LIS650 lecture 5 javascript, http and apache

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LIS650 lecture 5javascript, http and apache

• Thomas Krichel
• 2006-03-04

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today

• javascript
• http
• apache introduction

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javascript

• This is a client-side scripting language.
• Your web page is read by the client. If it
  contains instructions written in javascript, the
  client executes the command, provided it knows
  about javascript.
• Different browser capabilities when it comes to
  executing javascript did bedevil javascript at
  the outset.

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the ltscriptgt

• ltscriptgt is an element that calls a script.
• Interestingly enough, you can place ltscriptgt in
  the head or the body.
• It requires a type attribute that gives the type
  of the script language. e.g. type"text/javascript
  ".
• It takes a defer attribute. If set as defer"1"
  you tell the user agent that the script will
  generate no output. This helps the user agent in
  that case.

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example

• ltscript type"text/javascript"gt
• document.write("hello, world")
• lt/scriptgt
• This is an example of an automated script. The
  user has to do nothing to get the script to run.
• You can also trigger a script. To do that, we
  have to study some more HTML attributes. We will
  do that later.

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external script

• ltscriptgt takes the src argument that gives a URI
  where the script can be found. Such a script is
  called an external script.
• You can also create an external file, say
  hello.js with the line
• document.write("hello, world")
• Then you can call it up in the html file
• ltscript type"text/javascript"
  src"hello.js"/gt

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default script language

• You should set the default scripting language
  used in the document using the ltmeta/gt element in
  the ltheadgt
• ltmeta http-equiv"content-script-type"
  content"text/javascript"/gt
• If you don't the validator does not complain, but
  I don't see other ways to specify the language.

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Javascript history

• A programming language that was developed by
  Netscape for their browser in 1995.
• To counter, Mickeysoft developed Jscript.
• It has been standardized by the European Computer
  Manufacturers Association as ECMA 262.

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principal features

• It contains instructions for a user agent to
  execute. Javascript is not run by the server.
• It resembles Java, but not the same language.
• It is an object-oriented language.

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object

• In an object-oriented language, an object is the
  prime focus of attention.
• An object has properties and methods.
• Example from real life. Let a bus be an object.
• color of the bus is a property
• move to next station is a method

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objects in javascript

• Properties are accessed by
• object_name.property_name
• Methods are accessed by
• object_name.method_name()
• where object_name is the name of an object,
  property_name is the name of a property and
  method_name() is the name of an object. Note the
  use of the dot and the parenthesis.

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Example

• Syntax rules
• Comments are started with // and go to the end of
  the line.
• Instructions are terminated with semicolon
• Example
• // create a new object called bus
• new bus Object()
• // paint it white --- set a property
• bus.color white
• // move to next stop --- apply a method
• bus.movetonextstop()

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event attributes

• Event attributes can be given to elements (like
  any attribute, really)
• The name of the attributes gives a certain event
  that could happen to the element.
• The value of the event attribute is the script to
  be executed when the event occurs on the element
  that has the event attribute.
• Example
• ltp onmouseover"stink"gtCow shit is ... lt/pgt
• as the user moves the mouse over the
  paragraph, the browser fires up an imaginary
  script called stink that makes it start to stink.

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core event attributes I

• onclick occurs when the pointing device button
  is clicked over an element.
• ondblclick occurs when the pointing device
  button is double clicked over an element.
• onmousedown occurs when the pointing device
  button is pressed over an element.
• onmouseup occurs when the pointing device button
  is released over an element.
• onmouseover occurs when the pointing device is
  moved onto an element.

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core events attributes II

• onmousemove occurs when the pointing device is
  moved while it is over an element.
• onmouseout occurs when the pointing device is
  moved away from an element.
• onkeypress occurs when a key is pressed and
  released over an element.
• onkeydown occurs when a key is pressed down over
  an element.
• onkeyup occurs when a key is released over an
  element.

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special event attributes

• onfocus occurs when an element receives focus
  either by the pointing device or by tabbing
  navigation. This attribute may only be used with
  the ltagt element, and some form elements that we
  have not covered.
• onblur occurs when an element loses focus either
  by the pointing device or by tabbing navigation.
  It may be used with the same elements as onfocus.

