multiprocess: Add Ipc and Init interface definitions

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