Version 1 (modified by warner, 12 years ago) (diff)

describe Foolscap, adapted from the old newpb page

"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 two primary responsibilities of an RPC protocol are to:

  1. serialize an object graph, and reconstruct a useful equivalent on the remote side
  2. 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)

  • all methods take keyword arguments instead of positional arguments
  • most inert Python types are serializable, including unicode and sets
  • clients and servers are implemented as 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 "PB-URLs"
    • explicitly published objects can be accessed through well-known PB-URLs
  • 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
    • you can ask the deserializer about your current maximum memory/stackframe exposure, based upon what objects are visible and what
  • 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 first release is available in my home directory: This is an alpha release, more of a technology preview than anything else, but should serve to give potential users an idea of what to expect from newpb.

The latest Foolscap code lives in my SVN sandbox, svn://, in the 'foolscap' module (source:sandbox/warner/Foolscap/trunk). The documentation is in source:sandbox/warner/Foolscap/trunk/doc and includes both the protocol specification and a short user's manual. It is currently only available via SVN and as a separate module. 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.


Foolscap is not yet ready for production use. source:sandbox/warner/Foolscap/trunk/doc/newpb-todo.txt and source:sandbox/warner/Foolscap/trunk/doc/newpb-jobs.txt 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 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.