Review of Web Technologies I:
Introduction:
To make websites look and function a certain way,
web developers utilize different languages. The three core languages that make
up the World Wide Web are HTML5, CSS, and JavaScript.
In the IT world, the internet is an essential platform,
whether it’s for developing or for consumer use. When developing a website,
typically three main languages come into play. These languages are JavaScript,
CSS, and HTML. HTML is the backbone of most webpages. Essentially, it is used
to create the structure of how a specific website would look like, from the
headings to the paragraphs, the body, links, and even images.
Markup Languages:
Markup languages are the languages in which the web is
written. The most common markup language used is HTML, which uses tags to annotate
text so that a computer can then manipulate the text. Most markup languages are
human-readable and use annotations that are distinguishable from the annotated
text. There are many different kinds of markups and languages, but all are
consistent in the way in which they annotate documents.
Hypertext:
Hypertext is defined as the arrangement of information
inside a database that allows the user to receive information and to navigate
from one document to another by clicking on highlighted words or pictures
inside the primary document. Hypertext is the base of the World Wide Web,
because it enables the user to click on other links to get more information.
Hypertext is a term used for all links, whether it appears as texts or other
graphical part.
Hypertext Markup Language (HTML):
HTML is the conventional markup language used to create and
edit web pages and web applications. HTML is used for creating the basic
structure of a website. HTML consists of different elements preceded by an
opening tag, <tag>, and a closing tag, </tag>. The content between
the tags, <html> and </html>, is the content of the webpage. The
content between the tags, <head> and </head>, is the title of the
webpage. This text is displayed between the <title> and </title>
tags. The content between the tags, <body> and </body>, is the main
content of the webpage. The content can include links, paragraphs, headings,
and various other elements.
Here Are The Most Commonly Used HTML Tags:
Tag
|
Description
|
<h1> - <h6>
|
Gives
a web page a heading. 1 is the largest heading we can have and 6 is the smallest.
|
<p>
|
Starts
a paragraph on our web page.
|
<i>
|
Italic
font style.
|
<b>
|
Bold
font style.
|
<a>
|
Inserts
hyperlinks onto a web page.
|
<ul> &
<li>
|
Starts
an unordered or ordered list.
|
<!DOCTYPE>
|
Defines
the document type of the web page.
|
<!-- -->
|
Allows
us to insert comments into our HTML code. Comments aren't displayed in on the web page but are helpful for organization.
|
<img>
|
Inserts
an image onto a web page.
|
<br>
|
Inserts
a line break between bodies of text.
|
HTML Major Versions:
HTML 2.0:
Published in 1995, HTML 2.0 flushed out the RFC system,
allowing detailed mechanical explanations of the system.
HTML 3.2:
Published in 1997, HTML 3.2 performed major housecleaning on
the structure of HTML. It removed mathematical formulas, reconciled code
overlap, and adopted Netscape's Visual Markup Tags.
HTML 4.0:
Published at the end of 1997, HTML 4.0 introduced 3
different versions and browser-specific plugins. 4.0 Allowed custom experiences
tailored to specific browsers.
XHTML:
Released in 2000, XHTML fused HTML and XML into a language
that was very precise, almost too precise. XHTML is widely considered a tedious
and difficult language.
HTML 5.0:
Released in 2014, HTML 5.0 is the currently used version of
HTML. HTML 5.0 removed some of the tedium and severity of XHTML while keeping
its ability to remain precise and detailed.
Hypertext Transfer Protocol (HTTP):
HTTP is the protocol used by the World Wide Web that determines
how messages are formatted and transmitted. It also directs web servers and
browsers to what actions they should take in reaction to several commands. When
you open your web browser and enter a URL, you are using HTTP. The Web server
directs it to get and transmit the requested Web page based on the HTTP command
that is sent.
HTTP Protocol:
HTTP is an application used as the fundamental foundation of
communication on the web. HTTP is the first letter you type in when inputting a
web address. HTTP is a request-response protocol. The client might request
something and the HTTP allows the client to access the information. Like when
we updated our virtual machines the request we wanted was to go get updates for
the software and HTTP request went out and got updates. If you were on a bank
website or the wiki book site it would be https the‘s’ meaning secure. That
means that the computer is communicating on a secure network.
