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       1                 :            : // Copyright (c) 2021 The Bitcoin Core developers
       2                 :            : // Distributed under the MIT software license, see the accompanying
       3                 :            : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4                 :            : 
       5                 :            : #ifndef BITCOIN_INTERFACES_IPC_H
       6                 :            : #define BITCOIN_INTERFACES_IPC_H
       7                 :            : 
       8                 :            : #include <functional>
       9                 :            : #include <memory>
      10                 :            : #include <typeindex>
      11                 :            : 
      12                 :            : namespace ipc {
      13                 :            : struct Context;
      14                 :            : } // namespace ipc
      15                 :            : 
      16                 :            : namespace interfaces {
      17                 :            : class Init;
      18                 :            : 
      19                 :            : //! Interface providing access to interprocess-communication (IPC)
      20                 :            : //! functionality. The IPC implementation is responsible for establishing
      21                 :            : //! connections between a controlling process and a process being controlled.
      22                 :            : //! When a connection is established, the process being controlled returns an
      23                 :            : //! interfaces::Init pointer to the controlling process, which the controlling
      24                 :            : //! process can use to get access to other interfaces and functionality.
      25                 :            : //!
      26                 :            : //! When spawning a new process, the steps are:
      27                 :            : //!
      28                 :            : //! 1. The controlling process calls interfaces::Ipc::spawnProcess(), which
      29                 :            : //!    calls ipc::Process::spawn(), which spawns a new process and returns a
      30                 :            : //!    socketpair file descriptor for communicating with it.
      31                 :            : //!    interfaces::Ipc::spawnProcess() then calls ipc::Protocol::connect()
      32                 :            : //!    passing the socketpair descriptor, which returns a local proxy
      33                 :            : //!    interfaces::Init implementation calling remote interfaces::Init methods.
      34                 :            : //! 2. The spawned process calls interfaces::Ipc::startSpawnProcess(), which
      35                 :            : //!    calls ipc::Process::checkSpawned() to read command line arguments and
      36                 :            : //!    determine whether it is a spawned process and what socketpair file
      37                 :            : //!    descriptor it should use. It then calls ipc::Protocol::serve() to handle
      38                 :            : //!    incoming requests from the socketpair and invoke interfaces::Init
      39                 :            : //!    interface methods, and exit when the socket is closed.
      40                 :            : //! 3. The controlling process calls local proxy interfaces::Init object methods
      41                 :            : //!    to make other proxy objects calling other remote interfaces. It can also
      42                 :            : //!    destroy the initial interfaces::Init object to close the connection and
      43                 :            : //!    shut down the spawned process.
      44                 :            : class Ipc
      45                 :            : {
      46                 :            : public:
      47                 :            :     virtual ~Ipc() = default;
      48                 :            : 
      49                 :            :     //! Spawn a child process returning pointer to its Init interface.
      50                 :            :     virtual std::unique_ptr<Init> spawnProcess(const char* exe_name) = 0;
      51                 :            : 
      52                 :            :     //! If this is a spawned process, block and handle requests from the parent
      53                 :            :     //! process by forwarding them to this process's Init interface, then return
      54                 :            :     //! true. If this is not a spawned child process, return false.
      55                 :            :     virtual bool startSpawnedProcess(int argc, char* argv[], int& exit_status) = 0;
      56                 :            : 
      57                 :            :     //! Add cleanup callback to remote interface that will run when the
      58                 :            :     //! interface is deleted.
      59                 :            :     template<typename Interface>
      60                 :          0 :     void addCleanup(Interface& iface, std::function<void()> cleanup)
      61                 :            :     {
      62         [ #  # ]:          0 :         addCleanup(typeid(Interface), &iface, std::move(cleanup));
      63                 :          0 :     }
      64                 :            : 
      65                 :            :     //! IPC context struct accessor (see struct definition for more description).
      66                 :            :     virtual ipc::Context& context() = 0;
      67                 :            : 
      68                 :            : protected:
      69                 :            :     //! Internal implementation of public addCleanup method (above) as a
      70                 :            :     //! type-erased virtual function, since template functions can't be virtual.
      71                 :            :     virtual void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) = 0;
      72                 :            : };
      73                 :            : 
      74                 :            : //! Return implementation of Ipc interface.
      75                 :            : std::unique_ptr<Ipc> MakeIpc(const char* exe_name, const char* process_argv0, Init& init);
      76                 :            : } // namespace interfaces
      77                 :            : 
      78                 :            : #endif // BITCOIN_INTERFACES_IPC_H