multiprocess: Add echoipc RPC method and test

Add simple interfaces::Echo IPC interface with one method that just takes and
returns a string, to test multiprocess framework and provide an example of how
it can be used to spawn and call between processes.

src/Makefile.am

@@ -145,6 +145,7 @@ BITCOIN_CORE_H = \
   init.h \
   interfaces/base.h \
   interfaces/chain.h \
+  interfaces/echo.h \
   interfaces/handler.h \
   interfaces/init.h \
   interfaces/node.h \
@@ -513,6 +514,7 @@ libbitcoin_util_a_SOURCES = \
   compat/strnlen.cpp \
   fs.cpp \
   interfaces/base.cpp \
+  interfaces/echo.cpp \
   interfaces/init.cpp \
   interfaces/handler.cpp \
   logging.cpp \
@@ -733,13 +735,16 @@ if HARDEN
 endif
 
 libbitcoin_ipc_mpgen_input = \
+  interfaces/capnp/echo.capnp \
   interfaces/capnp/init.capnp
 EXTRA_DIST += $(libbitcoin_ipc_mpgen_input)
 %.capnp:
 
 if BUILD_MULTIPROCESS
 LIBBITCOIN_IPC=libbitcoin_ipc.a
 libbitcoin_ipc_a_SOURCES = \
+  interfaces/capnp/echo-types.h \
+  interfaces/capnp/echo.h \
   interfaces/capnp/init-types.h \
   interfaces/capnp/init.cpp \
   interfaces/capnp/init.h \

src/interfaces/capnp/echo-types.h

@@ -0,0 +1,7 @@
+// Copyright (c) 2020 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_CAPNP_ECHO_TYPES_H
+#define BITCOIN_INTERFACES_CAPNP_ECHO_TYPES_H
+#endif // BITCOIN_INTERFACES_CAPNP_ECHO_TYPES_H

src/interfaces/capnp/echo.capnp

@@ -0,0 +1,15 @@
+# Copyright (c) 2020 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("interfaces::capnp::messages");
+
+using Proxy = import "/mp/proxy.capnp";
+
+interface Echo $Proxy.wrap("interfaces::Echo") {
+    destroy @0 (context :Proxy.Context) -> ();
+    echo @1 (context :Proxy.Context, echo: Text) -> (result :Text);
+}

src/interfaces/capnp/echo.h

@@ -0,0 +1,11 @@
+// Copyright (c) 2020 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_CAPNP_ECHO_H
+#define BITCOIN_INTERFACES_CAPNP_ECHO_H
+
+#include <interfaces/capnp/echo.capnp.h>
+#include <interfaces/echo.h>
+
+#endif // BITCOIN_INTERFACES_CAPNP_ECHO_H

src/interfaces/capnp/init-types.h

@@ -4,4 +4,7 @@
 
 #ifndef BITCOIN_INTERFACES_CAPNP_INIT_TYPES_H
 #define BITCOIN_INTERFACES_CAPNP_INIT_TYPES_H
+
+#include <interfaces/capnp/echo.capnp.proxy-types.h>
+
 #endif // BITCOIN_INTERFACES_CAPNP_INIT_TYPES_H

src/interfaces/capnp/init.capnp

@@ -7,8 +7,10 @@
 using Cxx = import "/capnp/c++.capnp";
 $Cxx.namespace("interfaces::capnp::messages");
 
+using Echo = import "echo.capnp";
 using Proxy = import "/mp/proxy.capnp";
 
 interface Init $Proxy.wrap("interfaces::Init") {
     construct @0 (threadMap: Proxy.ThreadMap) -> (threadMap :Proxy.ThreadMap);
+    makeEcho @1 (context :Proxy.Context) -> (result :Echo.Echo);
 }

src/interfaces/capnp/init.h

@@ -5,6 +5,7 @@
 #ifndef BITCOIN_INTERFACES_CAPNP_INIT_H
 #define BITCOIN_INTERFACES_CAPNP_INIT_H
 
+#include <interfaces/echo.h>
 #include <interfaces/init.h>
 #include <mp/proxy.h>
 

