Web Technologies Interactive Responsiveness Function Hypertext Web E-Publishing Simple Response Web Fill-in Forms Object Web « Full-Blown » Client/Server JavaBeans/Applets ActiveX Controls Application Servers and OTMs ORB-Based interactions via CORBA or DCOM Shippable Places Object based documents: XML, DOM and XSL Dynamic HTML Scripts Cookies/Sessions Active Server Pages (ASPs) CORBA plug-ins (WAI) Push WebObjects Servlets Forms CGI Tables ISAPI NSAPI URL-Based File Server

Web Application Servers Application HTTP Over TCP/IP HTML Documents CGI Server Web Browser + Java Web Browser + HTML & Forms ClientMiddleware Internet Server

HTTP Request Syntax [ : ] … [ : ] blank line [entity body] HTTP Request Web Example GET /path/file.html HTTP/1.0 Accept: text/html Accept: audio/x User-agent: MacWeb request line request header fields entity body request line request header fields

HTTP Request Syntax [ ] [ : ] … [ : ] blank line [entity body] HTTP Response Web Example HTTP/ OK Server: Apache/1.1 Mime_version: 1.0 Content_type: text/html Content_length: 2000 …. response header header fields entity body response header header fields entity body (i.e html doc)

URI, URN & URL Uniform Resource Identifier (URI) F Uniform Resource Name (URN) and Uniform Resource Locator (URL) URN are meant to be persistent URL syntax: Target ResourceArgumentsService AddressIdentification Protocol Scheme

Parameters passing With cookies in header With GET method u Through URLs that link u Through forms With POST method u Only through forms

CGI-Model ClientServer Web BrowserWeb ServerEnvironment (variables) CGI Programm Submit N

Interaction problem HTTP is connectionless F Stateless (lacking persistence) F No out-of-the-box user tracking Replacement solution: u Cookies u HTTP-Authentication u Hidden fields

User tracking Authentication: password + user-id F HTTP-AUTH F Hidden field: token to be generated F Cookie: idem Session id with expiration time Problems F Password hidden F Session ending (clearing identification)

Support Apache included u Apache cookie (!) validity: browser session u UNIQUE_ID Apache environment variable PHP support u setCookie(« name », « value »,expiration)

Definitions I Message F The basic unit of HTTP communication, consisting of structured sequence of octets matching the HTTP syntax and transmitted via the connection. Request F An HTTP request message. Response F An HTTP response message. Resource F A netword data object or service that can be identified by a URI. Resources may be available in multiple representations (eg. Multiple languages, data formats, size, resolutions) or vary in other ways

Definitions II Entity F The information transferred as the payload of a request or response. An entity consists of metainformation in the form of entity-header fields and content in the form of an entity-body. Representation F An entity included with a response that is subject to content negotiation. There may exist multiple representation associated with a particular response status. Content Negociation F The mechanism for selecting the appropriate representation when servicing a request. The representation of entitites in any response can be negociated (including error responses).

Definitions III Variant F A resource may have one, or more than on, representation(s) associated with it at any given instant. Each of these representations is termed as ‘variant’. Use of the term ‘variant’ does not necessarily imply that the resource is subject to content negociation. Client F A program that establishes connections for the purpose of sending requests. User agent F The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user tools

Definitions IV Server F An application program that accepts connections in order to service requests by sending back responses. Any given program may be capable of being both a client and a server; these terms refer only to the role being performed by the program for a particular connection, rather than to the program’s capabilities in general. Proxy F An intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients. Requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy must implement both the client and server requirements.

Definitions V Cache F A program’s local store of response messages and the subsystem that controls its message storage, retrieval, and deletion. A cache stores cachable responses in order to reduce the response time and network bandwith consumption on future, equivalent requests. Any client or server may include a cache, though a cache cannot by used by a server that is acting as a tunnel. Cachable F A response is cachable if a cache is allowed to store a copy of the response message for use in answering subsequent requests (see rules in ref.). Even if a resource is cachable, there may be additional constraints on whether a cache can use the cached copy for a particular request.

Definitions VI Gateway F A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the origin server for the requested resource; the requesting client may not be aware that it is communicating with a gateway. Tunnel F An intermediary program which is acting as a blind relay between two connections. Once active, a tunnel is not considered a party to the HTTP communication, though the tunnel may have been initiated by an HTTP request. The tunnel ceases to exists when both ends of the relay connections are closed.