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