// 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_IPC_H

#define BITCOIN_INTERFACES_IPC_H

#include <functional>

#include <memory>

#include <typeindex>

namespace ipc {

struct Context;

} // namespace ipc

namespace interfaces {

class Init;

//! Interface providing access to interprocess-communication (IPC)

//! functionality. The IPC implementation is responsible for establishing

//! connections between a controlling process and a process being controlled.

//! When a connection is established, the process being controlled returns an

//! interfaces::Init pointer to the controlling process, which the controlling

//! process can use to get access to other interfaces and functionality.

//!

//! When spawning a new process, the steps are:

//!

//! 1. The controlling process calls interfaces::Ipc::spawnProcess(), which

//!    calls ipc::Process::spawn(), which spawns a new process and returns a

//!    socketpair file descriptor for communicating with it.

//!    interfaces::Ipc::spawnProcess() then calls ipc::Protocol::connect()

//!    passing the socketpair descriptor, which returns a local proxy

//!    interfaces::Init implementation calling remote interfaces::Init methods.

//! 2. The spawned process calls interfaces::Ipc::startSpawnProcess(), which

//!    calls ipc::Process::checkSpawned() to read command line arguments and

//!    determine whether it is a spawned process and what socketpair file

//!    descriptor it should use. It then calls ipc::Protocol::serve() to handle

//!    incoming requests from the socketpair and invoke interfaces::Init

//!    interface methods, and exit when the socket is closed.

//! 3. The controlling process calls local proxy interfaces::Init object methods

//!    to make other proxy objects calling other remote interfaces. It can also

//!    destroy the initial interfaces::Init object to close the connection and

//!    shut down the spawned process.

//!

//! When connecting to an existing process, the steps are similar to spawning a

//! new process, except a socket is created instead of a socketpair, and

//! destroying an Init interface doesn't end the process, since there can be

//! multiple connections.

class Ipc

{

public:

    virtual ~Ipc() = default;

    //! Spawn a child process returning pointer to its Init interface.

    virtual std::unique_ptr<Init> spawnProcess(const char* exe_name) = 0;

    //! If this is a spawned process, block and handle requests from the parent

    //! process by forwarding them to this process's Init interface, then return

    //! true. If this is not a spawned child process, return false.

    virtual bool startSpawnedProcess(int argc, char* argv[], int& exit_status) = 0;

    //! Connect to a socket address and make a client interface proxy object

    //! using provided callback. connectAddress returns an interface pointer if

    //! the connection was established, returns null if address is empty ("") or

    //! disabled ("0") or if a connection was refused but not required ("auto"),

    //! and throws an exception if there was an unexpected error.

    virtual std::unique_ptr<Init> connectAddress(std::string& address) = 0;

    //! Connect to a socket address and make a client interface proxy object

    //! using provided callback. Throws an exception if there was an error.

    virtual void listenAddress(std::string& address) = 0;

    //! Add cleanup callback to remote interface that will run when the

    //! interface is deleted.

    template<typename Interface>

    void addCleanup(Interface& iface, std::function<void()> cleanup)

    {

        addCleanup(typeid(Interface), &iface, std::move(cleanup));

    }

    //! IPC context struct accessor (see struct definition for more description).

    virtual ipc::Context& context() = 0;

protected:

    //! Internal implementation of public addCleanup method (above) as a

    //! type-erased virtual function, since template functions can't be virtual.

    virtual void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) = 0;

};

//! Return implementation of Ipc interface.

std::unique_ptr<Ipc> MakeIpc(const char* exe_name, const char* process_argv0, Init& init);

} // namespace interfaces

#endif // BITCOIN_INTERFACES_IPC_H