chap 1 web essentials

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Jackson, Web Technologies: A Computer Science Perspective, 2007 Prentice-Hall, Inc. All rights reserved. 0-13-185603-0

Chapter 1

Web Essentials: Clients, Servers,

and Communication

WEB TECHNOLOGIES

A COMPUTER SCIENCE PERSPECTIVE

JEFFREY C. JACKSON


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INTRODUCTION

Server

The software that distributes the information and themachine where the information and software reside

is called the server.

provides requested service to client

e.g., Web server sends requested Web page


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Web server:

Software that delivers Web pages and other documents to

browsers using the HTTP protocol

Web Page:

A web page is a document or

resource of information that is

suitable for the World Wide

Web and can be accessed

through a web browser.


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Website:

A collection of pages on the World Wide

Web that are accessible from the same

URL and typically residing on the same

server


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1.1The Internet

Technical origin:ARPANET(late 1960s) Launched in 1969

Project of U.S Dept of Defense(DoD)

One of earliest efforts to networkheterogeneous(Different manufactures &

Different OS), geographically dispersed

computers

Email first available on ARPANET in 1972(and quickly very popular!)

ARPANET access was limitedto select

DoD-funded organizations


7/100Jackson, Web Technologies: A Computer Science Perspective, 2007 Prentice-Hall, Inc. All rights reserved. 0-13-185603-0

The Advanced Research Projects Agency

Network (ARPANET) was one of the world's

first operational packet switching networks, the

first network to implement TCP/IP.

The network was initially funded by the

Advanced Research Projects Agency (ARPA,later DARPA) within the U.S. Department of

Defense for use by its projects at universities

and research laboratories in the US.



The Internet

Open-access networks

Regionaluniversity networks (e.g., SURAnet)

CSNETfor CS departments with no

ARPANET access. Later ARPA Internet allowed to access

outside networks such as CSNET.

The Connection Between CSNET to ARPA ismade by Phonenet(MODEM) approach.

This connection is asynchronous.

This involves long distance calls



Open-access networks

A full-service network provider offering Internet

solutions for business small and large, residential

users and non-profit groups.Regional Universities Network(RUN)

Is a network of six universities primarily from

regional Australia, as well as campuses in theAustralian capital cities and some international

campuses

Southeastern Universities Research Association

network (SURAnet) provided networking servicesfor universities and industries. SURAnetwas one

of the first and one of the largest Internet

providers in the United States.



The Computer Science Network(CSNET)

was a computer network that began

operation in 1981 in the United States. Its

purpose was to extend networking benefits,

for computer science departments at

academic and research institutions thatcould not be directly connected

to ARPANET, due to funding or

authorization limitations. CSNET was funded by the National

Science Foundation for an initial three-year

period from 1981 to 1984.



NSFNET(National Science Foundation)

(1985-1995)

Primary purpose: connect supercomputer

centers

Secondary purpose: provide backboneto

connect regional networks

Uses TCP/IP Synchronous

Communication.



Synchronous communication is said to occur

when two parties communicate in real-time.

Examples of synchronous communicationinclude telephone calls and two-way radio

communication.

In contrast, asynchronous communication is

non real-time communication.

Examples might be email, blog and messageboard postings, and especially text

messaging.


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Geographic distribution of the six supercomputers

centers connected by NSFNET backbone

Operated at only 56kbits/sec

No of machines connected increased

Upgraded to 1.5Mbit/s in 1988

45Mbits/s in 1991



The Internet Internet: the network of networks

connected via the public backbone andcommunicating using TCP/IP

communication protocol

Global Communication Network Commercial Internet dial-up access offered Economic

Increase network usage

Reduced unit cost

Backbone initially supplied by NSFNET,

privately funded (ISP fees) beginning in 1995

Private telecommunication firms


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1.2 Basic Internet Protocols

1.2.1 TCP/IP

1.2.2 UDP, DNS, and Domain Names

1.2.3 Higher Level Protocols

TCP/IPSingle Protocol

TCP/IP actually two different protocols.TCP-transport Layer IP-Network layer

Treated as one some bulk of services are built on the top of both the

TCP and IP protocols

-> e-mail, Web browsing, File downloads, accessing remote databases

IPis the fundamental protocol defining the Internet (as the name

implies!)
ftp://ftp.rfc-editor.org/in-notes/std/std5.txtftp://ftp.rfc-editor.org/in-notes/std/std5.txt


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How does the computer choose the next computer in the

route for a packet?

