Add ipc::Context and ipc::capnp::Context structs

These are currently empty structs but they will be used to pass some
function and object pointers from bitcoin application code to IPC hooks
that run, for example, when a remote object is created or destroyed, or
a new process is created.

2 files changed, 28 insertions, 2 deletions

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/protocol.cpp b/src/ipc/capnp/protocol.cpp
index 74c66c899a..37b57a9525 100644
--- a/src/ipc/capnp/protocol.cpp
+++ b/src/ipc/capnp/protocol.cpp
@@ -3,6 +3,7 @@
 // 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>
@@ -54,7 +55,7 @@ public:
     {
         assert(!m_loop);
         mp::g_thread_context.thread_name = mp::ThreadName(exe_name);
-        m_loop.emplace(exe_name, &IpcLogFn, nullptr);
+        m_loop.emplace(exe_name, &IpcLogFn, &m_context);
         mp::ServeStream<messages::Init>(*m_loop, fd, init);
         m_loop->loop();
         m_loop.reset();
@@ -63,13 +64,14 @@ public:
     {
         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, nullptr);
+            m_loop.emplace(exe_name, &IpcLogFn, &m_context);
             {
                 std::unique_lock<std::mutex> lock(m_loop->m_mutex);
                 m_loop->addClient(lock);
@@ -80,6 +82,7 @@ public:
         });
         promise.get_future().wait();
     }
+    Context m_context;
     std::thread m_loop_thread;
     std::optional<mp::EventLoop> m_loop;
 };