Contributing

We want to make Trust Wallet Core as good as it can be. If you want to contribute your help is greatly appreciated. Contributing is also a great way to learn more about blockchain technology and improve Trust Wallet. To make the process as smooth as possible please read this document and follow our guidelines. We are happy to review your code but please ensure that you have a clean pull request.

Wallet Core implements the cryptographic functionality of blockchains. This includes elliptic curve cryptography, hashing, address derivation and transaction signing. However it does not implement other aspects like networking and UI. Wallet core behaves like a black box for higher level users like Trust Wallet; it takes inputs from the blockchain and the user (for instance UTXOs, private keys, etc.) and produces an output (like a signed and encoded transaction). Keep this in mind when adding functionality.

This is a diagram representing how Trust Wallet interacts with Trust Wallet Core.

Library Design Guidelines

This library is designed so that it can be used from any other programming languages, and that every language has an idiomatic interface. Design goals also include minimizing the binary size and maximizing performance.

With these goals in mind we chose C/C++ for the implementation and a strict subset of C for the interface. This C interface is used to generate the idiomatic interfaces for every supported language. To augment the expressivity of the interface we also use Protocol Buffer objects that get serialized across the interface.

Keep this in mind when adding to the library:

  • Only expose C headers. Clients should not have access to the C++ interfaces.

  • C headers need to have annotations for the code generation tool, see below.

  • Use Protocol Buffers to represent models. C doesn't have good abstractions for variable-sized types.

  • Every time you modify the interface run the code generation tool and make sure the interface also makes sense in target languages.

There is a Sourcetrail project file might help you explore all the code (after build and run bootstrap.sh).

Pull Requests

Please follow these instructions when submitting a pull request (PR):

  • Create a personal fork of the project on GitHub.

  • Clone the fork on your local machine. Your remote repo on Github is called origin.

  • Add the official repository as a remote called upstream.

  • If you created your fork a while ago be sure to pull upstream changes into your local repository.

  • Create a new branch to work on! Branch from the latest upstream/master.

  • Implement/fix your feature, comment your code.

  • Write or adapt tests as needed.

  • Follow the code style of the project, including indentation. Use clang-format if you are unsure.

  • Run the tests.

  • Modify your commit history so that it tells a story using git's interactive rebase. Create a new branch if necessary.

  • Write your commit messages in the present tense. Your commit message should describe what the commit, when applied, does to the code, not what you did to the code.

  • Push your branch to your fork on Github, the remote origin.

  • From your fork open a pull request in the correct branch. Target the project's master branch.

  • If we request further changes push them to your branch. The PR will be updated automatically.

  • Once the pull request is approved and merged you can pull the changes from upstream to your local repo and delete

    your extra branch(es).

Is it not uncommon for a PR to accumulate commits and merges with time. The library is in constant change. If your PR falls out of sync with the upstream master you need to rebase. We can't reliably review code that is spread over too many other changes to the codebase. Please use git's interactive rebase and if necessary create a new PR.

Project organization

This project has a number of different pieces. Each piece lives in its own subfolder.

  • The docs folder contains documentation.

  • The src folder contains the C++ implementation of the core functionality.

  • The include folder contains the public C header files used to expose a cross-platform interface.

  • The codegen folder contains the code and templates used to generate code for different platforms and languages.

  • The jni folder contains the generated JNI interface and Java classes.

  • The android folder contains the Android Studio project and integration tests.

  • The swift folder contains the generated Swift code and Xcode project.

  • The trezor-crypto folder contains a fork of https://github.com/trezor/trezor-crypto/ with modifications.

  • The tests folder contains unit tests.

  • The tools folder contains scripts to automate common tasks.

  • The samples folder contains sample applications.

Prerequisites and Building

Please refer to build instructions for building the library locally.

Testing

After running bootstrap.sh run make -C build tests && build/tests/tests tests to run all the C++ unit tests. To run integration tests on each platform run the respective script in the tools folder:

  • Android: run tools/android-test or import android folder to Android Studio

  • iOS: run tools/ios-test or cd swift folder and open TrustWalletCore.xcworkspace

To run all tests in one go use the tools/tests script.

