NOTE: This document is a work in progress. You can submit an issue if you find a problem or have a suggestion. The source for this documentation is in our repository at locutus/docs/src. We welcome pull requests.

Development Guide

This guide will walk through how to develop a simple distributed web application using Locutus. To do that, we'll be using Rust for the contracts themselves and Typescript for developing the web application.

At the time of writing (September 2022) the Locutus network is not yet active. We've published this guide so that people can experiment with building and running Locutus applications locally, and provide feedback.

You can see some examples of working applications and contracts in the apps directory of the locutus repository, e.g.:

Installation

Development for Locutus requires installing some dependencies:

1. Rust & Cargo

Locutus is developed in Rust, on Linux/Mac this will install Rust and its build tool Cargo which Locutus also requires:

$ curl https://sh.rustup.rs -sSf | sh

2. LLVM

  • The LLVM compiler backend core libraries. Usually available at most OS package managers for Linux distributions and Mac OS.
$ sudo apt install llvm # For Ubuntu

3. Locutus Dev Tool (LTD)

Once you have a working installation of Cargo you can install the Locutus dev tools:

$ cargo install locutus

This command will install ldt (Locutus Dev Tool) and a working node that can be used for local development.

3.1 Usage

You can find more information about the available commands by executing ldt with the --help argument:

$ ldt --help

Locutus Development Tool 0.0.2
The Freenet Project Inc.

USAGE:
    ldt [DATA_DIR] <SUBCOMMAND>

ARGS:
    <DATA_DIR>    Overrides the default data directory where Locutus files are stored

OPTIONS:
    -h, --help       Print help information
    -V, --version    Print version information

SUBCOMMANDS:
    build        Builds and packages a contract
    execute      Node CLI
    help         Print this message or the help of the given subcommand(s)
    new          Create a new Locutus contract and/or app
    publish      Publishes a new contract to the network
    run-local    A CLI utility for testing out contracts against a Locutus local node

Creating a new contract

You can create a new contract skeleton by executing the new command with ldt. Two contract types are supported currently by the tool, regular contracts, and web application container contracts. Currently, the following technological stacks are supported (more to be added in the future):

  • Regular contracts:
    • Rust (default)
  • Web applications:
    • Container development:
      • Rust (default)
    • Web/state development:
      • Typescript. (default: using npm and webpack)
      • JavaScript.
      • Rust (WIP).

We will need to create a directory that will hold our web app and initialize it:

$ mkdir -p my-app/web
$ mkdir -p my-app/backend
$ cd my-app/web
$ ldt new web-app

will create the skeleton for a web application and its container contract for Locutus ready for development at the my-app/web directory.

Making a container contract

The first thing that we need is to write the code for our container contract. This contract's role is to contain the web application code itself, allowing it to be distributed over Locutus.

The new command has created the source ready to be modified for us, in your favorite editor open the following file:

$ ./container/src/lib.rs

In this case, and for simplicity's sake, the contract won't be performing any functions, but in a realistic scenario, this contract would include some basic security functionality like verifying that whoever is trying to update the contract has the required credentials.

To make our contract unique so it doesn't collide with an existing contract, we can generate a random signature that will be embedded with the contract.

For example in the lib.rs file we will write the following:

use locutus_stdlib::prelude::*;

pub const RANDOM_SIGNATURE: &[u8] = &[6, 8, 2, 5, 6, 9, 9, 10];

struct Contract;

#[contract]
impl ContractInterface for Contract {
    fn validate_state(
        _parameters: Parameters<'static>,
        _state: State<'static>,
        _related: RelatedContracts<'static>,
    ) -> Result<ValidateResult, ContractError> {
        unimplemented!()
    }

    fn validate_delta(
        _parameters: Parameters<'static>,
        _delta: StateDelta<'static>,
    ) -> Result<bool, ContractError> {
        unimplemented!()
    }

    fn update_state(
        _parameters: Parameters<'static>,
        _state: State<'static>,
        _data: Vec<UpdateData<'static>>,
    ) -> Result<UpdateModification<'static>, ContractError> {
        unimplemented!()
    }

    fn summarize_state(
        _parameters: Parameters<'static>,
        _state: State<'static>,
    ) -> Result<StateSummary<'static>, ContractError> {
        unimplemented!()
    }

    fn get_state_delta(
        _parameters: Parameters<'static>,
        _state: State<'static>,
        _summary: StateSummary<'static>,
    ) -> Result<StateDelta<'static>, ContractError> {
        unimplemented!()
    }
}

That's a lot of information, let's unpack it:

use locutus_stdlib::prelude::*;

Here we are importing the necessary types and traits to write a Locutus contract successfully using Rust.

pub const RANDOM_SIGNATURE: &[u8] = &[6, 8, 2, 5, 6, 9, 9, 10];

This will make our contract unique, notice the pub qualifier so the compiler doesn't remove this constant because is unused and is included in the output of the compiler.

struct Contract;

#[contract]
impl ContractInterface for Contract {
  ...
}

Here we create a new type, Contract for which we will be implementing the ContractInterface trait. To know more details about the functionality of a contract, delve into the details of the contract interface.

