理解Cookie规范：Java Web开发基础

作者：87zd
日期：2000-12-1 21:52:36
PERSISTENT CLIENT STATE
HTTP COOKIES 
Preliminary Specification - Use with caution

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INTRODUCTION 
Cookies are a general mechanism which server side connections (such as CGI scripts) can use to both store and retrieve information on the client side of the connection. The addition of a simple, persistent, client-side state significantly extends the capabilities of Web-based client/server applications.

OVERVIEW 
A server, when returning an HTTP object to a client, may also send a piece of state information which the client will store. Included in that state object is a description of the range of URLs for which that state is valid. Any future HTTP requests made by the client which fall in that range will include a transmittal of the current value of the state object from the client back to the server. The state object is called a cookie, for no compelling reason. 
This simple mechanism provides a powerful new tool which enables a host of new types of applications to be written for web-based environments. Shopping applications can now store information about the currently selected items, for fee services can send back registration information and free the client from retyping a user-id on next connection, sites can store per-user preferences on the client, and have the client supply those preferences every time that site is connected to. 

SPECIFICATION 
A cookie is introduced to the client by including a Set-Cookie header as part of an HTTP response, typically this will be generated by a CGI script. 
Syntax of the Set-Cookie HTTP Response Header
This is the format a CGI script would use to add to the HTTP headers a new piece of data which is to be stored by the client for later retrieval. 
Set-Cookie: NAME=VALUE; expires=DATE;
path=PATH; domain=DOMAIN_NAME; secure

NAME=VALUE
This string is a sequence of characters excluding semi-colon, comma and white space. If there is a need to place such data in the name or value, some encoding method such as URL style %XX encoding is recommended, though no encoding is defined or required. 
This is the only required attribute on the Set-Cookie header. 


expires=DATE 
The expires attribute specifies a date string that defines the valid life time of that cookie. Once the expiration date has been reached, the cookie will no longer be stored or given out. 
The date string is formatted as: