If you haven't, first read the guide to contributing. It contains important information about the library and how to contribute.

Blockchains, Coins and Tokens

• If you are interested in adding a new Token (e.g. ERC20): in this case no code changes are needed, see the Assets section.

• For new coins you need to implement address handling and signing functionality in wallet-core (described in this section). For new coins on already supported blockchains, or variations of already supported blockchains, please consider proper reuse of existing implementation.

Integration Criteria

The Trust Wallet development team is always striving to add more blockchains that will be essential for developers and wallet users. We choose blockchains carefully that will have the biggest impact for our community.

In general:

• The blockchain has launched mainnet and stably run at least 3 ~ 6 months without any major security incidents.

• The blockchain has extensive public documentation and tools available for developers to use.

• The native coin is listed in the top 30 coins on CoinMarketCap.

• The project needs to provide API/JSON-RPC access to the node with a load balancing setup for private use, see detail requirements here.

• The native coin is tradable on major exchanges.

After integrate into Trust Wallet, project should also provide timely support for any urgent matters.

Overview

Adding support for a new coin consists of these steps:

• Add coin definition -- contains basic parameters of the new coin, several definition source files are gneerated from the definitions

• Extend a few central files. There are a few central source files that need to be extended (some definitions, dispatching logic to coin implementations).

• C++ implementation of address handling and signing functionality. Optionally protobuf definitions might be needed for more complex parameters.

• Unit tests for coin definitions, and address and signing functionality

• C interface (basis for mobile integration)

• Java/JNI and Swift bindings -- these are generated

• Integration tests for testing through C interface, and through JN and Swift interfaces.

It helps to pick an existing coin, and refer to its implementation. Try to pick an existing coin that is similar to the new one, and check how/where is it implemented, tested, etc.

Note that unit tests are crucial in ensuring quality needed for multi-coin support. Functionality here can be well unit-tested, so don't ignore them. Coverage must not decrease! This is enforced automatically in the valiation of the pull requests.

Blockchain definitions

The first step to adding a blockchain is to define its configuration parameters. Add the definition to the coins.json file. Then run tools/generate-files to generate the C++ code from that. Add the corresponding definition to TWCoinType.h.

Skeleton

Scaffolding for a new coin is helped by a set of template files. Execute the command codegen/bin/newcoin <coinid>, where newcoin <coinid> is the ID of the new coin from coins.json. Check the generated files and their location. Usage of the templates is optional, but recommended.

Definition tests, first commit

Review tests in tests/X/TWCoinTypeTests.cpp (where X is the name of the blockchain), exactly as in other blockchains. Run the tests and make sure everything is passing before moving on to the next step. Create a commit with this change (don't create a pull request yet).

Note: don't forget to add new files to git. Note: don't forget to re-run cmake before building, to include new files in the build.

C++ Implementation

Implement the required functionality in C++. The code should be placed in the src/X folder where X is the name of the blockchain.

Don't just dump an existing codebase in the repo. The code needs to follow the code style and use existing hashing and cryptographic functionality if possible. Adding new dependencies is something we want to avoid at all costs. We want to keep the codebase and the binary library as small as possible.

If you do need to add a new cryptographic function or other building block please do so as a separate PR from the blockchain implementation.

Address encoding/decoding

The first step is to support the address format specific to the blockchain. Start with the generated source files src/X/Address.h and src/X/Address.cpp (where X is the blockchain name).

At minimum the address needs a string validation static method, a string constructor, a constructor from a public key, and a method to convert back to a string. Make sure you can parse a string representation of an address and detect invalid addresses. Write unit tests for this. Also make sure that you can derive an address string from a private key. Write unit tests for this as well.

For an example of this have a look at Cosmos Address.h and Address.cpp.

Make sure the dispatcher of address validation and derivation in src/Coin.cpp is also extended.

Transaction signing

The second step is supporting signing of transactions. Work on the src/X/Signer.h and src/X/Signer.cpp source files. Make sure you can generate a valid signature and a valid signed and encoded transaction. Write a unit tests for this.

For an example of this have a look at Binance's Signer.h and Signer.cpp.

Tests

The tests should be put in tests/X where X is the name of the blockchain. All C++ code needs to be unit tested.

The C++ implementation with tests should be the second commit.

C Interface

Once you are satisfied with your C++ implementation write a C interface for it. The C interface needs to be as small as possible so that clients don't need to worry about implementation details. If you are implementing blockchain Xxx create a TWXxxAddress.h to handle addresses associated to the blockchain and TWXxxSigner.h to handle transaction signing.

Please make sure you catch all C++ exceptions in C implementation.

Generate the idiomatic interface code by running tools/generate-files. If possible test the interface on Android, iOS and TypeScript. Optionally add integration test to each platform. This is required only if the interface is significantly different than the interface used for other blockchains.

The C interface, any Protobuf models, and integration tests should be third commit.

Blockchain checklist

The above steps are summarized below as a checklist:

• Coin Definition:

  • Add the coin definition to coins.json.

  • Execute tools/generate-files to generate coin-specific generated files.

  • Extend TWCoinType.h and TWBlockchain.h.

  • Extend src/Coin.cpp.

• Generate skeleton, using codegen/bin/newcoin <coinid>

  • Create tests in tests/X/TWCoinTypeTests.cpp.

• Implement functionality in C++. Put it in a subfolder of src/.

  • Address.

  • Transaction (if necessary).

  • Signer.

• Write unit tests. Put them in a subfolder of tests/.

  • Mnemonic phrase - > Address derivation test. Put this test in the CoinTests.cpp file.

  • Transaction signing tests, at least a mainnet transaction test.

  • Add stake, unstake, get rewards tests if the blockchain is PoS like.

• Add relevant constants in TWEthereumChainID, TWCurve, etc., as necessary.

• Write C interface header in include/TrustWalletCore and implement the interface in src/interface.

  • Address interface.

  • Signing interface.

• Validate generated code in Android an iOS projects. Write integration tests for each.

• Extend central derivation and validation tests: make sure the following tests are extended with the new coin: CoinAddressDerivationTests.cpp and CoinAddressValidationTests.cpp, TWHRPTests.cpp, CoinAddressDerivationTests.kt, CoinType+Address.swift, CoinAddressDerivationTests.swift.

• Upload coin icon to trustwallet/assets if necessary.

Bitcoin forks checklist

If you're adding a Bitcoin fork, you might not neeed to implement new Address or Signer class, please complete this checklist before you submit a pull request:

• Derive address according to definition in coins.json, p2pkh address for bip44 or native bech32 segwit address for bip84.

• Check SLIP-0132 :Registered HD version bytes.

• Check fee preference, use static fee or not, Trust will use fee that can be confirmed with in 2 blocks.

• Add tests to validate all possible addresses, p2pkh, p2sh and bech32.

• Add tests to derive xpub / xprv and cross check the values with other wallets, like ledger or trezor.

• Add tests to derive address from xpub at random index.

• Add tests to cover lock scripts for all addresses.

• Add tests to make sure transaction detail url in block explorer is correct.

• Add a mainnet transaction test, you can construct it by using wallet core and validate it by broadcasting it.