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State Maintenance - Hidden Fields
A shopping cart application is more difficult to implement than it
may seem. Because the HTTP protocol is stateless,
a Web server regards every connection as entirely new, with no
relationship to any previous or future connections.
However, a shopping cart application requires persistent
state maintenance - each HTML page sent contains
information derived from earlier pages.
A hidden field within a form is the simplest way
to maintain state. A hidden field is like any other FORM entity; it
is simply not displayed by the browser. It can be inspected using,
for example, the "View Source" option of the browser, where it will
look something like:
<input type="hidden" name="sid" value="XYZZY">.
- When an initial connection is made to the server, the HTML page
which is sent contains the indentifying hidden field value within
the page FORM.
- A subsequent HTTP CGI request issued by the browser to this
server will thus also contain the hidden field.
- The CGI which processes the FORM at the server can return the
same hidden field to the browser. The hidden field value thus acts
as a "session identifier" between the shopping cart application and
the browser.
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