1. CP476 Internet Computing Browser and Web Server 1 Web Browsers A client software program that allows you to access and view Web pages on the Internet –Examples Mosaic, Netscape, Mozilla, Firefox (4.9%) Opera, Safari (for Apple computer) Microsoft Internet Explorer (90%)| How a browser work? –Given a URL, a browser intimates a request to a DNS server to resolve the IP address of the host specified in URL. Lecture 6. Web Browser and Web Server Objective: to understand how a browser interacts with a web server.

2. CP476 Internet Computing Browser and Web Server 2 –Combining the IP address and the document path of the URL, the browser initiates a request for the document to a server, and the server responses to the request. Most requests are for existing documents, Some requests are for program execution, with the output being returned as a document –A browser provides a graphic interface for a rich, repository of rich text, hypertext, images, audio, video, and other document types – Basic components of a browser GUI Domain name resolution module Requesting module Response processing module A Web document parser module A document display engine.

3. CP476 Internet Computing Browser and Web Server 3 Case study: Mosaic –Mosaic is the first graphical browser for the WWW that supports hypermedia, developed by NCSA which quickly gained popular and became the industry standard. –HTTP is the primary protocol used by Mosaic to distribute documents from the HTTPD information management services to Mosaic clients. –Check the source code of Mosaic for detail

4. CP476 Internet Computing Browser and Web Server 4 Web Servers –A computer that provides World Wide Web services on the Internet. It includes hardware, operating system, Web server software, TCP/IP software, and Web pages and programs. –Web server software is an application program that serves Web pages to Web browsers using the HTTP protocol. –Provide responses to browser’s requests for either existing documents or dynamically built documents –Examples Apache (2/3) Internet Information Server (IIS) by Microsoft

5. CP476 Internet Computing Browser and Web Server 5 How does a Web server work? –The primary task of a Web server is to monitor a communication port on its host machine, accept HTTP commands through that port, and perform the operations specified by the commands. –Example of HTTP commands: GET, PUT, POST, HEAD, and DELET. All commands include a URL –When a Web server starts, it tell its OS it is ready to accept communications through a specific port, usually 80 –When the URL is received, it is translated into either a filename (in which case the file is returned to the requesting client), or a program name (which case the program is run and its output is sent to requesting client)

6. CP476 Internet Computing Browser and Web Server 6 Contemporary servers provide many services –Virtual hosts - multiple sites on the same system –Proxy servers - to serve documents from the document roots of other sites –Besides HTTP, support for FTP, Gopher, News, email –Support for database access

7. CP476 Internet Computing Browser and Web Server 7 Case study: Apache –Apache began with the NCSA server httpd. Working with Mosaic. –Apache is now an open source Web server originally formed by taking all the "patches" (fixes) to the NCSA Web server and making a new server out of it, as a project organized by Apache Software Foundation Apache has a long list of services beyond the basic process of serving documents to clients. –Services can be configured There are three configuration files: httpd.conf, srm.conf, and access.conf There are about 150 different directives can be specified –When Apache starts execution, it reads the three configuration files and sets its parameters accordingly

8. CP476 Internet Computing Browser and Web Server 8 The file structure of Apache –Apache has two separate directories document root server root –The document root is the root directory of all servable documents Example An Apache server runs on physcomp1 Name: Domain name: IP address: Document root: Server root: –The server can have virtual document trees. Sometimes a different disk, possibly on a different machine, is used after the original disk is filled

9. CP476 Internet Computing Browser and Web Server 9 –The server root is the root directory for all of the code that implements the server The server root usually has four files: One is the code for the server itself Three others are subdirectories conf - for configuration information logs - to store what has happened cgi-bin - for executable scripts The configuration file is named httpd.conf –The directives in the configuration file control the operation of the server –Configuration file format: Non-blank lines that do not begin with # must begin with a directive name, which may take parameters, separated by white space When Apache begins, it reads the configuration files and sets its parameters according to what it reads

10. CP476 Internet Computing Browser and Web Server 10 ServerName - default is what is returned by th hostname command, but it may be only the first part ServerName www.bloomers.comwww.bloomers.com ServerRoot - to set the server root address –Default is /usr/local/etc/httpd If it is stored elsewhere, tell Apache with: ServerRoot: set the document root ServerAdmin DocumentRoot - set the document root address

11. CP476 Internet Computing Browser and Web Server 11 Alias - to specify a virtual document tree – Takes two parameters, virtual path for URLs and the actual path – Example: – Alias /test/ /usr/local/apache/test/ – http://physcomp1.wlu.ca/test/test.html will be mapped to /usr/local/apache/test/test.htmlhttp://physcomp1.wlu.ca/test/test.html ScriptAlias - creates a virtual directory for cgi files ScriptAlias /cgi-bin/ /usr/local/etc/httpd/cgi-bin/ Redirect DirectoryIndex index.html contents.html index.cgi UserDir public_html (UserDir disabled) Log file –Tips for building your directory on phycomp1