Networks, WWW, HTTP - IIT

Networks, WWW, HTTPWeb Technologies I.

Zsolt Tóth

University of Miskolc

2018

Zsolt Tóth (University of Miskolc) Networks, WWW, HTTP 2018 1 / 35

Networks Internet

Table of Contents

1 NetworksInternetResourcesClient–Server Model

2 World Wide WebOverviewHTTP Protocol

HTTP CommandsHTTP Status Codes


Networks Internet

Open Systems Interconnection Model

Conceptual modelnot realized directlyvarious implementations

Layered structureEach layer

uses below layersserves above layershas well–defined function


Networks Internet

Internet Protocol Suite


Networks Internet

Transmission Control Protocol / IP

packet–switchingreliableorderederror–checking

ApplicationsWorld Wide Web (HTTP)email (POP, IMAP, SMTP)FTPSSHDHCPDNS


Networks Resources

Resource

Static contentTextHTMLimageaudio / videobinary file (pdf, doc, etc.). . .

Dynamic contentService

SSHFTPHTTP

Generated contentCGIPHP, PythonJSP, ASPREST / JSON


Networks Resources

Unified Resource Identifier

scheme:[//[user:password\@]host[:port]][/]path[?query][\#fragment]

Unified Resource LocatorLocation based identificationFits to computer networksUsage

web addressfile transferremote logindatabase access

Unified Resource NameName based identification

ISBN booksISSN journalsISAN audiovisual works


Networks Resources

URL Examples

http://www.origo.hu/index.htmlhttp://www.w3schools.com/http://localhost:8080/myApp/loginhttp://localhost:8080/calculator/add?a=5&b=3imap://imap.iit.uni-miskolc.hu:143imaps://imap.iit.uni-miskolc.hu:993smtp://smtp.iit.uni-miskolc.hu:25ftp://ftp.iit.uni-miskolc.hujdbc:mysql://localhost:3306/sakila?profileSQL=true


Networks Resources

Hosts Address

IPv432bit = 4 bytexxx.xxx.xxx.xxxUnique address (NAT)

IPv6Compatibility with IPv4128bit = 16byteUnique address

SubnetsNet Mask32 bit255.255.255.0192.168.2.1/24

Network Address TranslationHide subnetsRequest from the Internet XService to the Internet X


Networks Resources

Domain Name System

IP address↔ domain nameHierarchical structure"." is the rootworld–widedecentralizedDNS ServersHosts belongs to one domainDomains contains multiplehosts

Internet Assigned NumbersAgencyTop Level Domain

Generic TLDgov, edu, net,com, org, mil

Country Code TLDhu, es, ru,au, gb, us

www.iit.uni-miskolc.hu.www.abc.net.au.


Networks Client–Server Model

Client–Server Model

SimpleCentralizedServer

provides service orresourceruns on a publicly availablecomputerwaits for requests fromarbitrary clients

Clientrequests resources fromserverruns locally



Client–Server Model



Client

Thin clientSimple application

Browser

Representation, visualizationNo business logic

Check values

Low hardware requirementsWeb applications

Thick (fat, rich) clientsComplex applicationsLot of functionalitiesIndependent from the serverHigher hardwarerequirementsOff–line workInstallation

for each clients¿ Versioning ?



Server – Application

Application not computer!Waits for requestsSpecific purpose

Web serversMail serversApplication serversAuthentication serversFTP serversetc.

a computer – many serverapplications



Server – Computer

Executes server applicationFix IP AddressHigh performance

Expensive hardwareHigh upkeepCustom OS

One or multiple computersGRIDCloud Computing

Server room, data centers

As a developer,you will run a web/applicationserver and a database serverlocally.you will use various servers(SCM, CI, Issue tracker, etc.)you may deploy yourapplication to test and demoservers for presentationpurposes.you will never want to operateserver. That is the job ofsystem administrators!


