gitbook-docs/js-sdk/3_in_depth.md

In-depth

In-depth

Intro

In this section we will cover the JS SDK in-depth.

Fluence

@fluencelabs/fluence exports a facade Fluence which provides all the needed functionality for the most uses cases. It defined 4 functions:

• start: Start the default peer.

• stop: Stops the default peer

• getStatus: Gets the status of the default peer. This includes connection

• getPeer: Gets the default Fluence Peer instance (see below)

Under the hood Fluence facade calls the corresponding method on the default instance of FluencePeer. This instance is passed to the Aqua-compiler generated functions by default.

FluencePeer class

The second export @fluencelabs/fluence package is FluencePeer class. It is useful in scenarios when the application need to run everal different peer at once. The overall workflow with the FluencePeer is the following:

1. Create an instance of the peer
2. Startign the peer
3. Using the peer in the application
4. Stopping the peer

To create a new peer simple instantiate the FluencePeer class:

const peer = new FluencePeer();

The constructor simply creates a new object and does not initialize any workflow. The start function starts the Aqua VM, initializes the default call service handlers and optionally connect to the Fluence network. The function takes an optional object specifying additonal peer configuration. On option you will be using a lot is connectTo. It tells the peer to connect to a relay. For example:

await peer.star({
  connectTo: krasnodar[0],
});

connects the first node of the Kranodar network. You can find the officially maintained list networks in the @fluencelabs/fluence-network-environment package. The full list of supported options is described in the API reference

await peer.stop();

Using multiple peers in one applicaton

The peer by itself does not do any useful work. You should take advantage of functions generated by the Aqua compiler.

If your application needs several peers, you should create a separate FluncePeer instance for each of them. The generated functions accept the peer as the first argument. For example:

import { FluencePeer } from "@fluencelabs/fluence";
import {
  registerSomeService,
  someCallableFunction,
} from "./_aqua/someFunction";

async function main() {
  const peer1 = new FluencePeer();
  const peer2 = new FluencePeer();

  // Don't forget to initialize peers
  await peer1.start({
    connectTo: relay,
  });
  await peer2.start({
    connectTo: relay,
  });

  // ... more application logic

  //        Pass the peer as the first agument
  //                   ||
  //                   \/
  registerSomeService(peer1, {
    handler: async (str) => {
      console.log("Called service on peer 1: " str);
    },
  });

  //        Pass the peer as the first agument
  //                   ||
  //                   \/
  registerSomeService(peer2, {
    handler: async (str) => {
      console.log("Called service on peer 2: " str);
    },
  });

  //                Pass the peer as the first agument
  //                           ||
  //                           \/
  await someCallableFunction(peer1, arg1, arg2, arg3);


  await peer1.stop();
  await peer2.stop();
}

// ... more application logic

It is possible to combine usage of the default peer with another one. Pay close attention to which peer you are calling the functions against.

  // Registering handler for the default peer
  registerSomeService({
    handler: async (str) => {
      console.log("Called agains the default peer: " str);
    },
  });

  //            Pay close attention to this
  //                       ||
  //                       \/
  registerSomeService(someOthePeer, {
    handler: async (str) => {
      console.log("Called against the peer named someOtherPeer: " str);
    },
  });

Understanding the Aqua compiler output

Aqua compiler emits TypeScript or JavaScript which in turn can be called from a js-based environemt. The compiler outputs code for the following entities:

1. Exported func declarations are turned into callable async functioks
2. Exported service declarations are turned into functions which register callback handler in a typed manner
3. For every exported service the compiler generated it's interface under the name {serviceName}Def

Function definitions

For every exported function definition in aqua the compiler generated two overloads. One accepting the FluencePeer instance as the first argument, and one without it. Otherwise arguments are the same and correspond to the arguments of aqua functions. The last argument is always an optional config object with the following properties:

• ttl: Optional parameter which specify TTL time to live of particle with execution logic for the function

The return type is always a promise of the aqua function return type. If the function does not return anything, the return type will be Promise<void>.