src/interfaces/echo.cpp

@@ -0,0 +1,23 @@
+// Copyright (c) 2020 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/echo.h>
+
+#include <util/memory.h>
+
+namespace interfaces {
+namespace {
+class EchoImpl : public Echo
+{
+public:
+    std::string echo(const std::string& echo) override
+    {
+        return echo;
+    }
+};
+} // namespace
+
+std::unique_ptr<Echo> MakeEcho() { return MakeUnique<EchoImpl>(); }
+
+} // namespace interfaces

src/interfaces/echo.h

@@ -0,0 +1,29 @@
+// Copyright (c) 2020 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_ECHO_H
+#define BITCOIN_INTERFACES_ECHO_H
+
+#include <interfaces/base.h>
+
+#include <string>
+
+namespace interfaces {
+
+//! Simple string echoing interface for testing.
+class Echo : public Base
+{
+public:
+    virtual ~Echo() {}
+
+    //! Echo provided string.
+    virtual std::string echo(const std::string& echo) = 0;
+};
+
+//! Return implementation of Echo interface.
+std::unique_ptr<Echo> MakeEcho();
+
+} // namespace interfaces
+
+#endif // BITCOIN_INTERFACES_ECHO_H

src/interfaces/init.cpp

@@ -5,6 +5,7 @@
 #include <interfaces/init.h>
 
 #include <interfaces/chain.h>
+#include <interfaces/echo.h>
 #include <interfaces/ipc.h>
 #include <interfaces/node.h>
 #include <logging.h>
@@ -28,6 +29,8 @@ class CloseFn : public CloseHook
 
 LocalInit::LocalInit(const char* exe_name, const char* log_suffix) : m_exe_name(exe_name), m_log_suffix(log_suffix) {}
 LocalInit::~LocalInit() {}
+std::unique_ptr<Echo> LocalInit::makeEcho() { return {}; }
+std::unique_ptr<Echo> LocalInit::makeEchoIpc() { return {}; }
 NodeContext& LocalInit::node()
 {
     throw std::logic_error("Node accessor function called from non-node binary (gui, wallet, or test program)");

src/interfaces/init.h

@@ -17,6 +17,7 @@ struct NodeContext;
 
 namespace interfaces {
 class Base;
+class Echo;
 class IpcProcess;
 class IpcProtocol;
 
@@ -25,6 +26,7 @@ class Init
 {
 public:
     virtual ~Init() = default;
+    virtual std::unique_ptr<Echo> makeEcho() = 0;
 };
 
 //! Specialization of Init for current process.
@@ -33,8 +35,12 @@ class LocalInit : public Init
 public:
     LocalInit(const char* exe_name, const char* log_suffix);
     ~LocalInit() override;
+    std::unique_ptr<Echo> makeEcho() override;
     using MakeClientFn = std::function<Base&(Init&)>;
     void spawnProcess(const std::string& new_exe_name, const MakeClientFn& make_client);
+    //! Make echo implementation for `echoipc` test RPC. Spawn new process if
+    //! supported.
+    virtual std::unique_ptr<Echo> makeEchoIpc();
     virtual NodeContext& node();
     const char* m_exe_name;
     const char* m_log_suffix;

src/interfaces/init_bitcoin-node.cpp

@@ -5,6 +5,7 @@
 #include <interfaces/init.h>
 
 #include <interfaces/capnp/ipc.h>
+#include <interfaces/echo.h>
 #include <node/context.h>
 #include <util/memory.h>
 
