Recap ofP: Message Processing Language

Presented byPresented by

Abbie BarbirAbbie Barbirabbieb@nortelnetworks.com

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P: Message Processing Language

• P is a simple configuration language designed for specification of message processing instructions (service) at application proxies– P can be used to instruct an intermediary on how to

manipulate the application message that is being processed

• Original draft work was submitted by– Alex Rousskov (rousskov@measurement-factory.com) and – Andre Beck (abeck@lucent.com)• draft-ietf-opes-rules-p-02

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P Design Objectives

• P language primary objective is to express statements similar to:

– If message meets criteria C,

– Then apply service S;

• P programs mostly deal with formulating message-dependent conditions and executing authorized services

• P design is meant to be applicable for a variety of similar intermediary configuration tasks such as

– Access Control List (ACL) specification

– Message routing in proxy meshes or

– Load-balancing environments

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Characteristics of “P”• P is a single-assignment, lazy evaluation, strongly typed

functional programming language• Centered around the concept of an “object”, similar to objects

of object-oriented languages• An object is, essentially, a piece of data or information• Value of an object is indistinguishable from the object itself• Object type is defined by the semantics of applicable

operations and manipulations• Almost everything in P is an object, even a piece of code• General approach is application protocol agnostic– Supports loadable modules for adding support of (existing

and new) application protocols

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Open Issues/Problems

• What (message) information can the P interpreter access, i.e. what information can be part of a rule condition?

• For example:

– Complete message (including message body),

– Meta-information only (e.g. HTTP headers only),

– Where to draw the line?

– Does the WG have to specify this?

• Should the WG document an HTTP module for P?

– If yes, in what document?

• Should the WG define interfaces between P interpreters and module suppliers and/or callout services?

– How do services return results?

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Q&A