bitcoinj/designdocs/modular-architecture.md

Migration to a more modular bitcoinj architecture

Note: Packages that are not significant or are not changing are not shown (and are generally expected to remain in the core module/JAR).

Legend: Dashed lines represent Gradle "implementation" dependencies. Solid lines represent Gradle "api" dependencies (or internal package dependencies.)

bitcoinj 0.16.x (previous release)

flowchart TD
    E[examples] --> CORE
    T[tools] --> CORE
    FX[wallettemplate] --> CORE
    subgraph CORE [bitcoinj-core]
        W[o.b.wallet] --> CO
        W --> CR
        CO[o.b.core] --> CR
        CO --> W
        CR[o.b.crypto] --> CO
        CR --> W
    end
    CORE --> G[Guava]
    CORE --> BC[Bouncy Castle]
    CORE --> P[ProtoBuf]
    CORE .-> S[slf4j]
    CORE .-> A[jcip-annotations]

classDef external fill:#999;
class G,S,A,BC,P external;

bitcoinj 0.17

In release 0.17 there has been a large amount of refactoring to prepare the o.b.base and o.b.crypto packages to become independent modules/JARs in the following release. Those packages will still contain some deprecated methods that depend on other internal packages and external modules. Those deprecated methods will be removed in release 0.18 when o.b.base and o.b.crypto are moved to their own modules.

flowchart TD
    E[examples] --> CORE
    IT[integration-test] --> CORE
    T[tools] --> CORE
    FX[wallettemplate] --> CORE
    WT[wallettool] --> CORE
    subgraph CORE [bitcoinj-core]
        W[o.b.wallet] --> CO[o.b.core]
        CO --> W
        W --> CR
        CO --> CR
        CO --> B[o.b.base]
        CR[o.b.crypto] --> B
    end
    CORE --> G[Guava]
    CORE --> P[ProtoBuf]
    CORE --> BC[Bouncy Castle]
    CORE .-> S[slf4j]
    CORE .-> A[jcip-annotations]

classDef external fill:#999;
class G,S,A,BC,P external;

bitcoinj 0.18 (current plan)

In this release the bitcoinj-base module will be a standalone module with minimal external dependencies. All use of Elliptic Curve Cryptography will be factored out to use the secp-api module from secp256k1-jdk with API implementations provided for Bouncy Castle and (hopefully) the secp256k1 native ('C') library.

flowchart TD
    EJ[examples] --> CORE
    EK[examples-kotlin] --> CORE
    IT[integration-test] --> CORE
    T[tools] --> CORE
    FX[wallettemplate] --> CORE
    WT[wallettool] --> CORE
    subgraph CORE [bitcoinj-core]
        CO --> W
        W[o.b.wallet] --> CO[o.b.core]
        W --> CR[o.b.crypto]
        CO --> CR
    end
    CORE --> BASE
    subgraph BASE [bitcoinj-base]
        B[o.b.base]
    end
    CORE --> SECP[secp-api]
    SECP .-> SECPBC[secp-bouncy]
    SECP .-> SECPFFM[secp-ffm]
    SECPBC --> BC[Bouncy Castle]
    SECPFFM --> SECPC[libsecp256k1]
    CORE --> P[ProtoBuf]
    CORE .-> S[slf4j]
    CORE .-> JS[JSpecify]

classDef external fill:#999;
class G,S,JS,BC,SECPC,P external;

bitcoinj 0.19 (proposed)

In a proposed 0.19 release, we hope to do the following:

1. Separate the current ProtoBuf-based wallet implementation into it's own module. This will require creating a Wallet interface in core.
2. Eliminate dependencies on Guava for all modules.

Stretch goal:

3. Alternate wallet implementation, perhaps using SQLite.

flowchart TD
    E[examples] --> WALLET
    EK[examples-kotlin] --> WALLET
    IT[integration-test] --> WALLET
    T[tools] --> WALLET
    FX[wallettemplate] --> WALLET
    WT[wallettool] --> WALLET
    subgraph WALLET [bitcoinj-wallet-protobuf]
        W[o.b.wallet]
    end
    WALLET --> CORE
    WALLET --> P[ProtoBuf]
    subgraph CORE [bitcoinj-core]
        CO[o.b.core] --> CR[o.b.crypto]
    end
    CORE --> BASE
    CORE .-> S[slf4j]
    CORE .-> JS[JSpecify]
    CORE --> SECP
    SECP[secp-api] .-> SECPFFM[secp-ffm]
    SECP .-> SECPBOUNCY[secp-bouncy]
    SECPBOUNCY .-> BC[Bouncy Castle]
    SECPFFM .-> LP[libsecp256k1]
    subgraph BASE [bitcoinj-base]
        B[o.b.base]
    end

classDef external fill:#999;
class G,S,JS,BC,LP,P external;