multiprocess: Add echoipc RPC method and test

Add simple interfaces::Echo IPC interface with one method that just takes and
returns a string, to test multiprocess framework and provide an example of how
it can be used to spawn and call between processes.

3 files changed, 24 insertions, 0 deletions

diff --git a/src/ipc/capnp/echo.capnp b/src/ipc/capnp/echo.capnp
new file mode 100644
index 0000000000..df36ee0de3
--- /dev/null
+++ b/src/ipc/capnp/echo.capnp
@@ -0,0 +1,17 @@
+# Copyright (c) 2021 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+@0x888b4f7f51e691f7;
+
+using Cxx = import "/capnp/c++.capnp";
+$Cxx.namespace("ipc::capnp::messages");
+
+using Proxy = import "/mp/proxy.capnp";
+$Proxy.include("interfaces/echo.h");
+$Proxy.include("ipc/capnp/echo.capnp.h");
+
+interface Echo $Proxy.wrap("interfaces::Echo") {
+    destroy @0 (context :Proxy.Context) -> ();
+    echo @1 (context :Proxy.Context, echo: Text) -> (result :Text);
+}
diff --git a/src/ipc/capnp/init-types.h b/src/ipc/capnp/init-types.h
index c84b94802a..42031441b5 100644
--- a/src/ipc/capnp/init-types.h
+++ b/src/ipc/capnp/init-types.h
@@ -4,4 +4,7 @@
 
 #ifndef BITCOIN_IPC_CAPNP_INIT_TYPES_H
 #define BITCOIN_IPC_CAPNP_INIT_TYPES_H
+
+#include <ipc/capnp/echo.capnp.proxy-types.h>
+
 #endif // BITCOIN_IPC_CAPNP_INIT_TYPES_H
diff --git a/src/ipc/capnp/init.capnp b/src/ipc/capnp/init.capnp
index be6eecb4b9..e6d358c665 100644
--- a/src/ipc/capnp/init.capnp
+++ b/src/ipc/capnp/init.capnp
@@ -8,9 +8,13 @@ using Cxx = import "/capnp/c++.capnp";
 $Cxx.namespace("ipc::capnp::messages");
 
 using Proxy = import "/mp/proxy.capnp";
+$Proxy.include("interfaces/echo.h");
 $Proxy.include("interfaces/init.h");
 $Proxy.includeTypes("ipc/capnp/init-types.h");
 
+using Echo = import "echo.capnp";
+
 interface Init $Proxy.wrap("interfaces::Init") {
     construct @0 (threadMap: Proxy.ThreadMap) -> (threadMap :Proxy.ThreadMap);
+    makeEcho @1 (context :Proxy.Context) -> (result :Echo.Echo);
 }