A separate protocol BGP-4 is used to pass network connectivity

information between gateways so that each computer can choose

a good next hop for each packet it receives.

IP software adds error detection information ( a checksum)

to each packet Limitations of IP:

No guarantee of packet delivery (packets can bedropped)

Unreliable

Communication is one-way (source to destination)


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CheckSum Calculation Checksum Calculation

Sender side :

1. It treats segment contents as sequence of 16-bit integers.

2. All segments are added. Let's call it sum.

3. Checksum : 1's complement of sum.(In 1's complement all 0s are

converted into 1s and all 1s are converted into 0s). 4. Sender puts this checksum value in UDP checksum field.

Receiver side :

1. Calculate checksum

2. All segments are added and than sum is added with sender's checksum.

3. Check that any 0 bit is presented in checksum. If receiver side checksum

contains any 0 than, error is detected. So,the packet is discarded by

receiver.


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SENDER

1011101110111011

0000111100001111 DATA

1100101011001010 ( sum of all DATA)

0011010100110101 (1s Complement )

Header Checksum- 0011010100110101

Receiver:

1011101110111011

0000111100001111 DATA

1100101011001010 ( sum of all DATA)

0011010100110101 (Checksum)

1111111111111111 (If any bit 0 error Occurred)


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IP

Source

Gateway

Gateway

Network 1

Network 2

Destination

Network 3


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IP

Source

Gateway

Gateway

LAN 1

Internet Backbone

Destination

LAN 2


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TCP

Source Destination

Can I talk to you?

OK. Can I talk to you?

OK.

Heres a packet.

Got it.

Heres a packet.

Heres a resent packet.

Got it.

Establish

connection. {

{

{

Send packet

with

acknowledgment.

Resend packet if

no (or delayed)

acknowledgment.


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TCP


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1.2.2User Datagram Protocol (UDP)

Like TCP in that:

Builds on IP

Provides port concept

Unlike TCP in that:

No connection concept

No transmission guarantee

No two way connection

Advantage of UDP vs. TCP: Lightweight, so faster for one-time messages

less complexity in order to reduce overhead

D i N S i (DNS)
ftp://ftp.rfc-editor.org/in-notes/std/std6.txtftp://ftp.rfc-editor.org/in-notes/std/std6.txtftp://ftp.rfc-editor.org/in-notes/std/std13.txtftp://ftp.rfc-editor.org/in-notes/std/std13.txt


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Domain Name Service (DNS)

Easier to refer machines by names

DNS is the phone book for the Internet

Map back and forth between host names and IP addresses

DNS often uses UDP for communication

When a computer on the Internet needs DNS Service to convert

host names to IP uses UDP software to send UDP messages to

one of the DNS Servers

Host names

Labelsseparated by dots, e.g., www.example.org

Final label is top-level domain

Generic: .com, .org, .edu, .biz, etc.

Country-code: .us, .il(Israel), .mx, .de(germany) etc.

Top level domain names assigned by ICANN (Internet corporation

for assigned names and numbers)funded by U.S goverernment
ftp://ftp.rfc-editor.org/in-notes/std/std13.txthttp://www.example.org/http://www.icann.org/tlds/http://www.icann.org/tlds/http://www.icann.org/tlds/http://www.icann.org/tlds/http://www.example.org/ftp://ftp.rfc-editor.org/in-notes/std/std13.txt


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Top level domains divided into sub domains

Domains are divided into second-level

domains, which can be further divided into subdomains, etc.

E.g., in www.example.com, example is a second-

level domain Assignment of second level domain by registry

operator

A host name plus domain name information iscalled the fully qualified domain name of thecomputer

Above, www is the host name, www.example.com

is the FQDN
http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/http://www.example.com/


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Service names and port numbers are used to distinguish

between different services that run over transport protocols

such as TCP, UDP

When a service (serverprogram) initially is started, it is said tobind to its designated port number. As any client program

wants to use that server, it also must request to bind to the

designated port number.

Port numbers are from 0 to 65535. Ports 0 to 1024 are

reserved for use by certain privileged services. For the

HTTP service, port 80 is defined as a default and it does not

have to be specified in the Uniform Resource Locator (URL).

