7 files changed, 182 insertions, 0 deletions
diff --git a/src/ipc/capnp/.gitignore b/src/ipc/capnp/.gitignore
new file mode 100644
index 0000000000..036df1430c
--- /dev/null
+++ b/src/ipc/capnp/.gitignore
@@ -0,0 +1,2 @@
+# capnp generated files
+*.capnp.*
diff --git a/src/ipc/capnp/context.h b/src/ipc/capnp/context.h
new file mode 100644
index 0000000000..06e1614494
--- /dev/null
+++ b/src/ipc/capnp/context.h
@@ -0,0 +1,23 @@
+// 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.
+
+#ifndef BITCOIN_IPC_CAPNP_CONTEXT_H
+#define BITCOIN_IPC_CAPNP_CONTEXT_H
+
+#include <ipc/context.h>
+
+namespace ipc {
+namespace capnp {
+//! Cap'n Proto context struct. Generally the parent ipc::Context struct should
+//! be used instead of this struct to give all IPC protocols access to
+//! application state, so there aren't unnecessary differences between IPC
+//! protocols. But this specialized struct can be used to pass capnp-specific
+//! function and object types to capnp hooks.
+struct Context : ipc::Context
+{
+};
+} // namespace capnp
+} // namespace ipc
+
+#endif // BITCOIN_IPC_CAPNP_CONTEXT_H
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 $Proxy.wrap("interfaces::Echo") {
+    destroy @0 (context :Proxy.Context) -> ();
+    echo @1 (context :Proxy.Context, echo: Text) -> (result :Text);
+}
diff --git a/src/ipc/capnp/init-types.h b/src/ipc/capnp/init-types.h
new file mode 100644
index 0000000000..42031441b5
--- /dev/null
+++ b/src/ipc/capnp/init-types.h
@@ -0,0 +1,10 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_IPC_CAPNP_INIT_TYPES_H
+#define BITCOIN_IPC_CAPNP_INIT_TYPES_H
+
+#include <ipc/capnp/echo.capnp.proxy-types.h>
+
+#endif // BITCOIN_IPC_CAPNP_INIT_TYPES_H
diff --git a/src/ipc/capnp/init.capnp b/src/ipc/capnp/init.capnp
new file mode 100644
index 0000000000..e6d358c665
--- /dev/null
+++ b/src/ipc/capnp/init.capnp
@@ -0,0 +1,20 @@
+# Copyright (c) 2021 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+@0xf2c5cfa319406aa6;
+
+using Cxx = import "/capnp/c++.capnp";
+$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);
+}
diff --git a/src/ipc/capnp/protocol.cpp b/src/ipc/capnp/protocol.cpp
new file mode 100644
index 0000000000..37b57a9525
--- /dev/null
+++ b/src/ipc/capnp/protocol.cpp
@@ -0,0 +1,93 @@
+// 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.
+
+#include <interfaces/init.h>
+#include <ipc/capnp/context.h>
+#include <ipc/capnp/init.capnp.h>
+#include <ipc/capnp/init.capnp.proxy.h>
+#include <ipc/capnp/protocol.h>
+#include <ipc/exception.h>
+#include <ipc/protocol.h>
+#include <kj/async.h>
+#include <logging.h>
+#include <mp/proxy-io.h>
+#include <mp/proxy-types.h>
+#include <mp/util.h>
+#include <util/threadnames.h>
+
+#include <assert.h>
+#include <errno.h>
+#include <future>
+#include <memory>
+#include <mutex>
+#include <optional>
+#include <string>
+#include <thread>
+
+namespace ipc {
+namespace capnp {
+namespace {
+void IpcLogFn(bool raise, std::string message)
+{
+    LogPrint(BCLog::IPC, "%s\n", message);
+    if (raise) throw Exception(message);
+}
+
+class CapnpProtocol : public Protocol
+{
+public:
+    ~CapnpProtocol() noexcept(true)
+    {
+        if (m_loop) {
+            std::unique_lock<std::mutex> lock(m_loop->m_mutex);
+            m_loop->removeClient(lock);
+        }
+        if (m_loop_thread.joinable()) m_loop_thread.join();
+        assert(!m_loop);
+    };
+    std::unique_ptr<interfaces::Init> connect(int fd, const char* exe_name) override
+    {
+        startLoop(exe_name);
+        return mp::ConnectStream<messages::Init>(*m_loop, fd);
+    }
+    void serve(int fd, const char* exe_name, interfaces::Init& init) override
+    {
+        assert(!m_loop);
+        mp::g_thread_context.thread_name = mp::ThreadName(exe_name);
+        m_loop.emplace(exe_name, &IpcLogFn, &m_context);
+        mp::ServeStream<messages::Init>(*m_loop, fd, init);
+        m_loop->loop();
+        m_loop.reset();
+    }
+    void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) override
+    {
+        mp::ProxyTypeRegister::types().at(type)(iface).cleanup.emplace_back(std::move(cleanup));
+    }
+    Context& context() override { return m_context; }
+    void startLoop(const char* exe_name)
+    {
+        if (m_loop) return;
+        std::promise<void> promise;
+        m_loop_thread = std::thread([&] {
+            util::ThreadRename("capnp-loop");
+            m_loop.emplace(exe_name, &IpcLogFn, &m_context);
+            {
+                std::unique_lock<std::mutex> lock(m_loop->m_mutex);
+                m_loop->addClient(lock);
+            }
+            promise.set_value();
+            m_loop->loop();
+            m_loop.reset();
+        });
+        promise.get_future().wait();
+    }
+    Context m_context;
+    std::thread m_loop_thread;
+    std::optional<mp::EventLoop> m_loop;
+};
+} // namespace
+
+std::unique_ptr<Protocol> MakeCapnpProtocol() { return std::make_unique<CapnpProtocol>(); }
+} // namespace capnp
+} // namespace ipc
diff --git a/src/ipc/capnp/protocol.h b/src/ipc/capnp/protocol.h
new file mode 100644
index 0000000000..eb057949d2
--- /dev/null
+++ b/src/ipc/capnp/protocol.h
@@ -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.
+
+#ifndef BITCOIN_IPC_CAPNP_PROTOCOL_H
+#define BITCOIN_IPC_CAPNP_PROTOCOL_H
+
+#include <memory>
+
+namespace ipc {
+class Protocol;
+namespace capnp {
+std::unique_ptr<Protocol> MakeCapnpProtocol();
+} // namespace capnp
+} // namespace ipc
+
+#endif // BITCOIN_IPC_CAPNP_PROTOCOL_H