Transactions

This page outlines PEP related actions taken over a series of typical client/server transactions. Data issued by the client is in red and that by the server is blue. Included examples are:

Ignorant client makes request.
Server advertises other services.
Server invokes payment extension.

Ignorant client makes request

Client issues request

GET /countable/asdf.html HTTP/1.1
Host: pfunk.w3.org
Date: Mon, 9 Jun 1997 21:58:39 GMT

client requests resource

Server reponds with policy declaration

HTTP/1.1 420 Bad Extensions
Content-Length: 85
PEPInfo: {{id "http://pfunk.w3.org:8887/src/classes/AccessCounter"}{strength must}{for "/countable/" *}}
Date: Mon, 9 Jun 1997 21:59:38 GMT
Content-Type: text/html
<HTML><HEAD><TITLE>Bummer</TITLE></HEAD>
<BODY><H1>Bummer</H1>so sorry</BODY></HTML>

server has required extension for that resource in extension map
server sends back 420 error and PEPInfo with policy declaration
client parses PEPInfo
- loads local extension OR
- loads network extension
client adds extension to its extension map
sets flag in client to retry request

Client retries request

GET /countable/asdf.html HTTP/1.1
Host: pfunk.w3.org
Date: Mon, 9 Jun 1997 21:58:39 GMT
PEP: {{map "http://pfunk.w3.org:8887/src/classes/AccessCounter" AccessCounter-12345}{strength must}}
AccessCounter-12345: 1

client sees AccessCounter in extension map for /countable/*
loads instance
adds PEP extension declaration and instance

Server honors request

HTTP/1.1 200 OK
Content-Length: 95
PEPInfo: {{id "http://pfunk.w3.org:8887/src/classes/AccessCounter"}{strength must}{for "/countable/" *}}
Date: Mon, 9 Jun 1997 21:59:38 GMT
Content-Type: text/html
AccessCounter-12345: 1
<HTML><HEAD><TITLE>asdf</TITLE></HEAD>
<BODY><H1>asdf</H1>All accounted for, sir.</BODY></HTML>

server honors request and calls new instance of extension
client calls extension instance and honors reply

Server advertises other services

Client issues request

GET /asdf.html HTTP/1.1
Host: pfunk.w3.org
Date: Mon, 9 Jun 1997 21:58:39 GMT

client requests resource

Server reponds with policy declaration

HTTP/1.1 200 OK
Content-Length: 103
PEPInfo: {
    {id "http://pfunk.w3.org:8887/src/classes/PostPay"}{strength must}{for "/payola/" *}
    {id "http://pfunk.w3.org:8887/src/classes/AccessCounter"}{strength may}{for "/" *}
    {id "http://pfunk.w3.org:8887/src/classes/EscapeBody"}{strength must}{for "/escaped/" *}}
Date: Mon, 9 Jun 1997 21:59:38 GMT
Content-Type: text/html
<HTML><HEAD><TITLE>asdf</TITLE></HEAD>
<BODY><H1>asdf</H1>Pretty exciting, huh?</BODY></HTML>

server has required extension for that resource in extension map
server sends back 200 satus
server takes time to inform client of other available services by sending back a comprehensive PEPInfo with policy declaration
client parses PEPInfo, may choose to
- load local extensions OR
- load network extensions
client add extensions to its extension map

Note: This policy declaration announced AccessCounter as an optional extension that was valid anywhere from the root down. The server could have returned an extension declaration which the client could have ignored if it didn't understand it.

Server invokes payment extension

Client issues request

GET /payola/asdf.html HTTP/1.1
Host: pfunk.w3.org
Date: Mon, 9 Jun 1997 21:58:39 GMT

client requests resource

Server reponds with policy declaration

HTTP/1.1 200 OK
Content-Length: 103
PEP: {{map "http://pfunk.w3.org:8887/src/classes/PostPay" key=K1,price=P1}{strength must}}
K1: 118.23.205.22.1df34c8e
P1: $.20
Date: Mon, 9 Jun 1997 21:59:38 GMT
Content-Type: text/html
<HTML><HEAD><TITLE>fdsa</TITLE></HEAD>
<BODY><H1>fdsa</H1>?siht rof deyap uoy dalg uoy t'nerA</BODY></HTML>

server has required extension for that resource in extension map
server sends back 200 satus
server reponds to request with an encrypted message and invokes the PostPay extension
client parses PEP, may choose to
- contact server with key
- tell user to pay up or die
- present the encrypted response to the user
client add extensions to its extension map

Note: the server may assume that the majority of commercial clients will be honest. This allows it to not encrypt the response, saving the client a round trip with the key server. This would work until someone hacks up a proxy server to strip out the PEP header and allow even honest clients to cheat on payment.

Eric Prud'hommeaux, eric@w3.org,
@(#) $Id: Transactions.html,v 1.2 1997/08/03 00:39:00 eric Exp $