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 ​foolscap-0.1.4 .

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)

• 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 "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 in my ​home directory, in the file ​http://twistedmatrix.com/~warner/Foolscap/foolscap-0.1.4.tar.gz. This is an alpha release, since the protocol has not been finalized, and incompatible changes are being made every few months.

The latest Foolscap code lives in a mercurial repository, at ​http://foolscap.lothar.com/. The documentation is the 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 'todo' and 'newpb-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 my ​home directory.

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