Cascading Style Sheets (CSS):
CSS is a style sheet language standard set by W3C (World
Wide Web Consortium) used to create and edit the visual presentation of web
pages. CSS allows web developers to isolate a web page's content and visual
styles into separate documents and gives better page layout control. An
external CSS sheet is generally linked to HTML and XHTML, it also can be linked
to XML, SVG, and XUL. HTML and JavaScript, with CSS, is a vital part of the technology used by the majority of interfaces for websites. This is also used
in interfaces for mobile devices making the websites more engaging.
Here Are The Most Commonly Used CSS Tags:
Tag
|
Description
|
background
|
A shorthand property for setting all the background properties in one
declaration.
|
colour
|
Sets
the colour of the text.
|
opacity
|
Sets
the opacity level for an element.
|
border
|
Sets
all the border properties in one declaration.
|
border-color
|
Sets
the colour of the four borders.
|
float
|
Specifies
whether or not a box should float
|
padding
|
Sets
all the padding properties in one declaration.
|
/*...*/
|
Allows
you to insert comments into your CSS code. Comments aren't displayed in on the web page but are helpful for organization.
|
width
|
Sets
the width of an element.
|
clear
|
Specifies
which sides of an element where other floating elements are not allowed.
|
Types of CSS:
CSS can be incorporated with HTML in 3 different ways;
Inline, Internal, and External.
Inline Styles:
Inline styles add style to a single element on the page by
placing 'style' after the element we wish to be styled.
Ex: h2 style = "color:
blue"
Internal Styles:
Internal styles create a style for a single document because
the CSS is stored in the head of the HTML document. Internal styles are placed
using a <style> tag around all style selectors.
Ex: <style>
body {background-color: white;}
/*This is a comment!
'Body' is the selector,
'background-color' is the declaration*/
h2 {color: blue;}
</style>
External Styles:
External style sheets exist in separate documents from HTML
documents, allowing for better organization of style and structure. An external style sheet can be linked to all HTML documents making up a web site, allowing
a web developer to style the entire site (all pages) using one document.
Web Design Programs:
Web Design Programs help the webpage creator manage and
create the content of a website. Many Web Design programs have many built-in
tools that ease the process of creating a website. Such programs are
Dreamweaver and Sublime. There are also publishing programs like WordPress and Ghost that allow the user to have more of a GUI based interface for blogging
and managing a website.
Sublime:
Sublime is a text editor that allows web developers,
programmers, software engineers, etc. manipulate code. It's not only for HTML
and CSS it can be set-up for many different programming languages and new
productivity tools. One contribution that Sublime has that many do not is the
"Package Control" Tool. The tool gives you full access to an entire
library of content to better your coding experience. For example, there is a
package you can install called Emmet, helping in typing the massive amount of HTML,
if you type "Html:5" and press "tab" then emmet will push
out all the correct syntax for an HTML 5 document.
SASS:
SASS is somewhat like emmet but is more of a language. It is
a Ruby engraved language that gives CSS much more capabilities like variables
and nesting. Like emmet, it makes writing CSS much faster and more efficient
saving the programmer lots of time.
Dynamic Web Content:
Client-Side Scripting:
Generally refers to computer programs on the web that are
executed by the user's web browser, instead of on a web server, enabling web
pages to be scripted. Client-side scripts do not require additional software on
the server but instead utilize the user's web browser to understand the
scripting language in which it is written.
Server-Side Scripting:
Server-side scripting is a technique used in web development
that involves using scripts on a web server which produce a unique response for
each user's request to the website.
Combination Technologies:
When both client-side and server-side scripting collectively
builds a webpage it is known as a web application. This web application can
manage user interaction, security, and help improve performance between the
client and the server. Web applications can include anything from online stores to
instant messaging services as long as both server and client sides execute
scripts to achieve a common goal in unison.
