2.0

CHANGES:

capnp-rpc 2.0 switches from using Lwt to Eio.
The capnp-rpc-lwt package is now just Lwt wrappers around the Eio functions in capnp-rpc.
This allows libraries using the old Lwt API to be used with applications and libraries using the new Eio one,
in the same binary.
Because Lwt libraries (using capnp-rpc-lwt) can be used with Eio applications (using capnp-rpc-unix),
you should first upgrade your application and then upgrade the libraries afterwards.

It is recommended to upgrade in stages, checking your application still works after each step:

1. Upgrade to the latest Lwt version (opam install capnp-rpc-unix.1.2.4).
   This uses the new version of mirage-crypto, tls, etc,
   which may be incompatible with other libraries you are using.
   Get that sorted out before switching to capnp-rpc 2.0.

2. Use lwt_eio to allow using Eio and Lwt together in your application.
   This means replacing your call to Lwt_main.run with code to run Eio and Lwt together,
   as explained at the start of the lwt_eio README.

3. Upgrade your main application to capnp-rpc-unix 2.0.
   Calls to functions in the Capnp_rpc_unix and Capnp_rpc_net modules will need minor updates.
   They were previously called from Lwt context, so you'll need to wrap them with Lwt_eio.run_eio
   (or remove a Lwt_eio.run_lwt if you already updated the surrounding code).
   You should also use mirage-crypto-rng-eio to ensure randomness is available
   (capnp-rpc-unix no longer does this, although some other library might).

4. Upgrade code and libraries using Capnp_rpc_lwt:

   1. Replace open Capnp_rpc_lwt with open Capnp_rpc.Std.
   2. Replace all other uses of Capnp_rpc_lwt with just Capnp_rpc.
   3. In dune and opam files, replace capnp-rpc-lwt with capnp-rpc.
   4. Some modules are in Capnp_rpc but not the Capnp_rpc.Std subset.
      Those should now be fully qualified (e.g. replace Persistence with
      Capnp_rpc.Persistence).
   5. Replace Service.return_lwt with Lwt_eio.run_lwt.
      Replace Lwt.return (Ok x) with Service.return x.

Once all Lwt code is gone, you can remove the dependencies on lwt and lwt_eio.

New features:

• Allow numeric IPv6 listen addresses (@talex5 #296, requested by @BChabanne).

API changes:

• Eio port (@talex5 #280 #284 #298 #292 #297 #300 #304).

  This switches capnp-rpc from Lwt to Eio.
  One particularly nice side effect of this is that Service.return_lwt has gone,
  as there is no distinction now between concurrent and non-concurrent service methods.

  Uses of Capnp_rpc_lwt should be replaced by uses of Capnp_rpc
  (and the old Capnp_rpc is now an internal module, Capnp_rpc_proto).
  The new Capnp_rpc now provides Error, Exception and Debug aliases to the same modules in Capnp_rpc_proto,
  so that Capnp_rpc_proto doesn't need to be used directly.

  Capnp_rpc_lwt now provides (deprecated) compatibility wrappers, using lwt_eio.

  This also adds Capnp_rpc.Std with some common module aliases,
  to reduce the need to open Capnp_rpc (which is rather large).

• Deprecate Debug.failf (@talex5 #291).

Performance and bug fixes:

• Add buffering of outgoing messages (@talex5 #287 #303).
  Sending each message in its own TCP packet isn't very efficient, and also interacts very badly with Nagle's algorithm.
  See https://roscidus.com/blog/blog/2024/07/22/performance/ for details.

• Only disconnect socket when sending is done (@talex5 #295).
  Allows sending the reason for the disconnection in some cases.

• Fix type of Capability.call (@talex5 #293).
  It was previously unusable.

• Work around FreeBSD close problem (@talex5 #302).

Build:

• Update to capnp 3.6.0 (@talex5 #285).

• Update to dune 3.16 and fix warnings (@talex5 #282).

• Use String.starts_with instead of Astring (@talex5 #290).

• Remove unused tls-mirage dependency (@talex5 #289).

• Remove asetmap dependency (@talex5 #288).