C Headers

The wallet core code generator parses C headers for class and struct definitions. Headers need to be in the include/TrustWalletCode folder and start with the TW prefix followed by the class or sturct name. Inside each header file there needs to be exactly one class or struct defition.

A class definition starts with the TW_EXPORT_CLASS macro followed by a forward-declared struct. For example:

TW_EXPORT_CLASS
struct TWPrivateKey;

Similarly, a struct definition start with the TW_EXPORT_STRUCT macro followed by an inline-declared struct. For example:

TW_EXPORT_STRUCT
struct TWPublicKey {
    uint8_t bytes[TWPublicKeyUncompressedSize];
};

You can also define enumerations using the TW_EXPORT_ENUM() macro:

TW_EXPORT_ENUM(uint32_t)
enum TWCoinType {
    TWCoinTypeBitcoin = 0,
};

After the class or struct definition you can declare as many methods and properties as necessary. There are four types of declarations: static method, static property, method, and property. Each is declared by TW_EXPORT_STATIC_METHOD, TW_EXPORT_STATIC_PROPERTY, TW_EXPORT_METHOD, and TW_EXPORT_PROPERTY respectively. Each method or property name needs to start with the type name. For instance TWPublicKeyIsValid gets translated to the isValid property in the PublicKey type.

The types that methods can take and return are restricted to: bool, int, size_t, uint8_t, uint16_t, uint32_t, uint64_t, TWData, TWString, and any defined classses, structs or enums.

Methods always take the type as their first argument. The type needs to be a pointer if the type is a class and a struct if the type is a struct. Properties need to take the type as its only argument.

Static property declarations can take no arguments. Static methods can take any arguments.

Since C interface doesn't know how to handle C++ exception, we should catch all possible exceptions in the C implementation.

Coin definition

The wallet core code generator also parses coin configuration defined in registry.json, the generated code will be located at src/Generated/Coins.cpp. See the documentation of the fields here: https://github.com/trustwallet/wallet-core/blob/master/docs/registry-fields.md.

Example:

{
  "id": "bitcoin",
  "name": "Bitcoin",
  "coinId": 0,
  "symbol": "BTC",
  "decimals": 8,
  "blockchain": "Bitcoin",
  "derivation": [
    {
      "name": "segwit",
      "path": "m/84'/0'/0'/0/0",
      "xpub": "zpub",
      "xprv": "zprv"
    },
    {
      "name": "legacy",
      "path": "m/44'/0'/0'/0/0",
      "xpub": "xpub",
      "xprv": "xprv"
    }
  ],
  "curve": "secp256k1",
  "publicKeyType": "secp256k1",
  "p2pkhPrefix": 0,
  "p2shPrefix": 5,
  "hrp": "bc",
  "publicKeyHasher": "sha256ripemd",
  "base58Hasher": "sha256d",
  "explorer": {
    "url": "https://blockchair.com",
    "txPath": "/bitcoin/transaction/",
    "accountPath": "/bitcoin/address/",
    "sampleTx": "0607f62530b68cfcc91c57a1702841dd399a899d0eecda8e31ecca3f52f01df2",
    "sampleAccount": "17A16QmavnUfCW11DAApiJxp7ARnxN5pGX"
  },
  "info": {
    "url": "https://bitcoin.org",
    "source": "https://github.com/trezor/blockbook",
    "rpc": "",
    "documentation": "https://github.com/trezor/blockbook/blob/master/docs/api.md"
  }
}

Protocol Buffers

Since the C language doesn't provide good abstractions for variable-sized arrays and strings, the C interface uses Protocol Buffers. All models are defined in the src/proto folder. These models can then be used in the C interface by using the proto model name with underscores. For instance TW_Binance_Proto_SigningInput.

The proto file will be used to generate C++ classes and also classes in each supported client language (Swift, Java, etc.). The code generator will also generate the protobuf serialization code so that library clients don't have to worry about serialization. To generate the Protocol Buffers code run the tools/generate-files script when you modify the src/TrustWalletCore.proto file.

Code Style

Wallet core follows the LLVM Coding Standards for C++. We use clang-format to ensure a consistent code sytle. Do not reformat files that you didn't modify, or the header files in the include folder. You can install a clang-format extension for your IDE.

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