JavaScript:
JavaScript is a scripting language that is used along with
HTML and CSS as the three core components of the World Wide Web. JavaScript has
first-class functions and is used on most websites. JavaScript does not have
any I/O which means that it has to be embedded in the host environment.
JavaScript is also used in PDF documents, game development, and desktop and
mobile applications. JavaScript is most commonly used to make DHTML by adding
client-side behaviour to HTML pages.
Worldwide Web Consortium:
Worldwide Web Consortium (W3C) is an international community
of web members to meet the Web standards. It was founded by Tim Berners-Lee, an
inventor of the Web, back in the 20th century. W3C is designed to reach the full
potential of the Web and to make it accessible to all users from all over the
world. Also, another aim for W3C was to make standards to maintain the growth
of the Web in a single direction rather than splitting into competing groups.
Here are some of the standards for W3C:
a. Accessibility
b. Web
Authoring
c. Web
Performance
d. Cascading
Style Sheets
e. HTML5
f. Web
Fonts
g. Widgets
h. Media
Access
i. Mobile
Web Applications
j. Internationalization
of Web Design and Applications
k. Mobile
Web Authoring
l. XML
m. Graphics
n. RDF
o. HTTP
p. And
many more
Basic Internet Protocols:
Network protocols are the set of rules that governs data
communication. Types of protocols are explained below:
1. TCP (Transmission Control Protocol):
When information is sent over the Internet, it is generally
broken up into smaller pieces or "packets". The use of packets
facilitates speedy transmission since different parts of a message can be sent
by different routes and then reassembled at the destination. It is also a
safety measure to minimize the chances of losing information in the
transmission process. TCP is the means for creating the packets, putting them
back together in the correct order at the end, and checking to make sure that
no packets got lost in transmission. If necessary, TCP will request that a
packet be resent.
2. IP (Internet Protocol):
Internet Protocol (IP) is the method used to route
information to the proper address. Every computer on the Internet has to have
its own unique address known as the IP address. Every packet sent will contain
an IP address showing where it is supposed to go. A packet may go through several computer routers before arriving at its final destination and IP
controls the process of getting everything to the designated computer. Note
that IP does not make physical connections between computers but relies on TCP
for this function. IP is also used in conjunction with other protocols that
create connections.
3. HTTP (HyperText Transfer Protocol):
HTTP is a communication protocol. It defines a mechanism for
communication between the browser and the webserver. It is also called request and
response protocol because the communication between browser and server takes
place in request and response pairs. It uses port 80.
4. HTTPS(Hypertext Transfer Protocol over Secure Socket Layer):
HTTPS was first introduced by Netscape. HTTPS takes care of
secure communication between a web server and a web browser. HTTPS typically
handles credit card transaction and other sensitive data. A Web page using this
protocol will have https: at the front of its URL. It uses port 443.
5. FTP (File Transfer Protocol):
File Transport Protocol is a program that allows users and
computers to send and receive large portions of data through a private or public
network. It can also be used to send configuration files and software updates to
network devices, such as switches and routers. FTP uses ports for
communications and also uses encryption to protect the information being
received and sent. It uses port 20 for data transfer and port 21 for
connection.
6. SMTP (Simple Mail Transfer Protocol):
SMTP is a TCP/IP protocol used in sending and receiving
e-mail. However, since it is limited in its ability to queue messages at the
receiving end, it is usually used with one of two other protocols POP3 or IMAP
that let the user save the messages in a server mailbox and download them
periodically from the server. In other words, users typically use a program
that uses SMTP for sending e-mail and either POP3 or IMAP for receiving e-mail.
On UNIX based systems, send mail is the most widely-used SMTP server for
e-mail. It uses port 25.
7. POP (Post Office Protocol):
POP is one of the most commonly used protocols used to
receive e-mail on many e-mail clients. There are two different versions of POP:
POP2 and POP3. POP2 was an early standard of POP that was only capable of
receiving e-mail and required SMTP to send an e-mail. POP3 is the latest standard
and can send and receive e-mail only using POP, but can also be used to receive
e-mail and then use SMTP to send an e-mail.
