|Version 16 (modified by warner, 7 years ago)|
"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:
- serialize an object graph, and reconstruct a useful equivalent on the remote side
- 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.
(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 my SVN sandbox, svn://svn.twistedmatrix.com/svn/Twisted/sandbox/warner/Foolscap/trunk, 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. 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. The todo file and the jobs file 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.