This repo is built and maintained by the Galoy team. We welcome and appreciate new contributions and encourage you to check out the repo and join our community to get started.
To help get you started, we will explain a bit about how we've laid out the code here and some of the practices we use. Our layout details fall mostly into two categories:
This codebase is implemented using a well-typed approach where we rely on Typescript for catching & enforcing certain kinds of checks we would like to perform.
This approach helps to strenghthen guarantees that bugs/issues don't get to runtime unhandled if our types are implemented properly.
We define all our types in declaration files (*.d.ts) where typescript automatically adds any types to the context without needing to explicitly import. Declaration files have limitations on what can be imported & instantiated within them, so in the few cases where types derive from instances of things we would usually have to use special tricks to derive them.
The majority of our types are defined in the domain layer (see Architecture section below). We generally create types for the following scenarios:
These are unique types that are alternatives to generically typing things as Typescript's primitive types (e.g. string, number, boolean). Doing this helps us to add context to primitive types that we pass around and it allows the type checked to distinguish between different kinds of primitives throughout the code.
For example, an onchain address and a lightning network payment request are both strings, but they aren't interchangeable as a data type. Instead of using string type for these types we would define as follows using a "unique symbol":
type EncodedPaymentRequest = string & { readonly brand: unique symbol }
type OnChainAddress = string & { readonly brand: unique symbol }
These are types mostly used in function signature type definitions. They derive from implemented error classes and need to be imported in a special way to their type declaration file.
For example, an error may be defined in a module's error.ts file like this:
export class LightningError extends DomainError {
name = this.constructor.name
}
and then it is imported to its index.types.d.ts declaration file and made into a type like this:
type LightningError = import("./errors").LightningError
In the places where we would like to work with types defined in imported libraries, we have two options. When we would like to use them directly, we can simply import them. If we would like to re-use a type to create our own types, we would re-import to get those types into our declaration files.
For example, for a result type from the lightning library, we would import and re-use it like:
type GetPaymentResult = import("lightning").GetPaymentResult
type RawPaths = NonNullable<GetPaymentResult["payment"]>["paths"]
In this example, we need the type definition for the payment.paths property of the GetPaymentResult type from the library that we otherwise would not have direct access to.
Whenever we implement a new function, the argument and return types are assigned at the point of the function's implementation.
For example:
const myFunction = async (myArg: MyArg): Promise<ThingResult> => {
return doThing(myArg)
}
const myOtherFunction = async ({
myFirstArg,
mySecondArg,
}: {
myFirstArg: MyFirstArg
mySecondArg: MySecondArg
}): Promise<ThingResult> => {
return doThing(myFirstArg, mySecondArg)
}In cases where the function has a complex set of arguments, the argument type can be defined in a declaration file and then assigned at the point of function implementation.
// in '.d.ts' file
type MyFuncArgs = {
myFirstArg: MyFirstArg
mySecondArg: MySecondArg
}
// in other file
const myFunction = async ({
myFirstArg,
mySecondArg,
}: MyFuncArgs): Promise<ThingResult> => {
return doThing(myFirstArg, mySecondArg)
}We use functional constructors to define certain types of objects that we can call method on. The intention here is to instantiate the object first and then call methods on that object with method-specific args to execute some functionality.
For objects like these, the interface for the object is defined using a type declaration and methods are typed at this point.
For example, our fee calculator is typed as follows:
// In '.d.ts' file
type DepositFeeCalculator = {
onChainDepositFee({ amount, ratio }: onChainDepositFeeArgs): Satoshis
lnDepositFee(): Satoshis
}
// In implementation file
export const DepositFeeCalculator = (): DepositFeeCalculator => {
const onChainDepositFee = ({ amount, ratio }: onChainDepositFeeArgs) => {
return toSats(Math.round(amount * ratio))
}
return {
onChainDepositFee,
lnDepositFee: () => toSats(0),
}
}Note that the top-level function arguments (for DepositFeeCalculator) would still be typed at the point of implementation like with any other function, and it is only the method signatures that are included in declaration files.
We use the interface keyword to define objects with methods that are intended to be implemented outside of the domain. This most often happens with service implementations like our ILightningService interface that gets implemented as the LndService function.
Everything else about how we go about typing and implementing things with the interface keyword is the same as with how we handle "objects with methods" in our domain as described above.
Typescript's enum keyword has drawbacks that don't fully meet our typing needs. To get around this, we use the trick where we define our intended enum as a standard object and then import it into our type declarations.
For example:
// In implementation file
export const AccountStatus = {
Locked: "locked",
Active: "active",
} as const
// In declaration file
type AccountStatus =
typeof import("./index").AccountStatus[keyof typeof import("./index").AccountStatus]We use hexagonal architecture pattern (context).
Code goes into one of four layers:
- Domain layer (
./src/domain) - Services layer (
./src/services) - Application layer (
./src/app) - Application Access layer (
./src/servers)
Defines the models and business logic with related interfaces.
- Define all data types
- Implement operations on the data types that depends on conditionals or data transformations
- Define interfaces of external services
- Internal: None
- External: only utility libraries but must be as clean as possible
Implements all the adapters (specific implementations of the interfaces defined in domain layer) that use external services/resources
- Implement interfaces defined in domain layer
- Access to external resources (database, redis, bitcoind, lnd)
- Consumption of external services/APIs (twilio, geetest, price, hedging)
- Internal: Domain Layer
- External: all required dependencies
Implements the API of our solution, i.e. will be the access point for components/servers in the access application layer.
- Implement application logic
- Wallet methods (pay, getTransactions, …)
- Internal: Domain Layer. Keep in mind that access to services implementation must be through “indirect access”, i.e. the access application layer or the wiring up code/layer must create/inject them. (AR
TODO: double-check this) - External: only utility libraries that do not go against domain layer definition (Ex: lodash)
Responsible for wiring up the other layers and/or exposing the application to external clients or consumers.
This layer will have the entry points used by the infrastructure (pods).
- Entrypoint for the various use-case methods defined in the Application layer
- Cron jobs
- Http servers: Middleware related logic (JWT, graphql, …)
- Triggers
- Internal: Domain Layer, Application Layer and Services Layer. (AR
TODO: Confirm that this is not just Application layer) - External: all required dependencies required to expose the application (expressjs, apollo server, …)
Notes on our instrumentation approach and how this is reflected in the codebase.