library-structure.adoc

Library structure

Bitcoin Core compilation outputs a number of libraries, some which are designed to be used internally, and some which are designed to be re-used by external applications. The internally-used libraries generally have unstable APIs making them unsuitable for re-use, but libbitcoin_consensus and libbitcoin_kernel are designed to be re-used by external applications.

Bitcoin Core has a guide which describes the various libraries, their conventions, and their various dependencies. The dependency graph is shown below for convenience, but may not be up-to-date with the Bitcoin Core document.

Bitcoin library dependency graph

flowchart TB
    bitcoin-wallet --> libbitcoin_wallet_tool
    bitcoin-wallet --> libbitcoin_wallet

    bitcoin-qt ---> libbitcoin_wallet
    bitcoin-qt ---> libbitcoinqt
    bitcoin-qt ---> libbitcoin_node

    bitcoind ---> libbitcoin_wallet
    bitcoind --> libbitcoin_node

    bitcoin-cli ---> libbitcoin-cli

    libbitcoin_wallet_tool --> libbitcoin_wallet
    libbitcoin_wallet_tool --> libbitcoin_util

    libbitcoin-cli --> libbitcoin_common
    libbitcoin-cli --> libbitcoin_util

    libbitcoin_node --> libbitcoin_common
    libbitcoin_node --> libbitcoin_consensus
    libbitcoin_node --> libbitcoin_kernel
    libbitcoin_node --> libbitcoin_util

    libbitcoinqt --> libbitcoin_util
    libbitcoinqt --> libbitcoin_common

    libbitcoin_wallet --> libbitcoin_util
    libbitcoin_wallet --> libbitcoin_common

    libbitcoin_common --> libbitcoin_util
    libbitcoin_common --> libbitcoin_consensus

    libbitcoin_kernel --> libbitcoin_consensus
    libbitcoin_kernel --> libbitcoin_util

    classDef types fill:green,color:white,stroke:green;
    class bitcoin-wallet,bitcoind,bitcoin-cli,bitcoin-qt types

It follows that API changes to the libraries which are internally-facing can be done slightly easier than for libraries with externally-facing APIs, for which more care for compatibility must be taken.