Merge bitcoin/bitcoin#32297: bitcoin-cli: Add -ipcconnect option

4565cff72c bitcoin-gui: Implement missing Init::makeMining method (Ryan Ofsky)
fbea576c26 test: add interface_ipc_cli.py testing bitcoin-cli -ipcconnect (Ryan Ofsky)
0448a19b1b ipc: Improve -ipcconnect error checking (Ryan Ofsky)
8d614bfa47 bitcoin-cli: Add -ipcconnect option (Ryan Ofsky)
6a54834895 ipc: Expose an RPC interface over the -ipcbind socket (Ryan Ofsky)
df76891a3b refactor: Add ExecuteHTTPRPC function (Ryan Ofsky)
3cd1cd3ad3 ipc: Add MakeBasicInit function (Ryan Ofsky)

Pull request description:

  This implements an idea from sipa in https://github.com/bitcoin/bitcoin/issues/28722#issuecomment-2807026958 to allow `bitcoin-cli` to connect to the node via IPC instead of TCP, if the ENABLE_IPC cmake option is enabled and the node has been started with `-ipcbind`.

  This feature can be tested with:

  ```
  build/bin/bitcoin-node -regtest -ipcbind=unix -debug=ipc
  build/bin/bitcoin-cli -regtest -ipcconnect=unix -getinfo
  ```

  The -ipconnect parameter can also be omitted, since this change also makes `bitcoin-cli` prefer IPC over HTTP by default, and falling back to HTTP if an IPC connection can't be established.

  ---

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/issues/28722).

ACKs for top commit:
  achow101:
    ACK 4565cff72c
  pinheadmz:
    ACK 4565cff72c
  enirox001:
    Tested ACK 4565cff72c

Tree-SHA512: cb0dc521d82591e4eb2723a37ae60949309a206265e0ccfbee1f4d59b426b770426fafa1e842819a2fa27322ecdfcd226f31da70f91c2c31b8095e1380666f1f

src/interfaces/README.md

@@ -16,4 +16,6 @@ The following interfaces are defined here:
 
 * [`Ipc`](ipc.h) — used by multiprocess code to access `Init` interface across processes. Added in [#19160](https://github.com/bitcoin/bitcoin/pull/19160).
 
+* [`Rpc`](rpc.h) — used by `bitcoin-cli` to be able to call RPC methods over a unix socket instead of TCP.
+
 The interfaces above define boundaries between major components of bitcoin code (node, wallet, and gui), making it possible for them to run in [different processes](../../doc/multiprocess.md), and be tested, developed, and understood independently. These interfaces are not currently designed to be stable or to be used externally.

src/interfaces/init.h

@@ -9,6 +9,7 @@
 #include <interfaces/echo.h>
 #include <interfaces/mining.h>
 #include <interfaces/node.h>
+#include <interfaces/rpc.h>
 #include <interfaces/wallet.h>
 
 #include <memory>
@@ -36,6 +37,7 @@ public:
     virtual std::unique_ptr<Mining> makeMining() { return nullptr; }
     virtual std::unique_ptr<WalletLoader> makeWalletLoader(Chain& chain) { return nullptr; }
     virtual std::unique_ptr<Echo> makeEcho() { return nullptr; }
+    virtual std::unique_ptr<Rpc> makeRpc() { return nullptr; }
     virtual Ipc* ipc() { return nullptr; }
     virtual bool canListenIpc() { return false; }
     virtual const char* exeName() { return nullptr; }
@@ -55,6 +57,25 @@ std::unique_ptr<Init> MakeWalletInit(int argc, char* argv[], int& exit_status);
 
 //! Return implementation of Init interface for the gui process.
 std::unique_ptr<Init> MakeGuiInit(int argc, char* argv[]);
+
+//! Return implementation of Init interface for a basic IPC client that doesn't
+//! provide any IPC services itself.
+//!
+//! When an IPC client connects to a socket or spawns a process, it gets a pointer
+//! to an Init object allowing it to create objects and threads on the remote
+//! side of the IPC connection. But the client also needs to provide a local Init
+//! object to allow the remote side of the connection to create objects and
+//! threads on this side. This function just returns a basic Init object
+//! allowing remote connections to only create local threads, not other objects
+//! (because its Init::make* methods return null.)
+//!
+//! @param exe_name Current executable name, which is just passed to the IPC
+//!     system and used for logging.
+//!
+//! @param process_argv0 Optional string containing argv[0] value passed to
+//!     main(). This is passed to the IPC system and used to locate binaries by
+//!     relative path if subprocesses are spawned.
+std::unique_ptr<Init> MakeBasicInit(const char* exe_name, const char* process_argv0="");
 } // namespace interfaces
 
 #endif // BITCOIN_INTERFACES_INIT_H

src/interfaces/ipc.h

@@ -7,6 +7,7 @@
 
 #include <functional>
 #include <memory>
+#include <string>
 #include <typeindex>
 
 namespace ipc {

src/interfaces/rpc.h

@@ -0,0 +1,31 @@
+// Copyright (c) 2025 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_RPC_H
+#define BITCOIN_INTERFACES_RPC_H
+
+#include <memory>
+#include <string>
+
+class UniValue;
+
+namespace node {
+struct NodeContext;
+} // namespace node
+
+namespace interfaces {
+//! Interface giving clients ability to emulate HTTP RPC calls.
+class Rpc
+{
+public:
+    virtual ~Rpc() = default;
+    virtual UniValue executeRpc(UniValue request, std::string url, std::string user) = 0;
+};
+
+//! Return implementation of Rpc interface.
+std::unique_ptr<Rpc> MakeRpc(node::NodeContext& node);
+
+} // namespace interfaces
+
+#endif // BITCOIN_INTERFACES_RPC_H