A registry operator (also called a Network Information

Center (NIC)) is an entity that maintains the database ofdomain namesfor a given top-level domainand generates the

zone fileswhich convert domain namesto IP addresses.
http://whatis.techtarget.com/definition/0,289893,sid9_gci212964,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci211662,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci211795,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci213251,00.htmlhttp://itlaw.wikia.com/wiki/Databasehttp://itlaw.wikia.com/wiki/Domain_namehttp://itlaw.wikia.com/wiki/Top-level_domainhttp://itlaw.wikia.com/wiki/Zone_filehttp://itlaw.wikia.com/wiki/Domain_namehttp://itlaw.wikia.com/wiki/IP_addresshttp://itlaw.wikia.com/wiki/IP_addresshttp://itlaw.wikia.com/wiki/IP_addresshttp://itlaw.wikia.com/wiki/IP_addresshttp://itlaw.wikia.com/wiki/Domain_namehttp://itlaw.wikia.com/wiki/Domain_namehttp://itlaw.wikia.com/wiki/Domain_namehttp://itlaw.wikia.com/wiki/Zone_filehttp://itlaw.wikia.com/wiki/Zone_filehttp://itlaw.wikia.com/wiki/Zone_filehttp://itlaw.wikia.com/wiki/Top-level_domainhttp://itlaw.wikia.com/wiki/Top-level_domainhttp://itlaw.wikia.com/wiki/Top-level_domainhttp://itlaw.wikia.com/wiki/Top-level_domainhttp://itlaw.wikia.com/wiki/Top-level_domainhttp://itlaw.wikia.com/wiki/Domain_namehttp://itlaw.wikia.com/wiki/Domain_namehttp://itlaw.wikia.com/wiki/Domain_namehttp://itlaw.wikia.com/wiki/Databasehttp://whatis.techtarget.com/definition/0,289893,sid9_gci213251,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci211795,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci211662,00.htmlhttp://whatis.techtarget.com/definition/0,289893,sid9_gci212964,00.html


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1.2.3 Higher-level Protocols

IP ~ the telephone network

TCP ~ calling someone who answers,having a conversation, and hanging up

UDP ~ calling someone and leaving a

message

DNS ~ directory assistance (names with

numbers)

Many protocols build on TCP


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Many protocols build on TCP

Telephone analogy: TCP specifies how we initiate and

terminate the phone call, but some other protocol

specifies how we carry on the actual conversation Some examples:

SMTP(email)

FTP(file transfer)HTTP(transfer of Web documents)

Primary TCP-based protocol used for

communication between web servers and browsers

called HTTP

IP is key component in the definition of Internet

HTTP -WWW


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1.3 World Wide Web

Public Sharing of InformationInternet

Usenet newsgroup service1979

worldwide distributed Internetdiscussion system

Posting Information that could be read by users on othersystem

First Internet Chat software

Internet Relay Chat Various technologies were developed for supporting

information management and search on the internet.

Gopher-hierarchical view of documents

WAIS-(Wide area information system)-Used indexingARCHIESearch online info archives via FTP
http://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Internet


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Unique feature of Web: support for hypertext (textcontaining links)

Communication via Hypertext Transport Protocol(HTTP)

Document representation using Hypertext MarkupLanguage(HTML)

The Web is the collection of machines (Webservers) on the Internet that provide information,

particularly HTML documents, via HTTP.

Machines that access information on the Webare known as Web clients.

A Web browseris software used by an end user

to access the Web.


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1.3.1 Hypertext Transport Protocol (HTTP)

HTTPis based on the request-response

communication model:

Client sends a request

Server sends a response

HTTP is a statelessprotocol:

The protocol does not require the server to

remember anything about the client betweenrequests.
ftp://ftp.rfc-editor.org/in-notes/rfc2616.txtftp://ftp.rfc-editor.org/in-notes/rfc2616.txt


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Browsing the web

Normally implemented over a TCP connection (80 is

standard port number for HTTP) Typical browser-server interaction:

User enters Web address in browser

Browser uses DNS to locate IP address

Browser opens TCP connection to server

Browser sends HTTP request over connection

Server sends HTTP response to browser over

connectionBrowser displays body of response in the client area

of the browser window


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HTTP request Message

The information transmitted using HTTP is often

entirely text (readable form)

Start line followed by a message header and optional

message body

Start line

Example: GET / HTTP/1.1


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HTTP request Message

The information transmitted using HTTP is

often entirely text (readable form)

Connect to a web server using telnet

$ telnet www.example.org 80

Trying 192.0.34.166

Connected to www.example.com (192.0.34.166).

Escape character is ^].

