layout: page
title: Installation

Installation: Tools and C++ Runtime

The Cap'n Proto tools, including the compiler which takes .capnp files and generates source code for them, are written in C++. Therefore, you must install the C++ package even if your actual development language is something else.

This package is licensed under the MIT License.

Caveats

Cap'n Proto is in BETA

As of this writing, Cap'n Proto is in beta. The serialization layer is close to feature-complete and we don't anticipate any further changes to the wire format. That said, if you want to use it, you should keep in mind some caveats:

• Security: Cap'n Proto has not yet had a security review. Although Kenton has a background in security and is not aware of any vulnerabilities in the current code, it's likely that there are a few. For now, do not accept Cap'n Proto messages from parties you do not trust.
• API Stability: The Cap'n Proto programming interface may still change in ways that break existing code. Such changes are likely to be minor and should not affect the wire format.
• Performance: While Cap'n Proto is inherently fast by design, the implementation has not yet undergone serious profiling and optimization. Currently it only beats Protobufs in realistic-ish end-to-end benchmarks by around 2x-5x. We can do better.
• RPC: The RPC implementation particularly experimental, though it is used heavily by Sandstorm.io.

If you'd like to hack on Cap'n Proto, you should join the discussion group!

If you'd just like to receive updates as things progress, add yourself to the announce list.

Prerequisites

Supported Compilers

Cap'n Proto makes extensive use of C++11 language features. As a result, it requires a relatively new version of a well-supported compiler. The minimum versions are:

• GCC 4.8
• Clang 3.3
• Visual C++ 2015 (lite mode only)

If your system's default compiler is older that the above, you will need to install a newer compiler and set the CXX environment variable before trying to build Cap'n Proto. For example, after installing GCC 4.8, you could set CXX=g++-4.8 to use this compiler.

Supported Operating Systems

In theory, Cap'n Proto should work on any POSIX platform supporting one of the above compilers, as well as on Windows. We test every Cap'n Proto release on the following platforms:

• Android
• Linux
• Mac OSX
• Windows - Cygwin
• Windows - MinGW-w64 (lite mode and compiler binary only)
• Windows - Visual C++ (lite mode only)

Windows users: As of Visual Studio 2015, Visual C++ still does not support enough of C++11 to compile Cap'n Proto's reflection or RPC APIs. "Cap'n Proto Lite" omits these features from the library, giving you only the core serialization based on generated code.

Mac/Xcode users: You must use at least Xcode 5, and you must download the Xcode command-line tools under Xcode menu > Preferences > Downloads. Alternatively, compiler builds from Macports, Fink, or Homebrew are reported to work.

Installation: Unix

You may download and install the release version of Cap'n Proto like so:

curl -O https://capnproto.org/capnproto-c++-0.0.0.tar.gz
tar zxf capnproto-c++-0.0.0.tar.gz
cd capnproto-c++-0.0.0
./configure
make -j6 check
sudo make install

This will install capnp, the Cap'n Proto command-line tool. It will also install libcapnp, libcapnpc, and libkj in /usr/local/lib and headers in /usr/local/include/capnp and /usr/local/include/kj.

From Git

If you download directly from Git, you will need to have the GNU autotools -- autoconf, automake, and libtool -- installed. You will also need Subversion installed (in addition to Git) in order to fetch the Google Test sources (done by setup-autotools.sh).

git clone https://github.com/kentonv/capnproto.git
cd capnproto/c++
./setup-autotools.sh
autoreconf -i
./configure
make -j6 check
sudo make install

Installation: Windows

1. Download Cap'n Proto Win32 build:

   https://capnproto.org/capnproto-c++-win32-0.0.0.zip

2. Find capnp.exe, capnpc-c++.exe, and capnpc-capnp.exe under capnproto-tools-win32-0.0.0 in the zip and copy them to somewhere in your PATH.

If you don't care about C++ support, you can stop here. The compiler exe can be used with plugins provided by projects implementing Cap'n Proto in other languages.

If you want to use Cap'n Proto in C++ with Visual Studio, do the following:

1. Install CMake version 3.1 or later.

2. Use CMake to generate Visual Studio project files under capnproto-c++-0.0.0 in the zip file. You will need to enable the CMake project options CAPNP_LITE and EXTERNAL_CAPNP. You can use the CMake UI for this or run this shell command:

   cmake -G "Visual Studio 14 2015" -DCAPNP_LITE=1 -DEXTERNAL_CAPNP=1

3. Open the "Cap'n Proto" solution in Visual Studio.

4. Adjust the project build options (e.g. choice of C++ runtime library, dll vs. static, enable/disable exceptions and RTTI) to match the options of the project in which you plan to use Cap'n Proto.

5. Build the solution.

6. Find the compiled .lib files in the build directory under src/{capnp,kj}/{Debug,Release} and place them somewhere where your project can link against them.

7. Add the the src directory to your search path for #includes, or copy all the headers to your include directory.

From Git

If you download directly from Git, you'll need to compile the Cap'n Proto tools (the .exes) using MinGW-w64. This is easiest to do in Cygwin or on Linux. For example, on Debian or Ubuntu, you can install MinGW like so:

sudo apt-get install mingw-w64

You'll first need to install Cap'n Proto on the host system (using the Unix installation instructions, above). Then, do:

make distclean
./configure --host=i686-w64-mingw32 --with-external-capnp \
  --disable-shared CXXFLAGS='-static-libgcc -static-libstdc++'
make -j6 capnp.exe capnpc-c++.exe capnpc-capnp.exe

Now that you have the exes, you can proceed with the usual Windows compilation instructions.