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more special event attributes

• onsubmit occurs when a form is submitted. It
  only applies to the ltformgt element.
• onreset occurs when a form is reset. It only
  applies to the ltformgt element.
• some more are only used with other form
  elements...
• Let us look at some examples

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two stupid examples

• lthtmlgtltheadgtlttitlegtjavascript testlt/titlegt
• ltmeta http-equiv"content-script-type"
  content"text/javascript"/gtlt/headgt
• ltbodygtltp onmouseover"alert('Today is 'Date())"
  gttimelt/pgtlthr/gt
• ltp onmouseover
• "document.write('not funny')"gtjokelt/pgt
  lt/bodygtlt/htmlgt

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An even more silly example

• lthtmlgtltheadgtlttitlegtBush in the bushlt/titlegt
• ltmeta http-equiv"content-script-type" content
  "text/javascript"/gtltscript type"text/javascript"gt
  
• prbunew Image() prbu.src"bush.jpg"
• natbnew Image() natb.src"natgeo.jpg"
  lt/scriptgtlt/headgtltbodygtlth1gtBush in the
  bushlt/h1gtltdivgtltimg id"bush" src"bush.jpg"
  onmouseover"document.bush.srcnatb.src"
• onmouseout"document.bush.srcprbu.src"
  alt"bush in the bush"/gtlt/divgtlt/bodygtlt/htmlgt

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http

• Stands for the hypertext transfer protocol. This
  is the most important application layer protocol
  on the Internet today, because it provides the
  foundation for the world wide web.
• defined in Fielding, Roy T., James Gettys,
  Jeffrey C. Mogul, Paul J. Leach, Tim Berners-Lee
  Hypertext Transfer Protocol -- HTTP/1.1''
  (1999), RFC 2616

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history

• 1990 version 0.9 allows for transfer of raw
  data.
• 1996 rfc1945 defines version 1.0. by adding
  attributevalue headers.
• 1999 rfc 2616
• adds support for
• hierarchical proxies
• caching,
• virtual hosts and some
• Support for persistent connections
• is more stringent.

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rfc about http

• An application-level protocol for distributed,
  collaborative, hypermedia information systems.
• HTTP is also used as a generic protocol for
  communication between user agents and
  proxies/gateways to other Internet systems,
  including those supported by the SMTP, NNTP, FTP,
  Gopher, and WAIS protocols. In this way, HTTP
  allows basic hypermedia access to resources
  available from diverse applications.

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http assumes transport

• http assumes that there is a reliable way to
  transport data from one host on the Internet to
  another one.
• All http requests and responses are separate TCP
  connections. The default is TCP port 80, but
  other ports can be used.

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use of other standards

• http shares the same registry as the MIME
  multimedia email extensions. It is based at the
  IANA, at
• http//www.isi.edu/innotes/iana/
• assignments/media-types/media-types
• The default character set is ISO-8859-1.

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http resource identification

• identification of resources is assumed through
  Uniform Resource Identifiers (URI).
• As far as http is concerned, URIs are string.
• http can use absolute'' and relative'' URIs.
• A URL is a special case of a URI.

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Absolute http URL

• the absolute http URL is
• http//hostportabs_path?query
• If abs_path is empty, it is /.
• The scheme name "http" and the host name are
  case-insensitive.
• optional components are in

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special characters in URL

• Characters other than those in the reserved and
  unsafe character lists of RFC 2396 are
  equivalent to their HEX HEX where HEX is a
  hex number, usually the characters number in
  ASCII.
• Example to include a blank in a URI, you write
  20, because 32 is the position of the blank in
  ASCII.

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http messages

• There are two types of messages.
• Requests are sent form the client to the server.
• Responses are sent from the server to the client.
• The generic format is the same as for email
  messages
• start line
• message headers
• empty line
• body
• The request's start line is called the request
  line.
• The response start line is called the status
  line.