Notice the #[contract] macro call, this will generate the necessary code for the WASM runtime to interact with your contract ergonomically and safely. Trying to use this macro more than once in the same module will result in a compiler error, and only the code generated at the top-level module will be used by the runtime.

As a rule of thumb, one contract will require implementing the `ContractInterface`` exactly once.

Creating a web application

Now we have a working example of a contract, but our contract is an empty shell, which does not do anything yet. To change this, we will start developing our web application.

To do that, we can go and modify the code of the contract state, which in this case is the web application. Locutus offers a standard library (stdlib) that can be used with Typescript/JavaScript to facilitate the development of web applications and interfacing with your local node, so we will make our package.json contains the dependency:

{
  "dependencies": {
    "@locutus/locutus-stdlib": "0.0.2"
  }
}

Open the file src/index.ts in a code editor and you can start developing the web application.

An important thing to notice is that our application will need to interface with our local node, the entry point for our machine to communicate with other nodes in the network. The stdlib offers a series of facilities in which you will be able to communicate with the network ergonomically.

Here is an example of how you could write your application to interact with the node:

import { LocutusWsApi } from "@locutus/locutus-stdlib/webSocketInterface";

const handler = {
  onPut: (_response: PutResponse) => {},
  onGet: (_response: GetResponse) => {},
  onUpdate: (_up: UpdateResponse) => {},
  onUpdateNotification: (_notif: UpdateNotification) => {},
  onErr: (err: HostError) => {},
  onOpen: () => {},
};

const API_URL = new URL(`ws://${location.host}/contract/command/`);
const locutusApi = new LocutusWsApi(API_URL, handler);

const CONTRACT = "DCBi7HNZC3QUZRiZLFZDiEduv5KHgZfgBk8WwTiheGq1";

async function loadState() {
  let getRequest = {
    key: Key.fromSpec(CONTRACT),
    fetch_contract: false,
  };
  await locutusApi.get(getRequest);
}

Let's unpack this code:

const handler = {
  onPut: (_response: PutResponse) => {},
  onGet: (_response: GetResponse) => {},
  onUpdate: (_up: UpdateResponse) => {},
  onUpdateNotification: (_notif: UpdateNotification) => {},
  onErr: (err: HostError) => {},
  onOpen: () => {},
};

const API_URL = new URL(`ws://${location.host}/contract/command/`);
const locutusApi = new LocutusWsApi(API_URL, handler);

This type provides a convenient interface to the WebSocket API. It receives an object which handles the different responses from the node via callbacks. Here you would be able to interact with DOM objects or other parts of your code.

const CONTRACT = "DCBi7HNZC3QUZRiZLFZDiEduv5KHgZfgBk8WwTiheGq1";

async function loadState() {
  let getRequest = {
    key: Key.fromSpec(CONTRACT),
    fetch_contract: false,
  };
  await locutusApi.get(getRequest);
}

Here we use the API wrapper to make a get request (which requires a key and specifies if we require fetching the contract code or not) to get the state for a contract with the given address. The response from the node will be directed to the onGet callback. You can use any other methods available in the API to interact with the node.

Writing the backend for our web application

In the creating a new contract section we described the contract interface, but we were using it to write a simple container contract that won't be doing anything in practice, just carrying around the front end of your application. The core logic of the application, and a back end where we will be storing all the information, requires another contract. So we will create a new contract in a different directory for it:

$ cd ../backend
$ ldt new contract

This will create a regular contract, and we will need to implement the interface on a type that will handle our contract code. For example:

use locutus_stdlib::prelude::*;

pub const RANDOM_SIGNATURE: &[u8] = &[6, 8, 2, 5, 6, 9, 9, 10];

struct Contract;

struct Posts(...)

impl Posts {
  fn add_post(&mut self, post: Post) { ... }
}

struct Post(...)

#[contract]
impl ContractInterface for Contract {
    fn update_state(
        _parameters: Parameters<'static>,
        state: State<'static>,
        data: Vec<UpdateData<'static>>,
    ) -> Result<UpdateModification<'static>, ContractError> {
        let mut posts: Posts = serde_json::from_slice(&state).map_err(|_| ContractError::InvalidState)?;
        if let Some(UpdateData::Delta(delta)) = data.pop() {
          let new_post: Posts = serde_json::from_slice(&delta).map_err(|_| ContractError::InvalidState);
          posts.add_post(new_post)?;
        } else {
            Err(ContractError::InvalidUpdate)
        }
        Ok(UpdateModification::valid(posts.into()))
    }

    ...
}

In this simple example, we convert a new incoming delta to a post and the state to a list of posts we maintain, and we append the post to the list of posts. After that, we convert back the posts list to an state and return that.

