cannam@48: --- cannam@48: layout: post cannam@48: title: "Cap'n Proto v0.3: Python, tools, new features" cannam@48: author: kentonv cannam@48: --- cannam@48: cannam@48: The first release of Cap'n Proto came three months after the project was announced. The second cannam@48: release came six weeks after that. And the third release is three weeks later. If the pattern cannam@48: holds, there will be an infinite number of releases before the end of this month. cannam@48: cannam@48: Version 0.3 is not a paradigm-shifting release, but rather a slew of new features largely made cannam@48: possible by building on the rewritten compiler from the last release. Let's go through the cannam@48: list... cannam@48: cannam@48: ### Python Support! cannam@48: cannam@48: Thanks to the tireless efforts of contributor [Jason Paryani](https://github.com/jparyani), I can cannam@48: now comfortably claim that Cap'n Proto supports multiple languages. [His Python cannam@48: implementation](http://jparyani.github.io/pycapnp/) wraps the C++ library and exposes cannam@48: most of its features in a nice, easy-to-use way. cannam@48: cannam@48: And I have to say, it's _way_ better than the old Python Protobuf implementation that I helped put cannam@48: together at Google. Here's why: cannam@48: cannam@48: * Jason's implementation parses Cap'n Proto schema files at runtime. There is no need to run a cannam@48: compiler to generate code every time you update your schema, as with protobufs. So, you get cannam@48: to use Python the way Python was intended to be used. In fact, he's hooked into the Python cannam@48: import mechanism, so you can basically import a `.capnp` schema file as if it were a `.py` cannam@48: module. It's even convenient to load schema files and play with Cap'n Proto messages from the cannam@48: interactive interpreter prompt. cannam@48: * It's _fast_. Whereas the Python Protobuf implementation -- which we made the mistake of cannam@48: implementing in pure-Python -- is _slow_. And while technically there is an experimental cannam@48: C-extension-based Python Protobuf implementation (which isn't enabled by default due to various cannam@48: obscure problems), Jason's Cap'n Proto implementation is faster than that, too. cannam@48: cannam@48: Go [check it out](http://jparyani.github.io/pycapnp/)! cannam@48: cannam@48: By the way, there is also a budding [Erlang implementation](http://ecapnp.astekk.se/) cannam@48: (by Andreas Stenius), and work cannam@48: continues on [Rust](https://github.com/dwrensha/capnproto-rust) (David Renshaw) and cannam@48: [Ruby](https://github.com/cstrahan/capnp-ruby) (Charles Strahan) implementations. cannam@48: cannam@48: ### Tools: Cap'n Proto on the Command Line cannam@48: cannam@48: The `capnp` command-line tool previously served mostly to generate code, via the `capnp compile` cannam@48: command. It now additionally supports converting encoded Cap'n Proto messages to a human-readable cannam@48: text format via `capnp decode`, and converting that format back to binary with `capnp encode`. cannam@48: These tools are, of course, critical for debugging. cannam@48: cannam@48: You can also use the new `capnp eval` command to do something interesting: given a schema file and cannam@48: the name of a constant defined therein, it will print out the value of that constant, or optionally cannam@48: encode it to binary. This is more interesting than it sounds because the schema language supports cannam@48: variable substitution in the definitions of these constants. This means you can build a large cannam@48: structure by importing smaller bits from many different files. This may make it convenient to cannam@48: use Cap'n Proto schemas as a config format: define your service configuration as a constant in cannam@48: a schema file, importing bits specific to each client from other files that those clients submit cannam@48: to you. Use `capnp eval` to "compile" the whole thing to binary for deployment. (This has always cannam@48: been a common use case for Protobuf text format, which doesn't even support variable substitution cannam@48: or imports.) cannam@48: cannam@48: Anyway, check out the [full documentation]({{ site.baseurl }}capnp-tool.html) for cannam@48: more. cannam@48: cannam@48: ### New Features cannam@48: cannam@48: The core product has been updated as well: cannam@48: cannam@48: * Support for unnamed [unions]({{ site.baseurl }}language.html#unions) reduces the cannam@48: need for noise-words, improving code readability. Additionally, the syntax for unions has been cannam@48: simplified by removing the unnecessary ordinal number. cannam@48: * [Groups]({{ site.baseurl }}language.html#groups) pair nicely with unions. cannam@48: * [Constants]({{ site.baseurl }}language.html#constants) are now cannam@48: [implemented in C++]({{ site.baseurl }}cxx.html#constants). Additionally, they cannam@48: can now be defined in terms of other constants (variable substitution), as described earlier. cannam@48: * The schema API and `schema.capnp` have been radically refactored, in particular to take advantage cannam@48: of the new union and group features, making the code more readable. cannam@48: * More and better tests, bug fixes, etc. cannam@48: cannam@48: ### Users! cannam@48: cannam@48: Some news originating outside of the project itself: cannam@48: cannam@48: * [Debian Unstable (sid)](http://www.debian.org/releases/sid/) now features cannam@48: [a Cap'n Proto package](http://packages.debian.org/sid/capnproto), thanks to cannam@48: [Tom Lee](https://github.com/thomaslee). Of course, since package updates take some time, this cannam@48: package is still v0.2.1 as of this writing, but it will be updated to v0.3 soon enough. cannam@48: * Popular OSX-based text editor [TextMate](http://macromates.com/) now cannam@48: [uses Cap'n Proto internally](https://github.com/textmate/textmate/commit/5c02b4ff5cc0c7c319d3d4f127c8ee19b81f80b7), cannam@48: and the developer's feedback lead directly to several usability improvements included in this cannam@48: release. cannam@48: * Many people using Cap'n Proto _haven't bothered to tell us about it_! Please, if you use it, cannam@48: [let us know](https://groups.google.com/group/capnproto) about your experience, both what you like cannam@48: and especially what you don't like. This is the critical time where the system is usable but cannam@48: can still be changed if it's not right, so your feedback is critical to our long-term success. cannam@48: * I have revenue! A whopping [$1.25 per week](https://www.gittip.com/kentonv/)! >_> It's cannam@48: totally worth it; I love this project. (But thanks for the tips!)