POP3 is designed to delete mail on the server as soon as the
user has downloaded it. However, some implementations allow users or an
administrator to specify that mail is saved for some time. POP can be
thought of as a "store-and-forward" service. It uses port 110.
8. IMAP (Internet Mail Access Protocol):
IMAP (Internet Message Access Protocol) is a standard email protocol that stores email messages on a mail server but allows the end-user
to view and manipulate the messages as though they were stored locally on the
end user's computing device(s). This allows users to organize messages into
folders, have multiple client applications know which messages have been read,
flag messages for urgency or follow-up and save draft messages on the server.
IMAP can be contrasted with another client/server email
protocol, Post Office Protocol 3 (POP3). With POP3, the mail is saved for the end-user in a single mailbox on the server and moved to the end user's device when
the mail client opens. While POP3 can be thought of as a
"store-and-forward" service, IMAP can be thought of as a remote file
server. It uses port 143.
9. UDP (User Datagram Protocol):
The User Datagram Protocol is one of the core members of the
internet protocol suite. UDP uses a simple connectionless transmission model
with a minimum of protocol mechanism. UDP provides checksums for data
integrity, and port numbers for addressing different functions at the source
and destination of the datagram. It has no handshaking dialogues, and thus
exposes the user’s program to any unreliability of the underlying network and
so there is no guarantee of delivery, ordering, or duplicate protection. If
error correction facilities are needed at the network interface level, an application
may use the TCP or SCTP (Stream Control Transmission Protocol) which are design
for this purpose.
10. Telnet:
Telnet (short for TErminal NETwork) is a network protocol
used to provide a command-line interface for communicating with a device. Telnet
is used most often for remote management but also sometimes for the initial
setup for some devices, especially network hardware like switches, access
points, etc. Managing files on a website are also something Telnet is sometimes
used for. Telnet is sometimes written in uppercase as TELNET and may also be
misspelt as Telenet. It uses port 23.
11. DHCP (Dynamic Host Configuration Protocol):
DHCP (Dynamic Host
Configuration Protocol) is a protocol used to provide quick, automatic, and
central management for the distribution of IP addresses within a network. DHCP
is also used to configure the proper subnet mask, default gateway, and DNS
server information on the device. It uses port 68.
HTTP - Overview:
The Hypertext Transfer Protocol (HTTP) is an
application-level protocol for distributed, collaborative, hypermedia
information systems. This is the foundation for data communication for the
World Wide Web (i.e. internet) since 1990. HTTP is a generic and stateless
protocol which can be used for other purposes as well using extensions of its
request methods, error codes, and headers.
Basically, HTTP is a TCP/IP based communication protocol,
that is used to deliver data (HTML files, image files, query results, etc.) on
the World Wide Web. The default port is TCP 80, but other ports can be used as
well. It provides a standardized way for computers to communicate with each
other. HTTP specification specifies how clients' request data will be
constructed and sent to the server, and how the servers respond to these
requests.
Basic Features:
Three basic features make HTTP a simple but
powerful protocol:
1. HTTP Is Connectionless:
The HTTP client, i.e., a browser initiates an HTTP request
and after a request is made, the client disconnects from the server and waits
for a response. The server processes the request and re-establishes the
connection with the client to send a response back.
2. HTTP Is Media Independent:
It means any type of data can be sent by HTTP as long as
both the client and the server know how to handle the data content. It is
required for the client as well as the server to specify the content type using
appropriate MIME (Multipurpose Internet
Mail Extensions) type.
3. HTTP Is Stateless:
As mentioned above, HTTP is connectionless and it is a
direct result of HTTP being a stateless protocol. The server and client are
aware of each other only during a current request. Afterwards, both of them
forget about each other. Due to this nature of the protocol, neither the client
nor the browser can retain information between different requests across the
web pages.