@@ -20,6 +21,23 @@ class LocalInitImpl : public LocalInit
         m_protocol = capnp::MakeCapnpProtocol(m_exe_name, *this);
         m_process = MakeIpcProcess(argc, argv, m_exe_name, *m_protocol);
     }
+    std::unique_ptr<Echo> makeEcho() override { return MakeEcho(); }
+    std::unique_ptr<Echo> makeEchoIpc() override
+    {
+        // Spawn a new bitcoin-node process and call makeEcho to get a client
+        // pointer to a interfaces::Echo instance running in that process. This
+        // is just for testing. A slightly more realistic test would build a new
+        // bitcoin-echo executable, and spawn bitcoin-echo here instead of
+        // bitcoin-node. But using bitcoin-node avoids the need to build and
+        // install a new binary not useful for anything except testing
+        // multiprocess support.
+        std::unique_ptr<Echo> echo;
+        spawnProcess("bitcoin-node", [&](Init& init) -> Base& {
+            echo = init.makeEcho();
+            return *echo;
+        });
+        return echo;
+    }
     NodeContext& node() override { return m_node; };
     NodeContext m_node;
 };

src/interfaces/init_bitcoind.cpp

@@ -4,6 +4,7 @@
 
 #include <interfaces/init.h>
 
+#include <interfaces/echo.h>
 #include <node/context.h>
 #include <util/memory.h>
 
@@ -17,6 +18,16 @@ class LocalInitImpl : public LocalInit
         m_node.init = this;
         m_request_context.Set(m_node);
     }
+    std::unique_ptr<Echo> makeEchoIpc() override
+    {
+        // The bitcoind binary isn't linked against libmultiprocess and doesn't
+        // have IPC support, so just create a local interfaces::Echo object and
+        // return it so the `echoipc` RPC method will work, and the python test
+        // calling `echoipc` doesn't have to care whether it is testing a
+        // bitcoind process without IPC support, or a bitcoin-node process with
+        // IPC support.
+        return MakeEcho();
+    }
     NodeContext& node() override { return m_node; };
     NodeContext m_node;
 };

src/rpc/misc.cpp

@@ -5,6 +5,8 @@
 
 #include <httpserver.h>
 #include <interfaces/chain.h>
+#include <interfaces/echo.h>
+#include <interfaces/init.h>
 #include <key_io.h>
 #include <node/context.h>
 #include <outputtype.h>
@@ -597,6 +599,24 @@ static UniValue echo(const JSONRPCRequest& request)
     return request.params;
 }
 
+static UniValue echoipc(const JSONRPCRequest& request)
+{
+    RPCHelpMan{
+        "echoipc",
+        "\nEcho back the input argument, passing it through a spawned process in a multiprocess build.\n"
+        "This command is for testing.\n",
+        {{"echo", RPCArg::Type::STR, RPCArg::Optional::NO, "The string to echo",}},
+        RPCResult{RPCResult::Type::STR, "echo", "The echoed string."},
+        RPCExamples{HelpExampleCli("echo", "\"Hello world\"") +
+                    HelpExampleRpc("echo", "\"Hello world\"")},
+    }.Check(request);
+
+    NodeContext* context = request.context.Has<NodeContext>() ? &request.context.Get<NodeContext>() : nullptr;
+    if (!context || !context->init) throw JSONRPCError(RPC_INTERNAL_ERROR, "IPC not available");
+    std::unique_ptr<interfaces::Echo> echo = context->init->makeEchoIpc();
+    return echo->echo(request.params[0].get_str());
+}
+
 void RegisterMiscRPCCommands(CRPCTable &t)
 {
 // clang-format off
@@ -617,6 +637,7 @@ static const CRPCCommand commands[] =
     { "hidden",             "mockscheduler",          &mockscheduler,          {"delta_time"}},
     { "hidden",             "echo",                   &echo,                   {"arg0","arg1","arg2","arg3","arg4","arg5","arg6","arg7","arg8","arg9"}},
     { "hidden",             "echojson",               &echo,                   {"arg0","arg1","arg2","arg3","arg4","arg5","arg6","arg7","arg8","arg9"}},
+    { "hidden",             "echoipc",                &echoipc,                {"arg"}},
 };
 // clang-format on
 

test/functional/rpc_misc.py

@@ -61,6 +61,7 @@ def run_test(self):
         node.logging(include=['qt'])
         assert_equal(node.logging()['qt'], True)
 
+        assert_equal(node.echoipc("hello"), "hello")
 
 if __name__ == '__main__':
     RpcMiscTest().main()