GET / HTTP/1.1

Host: www.example.org

HTTP/1.1 200 OK

Date: Thu, 09 Oct 2003 20:30:49 GMT

{Send

Request

{Receive

Response

Connect {


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1 4 2 HTTP i


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1.4.2 HTTP version

1997 HTTP 1.1 was formally defined

The version string for HTTP/1.1 must appear inthe start line exactly as shown with all capital

letters and no embedded white space

1.4.3 Request-URI Second part of start line

Concatenation of the string http://

Value of the host header field www.example.org

Request-URI forms a string known as URI An URI is an identifier that is intended to be

associated with a particular resource on the

WWW.
http://www.example.org/http://www.example.org/


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Every URI has two parts

Scheme appears before the colon :

Another part depends on the scheme web addresses ( most partuse http scheme)

URI is case sensitive generally written in lowercase

URI representing the location of a resource on the web

called the URL.

Another type URNdesigned to be a unique name for a

resource.

Syntax:scheme:scheme-depend-part Ex: In http://www.example.com/the scheme is http

URI f
http://www.example.com/http://www.example.com/


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URIs are of two types:

Uniform Resource Name (URN)

Can be used to identify resources with uniquenames, such as books (which have unique

ISBNs)

Scheme is urn

Ex:

Three colon separated parts

scheme name

Namespace identifier

Namespace specific string
ftp://ftp.rfc-editor.org/in-notes/rfc2396.txt


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Uniform Resource Locator (URL)

Specifies location at which a resource can be

found In addition to http, some other URL schemes

are https, ftp, mailto, and file

1.4.4 HTTP request method
ftp://ftp.rfc-editor.org/in-notes/rfc2396.txtftp://ftp.rfc-editor.org/in-notes/rfc2396.txt


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q The method part of the start line of an HTTP request written in

uppercase letters

GET is the most common HTTP method; it says "give me

this resource". Other methods include POST and HEAD.

Method names are always uppercase

POSTused to send information collected from a form displayed

within a browser

The path is the part of the URL after the host name, also called

the request URI

The HTTP version always takes the form "HTTP/x.x",

uppercase.

M th d D i ti


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Method Description

OPTIONS Return a list of HTTP methods used to access

the resource

GET Retrieves the requested URI, including the

headers and body (that is, the content).

HEAD Retrieves only the headers for the requested URI

and not the body.POST Sends information to the server from HTML

forms.

PUT Uploads the file indicated in the URI to a server.

DELETE Deletes the URI from a server.

TRACE Return a copy of the complete HTTP request

message for test purposes.


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H d fi ld f t


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Header field features:

First header names not case sensitive

Header field value wrap onto several linesHeader field values using MIME types

Many header field values use quality values to

indicate preferences

Quality value specified by a string of the form

q=num

Num is a decimal number between 0 and 1


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Multipurpose Internet Mail Extensions (MIME)

Standard used to pass variety of information includes

graphics and applications through e-mails as well as

through Internet message protocols.

Has two parts

Content type of the message case insensitivestring

Subtype or private type indicated by x- or X-

MIME content type syntax:top-level type/subtype

Examples: text/html, image/jpeg

Q


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HTTP Quality Values and Wildcards

Example header field with quality values:accept:

text/xml,text/html;q=0.9,text/plain;q=0.8, image/jpeg,

image/gif;q=0.2,*/*;q=0.1 Quality value applies to all preceding items

Higher the value, higher the preference

Note use of wildcards to specify quality 0.1 for anyMIME type not specified earlier


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1.5 HTTP Response Message


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Structure of the response:

status line

header field(s) (one or more)

blank line

optional message body

1.5.1 Response Status LineExample: HTTP/1.1 200 OK

Three space-separated parts:

HTTP version used by server software status code (numeric)

reason phrase (intended for human use)

Status code


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Three-digit number

First digit is class of the status code:

1=Informationalprovide information to client. 2=Success

3=Redirection (alternate URL is supplied)

4=Client Error Request not valid

5=Server Error Error occurred during server processing

Other two digits provide additional information

200 OK

301 Moved Permanently

307 Temporary redirect

401 Unauthorized

403 Forbidden

404 Not Found

500 Internal Server Error

1 5 2 Response header fields


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1.5.2 Response header fields

Common header fields:

Connection, Content-Type, Content-Length

Date: date and time at which response was generated(required).supplied by server.

