Cap’n Proto is an insanely fast data interchange format and capability-based RPC system.

Lua-capnproto is a pure lua implementation of Cap'n Proto based on LuaJIT.

This project is still under early development and is not production-ready.

Suppose you have a Cap'n Proto file called example.capnp. You can compile this file like this:

$capnp compile -olua example.capnp

The default output file is example_capnp.lua

local example_capnp = require "example_capnp"

Check out example/AddressBook.capnp and example/main.lua for how to use generated lua file.

To install lua-capnproto, you need to install Cap'n Proto https://kentonv.github.io/capnproto/install.html, LuaJIT https://luajit.org/install.html and luarocks https://luarocks.org/en/Download first.

Currently, lua-capnproto only works with LuaJIT v2.1. You can install LuaJIT v2.1 using the following commands:

$git clone https://luajit.org/git/luajit-2.0.git
$git checkout v2.1
$make && sudo make install
$sudo ln -sf luajit-2.1.0-alpha /usr/local/bin/luajit

Then you can install lua-capnproto using the following commands:

$sudo luarocks install lua-capnproto

Let's compile an example file to test whether lua-capnproto was installed successfully:

$capnp compile -olua proto/example.capnp proto/enums.capnp proto/lua.capnp proto/struct.capnp

Normally, you should see no errors and a file named "proto/example_capnp.lua" is generated.

Please see my blog post on how to use lua-capnproto here.

If you want to run unit tests, you need to install lunitx and lua-cjson:

$sudo luarocks install lua-cjson
$sudo luarocks install lunitx

If your Linux distribution have Lua 5.2 installed, using this instruction to install required lua modules.

To run tests:

$./test.sh

• Currently, lua-capnproto only works with LuaJIT v2.1. This is because lua-capnproto needs 64 bit integer support and 64bit number bit operations, but only LuaJIT v2.1 provides a decent way to do all these. I'm working on LuaJIT 2.0/ Lua 5.1 / Lua 5.2 support, hopefully you can use lua-capnproto with your favorite lua soon.
• Cap'n Proto RPC is not implemented yet