Gholamhossein Tavasoli ZNU Fall 2013 Definitions A computer, - - PowerPoint PPT Presentation

Gholamhossein Tavasoli ZNU – Fall 2013

 Definitions

• A computer, responsible for accepting HTTP requests

from clients, and serving them Web pages

• A computer program that provides the above

mentioned functionality

 Common features

• Accepting HTTP requests from the network
• Providing HTTP response to the requester

▪ Typically consists of an HTML

• Usually capable of logging

▪ Client requests/Server responses

 Returned content

• Static

▪ Comes from an existing file

• Dynamic

▪ Dynamically generated by some other program/script called by the Web server.

 Path translation

• Translate the path component of a URL into a

local file system resource

▪ Path specified by the client is relative to the server’s root dir

 Created to define the communication between a

web server and a client

 It's the network protocol used to deliver virtually

all files and other data (collectively called resources) on the World Wide Web

 A browser is an HTTP client because it sends

requests to an HTTP server (Web server), which then sends responses back to the client.

 The standard (and default) port for HTTP servers

to listen on is 80, though they can use any port.

 Like most network protocols, HTTP uses the

client‐server model: An HTTP client opens a connection and sends a request message to an HTTP server; the server then returns a response message, usually containing the resource that was requested

• I would like to open a

connection

• GET <file location>
• Display response
• Close connection
• OK
• Send page or error message
• OK

Client Server

 Format of a http message:

<initial line, different for request vs. response> Header1: value1 Header2: value2 Header3: value3 <optional message body goes here, like file contents

• r query data; it can be many lines long, or even

binary data >



A typical initial request line:

• GET /path/to/file/index.html HTTP/1.0

 Initial response line:

• HTTP/1.0 200 OK
• HTTP/1.0 404 Not Found



Status code:

• 1xx indicates an informational message only
• 2xx indicates success of some kind
• 3xx redirects the client to another URL
• 4xx indicates an error on the client's part
• 5xx indicates an error on the server's part



Common status codes:

• 200 OK
• 404 Not Found
• 301 Moved Permanently
• 302 Moved Temporarily
• 303 See Other (HTTP 1.1 only)
• 500 Server Error

 Typical request headers:

• From: email address of requester
• User‐Agent: for example User‐

agent: Mozilla/3.0Gold

 Typical response headers:

• Server: for example Server: Apache/1.2b3‐dev
• Last‐modified: fro example Last‐Modified: , 19

Feb 2006 23:59:59 GMT

 In a response, this is where the requested resource is

returned to the client (the most common use of the message body), or perhaps explanatory text if there's an error.

 In a request, this is where user‐entered data or

uploaded files are sent to the server.

 If an HTTP message includes a body, there are usually

header lines in the message that describe the body. In particular,

 The Content‐Type: header gives the MIME‐type of the

data in the body, such as text/html or image/gif.

 The Content‐Length: header gives the number of

bytes in the body.

 To retrieve the file at the URL

http://www.sourceforge.net

 Request:

 To retrieve the file at the URL

http://www.sourceforge.net

 Response:

 GET: request a resource by URL  HEAD

• is just like a GET request, except it asks the server

to return the response headers only, and not the actual resource (i.e. no message body).

• This is useful to check characteristics of a resource

without actually downloading it, thus saving bandwidth.

 POST

• A POST request is used to send data to the server to

be processed in some way, like by a PHP script.

• There's a block of data sent with the request, in the

message body. There are usually extra headers to describe this message body, like Content‐Type: and Content‐Length:.

• The request URI is not a resource to retrieve; it's

usually a program to handle the data you're sending.

• The HTTP response is normally program output, not a

static file.

 PUT, DELETE, TRACE, CONNECT, OPTIONS

 A multithreaded Web server with a front end

and processing modules.

 each processing module performs a series of

steps:

• Resolve the name of the Web page requested.
• Authenticate the client.
• Perform access control on the client.
• Perform access control on the Web page.
• Check the cache.
• Fetch the requested page from disk.
• Determine the MIME type to include in the response.
• Take care of miscellaneous odds and ends.
• Return the reply to the client.
• Make an entry in the server log.

