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       1              : // Copyright (c) 2021-present 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_IPC_PROTOCOL_H
       6              : #define BITCOIN_IPC_PROTOCOL_H
       7              : 
       8              : #include <interfaces/init.h>
       9              : #include <ipc/util.h>
      10              : 
      11              : #include <functional>
      12              : #include <memory>
      13              : #include <typeindex>
      14              : 
      15              : namespace ipc {
      16              : struct Context;
      17              : 
      18              : //! IPC protocol interface for calling IPC methods over sockets.
      19              : //!
      20              : //! There may be different implementations of this interface for different IPC
      21              : //! protocols (e.g. Cap'n Proto, gRPC, JSON-RPC, or custom protocols).
      22            2 : class Protocol
      23              : {
      24              : public:
      25            2 :     virtual ~Protocol() = default;
      26              : 
      27              :     //! Return Init interface that forwards requests over given connection
      28              :     //! stream. Socket communication is handled on a background thread.
      29              :     //!
      30              :     //! @note It could be potentially useful in the future to add
      31              :     //! std::function<void()> on_disconnect callback argument here. But there
      32              :     //! isn't an immediate need, because the protocol implementation can clean
      33              :     //! up its own state (calling ProxyServer destructors, etc) on disconnect,
      34              :     //! and any client calls will just throw ipc::Exception errors after a
      35              :     //! disconnect.
      36              :     virtual std::unique_ptr<interfaces::Init> connect(mp::Stream stream) = 0;
      37              : 
      38              :     //! Listen for connections on provided socket id, accept them, and handle
      39              :     //! requests on accepted connections. This method doesn't block, and
      40              :     //! performs I/O on a background thread.
      41              :     virtual void listen(mp::SocketId listen_fd, interfaces::Init& init) = 0;
      42              : 
      43              :     //! Handle requests from a stream provided by the make_stream callback,
      44              :     //! forwarding them to the provided Init interface. Socket communication is
      45              :     //! handled on the current thread, and this call blocks until the socket is
      46              :     //! closed. A callback is used to specify the stream because this method
      47              :     //! initializes the event loop and it may not be possible to create the
      48              :     //! stream before the event loop is initialized.
      49              :     //!
      50              :     //! @note: If this method is called, it needs to be called before connect()
      51              :     //! or listen() methods, because for ease of implementation this method is
      52              :     //! inflexible and always runs the event loop in the foreground thread. It
      53              :     //! can share its event loop with the other methods but can't share an event
      54              :     //! loop that was created by them. This isn't a problem because serve() is
      55              :     //! only called by spawned child processes that call it immediately to
      56              :     //! communicate back with parent processes.
      57              :     virtual void serve(interfaces::Init& init, const std::function<mp::Stream()>& make_stream) = 0;
      58              : 
      59              :     //! Make stream object from socket id.
      60              :     virtual mp::Stream makeStream(mp::SocketId socket) = 0;
      61              : 
      62              :     //! Disconnect any incoming connections that are still connected.
      63              :     virtual void disconnectIncoming() = 0;
      64              : 
      65              :     //! Add cleanup callback to interface that will run when the interface is
      66              :     //! deleted.
      67              :     virtual void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) = 0;
      68              : 
      69              :     //! Context accessor.
      70              :     virtual Context& context() = 0;
      71              : };
      72              : } // namespace ipc
      73              : 
      74              : #endif // BITCOIN_IPC_PROTOCOL_H