Hypertext Transfer Protocol

Kyle RothMark Hoover

What is HTTP

● Protocol– Mainly used for accessing data on the World Wide

Web.– Similar to FTP and SMTP

● HTTP and FTP transfer files and use services of TCP● HTTP only uses one TCP connection.● HTTP and SMTP messages look similar● HTTP messages are only interpreted by the browser

– HTTP typically uses TCP, but only presumes reliable transport

– HTTP uses a request/response model

Request/Response

World Wide Web

● The Wold Wide Web is a distributed client/server service

● HTTP provides uniformity over requests and responses

● HTTP requests are requests for Web Documents

● HTTP responses are Web Documents

HTTP Messages

● There are two types of HTTP messages● Request Message

– Request Line– Header– Body

● Response Message– Status Line– Header– Body

HTTP Message

Request Line and Status Line

● Request Line– Request Type– URL– HTTP Version

● Status Line– HTTP Version– Status Code– Status phrase

Request Type

● The Request type defines the type of action that the client is requesting

● GET – Requests a document from the server

● HEAD – Requests information about a document, but not the document itself

● POST – Sends some information from client to server

● PUT – Sends a document from client to server

● TRACE – Echoes the incoming request

● CONNECT – Reserved

● OPTION – Inquires about available options

URL

● Standard for specifying any kind of information on the Internet

● Defines– Protocol – HTTP– Host – Referred to by an alias (typically www)– Port – Specifies port number of the server (optional)– Path – Pathname to the file

Status Code/Phrase

● The Status code reports the success of the request– 100 Range – Informational– 200 Range – Successful request– 300 Range – Redirection– 400 Range – Client Side Error– 500 Range – Server Side Error

Status Codes

Status Codes

HTTP Header

● Header contains additional information● The header can specify format constraints● Four categories of headers

– General – Information about the message– Request – Specifies client's configuration and

preferred format– Response – Specifies server's configuration and

special information about the request– Entity – Information about the body

General Header

Request Header

Response

Entity

HTTP Transaction

Nonpersistent Connections

● Persistent connections are default in HTTP version 1.1

● One connection is made for each request/response– Client opes a connection and sends a request– Server sends the response and closes the

connection– Client reads data, then closes the connection

● Requires N connections for N files

Persistent Connections

● Persistent connections remove the high overhead of non persistent connections

● The connection remains open until the client requests it to be closed, or the connection times out

● Length of data is sent when applicable

Proxy Servers

● Proxy servers act as go betweens for the actual servers

● Proxy servers maintain a cache of recent requests

● HTTP requests are sent to proxy servers, which check their cache

● The actual server is only accessed when the proxy server does not have the requested information– The proxy server polls the server for the requested

information and updates its cache

Proxy Servers

● This reduces traffic coming into the original server.– Latency is improved

● Requires that the client is configured to access the proxy instead of the target server