[ANN] capnp-rpc 0.4.0

I’m pleased to announce the release of capnp-rpc 0.4.0, an OCaml implementation of the Cap’n Proto RPC specification.

If you haven’t used the library before, please see the documentation and tutorial. Cap’n Proto RPC aims to provide secure, efficient, typed communications between multiple parties.

This library is now being used to build ocaml-ci, where it is used for all communication between the web frontend and backend services, and to provide a command-line client.

Main changes since v0.3

Breaking changes:

  • Wrap errors with the `Capnp tag to make it easier to compose with other types of error.

  • Prefix all command-line options with capnp-.
    e.g. --listen-address is now --capnp-listen-address.
    The old names were confusing for applications that supported other protocols too (e.g. a web server).

New features:

  • Add Capability.with_ref convenience function.
    This automatically calls dec_ref when done.

  • Add Unix Cap_file module to load and save Sturdy_refs.
    In particular, this ensures that saved cap files get a mode of 0o600, since they contain secrets.

  • Export cmdliner network address parsing.
    This is useful if you don’t want to use the default option parsing.
    For example, if you want to make Cap’n Proto an optional feature of your program.

  • Upgrade from uint (which is deprecated) to the newer stdint.
    The latest version of uint is just a wrapper around stdint,
    so this shouldn’t break anything if you are using the latest version.

  • Put cmdliner options in their own man-page section.
    Use Capnp_rpc_unix.manpage_capnp_options to control where in your man-page they appear.

  • Enable SO_KEEPALIVE for TCP connections.
    For use with Docker’s libnetwork, try something like this in your stack.yml:

      - 'net.ipv4.tcp_keepalive_time=60'