= 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-0.1.5.tar.gz foolscap-0.1.5] ([/releases/foolscap-0.1.5.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-0.1.5.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 http://www.selenic.com/mercurial/wiki/] 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 (which also has a [http://foolscap.lothar.com/repos/trunk?style=gitweb gitweb-style view]), 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. Rendered HTML from the most recent release lives [/docs/ here], and [/docs/using-foolscap.html using-foolscap.html] is probably the best place to start. Some day, Foolscap may 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 0.1.5 (as well as older releases) are available in the [/releases/ releases directory]. == Links == * Foolscap takes many ideas from the [http://www.erights.org/ E Language]. Foolscap is my attempt to make the concepts of E available to python+twisted programmers. * The Twisted wiki has [http://twistedmatrix.com/trac/wiki/FoolsCap a page] on Foolscap where this information used to live. == Trac Hints == The old Trac starting page was moved to OldWikiStart For a complete list of local wiki pages, see TitleIndex.