multiprocess: Add Ipc and Init interface definitions

src/Makefile.am

@@ -159,6 +159,8 @@ BITCOIN_CORE_H = \
   init/common.h \
   interfaces/chain.h \
   interfaces/handler.h \
+  interfaces/init.h \
+  interfaces/ipc.h \
   interfaces/node.h \
   interfaces/wallet.h \
   key.h \
@@ -559,6 +561,7 @@ libbitcoin_util_a_SOURCES = \
   compat/strnlen.cpp \
   fs.cpp \
   interfaces/handler.cpp \
+  interfaces/init.cpp \
   logging.cpp \
   random.cpp \
   randomenv.cpp \

src/interfaces/init.cpp

@@ -0,0 +1,15 @@
+// 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/chain.h>
+#include <interfaces/init.h>
+#include <interfaces/node.h>
+#include <interfaces/wallet.h>
+
+namespace interfaces {
+std::unique_ptr<Node> Init::makeNode() { return {}; }
+std::unique_ptr<Chain> Init::makeChain() { return {}; }
+std::unique_ptr<WalletClient> Init::makeWalletClient(Chain& chain) { return {}; }
+Ipc* Init::ipc() { return nullptr; }
+} // namespace interfaces

src/interfaces/init.h

@@ -0,0 +1,36 @@
+// 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_INTERFACES_INIT_H
+#define BITCOIN_INTERFACES_INIT_H
+
+#include <memory>
+
+struct NodeContext;
+
+namespace interfaces {
+class Chain;
+class Ipc;
+class Node;
+class WalletClient;
+
+//! Initial interface created when a process is first started, and used to give
+//! and get access to other interfaces (Node, Chain, Wallet, etc).
+//!
+//! There is a different Init interface implementation for each process
+//! (bitcoin-gui, bitcoin-node, bitcoin-wallet, bitcoind, bitcoin-qt) and each
+//! implementation can implement the make methods for interfaces it supports.
+//! The default make methods all return null.
+class Init
+{
+public:
+    virtual ~Init() = default;
+    virtual std::unique_ptr<Node> makeNode();
+    virtual std::unique_ptr<Chain> makeChain();
+    virtual std::unique_ptr<WalletClient> makeWalletClient(Chain& chain);
+    virtual Ipc* ipc();
+};
+} // namespace interfaces
+
+#endif // BITCOIN_INTERFACES_INIT_H

src/interfaces/ipc.h

@@ -0,0 +1,48 @@
+// 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_INTERFACES_IPC_H
+#define BITCOIN_INTERFACES_IPC_H
+
+#include <functional>
+#include <memory>
+#include <typeindex>
+
+namespace interfaces {
+class Init;
+
+//! Interface providing access to interprocess-communication (IPC)
+//! functionality.
+class Ipc
+{
+public:
+    virtual ~Ipc() = default;
+
+    //! Spawn a child process returning pointer to its Init interface.
+    virtual std::unique_ptr<Init> spawnProcess(const char* exe_name) = 0;
+
+    //! If this is a spawned process, block and handle requests from the parent
+    //! process by forwarding them to this process's Init interface, then return
+    //! true. If this is not a spawned child process, return false.
+    virtual bool startSpawnedProcess(int argc, char* argv[], int& exit_status) = 0;
+
+    //! Add cleanup callback to remote interface that will run when the
+    //! interface is deleted.
+    template<typename Interface>
+    void addCleanup(Interface& iface, std::function<void()> cleanup)
+    {
+        addCleanup(typeid(Interface), &iface, std::move(cleanup));
+    }
+
+protected:
+    //! Internal implementation of public addCleanup method (above) as a
+    //! type-erased virtual function, since template functions can't be virtual.
+    virtual void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) = 0;
+};
+
+//! Return implementation of Ipc interface.
+std::unique_ptr<Ipc> MakeIpc(const char* exe_name, const char* process_argv0, Init& init);
+} // namespace interfaces
+
+#endif // BITCOIN_INTERFACES_IPC_H