Server-Information identifying the server software

Location: alternate URI if status is redirectionLast-Modified: date and time the requested resource

was last modified on the server

Expires: date and time after which the clientscopy of

the resource will be out-of-dateETag: a unique identifier for this version of therequested resource (changes if resource changes)

A hash code of resource returned.

1.5.3Cache ControlA h i l l f i f ti bt i d f


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A cacheis a local copy of information obtained from someother source

A copy of information placed in cache to improve system

performanceEx: icon appearing multiple times in a Web page

Advantages

Most web browsers use cache to store requested resources

so that subsequent requests to the same resource will notnecessarily require an HTTP request/response

HTTP caching when successful leads to quicker displayby the browser

Reduced network communication Reduce load on the web Server

Drawbacks

Information in a cache become invalid

V lid i h d


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Validating cached resource:

Send HTTP HEAD request and check Last-

Modified or ETag header in response

Compare current date/time with Expires header

sent in response containing resourceComparing the Etag returned by head request with

Etag stored with the cached resource

If Etag values match, then the cached copy is valid

1.5.4 Character Sets


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Characters represented in web documents

Every document is represented by a string of integer values (code

points)

The mapping from code points to characters is defined by a

character set

Ex: US-ASCII (7- bit Integer) char set used to represent the

characters used in HTTP header field names

In java the char set used internally by browser is defined by

UNICODE.

Character Encoding is a bit string that must be decoded into a code-point

integer that is then mapped to a character according to the definition

provided by some character set.

An encoding represents code points using variable-length


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An encoding represents code points using variable length

byte strings

Most common examples are Unicode-based encodings

UTF-8 and UTF-16 IANA maintains complete list of Internet-recognized

character sets/encodings

Some header fields have character set values:

Accept-Charset: request header listing character setsthat the client can recognize

Ex: accept-charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7

Content-Type: can include character set used torepresent the body of the HTTP message

Ex: Content-Type: text/html; charset=UTF-8

Typical US PC produces ASCII documents
http://www.iana.org/assignments/character-setshttp://www.iana.org/assignments/character-setshttp://www.iana.org/assignments/character-setshttp://www.iana.org/assignments/character-setshttp://www.iana.org/assignments/character-sets


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Typical US PC produces ASCII documents

US-ASCII character set can be used for such documents,

but is not recommended

UTF-8 and ISO-8859-1 are supersets of US-ASCII and

provide international compatibility

UTF-8 can represent all ASCII characters using a

single byte each and arbitrary Unicode characters using

up to 4 bytes each

ISO-8859-1 is 1-byte code that has many characters

common in Western European languages, such as

1.6 Web Clients


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Is a software that access a web server by sending HTTP

request message and processing the resulting HTTP response

Most common form of web client software

Web browsers running on desktop or laptop

Many possible web clients:Text-only browser(lynx)

Mobile phones

Robots (software-only clients, e.g., search engine

crawlers)not designed to be used directly by humans at

all.

etc.

User agent


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User agent

Any web client that is designed to directly support

user access to web servers.

Early browsers text-based ran on specialized

platforms

First graphical browser running on general-purpose

platforms: Mosaic (1993) by NCSA (National Centrefor supercomputer applications)

Then came Netscape Navigator

Microsoft Internet Explorer Browser war between Netscape Navigator and

Microsoft Internet Explorer

Microsoft was victorious

N t i d b A i li


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Netscape was acquired by America online

Launched Mozilla Firefox

All the major modern browsers support a common set ofbasic user features

Provide similar support for HTTP communication

1.6.1 Basic Browser Function


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Window split into several rectangular regions known as

Bars

5 Standard region in Mozilla 1.4Primary regionClient area display document

Title bartitle assigned by document author to the

document currently displayed within the client area

Menu bardropdown menus and GUI

N i ti t lb h b tt t l (B k F d


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Navigation toolbarpush-button controls(Back, Forward

Stop Print and Reload)

Contains a text box known as Location barUser can

enter the url in order to request the browser to display the

document located at the specified URL.

Status bardisplays messages and icons related to the status

of the browser Browser make HTTP request on behalf of the user

Browser Primary tasks:

Reformat the URL entered as a valid HTTP request

message

If server specified by host name, use DNS

Establish TCP connection using IP of the specified address


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Some Mozilla Status Messages


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Browser uses authority to connect via TCP


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Browser uses authority to connect via TCP

Request-URI included in start line (/ used for path if none

supplied)

Fragment identifier not sent to server (used to scroll

browser client area)

1.6.3 User Controllable Features

Graphical Browsers features: Save : Most documents can be saved by the user to the

client machines file system.

