HTTP Protocol Basic

Editor's Notes

• #6: http://www.tcpipguide.com/free/t_ApplicationLayerLayer7.htm
• #7: 1.0 http://www.ietf.org/rfc/rfc1945.txt1.1 http://www.w3.org/Protocols/rfc2616/rfc2616.html2.0 http://tools.ietf.org/html/draft-ietf-httpbis-http2-04The Hypertext Transfer Protocol (HTTP) is designed to enable communications between clients and servers.HTTP works as a request-response protocol between a client and server.A web browser may be the client, and an application on a computer that hosts a web site may be the server.Example: A client (browser) submits an HTTP request to the server; then the server returns a response to the client. The response contains status information about the request and may also the requested content.
• #8: A part of TCP/IP protocols suite
• #9: 0.9: The first version of HTTP, HTTP/0.9, was part of the early World Wide Web and was a very simple request/response protocol with limited capabilities that could transfer only text files.1.0 http://www.ietf.org/rfc/rfc1945.txtThe first widely-used version was HTTP/1.0, which is a more complete protocol that allows the transport of many types of files and resources.1.1 http://www.w3.org/Protocols/rfc2616/rfc2616.htmlMultiple host name. Multiple host on 1 IPPerformance, security2.0 http://tools.ietf.org/html/draft-ietf-httpbis-http2-04
• #10: HTTP is a client/server-oriented, request/reply protocol. Basic communication consists of an HTTP Request message sent by an HTTP client to an HTTP server, which returns an HTTP Response message back to the client.
• #11: Proxy:A proxy is a forwarding agent, receiving requests for a URI in its absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server.Gateway: receiving agent. A router that routes the data transmission.
• #13: Persistent connections are connections between a Web client and a server that can be reused for more than one exchange of a request and a response.In HTTP/1.0, the default action for the server was to close the connection when it had received a request from the Web client and sent a response. If the Web client wanted the server to keep the connection open, it had to send a Connection: Keep-Alive header on the request.For HTTP/1.1, persistent connections are the default. When a connection is made between a Web client and a server, the server should keep the connection open by default. The connection should only be closed if the Web client requests closure by sending a Connection: close header, or if the server's timeout setting is reached, or if the server encounters an error.Persistent connections improve network performance because a new connection does not have to be established for each request. Establishing a new connection consumes significant additional network resources compared to making a request using an existing connection.DEMO using telnetDraw HTML document on the WHITEBOARD
• #14: http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.htmlTelnet demo Get and HeadGET:Retrieve a resource.HEAD Like GET, but returns just the HTTP header.POST create new resourceOPTIONS Get information about how the server allows to communicate with. OPTIONS * HTTP/1.1 Host: example.com HTTP/1.1 200 OK Date: … Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE Content-Length: 0PUT Send data to the server.DELETE Delete an existing resource.TRACE Return the request headers sent by the client.
• #15: Demo Web sniffer tool
• #18: In this example, the client issues a GET request to ask for a document named "/index.html"; and negotiates to use HTTP/1.0 protocol. A blank line is needed after the request header. This request message does not contain a body.The server receives the request message, interprets and maps the request-URI to a document under its document directory. If the requested document is available, the server returns the document with a response status code "200 OK". The response headers provide the necessary description of the document returned, such as the last-modified date (Last-Modified), the MIME type (Content-Type), and the length of the document (Content-Length). The response body contains the requested document. The browser will format and display the document according to its media type (e.g., Plain-text, HTML, JPEG, GIF, and etc.) and other information obtained from the response headers.
• #26: DEMO using chrome to access resources
• #27: Important especially in authenticationNo cookie -> no sessionDEMO login google, yahoo
• #28: The cache, which is local copies of resources, works because many resources change infrequently. When a browser can reuse a local copy, it saves the time to set up a connection as well as the time to download. The key to making the cache work effectively is HTTP caching headers, which are sent by the web server to specify how long a resource is valid and when it last changed.
• #29: The Expires header specifies a date after which a resource is invalid. max-age specifies how long a resource is after it is downloaded.DEMOhttp://stevesouders.com/hpws/expiresoff.phphttp://stevesouders.com/hpws/expireson.php
• #30: If-Modified-Since, If-Unmodified-Since, If-Match, If-None-Match