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Add Cap'n Proto source

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+---
+layout: post
+title: "Cap'n Proto 0.5: Generics, Visual C++, Java, C#, Sandstorm.io"
+author: kentonv
+---
+
+Today we're releasing Cap'n Proto 0.5. We've added lots of goodies!
+
+### Finally: Visual Studio
+
+Microsoft Visual Studio 2015 (currently in "preview") finally supports enough C++11 to get Cap'n
+Proto working, and we've duly added official support for it!
+
+Not all features are supported yet. The core serialization functionality sufficient for 90% of users
+is available, but reflection and RPC APIs are not. We will turn on these APIs as soon as Visual C++
+is ready (the main blocker is incomplete `constexpr` support).
+
+As part of this, we now support CMake as a build system, and it can be used on Unix as well.
+
+In related news, for Windows users not interested in C++ but who need the Cap'n Proto tools for
+other languages, we now provide precompiled Windows binaries. See
+[the installation page]({{site.baseurl}}install.html).
+
+I'd like to thank [Bryan Boreham](https://github.com/bboreham),
+[Joshua Warner](https://github.com/joshuawarner32), and [Phillip Quinn](https://github.com/pqu) for
+their help in getting this working.
+
+### C#, Java
+
+While not strictly part of this release, our two biggest missing languages recently gained support
+for Cap'n Proto:
+
+* [Marc Gravell](https://github.com/mgravell) -- the man responsible for the most popular C#
+  implementation of Protobufs -- has now implemented
+  [Cap'n Proto in C#](https://github.com/mgravell/capnproto-net).
+* [David Renshaw](https://github.com/dwrensha), author of our existing Rust implementation and
+  [Sandstorm.io](https://sandstorm.io) core developer, has implemented
+  [Cap'n Proto in Java](https://github.com/dwrensha/capnproto-java).
+
+### Generics
+
+Cap'n Proto now supports [generics]({{site.baseurl}}language.html#generic-types),
+in the sense of Java generics or C++ templates. While working on
+[Sandstorm.io](https://sandstorm.io) we frequently found that we wanted this, and it turned out
+to be easy to support.
+
+This is a feature which Protocol Buffers does not support and likely never will. Cap'n Proto has a
+much easier time supporting exotic language features because the generated code is so simple. In
+C++, nearly all Cap'n Proto generated code is inline accessor methods, which can easily become
+templates. Protocol Buffers, in contrast, has generated parse and serialize functions and a host
+of other auxiliary stuff, which is too complex to inline and thus would need to be adapted to
+generics without using C++ templates. This would get ugly fast.
+
+Generics are not yet supported by all Cap'n Proto language implementations, but where they are not
+supported, things degrade gracefully: all type parameters simply become `AnyPointer`. You can still
+use generics in your schemas as documentation. Meanwhile, at least our C++, Java, and Python
+implementations have already been updated to support generics, and other implementations that
+wrap the C++ reflection API are likely to work too.
+
+### Canonicalization
+
+0.5 introduces a (backwards-compatible) change in
+[the way struct lists should be encoded]({{site.baseurl}}encoding.html#lists), in
+order to support [canonicalization]({{site.baseurl}}encoding.html#canonicalization).
+We believe this will make Cap'n Proto more appropriate for use in cryptographic protocols. If
+you've implemented Cap'n Proto in another language, please update your code!
+
+### Sandstorm and Capability Systems
+
+[Sandstorm.io](https://sandstorm.io) is Cap'n Proto's parent project: a platform for personal
+servers that is radically easier and more secure.
+
+Cap'n Proto RPC is the underlying communications layer powering Sandstorm. Sandstorm is a
+[capability system](http://www.erights.org/elib/capability/overview.html): applications can send
+each other object references and address messages to those objects. Messages can themselves contain
+new object references, and the recipient implicitly gains permission to use any object reference
+they receive. Essentially, Sandstorm allows the interfaces between two apps, or between and app
+and the platform, to be designed using the same vocabulary as interfaces between objects or
+libraries in an object-oriented programming language (but
+[without the mistakes of CORBA or DCOM]({{site.baseurl}}rpc.html#distributed-objects)).
+Cap'n Proto RPC is at the core of this.
+
+This has powerful implications: Consider the case of service discovery. On Sandstorm, all
+applications start out isolated from each other in secure containers. However, applications can
+(or, will be able to) publish Cap'n Proto object references to the system representing APIs they
+support. Then, another app can make a request to the system, saying "I need an object that
+implements interface Foo". At this point, the system can display a picker UI to the user,
+presenting all objects the user owns that satisfy the requirement. However, the requesting app only
+ever receives a reference to the object the user chooses; all others remain hidden. Thus, security
+becomes "automatic". The user does not have to edit an ACL on the providing app, nor copy around
+credentials, nor even answer any security question at all; it all derives automatically and
+naturally from the user's choices. We call this interface "The Powerbox".
+
+Moreover, because Sandstorm is fully aware of the object references held by every app, it will
+be able to display a visualization of these connections, allowing a user to quickly see which of
+their apps have access to each other and even revoke connections that are no longer desired with
+a mouse click.
+
+Cap'n Proto 0.5 introduces primitives to support "persistent" capabilities -- that is, the ability
+to "save" an object reference to disk and then restore it later, on a different connection.
+Obviously, the features described above totally depend on this feature.
+
+The next release of Cap'n Proto is likely to include another feature essential for Sandstorm: the
+ability to pass capabilities from machine to machine and have Cap'n Proto automatically form direct
+connections when you do. This allows servers running on different machines to interact with each
+other in a completely object-oriented way. Instead of passing around URLs (which necessitate a
+global namespace, lifetime management, firewall traversal, and all sorts of other obstacles), you
+can pass around capabilities and not worry about it. This will be central to Sandstorm's strategies
+for federation and cluster management.
+
+### Other notes
+
+* The C++ RPC code now uses `epoll` on Linux.
+* We now test Cap'n Proto on Android and MinGW, in addition to Linux, Mac OSX, Cygwin, and Visual
+  Studio. (iOS and FreeBSD are also reported to work, though are not yet part of our testing
+  process.)