File|Save Page As

Find in Page:Standard documents (text and HTML) can

be searched with a function similar to word processors

Edit | Find in This Page


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Style definitionView|Text Zoom View|Use Style

D t t I f ti Vi | S R HTML


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Document meta-InformationView|page SourceRaw HTML

View|Page Infometa information

ThemesLook of one or more browser bars(Skin)

View | Apply Theme|Get New Themes

History Automatically maintain a list of all pages visited within the last

several days Go|History

BookmarksSave the URL for that page for an indefinite length of time

1.6.4 Additional Functionality Automatic URL Completion

Script Execution [ Browsers run programs to perform variety of tasks ,

validation]

Event Handling [Clicking on a link or button occurrence of event, Button

Clicks and mouse movement]

Management of form GUI: Web page contains a form with fill-in fields

browser allow user to perform std text-editing functions, button image,Text

Cursor]

Secure Communication: User send sensitive


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Secure Communication: User send sensitive

information to server and the browser encode this

information and prevent it from any other machines,

Credit Card Number]

Plug-in Execution: Support Plug-in Protocol.Display

of non-HTML documents (e.g., PDF) viaplug-ins

Help|About Plug-ins1.7 WEB SERVERS

Tomcat 5.0

1.7.1 Server FeaturesAccept HTTP request from web clients and return

an appropriate resource in the HTTP response

Basic functionality:


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Server calls on TCP software and waits for connection req toone or more ports

When a connection request is received , the server dedicates asubtask(Single copy of server software handling a singleclient connection)

Subtask establish connection and receives request

Subtask examines the host header field to determine the host

and invokes software for this host Virtual host software Map Request-URI to specific resource

on the server.

It maps Request-URI to specific resource associated

with the virtual host File: Return file in HTTP response (MIME Type)

Program: Run program and return output in HTTP

response

Log information about the request and response such as IPdd d h d i l i fil


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address and the status code in a plain-text file.

If the TCP connection is kept alive , the server subtask continuesto monitor the connection, the client send another request or

initiates a connection close.

Few Definitions

All modern servers concurrently process multiple requests

Multiple copies of the server running

simultaneously(Concurrency)

SubtaskSingle copy of server software handling a single client

connection

Virtual HostHTTP request include a host header field

Multiple host names mapped by a DNS to a single IP address

Web server determine which virtual host is being requested by

examining the host header field.

1.7.2 Server History NCSA httpd web server


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NCSA httpdweb server

NCSA discontinued development of server in 1990

Several individuals began developing their own updates called

patches

Patchy server known as Apache ServerFree openserver

source in April 1995

Microsoft began developmentIIS (Internet Information

Server)

IIS include all features found in apache

Drawbacks

IIS Run only on Windows System Run programs written in VB script

Apacheruns on Windows , Linux, and Macintosh

Run programs written in Perl and PHP

A number of IIS and Apache server run java programs


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When running a java program , both servers are configured to

run the program by using a separate software called Servlet

Container Servlet Container provides JVM that runs java

programs(known as Servlet)

It provides communication between the servlet and the Apache

or IIS Server Tomcat is a popular free open-source servlet container by

Apache software foundation

Tomcat can also run as a standalone web server that

communicates directly with web clients Tomcat 5.0 Web Server

1.7.3 Server Configuration and Tuning


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Modern servers have large number of Configuration

parameters

Server Configuration broken into two areas: External Communication

Internal Processing

In Tomcat two separate Java Packages:

Coyote

Catalina

CoyoteProvides HTTP 1.1 communication

CatalinaActual Servlet Container

Coyote parameters affecting External Communication:IP addresses and TCP ports

Number of subtasks created when server initialized

Max number of threads allowed to exist simultaneously


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Internal Catalina parameters affect functionality:


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Which client machines may send HTTP request to the server

Which virtual host are listening for TCP connection

What logging will be performed How the requestURI mapped to servers resources

Password protection of resources

Use of server-side caching

Install Tomcat 5.0 at the default port 8080

Open browser browse to the URL

http://localhost:8080

Click the Server Administration link cause a log-

in page to be displayed.
http://localhost:8080/http://localhost:8080/http://localhost:8080/http://localhost:8080/http://localhost:8080/http://localhost:8080/


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Tomcat included in JWSDP

JWSDP Service entry in the list on left side

Click on the icon to reveal the associated server

components

Service has Five Components:

Connector, Host, Logger, Realm, and Valve


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Connector is a coyote component handles HTTP

communication

Clicking on the connector will produce the window

containing the dropdown menus of possible action

that can be performed for this component


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Connector AttributesWhen you create or modify any type of Connector, the attributes


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shown in flowing table may be set, as needed.