Basic Architecture:
The following diagram shows a very basic architecture of a
web application and depicts where HTTP sits:
The HTTP protocol is a request/response protocol
based on the client/server-based architecture where web browsers, robots and
search engines, etc. act like HTTP clients, and the Web server acts as a
server.
1. Client:
The HTTP client sends a request to the server in the form of
a request method, URI, and protocol version, followed by a MIME (Multipurpose Internet Mail Extensions) like a message containing request modifiers, client information, and possible body
content over a TCP/IP connection.
2. Server:
The HTTP server responds with a
status line, including the message's protocol version and a success or error
code, followed by a MIME (Multipurpose
Internet Mail Extensions) like message containing server information,
entity Meta information, and possible entity-body content.
HTTP - Messages:
HTTP is based on the client-server architecture model and a
stateless request/response protocol that operates by exchanging messages across
a reliable TCP/IP connection.
An HTTP "client" is a program (Web browser or any other client) that establishes a connection to a server for the purpose of
sending one or more HTTP request messages. An HTTP "server" is a
program (generally a web server like Apache Web Server or Internet Information
Services IIS, etc.) that accepts connections to serve HTTP requests by
sending HTTP response messages.
HTTP makes use of the Uniform Resource Identifier (URI) to
identify a given resource and to establish a connection. Once the connection is
established, HTTP messages are passed in a format similar to
that used by the Internet mail [RFC (Remote
Function Call) 5322] and the Multipurpose Internet Mail Extensions (MIME)
[RFC2045]. These messages include requests from the client to
server and responses from server to client which will have the
following format: HTTP-message = <Request> | <Response>; HTTP/1.1 messages
HTTP requests and HTTP responses use a generic message
format of RFC 822 for transferring the required data. This generic message
format consists of the following four items.
1. A Start-line
2. Zero or more header fields followed by CRLF
(Carriage Return, Line Feed)
3. An empty line (i.e. a line with nothing
preceding the CRLF) indicating the end of the header fields
4. Optionally a message body
Message Start-Line:
A start-line will have the following generic syntax: start-line
= Request-Line | Status-Line
Example:
GET /hello.htm HTTP/1.1 (This is Request-Line sent
by the client)
HTTP/1.1 200 OK (This is Status-Line sent by the
server)
Header Fields:
HTTP header fields provide required information about the
request or response, or about the object sent in the message body. There are
four types of HTTP message headers:
a. General-header: These header fields have general applicability for
both request and response messages.
b. Request-header: These header fields have applicability only for
request messages.
c. Response-header: These header fields have applicability only for
response messages.
d. Entity-header: These header fields define Meta information about the
entity-body or, if nobody is present, about the resource identified by the request.
All the above-mentioned headers follow the same generic
format and each of the header field consists of a name followed by a colon (:)
and the field value as follows:
message-header = field-name ":" [
field-value ]
Following are the examples of various header fields:
User-Agent: curl/7.16.3 libcurl/7.16.3
OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.com
Accept-Language: en, mi
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
ETag: "34aa387-d-1568eb00"
Accept-Ranges: bytes
Content-Length: 51
Vary: Accept-Encoding
Content-Type: text/plain
Message Body:
The message body part is optional for an HTTP message but if
it is available, then it is used to carry the entity-body associated with the
request or response. If the entity-body is associated, then usually Content-Type and Content-Length headers
lines specify the nature of the body associated.
A message body is the one which carries the actual HTTP
request data (including form data and uploaded, etc.) and HTTP response data
from the server (including files, images, etc.). Shown below is the simple
content of a message body:
<html>
<body>
<h1>Hello, World!</h1>
</body>
</html>
HTTP Requests Message:
An HTTP client sends an HTTP request to a server in the form
of a request message which includes the following format:
1. A
Request-line
2. Zero
or more header (General|Request|Entity) fields followed by CRLF
3. An empty line (i.e. a line with nothing preceding the CRLF) indicating the end of
the header fields
4. Optionally
a message-body
1. Request-Line:
The Request-Line begins with a method token, followed by the
Request-URI and the protocol version, and ending with CRLF. The elements are
separated by space SP characters.