 Berners‐Lee wrote two programs

• A browser called WorldWideWeb
• The world’s first Web server, which ran on

NeXSTEP

▪ The machine is on exhibition at CERN’s public museum

 Apache HTTP Server, Apache Software

Foundation

 Internet Information Services (IIS),

Microsoft

 NGINX, Nginx, Inc.  LiteSpeed, LiteSpeedTechnologies, Inc.  Lighttpd

 Apache is used by 61.9% of all the websites

whose web server we know.

 Microsoft‐IIS is used by 16.5% of all the

websites whose web server we know.

 Nginx is used by 16.1% of all the websites

whose web server we know.

 LiteSpeed is used by 1.9% of all the websites

whose web server we know.

 Apache 1

 Apache 2

 NGINX

 Caching  Content negotiation

• A resource may be available in several different

representations.

• For example, it might be available in different languages
• r different media types, or a combination.
• One way of selecting the most appropriate choice is to

give the user an index page, and let them select.

• However it is often possible for the server to choose

automatically by the help of request headers: Accept‐Language: fr; q=1.0, en; q=0.5 Accept: text/html; q=1.0, text/*; q=0.8, image/gif; q=0.6, image/jpeg; q=0.6, image/*; q=0.5, */*; q=0.1

 Log files

• In order to effectively manage a web server, it is

necessary to get feedback about the activity and performance of the server as well as any problems that may be occurring

 Error log:

• [Wed Oct 11 14:32:52 2000] [error] [client 127.0.0.1]

client denied by server configuration: /export/home/live/ap/htdocs/test

 Access log:

• Common log format:

▪ 127.0.0.1 ‐ frank [10/Oct/2000:13:55:36 ‐0700] "GET /apache_pb.gif HTTP/1.0" 200 2326

• Combined log format:

▪ 127.0.0.1 ‐ frank [10/Oct/2000:13:55:36 ‐0700] "GET /apache_pb.gif HTTP/1.0" 200 2326 "http://www.example.com/start.html" "Mozilla/4.08 [en] (Win98; I ;Nav)"

 Mapping URLs to file system locations:

• DocumentRoot
• Alias directive:

▪ Alias /docs /var/web ▪ the URL http://www.example.com/docs/dir/file.html will be served from /var/web/dir/file.html.

• AliasMatch:

▪ ScriptAliasMatch ^/~([a‐zA‐Z0‐9]+)/cgi‐bin/(.+) /home/$1/cgi‐ bin/$2 ▪ will map a request to http://example.com/~user/cgi‐ bin/script.cgi to the path /home/user/cgi‐bin/script.cgi and will treat the resulting file as a CGI script

• User Directories:

▪ http://www.example.com/~user/file.html

 Mapping URLs to file system locations:

• URL redirection:

▪ Redirect permanent /foo/ http://www.example.com/bar/

• Reverse proxy:

▪ Apache also allows you to bring remote documents into the URL space of the local server. ▪ This technique is called reverse proxying because the web server acts like a proxy server by fetching the documents from a remote server and returning them to the client. ▪ ProxyPass /foo/ http://internal.example.com/bar/

• Mod_speling for file not found errors

 Access control to filesystem  Virtual hosting

• The term Virtual Host refers to the practice of

running more than one web site (such as www.company1.com and www.company2.com)

• n a single machine.

 Virtual hosts can be "IP‐based", meaning that

you have a different IP address for every web site

• The server must have a different IP address for

each IP‐based virtual host.

• Most commonly, this is used to serve different

websites on different ports or interfaces.

• This can be achieved by the machine having

several physical network connections, or by use of virtual interfaces which are supported by most modern operating systems

 Virtual hosts can be "IP‐based", meaning that

you have a different IP address for every web site

• The server must have a different IP address for

each IP‐based virtual host.

• Most commonly, this is used to serve different

websites on different ports or interfaces.

• This can be achieved by the machine having

several physical network connections, or by use of virtual interfaces which are supported by most modern operating systems

 or "name‐based", meaning that you have

multiple names running on each IP address. The fact that they are running on the same physical server is not apparent to the end user.

• more convenient