Common Connector AttributesAttribute Description

Accept

CountLength of TCP Connection wait queue

Connection

Timeout

The number of milliseconds this Connector will

wait, after accepting a connection. The default

value is 60000 (i.e. 60 seconds).

IP AddressSpecifies which address will be used for listeningon the specified port, for servers with more than

one IP address.


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Port

Number

Port Number on which this connection will listen

for TCP connection request

Minimum

The number of request processing threads that

will be created when this Connector is first

started. The default value is 5.

Maximum

The maximum number of request processing

threads to be created by this Connector, which

therefore determines the maximum number of

simultaneous requests that can be handled. If not

specified, this attribute is set to 75.

1.7.4 Defining Virtual Hosts

C fi i H El


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Configuring Host Elements

The Host element represents a virtual host, which is an association

of a network name for a server (such as www.mycompany.com)with the particular server on which Tomcat is running.

Host Attributes

The attributes shown in following table may be viewed, set, or

modified for a Host.

Host Attributes


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os bu es

Attribute Description

Name FQDN that clients will use to access the virtual host

Applicati

on Base

Directory Containing Web Applications

The Application Base directory for this virtual host.

This is the path name of a directory that may contain

Web applications to be deployed on this virtual host.You may specify an absolute path name for this

directory, or a path name that is relative to the

directory under which Tomcat is installed.

Deployon

startup

Boolean value indicating whether or not webapplications should be automatically initialized when

the server starts

A i i


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Web Applications

Collection of files and programs that work

together to provide particular functions to web

users

Absolute path nameTraces the path from the

/(root) directory. Absolute path names always

begin with the slash (/) symbol.

Relative path nameTraces the path from the

current directory through its parent or itssubdirectories and files.

1.7.5 Logging

Web server logs record information about server activity


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Web server logs record information about server activity

Access log is a file that records information about every HTTP

request processed by the server

Message logsvariety of debugging and other information

generated by web server

Access logging is performed by adding a valve component

The Primary fields are given in the table:Logger Attributes

Attribute Description

Directory Where log file will be written

Pattern Information to be written to log

PrefixThe prefix added to the start of each log

file's name.

SuffixThe suffix added to the end of each log file's

name


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name.

TimestampWhether or not all logged messages are to be

date and time stamped. Set to True and false

Resolve HostsWhether IP address or host name to be written

in log file

Tomcat writes the log information in a log file which in a plaintext format. In general, the log entry has the following format:

%h %l %t %r%s %b

%h - Remote host name

%l - Remote logical user name

%t - Date and time, in Common Log Format

%r - First line of the request URI

%s - HTTP status code of the response

%b - Bytes sent in body of response, excluding HTTP headers,

Access log in common format:


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g

1.7.6 Access Control


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Provide automatic password protection for resources

Access control:

Password protection (e.g., admin pages)

Users and roles defined in

conf/tomcat-users.xml

Deny access to machines Useful for denying access to certain users by

denying access from the machines they use

List of denied machines maintained in

RemoteHostValve (deny by host name) orRemoteAddressValve (deny by IP address)


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Secure Servers


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Secure Servers

BrowserWeb

Server

Id like to talk securely to you (over port 443)

Heres my certificate and encryption data

Heres an encrypted HTTP request

Heres an encrypted HTTP response

Heres an encrypted HTTP request

Heres an encrypted HTTP response

TLS/

SSL

TLS/

SSL

HTTP

Requests

HTTP

Responses

HTTP

Requests

HTTP

Responses

Secure Servers


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Man-in-the-Middle Attack

Browser

Fake

DNS

Server

Whats IP

address forwww.example.org?

100.1.1.1

Fake

www.example.org

100.1.1.1

Realwww.example.org

My credit card number is

Secure Servers


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Preventing Man-in-the-Middle

Browser

Fake

DNS

Server

Whats IP

address forwww.example.org?

100.1.1.1

Fake

www.example.org

100.1.1.1

Realwww.example.org

Send me a certificate of identity

chap 1 web essentials

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