initial

.gitignore

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+_*
+result

capnp-rpc-demo.opam

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+opam-version: "2.0"
+depends: [
+  "ocaml" {>= "4.08.0"}
+  "eio_main"
+  "capnp-rpc-lwt"
+  "logs"
+]
+build: [
+  ["dune" "build" "-p" name "-j" jobs]
+  ["dune" "runtest" "-p" name "-j" jobs] {with-test}
+]

dune

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+(executable
+ (name main)
+ (libraries eio_main capnp-rpc-lwt logs.fmt)
+ (flags (:standard -w -53-55)))
+
+(rule
+ (targets echo_api.ml echo_api.mli)
+ (deps    echo_api.capnp)
+ (action (run capnp compile -o %{bin:capnpc-ocaml} %{deps})))

dune-project

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+(lang dune 2.9)
+(name capnp-rpc-demo)
+(formatting disabled)

echo.ml

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+(* $MDX part-begin=server *)
+module Api = Echo_api.MakeRPC(Capnp_rpc_lwt)
+
+open Capnp_rpc_lwt
+
+let local =
+  let module Echo = Api.Service.Echo in
+  Echo.local @@ object
+    inherit Echo.service
+
+    method ping_impl params release_param_caps =
+      let open Echo.Ping in
+      let msg = Params.msg_get params in
+      release_param_caps ();
+      let response, results = Service.Response.create Results.init_pointer in
+      Results.reply_set results ("echo:" ^ msg);
+      Service.return response
+  end
+(* $MDX part-end *)
+
+(* $MDX part-begin=client *)
+module Echo = Api.Client.Echo
+
+let ping t msg =
+  let open Echo.Ping in
+  let request, params = Capability.Request.create Params.init_pointer in
+  Params.msg_set params msg;
+  Capability.call_for_value_exn t method_id request |> Results.reply_get
+(* $MDX part-end *)

echo_api.capnp

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+@0xb287252b6cbed46e;
+
+interface Echo {
+  ping @0 (msg :Text) -> (reply :Text);
+}

flake.nix

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+{
+  inputs = {
+    opam-nix.url = "github:tweag/opam-nix";
+    flake-utils.url = "github:numtide/flake-utils";
+    opam-nix.inputs.nixpkgs.follows = "nixpkgs";
+  };
+  outputs = { self, nixpkgs, flake-utils, opam-nix, ... }@inputs:
+    let package = "capnp-rpc-demo";
+    in flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        opam-nix-lib = opam-nix.lib.${system};
+        devPackagesQuery = {
+          ocaml-lsp-server = "*";
+          ocamlformat = "*";
+        };
+        query = {
+          ocaml-base-compiler = "*";
+        };
+        overlay = final: prev: {
+          "${package}" = prev.${package}.overrideAttrs (_: {
+            # Prevent the ocaml dependencies from leaking into dependent environments
+            doNixSupport = false;
+            nativeBuildInputs = [ pkgs.dune_3 ];
+          });
+        };
+        resolved-scope =
+          let scope = opam-nix-lib.buildOpamProject' { } ./. (query // devPackagesQuery); in
+          scope.overrideScope' overlay;
+        materialized-scope =
+          # to generate:
+          #   nix shell github:tweag/opam-nix#opam-nix-gen -c opam-nix-gen -p ocaml-lsp-server -p ocamlformat -p ocaml-base-compiler aeon . package-defs.json
+          let scope = opam-nix-lib.materializedDefsToScope { sourceMap.${package} = ./.; } ./package-defs.json; in
+          scope.overrideScope' overlay;
+      in rec {
+        packages = {
+          resolved = resolved-scope;
+          materialized = materialized-scope;
+          default = resolved-scope.${package};
+        };
+        defaultPackage = packages.default;
+
+        devShells = 
+          let
+            mkDevShell = scope:
+              let
+                devPackages = builtins.attrValues
+                  (pkgs.lib.getAttrs (builtins.attrNames devPackagesQuery) scope);
+              in pkgs.mkShell {
+                inputsFrom = [ scope.${package} ];
+                buildInputs = devPackages;
+              };
+          in rec {
+            resolved = mkDevShell resolved-scope;
+            materialized = mkDevShell materialized-scope;
+            default = resolved;
+          };
+      }) // {
+    nixosModules.default = {
+      imports = [ ./module.nix ];
+    };
+  };
+}
+

main.ml

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+open Eio.Std
+
+let () =
+  Logs.set_level (Some Logs.Warning);
+  Logs.set_reporter (Logs_fmt.reporter ())
+
+let () =
+  Eio_main.run @@ fun _ ->
+  let service = Echo.local in
+  let reply = Echo.ping service "foo" in
+  traceln "Got reply %S" reply