Request-Line = Method SP Request-URI SP HTTP-Version
CRLF
2. Request Method:
The request method indicates
the method to be performed on the resource identified by the given Request-URI.
The method is case-sensitive and should always be mentioned in uppercase. The
following table lists all the supported methods in HTTP/1.1.
S.N.
|
Method and Description
|
1
|
GET
The
GET method is used to retrieve information from the given server using a
given URI. Requests using GET should only retrieve data and should have no other effect on the data.
|
2
|
HEAD
Same
as GET, but it transfers the status line and the header section only.
|
3
|
POST
A POST request is used to send data to the server, for example, customer
information, file upload, etc. using HTML forms.
|
4
|
PUT
Replaces
all the current representations of the target resource with the uploaded content.
|
5
|
DELETE
Removes
all the current representations of the target resource given by URI.
|
6
|
CONNECT
Establishes
a tunnel to the server identified by a given URI.
|
7
|
OPTIONS
Describe
the communication options for the target resource.
|
8
|
TRACE
Performs
a message loop backtests along with the path to the target resource.
|
3. Request-URI:
The Request-URI is a Uniform Resource Identifier and
identifies the resource upon which to apply the request. Following are the most
commonly used forms to specify a URI:
Request-URI = "*" | absoluteURI | abs_path
| authority
S.N.
|
Method and Description
|
1
|
The asterisk * is used when an HTTP request does not apply to a
particular resource, but to the server itself, and is only allowed when the method used does not necessarily apply to a resource. For example:
OPTIONS
* HTTP/1.1
|
2
|
The absoluteURI is
used when an HTTP request is being made to a proxy. The proxy is requested to
forward the request or service from a valid cache, and return the response.
For example:
GET http://bcanotespu.blogspot.com/pub/WWW/TheProject.html
HTTP/1.1
|
3
|
The most common form of Request-URI is used to identify a resource on an
origin server or gateway. For example, a client wishing to retrieve a
resource directly from the origin server would create a TCP connection to
port 80 of the host " bcanotespu.blogspot.com
" and send the following lines:
GET /pub/WWW/TheProject.html HTTP/1.1
Host: bcanotespu.blogspot.com
Note
that the absolute path cannot be empty; if none is present in the original
URI, it MUST be given as "/" (the server root).
|
4. Request Header Fields:
The request-header fields allow the client to pass
additional information about the request, and about the client itself, to the
server. These fields act as request modifiers. Here is a list of some important
Request-header fields that can be used based on the requirement:
a. Accept-Charset
b. Accept-Encoding
c. Accept-Language
d. Authorization
e. Expect
f. From
g. Host
h. If-Match
i. If-Modified-Since
j. If-None-Match
k. If-Range
l. If-Unmodified-Since
m. Max-Forwards
n. Proxy-Authorization
o. Range
p. Referer
q. TE
r. User-Agent
Examples of Request Message:
Now let's put it all together to form an HTTP request to
fetch hello.htm page from the web server running on
tutorialspoint.com
GET /hello.htm HTTP/1.1
User-Agent: Mozilla/4.0 (compatible; MSIE5.01;
Windows NT)
Host:bcanotespu.blogspot.com
Accept-Language: en-us
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
Here we are not sending any request data to the server
because we are fetching a plain HTML page from the server. Connection is a
general-header and the rest of the headers are request headers. The following example shows how to send form data to the server using the request message body:
POST /cgi-bin/process.cgi HTTP/1.1
User-Agent: Mozilla/4.0 (compatible; MSIE5.01;
Windows NT)
Host: bcanotespu.blogspot.com
Content-Type: application/x-www-form-urlencoded
Content-Length: length
Accept-Language: en-us
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
licenseID=string&content=string&/paramsXML=string
Here the given URL /cgi-bin/process.cgi will
be used to process the passed data and accordingly, a response will be
returned. Here content-type tells the server that the passed
data is a simple web form data and length will be the actual
length of the data put in the message body. The following example shows how we
can pass plain XML to our web server:
POST /cgi-bin/process.cgi HTTP/1.1
User-Agent: Mozilla/4.0 (compatible; MSIE5.01;
Windows NT)
Host: bcanotespu.blogspot.com
Content-Type: text/xml; charset=utf-8
Content-Length: length
Accept-Language: en-us
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
<?xml version="1.0" encoding="utf-8"?>
<string
xmlns="http://clearforest.com/">string</string>
HTTP Responses Message:
After receiving and interpreting a request message, a server
responds with an HTTP response message:
1. A
Status-line
2. Zero
or more header (General|Response|Entity) fields followed by CRLF
3. An empty line (i.e., a line with nothing preceding the CRLF) indicating the end of
the header fields.
