperative) manner by Martin Kruliš (v1.1)20

 Model-View-Controller ◦ Controller  Integrates business (application) logic  Issues commands to view and model  Process user requests  Requests for displaying content (typically GET request)  Requests for modifying app. status (typically POST req.)  Typically implements other design patterns  Front controller, command, …  Alternative – Model-View-Presenter  More advanced form of MVC  View is more separated and does not access model directly by Martin Kruliš (v1.1)21

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