Sereal - A binary serialization format
This repository is the home of the Sereal data serialization format. This format was started because the authors had technical reasons for producing a better Storable.
Before we embarked on this project we had a look at various prior art. This included a review of Google Protocol Buffers and of the MessagePack protocol. Neither suited our needs so we designed this, liberally borrowing ideas from the other projects.
We wanted to be able serialize shared references properly. Many serialization formats do not support this out of the box.
- Weak References
Given that perl uses a reference counting garbage collection scheme, Perl has the concept of a special type of reference called a "weakref" which is used to create cyclic reference structures which do not leak memory. Unlike most of the existing solutions, we need to handle these structures correctly, thus avoiding a perfectly valid data structure to be converted to one that will cause a memory leak on a remote system. For cross-language compatibility, weak references can very easily be ignored by other decoder implementations.
Perl supports aliases. These are a special kind of reference which is effectively a C level pointer instead of a Perl language-level reference. We needed to be able to represent these as well.
Promoting a plain data structure reference to an object, as is customary in dynamic languages, can be dangerous in some circumstances. We needed to be able to serialize objects safely and reliably, and we wanted a sane control mechanism for doing so.
- Regular Expression Objects
In Perl, a regular expression is a native type. We wanted to be able serialize these at a native level without losing data such as modifiers.
- Space Efficiencies
We want to be able to represent common structures as small as is reasonable. Although not to the extreme that this makes the protocol error prone and ludicrously difficult to implement. The steps taken include removing redundancy from the serialized structure (such as hash keys or classnames) automatically. The protocol supports this kind of redundancy removal, but an encoder implementation can choose to which extent it makes use of the technique.
- Speed Efficiencies
We want to be able to serialize and deserialize quickly. Some of the design decisions and trade-offs were aimed squarely at performance.
- Separate Decoder and Encoder
We wanted to separate the functions of serializing from deserializing so they could be upgraded independently.
- Forward/Backward Compatibility
We wanted the protocol to be robust to forward/backwards compatibility issues. It should be possible to partially read new formats with an old decoder, and output old formats with a new encoder.
- Language Agnosticism
We want the format to be usable by other languages, especially dynamic languages. We hope to have a Java port soon, right Eric? In aim of making this easier we have structured our repo so that implementations from other languages can be easily added, and we would welcome any contributions along these lines.
There are some graphs of how the Perl implementations Sereal performs as compared to the alternatives at Sereal Performance Graphs
You can find the specification at sereal_spec.pod
Yves Orton <firstname.lastname@example.org>
Steffen Mueller <email@example.com>
Ævar Arnfjörð Bjarmason <firstname.lastname@example.org>
This protocol was originally developed for Booking.com. With approval from Booking.com, this module was generalized and published on CPAN, for which the authors would like to express their gratitude.
Copyright (C) 2012 by Steffen Mueller
Copyright (C) 2012 by Yves Orton