4. Optionally
a message-body
1. Message Status-Line:
Status-Line consists of the protocol version followed by a
numeric status code and its associated textual phrase. The elements are
separated by space SP characters.
Status-Line = HTTP-Version SP Status-Code SP
Reason-Phrase CRLF
2. HTTP Version:
A server supporting HTTP version 1.1 will return the
following version information:
HTTP-Version = HTTP/1.1
3. Status Code:
The Status-Code element is a 3-digit integer where first
digit of the Status-Code defines the class of response and the last two digits
do not have any categorization role. There are 5 values for the first digit:
S.N.
|
Code and Description
|
1
|
1xx:
Informational
It
means the request was received and the process is continuing.
|
2
|
2xx:
Success
It
means the action was successfully received, understood, and accepted.
|
3
|
3xx:
Redirection
It
means further action must be taken to complete the request.
|
4
|
4xx:
Client Error
It
means the request contains incorrect syntax or cannot be fulfilled.
|
5
|
5xx:
Server Error
It
means the server failed to fulfil an apparently valid request.
|
HTTP status codes are extensible and HTTP applications are
not required to understand the meaning of all registered status codes.
4. Response Header Fields:
The response-header fields allow the server to pass
additional information about the response which cannot be placed in the Status-
Line. These header fields give information about the server and about further
access to the resource identified by the Request-URI.
a. Accept-Ranges
b. Age
c. ETag
d. Location
e. Proxy-Authenticate
f. Retry-After
g. Server
h. Vary
i. WWW-Authenticate
Examples of Response Message:
Now let's put it all together to form an HTTP response for a
request to fetch the hello.htm page from the webserver
running on tutorialspoint.com
HTTP/1.1 200 OK
Date: Mon, 27 Jul 2009 12:28:53 GMT
Server: Apache/2.2.14 (Win32)
Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
Content-Length: 88
Content-Type: text/html
Connection: Closed
<html>
<body>
<h1>Hello, World!</h1>
</body>
</html>
The following example shows an HTTP response message
displaying error condition when the web server could not find the requested
page:
HTTP/1.1 404 Not Found
Date: Sun, 18 Oct 2012 10:36:20 GMT
Server: Apache/2.2.14 (Win32)
Content-Length: 230
Connection: Closed
Content-Type: text/html; charset=iso-8859-1
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML
2.0//EN">
<html>
<head>
<title>404 Not Found</title>
</head>
<body>
<h1>Not Found</h1>
<p>The requested URL /t.html was not found on this
server.</p>
</body>
</html>
Following is an example of an HTTP response message showing
error condition when the webserver encountered a wrong HTTP version in the
given HTTP request:
HTTP/1.1 400 Bad Request
Date: Sun, 18 Oct 2012 10:36:20 GMT
Server: Apache/2.2.14 (Win32)
Content-Length: 230
Content-Type: text/html; charset=iso-8859-1
Connection: Closed
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML
2.0//EN">
<html>
<head>
<title>400 Bad Request</title>
</head>
<body>
<h1>Bad Request</h1>
<p>Your browser sent a request that this server could not
understand.</p>
<p>The request line contained invalid characters following the
protocol string.</p>
</body>
</html>
Different Architectures of Connection:
Client-Server Architecture:
The Client-Server network model is a widely used, network
model. Here, Server is a powerful system that stores the data
or information in it. On the other hands, the Client is the
machine which let the users access the data on the remote server.
