= Foolscap =

"Foolscap" is the name for the next-generation RPC protocol, intended to replace Perspective Broker. It has been under development (on and off) by Brian Warner for several years.

The current release is [/releases/foolscap-0.1.4.tar.gz foolscap-0.1.4]  ([/releases/foolscap-0.1.4.tar.gz.sig gpg sig]).

The two primary responsibilities of an RPC protocol are to:

 1. serialize an object graph, and reconstruct a useful equivalent on the remote side
 1. allow the holder of a !RemoteReference in one process to invoke methods on a Referenceable in a different one

In addition, there are details like object naming, connection establishment, controlling object serialization, reference lifetime, and error reporting.

== New features ==
(relative to oldpb, aka twisted.spread)

 * most inert Python types are serializable, including unicode and sets
 * clients and servers are implemented as [http://twistedmatrix.com/documents/current/api/twisted.application.service.html Services], which share connections when possible and are easy to shut down
 * links are encrypted/authenticated by default (using SSL)
 * all objects are accessed through secure/unguessable "FURLs"
  * explicitly published objects can be accessed through well-known FURLs
 * you can declare method signatures (with "constraints", either in Interface classes or as method attribute/decorators)
  * this enables defenses against resource-consumption DoS attacks, including stack-frame-exhaustion attacks
  * (TODO) you can ask the deserializer about your current maximum memory/stackframe exposure, based upon what objects are visible and what methods they declare
 * serializers for third-party classes can be registered using Adapters
 * serializers are more "streaming" than in oldpb
  * serializers can pause themselves, deferring serialization until later
  * serializers can be paused when the network pipe is full
 * newpb is architected to make it possible to rewrite serializers/deserializers in C, for speed
 * object graph depth is limited by available heap memory, not available stack depth

== Show Me The Code ==

The current release is available [/releases/foolscap-0.1.4.tar.gz here]. This is an alpha release, since the protocol has not been finalized, and incompatible changes are being made every few months. Older releases are available [/releases/ here].

The latest Foolscap code lives in a mercurial repository, at http://foolscap.lothar.com/repos/ . To retrieve a copy of the trunk use the following command:

{{{
hg clone http://foolscap.lothar.com/repos/trunk foolscap-trunk
}}}

There are two online source-code browsers, the native hgwebdir.cgi at http://foolscap.lothar.com/repos/trunk and the Trac Mercurial plugin at the [/trac/browser Browse Source] link above. Both are pretty handy.

The documentation is in the [source:doc/ doc/ directory] and includes both the protocol specification and a short user's manual. Some day, it will probably be shipped as part of the "Twisted-Core" distribution, but only after the protocol and code have stabilized a bit.

== Status ==

Foolscap is not yet ready for production use. The [source:doc/todo.txt 'todo.txt'] and [source:doc/jobs.txt 'jobs.txt'] files contain some of the things that need finishing before it will be ready. Connection negotiation needs to be changed to use variable-length certificate digests and certificate chains and variable-length object names, various questions about making objects "giftable" by default or not need to be answered and implemented, and we need to acquire operational experience with Foolscap as a whole to think about usability.

Release 0.1.4 is available in the [/releases/ releases directory].



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