IBC#004: The NodeContext structure

Variables and parameters for the application

Hi everyone! Welcome to the 4th episode of Inside Bitcoin Code!

As we discussed in IBC#003, a NodeContext object is instantiated in the main() function. Let’s find it out what it is and what is needed for inside Bitcoin Core.

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NodeContext: What is it?

A NodeContext object contains references to the chain state and the connection state. This object is needed in order to avoid multiple declaration of the same variables and parameters, thus making it possible to access them from different parts of the code.

It is defined as a struct (a similar concept to classes¹) containing a collection of references.

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NodeContext: The structure

Here, the complete NodeContext structure is reported:

struct NodeContext {
    //! libbitcoin_kernel context
    std::unique_ptr<kernel::Context> kernel;
    //! Init interface for initializing current process and connecting to other processes.
    interfaces::Init* init{nullptr};
    std::unique_ptr<AddrMan> addrman;
    std::unique_ptr<CConnman> connman;
    std::unique_ptr<CTxMemPool> mempool;
    std::unique_ptr<const NetGroupManager> netgroupman;
    std::unique_ptr<CBlockPolicyEstimator> fee_estimator;
    std::unique_ptr<PeerManager> peerman;
    std::unique_ptr<ChainstateManager> chainman;
    std::unique_ptr<BanMan> banman;
    ArgsManager* args{nullptr}; // Currently a raw pointer because the memory is not managed by this struct
    std::unique_ptr<interfaces::Chain> chain;
    //! List of all chain clients (wallet processes or other client) connected to node.
    std::vector<std::unique_ptr<interfaces::ChainClient>> chain_clients;
    //! Reference to chain client that should used to load or create wallets
    //! opened by the gui.
    interfaces::WalletLoader* wallet_loader{nullptr};
    std::unique_ptr<CScheduler> scheduler;
    std::function<void()> rpc_interruption_point = [] {};
    std::unique_ptr<KernelNotifications> notifications;

    //! Declare default constructor and destructor that are not inline, so code
    //! instantiating the NodeContext struct doesn't need to #include class
    //! definitions for all the unique_ptr members.
    NodeContext();
    ~NodeContext();
};

As it can be noted, all the members of this struct are defined as pointers², both raw and smart (we will talk about them in Learn2Code soon).

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NodeContext: Step-by-step

Let’s look at the structure in detail:

• Structure holding the kernel library’s logically global state

  std::unique_ptr<kernel::Context> kernel;

• Raw pointer to the interface initialization; initializes the current process and connects to other process.

  interfaces::Init* init{nullptr};

• Address manager

  std::unique_ptr<AddrMan> addrman;

• Connection manager

  std::unique_ptr<CConnman> connman;

• Mempool

  std::unique_ptr<CTxMemPool> mempool;

• Network group manager

  std::unique_ptr<const NetGroupManager> netgroupman;

• Fee-rate estimator

  std::unique_ptr<CBlockPolicyEstimator> fee_estimator;

• Connection manager between peer nodes

  std::unique_ptr<PeerManager> peerman;

• Interface for creating and interacting with one or two chain states

  std::unique_ptr<ChainstateManager> chainman;

• Ban manager, manages banned peers

  std::unique_ptr<BanMan> banman;

• Command line arguments validation and interpretation

  ArgsManager* args{nullptr};

• Interface to give clients ability to access the chain state

  std::unique_ptr<interfaces::Chain> chain;

• List of all chain clients (i.e. wallets) connected to the node

  std::vector<std::unique_ptr<interfaces::ChainClient>> chain_clients;

• Reference used to create or load wallets

  interfaces::WalletLoader* wallet_loader{nullptr};

• Class for background tasks

  std::unique_ptr<CScheduler> scheduler;

• Functions that calls an error if RPC is not running

  std::function<void()> rpc_interruption_point = [] {};

• Manages notifications from the kernel

  std::unique_ptr<KernelNotifications> notifications;

• Default constructor and destructor for the NodeContext structure

  NodeContext();
  ~NodeContext();

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Aaaaand we are done for today!

Thank you for reading Inside Bitcoin Code! If you have any suggestion, question or request leave a comment.

See you next week!

1. Coding#103

2. Pointers