The system administrator manages the data
on the server. The client machines and the server are connected through a network.
It allows the clients to access data even if the client machine and server are
far apart from each other.
In Client-Server model, the client process on the client
machine sends the request to the server process on the server
machine. When the server receives the client request, it lookouts for the
requested data and sends it back with the reply.
As all the services are provided by a centralized server,
there may be chances of server getting bottlenecked, slowing down
the efficiency of the system.
Peer-to-Peer Architecture:
Unlike Client-Server, the Peer-to-Peer model does not
distinguish between client and server instead each node can
either be a client or a server depending on whether the node is requesting or providing the
services. Each node is considered as a peer.
To become a part of peer-to-peer, a node must
initially join the network. After joining it must start to
provide services to and must request the services from other nodes in the
peer-to-peer system. There are two ways to know which node
provides which services; they are as follow:
a. When
a node enters the peer-to-peer system, it must register the
services it will be provided, into a centralized lookup service on
the network. When a node desires for any specific service it must contact
centralized lookup services to check out which node will provide the desired
services. Rest of the communication is done by the desiring node and the
service providing node.
b.m A
node desiring for the specific services must broadcast the
request for services to all other nodes in the peer-to-peer system. The node
providing the requested service will respond to the node
making the request.
Peer-to-Peer network has the advantage over client-server
that the server is not bottlenecked as the services are provided
by the several nodes distributed in a peer-to-peer system.
Difference between Client-Server and Peer To Peer Architecture:
Basis
|
Client-Server
|
Peer-To-Peer:
|
Basic
|
There is a specific
server and specific clients connected to the server.
|
Clients and server
are not distinguished; each node act as client and server.
|
Service
|
The client request
for service and server respond with the service.
|
Each node can
request for services and can also provide the services.
|
Focus
|
Sharing the
information.
|
Connectivity.
|
Data
|
The data is stored
in a centralized server.
|
Each peer has its
own data.
|
Server
|
When several clients
request for the services simultaneously, a server can get bottlenecked.
|
As the services are
provided by several servers distributed in the peer-to-peer system, a server
in not bottlenecked.
|
Expense
|
The client-server
are expensive to implement.
|
Peer-to-peer is
less expensive to implement.
|
Stability
|
Client-Server is
more stable and scalable.
|
Peer to Peer suffers
if the number of peers increases in the system.
|
Differentiate between Client Side and Server Side Scripting Language:
Client
Side Scripting Language
|
Server
Side Scripting Language
|
Client-side
scripting is used when the user’s browser already has all the code and the page is altered based on the user's input.
|
Server-side
scripting is used to create dynamic pages based on several conditions when
the user's browser makes a request to the server.
|
The Web Browser executes the client-side scripting that resides at the user’s
computer.
|
The Web Server executes the server-side
scripting that produces the page to be sent to the browser.
|
The browser
receives the page sent by the server and executes the client-side scripts.
|
Server executes server-side scripts to send
out a page but it does not execute client-side scripts.
|
Client-side
scripting cannot be used to connect to the databases on the webserver.
|
Server-side scripting is used to connect
to the databases that reside on the webserver.
|
Client-side
scripting can’t access the file system that resides at the webserver.
|
Server-side scripting can access the file
system residing at the webserver.
|
The files and
settings that are local at the user’s computer can be accessed using Client
side scripting.
|
The settings that belong to the Web server can be
accessed using Server-side scripting.
|
Client-side
scripting is possible to be blocked by the user.
|
Server-side scripting can’t be blocked by the
user.
|
Response from
a client-side script is faster as compared to a server-side script because
the scripts are processed on the local computer.
|
Response from a server-side script is slower
as compared to a client-side script because the scripts are processed on the
remote computer.
|
Examples of
Client side scripting languages : JavaScript, VB script, etc.
|
Examples of Server-side scripting languages:
PHP, JSP, ASP, ASP.Net, Ruby, Perl and many more.
|
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