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_INTERFACES_IPC_H
 6  #define BITCOIN_INTERFACES_IPC_H
 7  
 8  #include <functional>
 9  #include <memory>
10  #include <string>
11  #include <typeindex>
12  
13  namespace ipc {
14  struct Context;
15  } // namespace ipc
16  
17  namespace interfaces {
18  class Init;
19  
20  //! Interface providing access to interprocess-communication (IPC)
21  //! functionality. The IPC implementation is responsible for establishing
22  //! connections between a controlling process and a process being controlled.
23  //! When a connection is established, the process being controlled returns an
24  //! interfaces::Init pointer to the controlling process, which the controlling
25  //! process can use to get access to other interfaces and functionality.
26  //!
27  //! When spawning a new process, the steps are:
28  //!
29  //! 1. The controlling process calls interfaces::Ipc::spawnProcess(), which
30  //!    calls ipc::Process::spawn(), which spawns a new process and returns a
31  //!    socketpair file descriptor for communicating with it.
32  //!    interfaces::Ipc::spawnProcess() then calls ipc::Protocol::connect()
33  //!    passing the socketpair descriptor, which returns a local proxy
34  //!    interfaces::Init implementation calling remote interfaces::Init methods.
35  //! 2. The spawned process calls interfaces::Ipc::startSpawnProcess(), which
36  //!    calls ipc::Process::checkSpawned() to read command line arguments and
37  //!    determine whether it is a spawned process and what socketpair file
38  //!    descriptor it should use. It then calls ipc::Protocol::serve() to handle
39  //!    incoming requests from the socketpair and invoke interfaces::Init
40  //!    interface methods, and exit when the socket is closed.
41  //! 3. The controlling process calls local proxy interfaces::Init object methods
42  //!    to make other proxy objects calling other remote interfaces. It can also
43  //!    destroy the initial interfaces::Init object to close the connection and
44  //!    shut down the spawned process.
45  //!
46  //! When connecting to an existing process, the steps are similar to spawning a
47  //! new process, except a socket is created instead of a socketpair, and
48  //! destroying an Init interface doesn't end the process, since there can be
49  //! multiple connections.
50  class Ipc
51  {
52  public:
53      virtual ~Ipc() = default;
54  
55      //! Spawn a child process returning pointer to its Init interface.
56      virtual std::unique_ptr<Init> spawnProcess(const char* exe_name) = 0;
57  
58      //! If this is a spawned process, block and handle requests from the parent
59      //! process by forwarding them to this process's Init interface, then return
60      //! true. If this is not a spawned child process, return false.
61      virtual bool startSpawnedProcess(int argc, char* argv[], int& exit_status) = 0;
62  
63      //! Connect to a socket address and return a pointer to its Init interface.
64      //! Returns a non-null pointer if the connection was established, returns
65      //! null if address is empty ("") or disabled ("0") or if a connection was
66      //! refused but not required ("auto"), and throws an exception if there was
67      //! an unexpected error.
68      virtual std::unique_ptr<Init> connectAddress(std::string& address) = 0;
69  
70      //! Listen on a socket address exposing this process's init interface to
71      //! clients. Throws an exception if there was an error.
72      virtual void listenAddress(std::string& address) = 0;
73  
74      //! Disconnect any incoming connections that are still connected.
75      virtual void disconnectIncoming() = 0;
76  
77      //! Add cleanup callback to remote interface that will run when the
78      //! interface is deleted.
79      template<typename Interface>
80      void addCleanup(Interface& iface, std::function<void()> cleanup)
81      {
82          addCleanup(typeid(Interface), &iface, std::move(cleanup));
83      }
84  
85      //! IPC context struct accessor (see struct definition for more description).
86      virtual ipc::Context& context() = 0;
87  
88  protected:
89      //! Internal implementation of public addCleanup method (above) as a
90      //! type-erased virtual function, since template functions can't be virtual.
91      virtual void addCleanup(std::type_index type, void* iface, std::function<void()> cleanup) = 0;
92  };
93  
94  //! Return implementation of Ipc interface.
95  std::unique_ptr<Ipc> MakeIpc(const char* exe_name, const char* process_argv0, Init& init);
96  } // namespace interfaces
97  
98  #endif // BITCOIN_INTERFACES_IPC_H