npm package: @ganache/flavor
Description: Ganache's flavors enumeration and TypeScript types
Author: David Murdoch
Latest version: 0.10.2

# `@ganache/flavor`

Ganache's flavor TypeScript types, helpers, and utility functions.

Ganache Flavors are plugins that can be used to launch test networks for chains
other than Ganache's built-in Ethereum networks. They are loaded at runtime via
Ganache's `--flavor` flag.

### Warnings and Gotchas

Ganache flavors are experimental, incomplete, and subject to change without
notice.

Ganache flavors are Ethereum JSON-RPC (2.0) inspired, and we are still working
to understand the needs of other chains and how to extend the Ganache flavor
model to support transports other than JSON-RPC 2.0 over HTTP/WS.

An example of shortcomings for non JSON-RPC chains:

- ganache only accepts POST requests over a single configurable path (defaults
  to `/`). If you have a need for something else, like JSON over REST, gRPC, SOAP,
  etc, please open an issue describing your use case.
- websocket subscription-based messaging is very limited and only supports
  responsing like Ethereum JSON-RPC does.

### How to create an experimental ganache flavor

To create a new flavor, you must create a new package that exports a `Flavor`. A
flavor is a JavaScript object that implements the `Flavor` TypeScript interface.

Here is an example of a "Hello World"-style flavor in TypeScript:

```typescript
import { Flavor, Connector, CliSettings } from "@ganache/flavor";

export type Provider = { sayHi: (name: string) => string };
export type RequestPayload = { name: string };
export type ResponsePayload = { result: string };

const provider: Provider = {
  sayHi(name: string) {
    return `Hello, ${name}`;
  }
};

const helloConnector: Connector<Provider, RequestPayload, ResponsePayload> = {
  // the `provider` is yours to implement however you'd like. In programmatic
  // usage it will be returned to the user when they call
  // `Ganache.provider()` or `Ganache.server().provider`
  provider,

  async connect(): Promise<void> {
    // ganache will `await` the return of your `connect` method before
    // forwarding any requests to your connector.
    // if your connector doesn't need to do any async work to initialize you
    // can leave this empty.
  },

  parse(message: Buffer) {
    // the `message` doesn't have to be JSON, you can use any data interchange
    // format you'd like.
    // NOTE: If your connector's `parse` method throws, Ganache does
    // _not_ call your `formatError` and instead returns a `400 Bad Request`
    // response.
    return JSON.parse(message);
  },

  async handle(
    this: typeof helloConnector,
    payload: RequestPayload
  ): Promise<{ value: unknown }> {
    if (!payload || typeof payload.name !== "string") {
      // you can throw an Exception here and ganache will catch the error and
      // pass it to your `formatError` function.
      throw new Error("payload must have a `name` property of type `string`");
    }

    // in this "Hello World" example we only have one method, but you can
    // implement as many as you need in any way you want. Here we just call the
    // our provider's `sayHi` with the user provided `payload`'s `name`
    //  property.
    const value = this.provider.sayHi(payload.name);

    // Your `handle` function MUST always return any object with a `value`
    // property. The value of `value` MAY itself be a `Promise`. The _resolved_
    // `value` will be passed to your connector's `format` function.
    //
    // NOTE: if a client is connected via WebSockets, and the the `value` is a
    // `PromiEvent` (a `Promise` that also has an `on` function) that emits a
    // `"message"` event Ganache will subscribe to the `"message"` event. If
    // the `PromiEvent` then emits a "message" its event data will be sent to
    // the client.
    // ATTENTION: A flavor cannot `format` this message though; it will always
    // be sent as am Ethereum JSON-RPC 2.0 subscription style message. This
    // behavior will change in the future *without notice*. It is not recommened
    // that you use the PromiEvent feature at this time.
    return { value };
  },

  format(result: ResponsePayload, payload: RequestPayload) {
    console.log(
      `formatting result (${result.result}) for payload (${payload.name})`
    );
    // You don't have to return a string here, you can also return a Buffer
    // and the serialization doesn't have to be JSON. However...
    // ATTENTION: ganache flavors don't yet support changing the `content-type`
    // header so it always returns `content-type: application/json`. This will
    // change in the future and flavors will be able to specify their own
    // content-type and other HTTP headers.
    //
    // You can also return a Generator (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Generator)
    // which will cause ganache to send the response in chunks (one chunk for
    // yield). This is useful if your response data is too large for Node.js to
    // handle (string and Buffer sizes are limited to about 1-2GB, and memory is
    // capped to 4GB on most systems).
    return JSON.stringify({ result });
  },

  formatError(error: Error, payload: RequestPayload) {
    // Ganache calls your `formatError` if any errors occured while processing
    // a request.

    console.log(`formatting error (${error.message}) for payload (${payload})`);
    // you don't have to return a string here, you can also return a Buffer
    // and the serialization doesn't have to be JSON
    return JSON.stringify({ error: error.message });
  },

  async close() {
    // ganache calls your connector's `close` function when shutting down.
    // This is where you'd perform clean up, like closing database connections
    // or cleaning temporary files.
  }
};

type HelloFlavor = Flavor<"hello-chain", typeof helloConnector>;

const HelloFlavor: HelloFlavor = {
  flavor: "hello-chain",
  options: {
    // see the `example/` directory for how Options work
  },
  connect(providerOptions: never) {
    return helloConnector;
  },
  // the `ready` function is required for your flavor to work with ganache on
  // the CLI
  ready: ({
    provider,
    options
  }: {
    provider: Provider;
    options: { server: CliSettings };
  }) => {
    // this function is only called after ganache has fully initialized, and is
    // only called when used via ganache cli (it is not used when your flavor is
    // used programatically)
    console.log(
      `Hello Chain server is running at http://${options.server.host}:${options.server.port}`
    );
  }
};

/**
 * Your flavor needs to be exported as `default` so Ganache can find it.
 */
export default HelloFlavor;
```

Check out the [example implementation](./example) for a more-in-depth example.