World Wide Web Overview

Table of Contents

1 NetworksInternetResourcesClient–Server Model

2 World Wide WebOverviewHTTP Protocol

HTTP CommandsHTTP Status Codes



History

Hypertext system1990-91 First web serverExpansion (’91-’95)Commercialization (’95-2000)Dot–com bubble (’97-2000)Present (since 2000)

UbiquitousSocial networkMultimediaSemantic web



Architecture



Web Server

ApplicationStatic IPListen on port (80,8080,. . . )Communicate via HTTP

Major providersMarket share of active sites(Netcraft Sept 2015)

1 Apache (≈50.5%)2 nginx (≈14.3%)3 Microsoft (≈10.2%)4 Google (≈7.8%)



HyperText Transfer Protocol

Application LayerInformation SystemsRequests and responsesDefines

Methods / verbsStatus codes

Designed to exchange HTMLdocuments

HTTPSis not a standalone protocoluses secure communication

Secure Socket LayerTransport Layer Security


HTML

Plain TextTagsStandardBrowsers

visualizeinterpret

1 <html><head>

3 </head>

5 <body>

7 </body></html>


Browser

ChallengesBrowsers visualize the sameHTML standardizeddifferently.So sites have to be optimizedto browser (IE)Customers have specialneeds:

we want to include videosso please use HTML 5the site has to becompatible with InternetExplorer 7



Browser


World Wide Web HTTP Protocol

HTTP Protocol

Application protocolData communicationVersions

HTTP/0.9HTTP/1.0HTTP/1.1HTTP 2.0

DefinesMethodsStatus codes

Typical clientsBrowsersWeb robotsMobil applications



HTTP Methods

HEADGETPOSTPUTDELETE

TRACEOPTIONSCONNNECTPATCH



GET, HEAD

GETsafeidempotentRequest a pageURL encoding

GET path HTTP/1.1

HEADsafeidempotentRequest the head part onlyRetrieve meta–information

HEAD path HTTP/1.1



POST, PUT, DELETE, PATCH

POSTRequest a pageParameters are encoded inthe requestCan send more data than GET

Form dataFile upload

PUTStore an entity.IdempotentFile upload

DELETERemoves an entity.Idempotent

PATCHPartial modification of anentity.



CONNECT, OPTIONS, TRACE

CONNECTuse tunnel such as SSL

OPTIONSQuery HTTP methodssupported.

TRACEEcho HTTP request.

Web servers not alwayssupports all of these methods!You can check them withtelnet or netcat.



HTTP Status Codes

Part of the responseSent by the serverClients computesImportant for AJAX, REST

Categories1XX Informational2XX Successful3XX Redirection4XX Bad Request5XX Sever Error



1XX

HTTP/1.1to switch from HTTP/1.0 toHTTP/1.1Unknown 1XX→ Ignore

100 Continue101 Switching Protocols

HTTP/1.0↓

HTTP/1.1

102 Processing



2XX

Requestreceivedunderstoodacceptedprocessed

200 OKGET HEADPOST TRACE

201 Created202 Accepted203 Non–Authoritative

Information204 No Content205 Reset content206 Partial cntent



3XX

for the User AgentBrowser modifies therequest automatically.Caused by

site moved.usage of proxyredirection

300 Multiple chices301 Moved Permanently302 Found303 See Other304 Not Modified305 Use Proxy306 Unused307 Temporary Redirect



4XX



4XX

Bad RequestClient–side problemAny request can cause it.Examples:

bad web addressauthentication required

400 Bad Request401 Unauthorized402 Payment Required403 Forbidden404405 Method Not Allowed406 Not Acceptable. . .



5XX

Server ErrorCan be caused by anyrequest.There is a problem at theserver side.All users, who use thesystem, will get the errorcode.For example,

exception do not handleddatabase unavailable

It can show the poor job of thedevelopers.

501 Not Implemented502 Bad Gateway503 Servie Unavailable504 Gateway Timeout505 HTTP Version Not

Supported


Networks, WWW, HTTP - IIT

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