If we subscribe to the contract changes or our web app, we will receive a notification with the updates after they are successful, and we will be able to render them in our browser. We can do that, for example, using the API:

function getUpdateNotification(notification: UpdateNotification) {
  let decoder = new TextDecoder("utf8");
  let updatesBox = DOCUMENT.getElementById("updates") as HTMLPreElement;
  let newUpdate = decoder.decode(Uint8Array.from(notification.update));
  let newUpdateJson = JSON.parse(newUpdate);
  updatesBox.textContent = updatesBox.textContent + newUpdateJson;
}

Building and packaging a contract

Now that we have the front end and the back end of our web app, we can package the contracts and run them in the node to test them out.

In order to do that, we can again use the development tool to help us out with the process. But before doing that, let's take a look at the manifesto format and understand the different parameters that allow us to specify how this contract should be compiled (check the manifest details for more information). In the web app directory, we have a locutus.toml file which contains something similar to:

[contract]
type = "webapp"
lang = "rust"

...

[webapp.state-sources]
source_dirs = ["dist"]

This means that the dist directory will be packaged as the initial state for the webapp (that is the code the browser will be interpreting and in the end, rendering).

If we add the following keys to the manifesto:

[webapp.dependencies]
posts = { path = "../backend" }

The WASM code from the backend contract will be embedded in our web application state, so it will be accessible as a resource just via the local HTTP gateway access and then we can re-use it for publishing additional contracts.

Currently, wep applications follow a standarized build procedure in case you use ldt and assumptions about your system. For example, in the case of a type = "webapp" contract, if nothing is specified, it will assume you have npm and the tsc compiler available at the directory level, as well as webpack installed.

This means that you have installed either globally or at the directory level, e.g. globally:

$ npm install -g typescript
$ npm install -g webpack
$ npm install -g webpack-cli

or locally (make sure your package.json file has the required dependencies):

$ npm install typescript --save-dev
$ npm install webpack --save-dev
$ npm install webpack-cli --save-dev

If, however, you prefer to follow a different workflow, you can write your own by enabling/disabling certain parameters or using a blank template. For example:

[contract]
lang = "rust"

[state]
files = ["my_packaged_web.tar.xz"]

Would just delegate the work of building the packaged tar to the developer. Or:

[contract]
type = "webapp"
lang = "rust"

[webapp]
lang = "typescript"

[webapp.typescript]
webpack =  false

would disable usign webpack at all.

Now that we understand the details, and after making any necessary changes, in each contract directory we run the following commands:

$ ldt build

This command will read your contract manifest file (locutus.toml) and take care of building the contract and packaging it, ready for the node and the network to consume it.

Under the ./build/locutus directory, you will see both a *.wasm file, which is the contract file, and contract-state, in case it applies, which is the initial state that will be uploaded when initially putting the contract.

Web applications can access the code of backend contracts directly in their applications and put new contracts (that is, assigning a new location for the code, plus any parameters that may be generated dynamically by the web app, and the initial state for that combination of contract code + parameters) dynamically.

Let's take a look at the manifest for our web app container contract:

Testing out contracts in the local node

Once we have all our contracts sorted and ready for testing, we can do this in local mode in our node. For this the node must be running, we can make sure that is running by running the following command as a background process or in another terminal; since we have installed it:

$ locutus-node

You should see some logs printed via the stdout of the process indicating that the node HTTP gateway is running.

Once the HTTP gateway is running, we are ready to publish the contracts to our local Locutus node:

$ cd ../backend && ldt publish --code="./build/locutus/backend.wasm" --state="./build/locutus/contract-state"
$ cd ../web && ldt publish --code="./build/locutus/web.wasm" --state="./build/locutus/contract-state"

In this case, we're not passing any parameters (so our parameters will be an empty byte array), and we are passing an initial state without the current backend contract. In typical use, both the parameters would have meaningful data, and the backend contract may be dynamically generated from the app and published from there.

Once this is done, you can start your app just by pointing to it in the browser: http://127.0.0.1:50509/contract/web/<CONTRACT KEY>

For example http://127.0.0.1:50509/contract/web/CYXGxQGSmcd5xHRJNQygPwmUJsWS2njh3pdVjfVz9EV/

Iteratively you can repeat this process of modifying, and publishing locally until you are confident with the results and ready to publish your application.

Since the web is part of your state, you are always able to update it, pointing to new contracts, and evolving it over time.

Limitations

  • Publishing to the Locutus network is not yet supported.

  • Only Rust is currently supported for contract development, but we'll support more languages like AssemblyScript in the future.

  • Binaries for all the required tools are not yet available, they must be compiled from source