Martin Kruliš 3. 12. 2015 by Martin Kruliš (v1.1)1

by Martin Kruliš (v1.1) 1

Server-side ScriptingMartin Kruliš

3. 12. 2015


Serving Static Pages

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Web Server (Revision)

Web ServerClient

`

HTTP RequestGET /myweb/index.html...

Internet

HTTP ResponseHTTP/1.1 200 OKContent-Length: 1019Content-Type: text/html;...<contents of index.html>

index.html

Apache configuration

/var/www/myweb/


Serving Dynamic Content

3. 12. 2015


Web ServerClient

`

HTTP RequestGET /myweb/app.cgi...

Internet

HTTP ResponseHTTP/1.1 200 OKContent-Length: 2049Content-Type: text/html;...<contents generated by cgi>

/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

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CGI

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)

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FastCGI


Integrating Scripting Modules

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Web ServerClient

`

HTTP RequestGET /myweb/index.php...

Internet

HTTP ResponseHTTP/1.1 200 OKContent-Length: 1984Content-Type: text/html;...<contents generated by php>

/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 <?php, ?> marks The PHP interpret process the script and replace its

body with its output in the document

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PHP

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)

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WSGI

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

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ASP.NET


ASP.NET◦ WebForms

Event-based model, events may be processed at server

The forms automatically serializes the whole state◦ Razor syntax

Block starts with @ 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 action3. 12. 2015

ASP.NET


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)

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JSP


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

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Ruby on Rails


Representational State Transfer (REST)◦ Architectural abstraction for distributed systems◦ The application is formed by resources

Resources are identified by URLhttp://myapp.com/galery/2013http://myapp.com/galery/2013/photo/42

◦ 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 http://myapp.com/galery/2013 DELETE http://myapp.com/galery/2013/photo/42

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Ruby on Rails


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

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Node.js

Example 4


Web Programming Languages Usage (March 2013)

PHPASP.NETJSPColdFusionPerlRubyPython

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Statistics


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

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Server-side Scripting


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

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Server-side Scripting


Model-View-Controller

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Web Design Patterns

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, …

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Web Design Patterns


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

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Web Design Patterns


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

3. 12. 2015

Web Design Patterns

by Martin Kruliš (v1.1) 223. 12. 2015

Discussion

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Martin Kruliš 3. 12. 2015 by Martin Kruliš (v1.1)1