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overall operation server side

• Server sends response, required items are
• status line
• protocol version
• success or error code
• optional items are
• server information
• body

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overall operation client side

• Client sends request, required items are
• method
• request URI
• protocol version
• optional items are
• request modifiers
• client information
• Let us now look at different methods

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GET and HEAD method

• The GET method means retrieve whatever
  information (in the form of an entity) is
  identified by the Request-URI. If the Request-URI
  refers to a data-producing process, it is the
  produced data which shall be returned as the
  entity in the response and not the source text of
  the process.
• The HEAD method is identical to GET except that
  the server MUST NOT return a message-body in the
  response.

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The POST method

• The POST method is used to request that the
  origin server accept the entity enclosed in the
  request as a new subordinate of the resource
  identified by the Request-URI in the
  Request-Line. POST is designed to allow a uniform
  method to cover the following functions
• Annotation of existing resources
• Posting a message to a bulletin board, newsgroup,
  mailing list, or similar group of articles
• Providing a block of data, such as the result of
  submitting a form, to a data-handling process
• Extending a database through an append operation.

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PUT and DELETE methods

• The PUT method requests that the enclosed entity
  be stored under the supplied Request-URI. If the
  Request-URI refers to an already existing
  resource, the enclosed entity should be
  considered as a modified version of the one
  residing on the origin server.
• The DELETE method requests that the origin server
  delete the resource identified by the Request-URI.

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The request headers

• Accept Accept-Charset
• Accept-Encoding Accept-Language
• Authorization Expect
• From Host
• If-Match If-Modified-Since
• If-None-Match If-Range
• If-Unmodified-Since Max-Forwards
• Proxy-Authorization Range
• Referer TE
• User-Agent

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Entity headers, common to response and request

• Allow
• Content-Encoding
• Content-Language
• Content-Length
• Content-Location
• Content-MD5
• Content-Range
• Content-Type
• Expires
• Last-Modified

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The status line

• The status line is a set of lines that are of
  the form
• HTTP-Version Status-Code Reason-Phrase
• The status code is a 3-digit number used by the
  computer.
• The reason line is a friendly note for a human to
  read.

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Status code classes

• 1 Informational Request received, continuing
  process
• 2 Success The action was successfully received,
  understood, and accepted
• 3 Redirection Further action must be taken in
  order to complete the request
• 4 Client Error The request contains bad syntax
  or cannot be understood
• 5 Server error The request is valid but can not
  be executed by the server

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Error codes

• 100 Continue
• 101 Switching Protocols
• 200 OK
• 201 Created
• 202 Accepted
• 203 Non-Authoritative Information
• 204 No Content
• 205 Reset Content
• 206 Partial Content

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Error codes II

• 300 Multiple Choices
• 301 Moved Permanently
• 302 Found
• 303 See Other
• 304 Not Modified
• 305 Use Proxy
• 307 Temporary Redirect

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Error codes III

• 400 Bad Request
• 401 Unauthorized
• 402 Payment Required
• 403 Forbidden
• 404 Not Found
• 405 Method Not Allowed
• 406 Not Acceptable
• 407 Proxy Authentication Required
• 408 Request Time-out

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Error codes IV

• 409 Conflict
• 410 Gone
• 411 Length Required
• 412 Precondition Failed
• 413 Request Entity Too Large
• 414 Request-URI Too Large
• 415 Unsupported Media Type
• 416 Requested range not satisfiable
• 417 Expectation failed

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Error codes V

• 500 Internal Server Error
• 501 Not Implemented
• 502 Bad Gateway
• 503 Service Unavailable
• 504 Gateway Time-out
• 505 HTTP Version not supported

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Response headers

• Accept-Ranges
• Age
• Etag
• Location
• Proxy-Authenticate
• Retry-After
• Server
• Vary
• WWW-Authenticate

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example response

• HTTP/1.1 200 OK
• Date Fri, 14 Oct 2005 011401 GMT
• Server Apache/2.0.54 (Debian GNU/Linux)
• Last-Modified Fri, 07 Oct 2005 164030 GMT
• ETag "11f711-9f1-b314bb80"
• Accept-Ranges bytes
• Content-Length 2545
• Connection close
• Content-Type text/html charsetUTF-8
• lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
  Strict//EN"
• "http//www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd
  "gt
• lthtmlgtltheadgtlttitlegtThomas Krichel's homepage

