Hypertext Transfer Protocol

Editor's Notes

• #2: The standards development of HTTP was coordinated by the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C),
• #4: European Organization for Nuclear Hypertext is structured text that uses logical links (hyperlinks) between nodes containing text coined by Ted Nelson in 1965 in the Xanadu Project inspired by Vannevar Bush's vision (1930s) of the microfilm-based information retrieval and management "memex“ Berners-Lee first proposed the "WorldWideWeb" project in 1989 ---  inventing the original HTTP along with HTML
• #6: Big picture Functions as a request-response protocol in the client-server computing model. Application layer protocol. Stateless protocol. TCP connection. Uses URL addressing Method request Response codes Uses Caching and conditional get Session maintenance
• #8: new TCP connection for each request- to – 1 request for multiple request (1.0)Keep-Alive header --- but -- design did not interoperate with intermediate proxies  clients, servers, and proxies assume that a connection will be kept open after the transmission of a request and its response. resource-management reasons, the protocol permits it to send a Connection: close  Piplinning to increase speed
• #9: server --arbitrary piece info – client --sav info---and return next request ---origin server cookies –contain ---credit card numbers, user names and passwords, or other personal information Comppression :While HTTP/1.0 included some support for compression, it did not provide adequate mechanisms for negotiating the use of compression, end-to-end and hop-by-hop compression. HTTP/1.1 adds the  transfer -Encoding header(data sent in chucks) HTTP/1.1 (unlike HTTP/1.0) carefully specifies the  Accept-Encoding header Chunked transfer encoding is a data transfer mechanism in version 1.1 of the Hypertext Transfer Protocol (HTTP) in which data is sent in a series of "chunks Range requests:: need only part of a resource complete a response transfer
• #10:  Expires header, with a time until which a cache could return the response without violating semantic transparency  Validity : 304 (Not Modified) status code, implying that the cache entry is valid, or it may send a normal 200 (OK) response to replace the cache entry. Cache –control It did not allow either origin servers or clients to give full and explicit instructions to caches. If-Modified-Since header ->  uses absolute timestamps with one-second resolution -> lead to caching errors either because of clock synchronization errors, or because of lack of resolution ->Entity tag  the origin server construct it (such as a fine-grained timestamp or an internal database pointer uniqueness requirement. If-None-Match, which allows a client to present one or more entity tags from its cache entries for a resource(304 (Not Modified) response with an ETag header that indicates which cache entry is currently valid) Cache-Control header allowing an extensible set of cache-control directives to be transmitted in both requests and responses private (Single-user-agent caches are effectively allowed)and no-store - delete cache is anyallow servers and clients to prevent the storage of some or all of a Response ----no-cache" is defined to mean exactly the same thing as "Cache-control: private", but with no exception for user-agent caches.
• #11: Request: Get URI ver ------- HOST------User agent-----Accept Response: Ver 200 ok ----date---server---lastmodified----content length---content type ----CRLF body Uniform Resource Identifier: identifies a resource either by location, or a name, or both URIs identify and URLs locate  URL is one type of Uniform Resource Identifier (URI);  URL has two main components: Protocol identifier: For the URL http://example.com , the protocol identifier is http . Resource name: For the URLhttp://example.com , http://www.example.com/index.html, which indicates a protocol (http), a hostname (www.example.com), and a file name (index.html). A URI can be further classified as a locator, a name, or both Host header to – host multiple sites CRLF: Carriag return line feed
• #13: a HTTP HEAD request is checking if a given url is serviceable, a given file exists, etc --  information about a document– last modified
• #14: Do not modify resources- retrieval only Idempotent Method: Can be called many times , same outcome Post: login to web page Diffrnce b/w get and post
• #15: FACEBOOK account creation – post Data upload – put GET – request face book
• #17:  100 Continue:  initial part of the request has been received and has not yet been rejected by the server. The client SHOULD continue by sending the remainder 200 OK:  request has succeeded. The information returned with the response is dependent on the method used in the request 201 Created: new resource being created. 202 Accepted:request has been accepted for processing, but the processing has not been completed  204 response MUST NOT include a message-body, and thus is always terminated by the first empty line after the header fields. 301 Moved Permanently – location header in response 302 Found- temp moved 304 Not Modified- response to conditional get 305 Use Proxy-  Location field 400 Bad Request- malformed syntax  401 Unauthorized- response WWW-Authenticate header field , response Authorization header field 403 Forbidden , 404 Not Found,  405 Method Not Allowed , 407 Proxy Authentication Required , 408 Request Timeout 500- internel server error , 503- service unavailable , 505 – http version not supported
• #18: specific state and authenticated user Name , Value , google , location , expire size
• #19: HTTPS is authentication of the visited website and to protect the privacy and integrity of the exchanged data. HTTPS provides authentication of the website and associated web server with which one is communicating, which protects against man-in-the-middle attacks.  bidirectional encryption of communications between a client and server-- protects against eavesdropping and tampering . SSL is especially suited for HTTP since it can provide some protection even if only one side of the communication is authenticated : by the client examining the server's certificate
• #20: Hash(MD5) message authentication code Key exchange- RSA DSA ,DEFI Cipher : RC4 AES HASH:md5 sh1 sh2