Consider the following example:

func myFunc(arg0: string, arg1: string):
    -- implementation

The compiler will generate the following overloads:

export async function myFunc(
  arg0: string,
  arg1: string,
  config?: { ttl?: number }
): Promise<void>;

export async function callMeBack(
  peer: FluencePeer,
  arg0: string,
  arg1: string,
  config?: { ttl?: number }
): Promise<void>;

Service definitions

service ServiceName:
    -- service interface

For every exported service declaration the compiler will generate two entities: service interface under the name {serviceName}Def and a function named register{serviceName} with several overloads. First let's describe the most complete one using the following example:

export interface ServiceNameDef {
  //... service function definitions
}

export function registerServiceName(
  peer: FluencePeer,
  serviceId: string,
  service: ServiceNameDef
): void;

• peer - the Fluence Peer instance where the handler should be registered. The peer can be ommited. In that case the default Fluence Peer will be used instead
• serviceId - the name of the service id. If the service was defined with the default service id in aqua code, this argument can be ommited.
• service - the handler for the service.

Depending on whether or not the services was defined with the default id the number of overloads will be different. In the case it is defined, there would be four overloads:

// (1)
export function registerServiceName(
  //
  service: ServiceNameDef
): void;

// (2)
export function registerServiceName(
  serviceId: string,
  service: ServiceNameDef
): void;

// (3)
export function registerServiceName(
  peer: FluencePeer,
  service: ServiceNameDef
): void;

// (4)
export function registerServiceName(
  peer: FluencePeer,
  serviceId: string,
  service: ServiceNameDef
): void;

1. Uses default Fluence Peer and the default id taken from aqua definition
2. Uses default Fluence Peer and specifies the service id explicitly
3. The default id is taken from aqua definition. The peer is specified explicitly
4. Specifying both peer and the service id.

If the default id is not defined in aqua code the overloads will exclude ones without service id:

// (1)
export function registerServiceName(
  serviceId: string,
  service: ServiceNameDef
): void;

// (2)
export function registerServiceName(
  peer: FluencePeer,
  serviceId: string,
  service: ServiceNameDef
): void;

1. Uses default Fluence Peer and specifies the service id explicitly
2. Specifying both peer and the service id.

Service interface

The service interface type follows closely the definition in aqua code. It has the form of the object which keys correspond to the names of service members and the values are functions of the type translated from aqua definition see Type convertion. For example, for the following aqua definition:

service Calc("calc"):
    add(n: f32)
    subtract(n: f32)
    multiply(n: f32)
    divide(n: f32)
    reset()
    getResult() -> f32

The typescript interface will be:

export interface CalcDef {
  add: (n: number, callParams: CallParams<"n">) => void;
  subtract: (n: number, callParams: CallParams<"n">) => void;
  multiply: (n: number, callParams: CallParams<"n">) => void;
  divide: (n: number, callParams: CallParams<"n">) => void;
  reset: (callParams: CallParams<null>) => void;
  getResult: (callParams: CallParams<null>) => number;
}

CallParams will be described later in the section

Type convertion

Basic types convertion is pretty much straightforward:

• string is converted to string in typescript
• bool is converted to boolean in typescript
• All number types `u8`, `u16`, `u32`, `u64`, `s8`, `s16`, `s32`, `s64`, `f32`, `f64` are converted to number in typescript

Arrow types translate to functions in typescript which have their arguments translated to typescript types. In addition to arguments defined in aqua, typescript counterparts have an additional argument for call params. For the majority of use cases this parameter is not needed and can be ommited.

The type convertion works the same way for service and func definitions. For example a func with a callback might look like this:

func callMeBack(callback: string, i32 -> ()):
    callback("hello, world", 42)

The type for callback argument will be:

callback: (arg0: string, arg1: number, callParams: CallParams<'arg0' | 'arg1'>) => void,

For the service definitions arguments are named see calc example above

Call params and tetraplets

Each service call is accompanied by additional information specific to Fluence Protocol. Including initPeerId - the peer which initiated the particle execution, particle signature and most importantly security tetraplets. All this data is contained inside the last callParams argument in every generated function definition. These data is passed to the handler on each function call can be used in the application.

Tetraplets have the form of:

{
  argName0: SecurityTetraplet[],
  argName1: SecurityTetraplet[],
  // ...
}

To learn more about tetraplets and application security see Security

To see full specification of CallParms type see Api reference