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The body

• The entity-body (if any) sent with an HTTP
  request or response is in a format and encoding
  defined by the entity-header fields.
• When an entity-body is included with a message,
  the data type of that body is determined via the
  header fields Content-Type and Content-Encoding

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example status redirect

• If you use Apache, you can create a file
  .htaccess (note the dot!) with a line
• redirect 301 old_url new_url
• old_url must be a relative path from the top of
  your site
• new_url can be any URL, even outside your site
• This works on wotan by virtue of configuration
  set for apache for your home directory. Examples
• redirect 301 /krichel http//openlib.org/home/kri
  chel
• redirect 301 Cantcook.jpg http//www.foodtv.com

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Apache

• Is a free, open-source web server that is
  produced by the Apache Software Foundation, see
  http//www.apache.org
• It has over 50 of the market share.
• It runs best on UNX systems but can run an a
  Mickeysoft OS as well.
• I will cover it here because it is freely
  available.
• Wotan runs version 2.

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Apache in debian

• /etc/apache2/apache.conf is set main
  configuration file.
• /etc/init.d/apache2 action, where action is one
  of
• start
• stop
• restart
• is used to fire the daemon up or down.
• The daemon runs user www-data

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Virtual host

• On a single installation of Apache several web
  servers can be supported.
• That means the server can behave in a different
  way according to how it is being addressed.
• The easiest way to implement addressing a server
  in different was is through DNS host names.

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directives in apache.conf

• This file contains directives that control the
  operation of the Apache server process as a
  whole.
• Some of them are
• the server root, where it finds its configuration
• the time out for requests
• which port to listen
• another part of apache.conf has extensive
  settings to deal with content
• different languages
• different character sets
• different MIME types

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Modules

• To extend Apache, modules have written. The
  modules are kept in a directory modules-available
• Modules that are enabled are listed in the
  directory modules-enabled.
• Looking at this gives you vital information about
  what the server can do.

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Server directives

• User
• Gives the user name apache runs under
• Group
• Gives the group name the server runs under
• ServerAdmin
• Email of a human who runs the default server
• ServerName
• The name of the default server
• DocumentRoot
• The top level directory of the default server

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Directory options

• Many options for a directory can be set with
• ltdirectory namegt instructionsltdirectorygt
• Name is the name of a directory.
• Instructions can be a whole lot of stuff.

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Directory instructions

• Options sets global options for the directory, it
  can be
• None
• All
• Or any of
• Indexes (form directory indexes?)
• Includes (allow server side includes?)
• FollowSymlinks (allow to follow symbolic links)
• ExecCGI (allow cgi-scripts?)
• MultiViews (allow flexibility in URLs)

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Access control

• Can be part of ltdirectorygt to set directory level
  access control
• Example
• Allow from friendly.com
• Deny from evil.com
• Sometimes you have to set the order, example
• Order allow, deny

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Authentication

• This is used to enable password access. In that
  case the authentication is handled by a file
  .htaccess in the directory.
• The AllowOverride instruction is used to state
  what the user can do within the .htaccess file.
  Depending on its values, you can password protect
  a web site.
• We will not discuss this further here.

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UserDir

• This sets the directory that is created by the
  user in her home directory to be accessed by
  requests to user.
• On wotan, we have
• UserDir public_html
• That is the default, actually.

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logs

• The web server logs every transaction.
• The are severeal types of logs that used to be
  kept separately, in early days.
• 209.73.164.50 - - 26/Jan/2003091951 -0500
  "GET /ramon/videos/ntsc175.html
• HTTP/1.1" 206 808
• Additional information may be kept in the referer
  and user agent log.
• The referer log may have some interesting
  information on who links to your pages.

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virtual hosts

• Most apache directive can be wrapped in a
  ltvirtualhostgt lt/virtualhostgt grouping. This
  implies that the only hold for the virtual host.
  Example
• ltVirtualHost gt
• ServerAdmin krichel_at_openlib.org
• DocumentRoot /home/connect/public_html
• ServerName connections2003.liu.edu
• ErrorLog /var/log/apache/connections2003-erro
  r.log
• CustomLog /var/log/apache/connectios2003-acce
  ss.log common
• lt/VirtualHostgt

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http//openlib.org/home/krichel

• Thank you for your attention!