Ergo Headless dApp Framework

The premier Rust framework for developing Ergo Headless dApps. The Ergo HDF provides developers with the very first portable UTXO-based headless dApp development framework on any blockchain.

What Are Headless dApps?

Headless dApps are a brand new technical and business model for developing dApps that is just beginning to take hold in the wider Blockchain sphere. In short, headless dApps are the pure and portable self-contained logic for reading and participating in on-chain smart contract protocols.

In other words, headless dApps are a piece of software which expose the complex on-chain protocols to the off-chain world with a streamlined interface that anyone can build on top of. What is key here is that headless dApps, as their name suggests, have no frontend built on top of them (thus "headless").

What headless dApps do provide is the freedom for an entire decentralized ecosystem to be built on top of them. Because headless dApps by default are pure and portable, they can be compiled to any desktop OS, mobile OS, or browser. Because they have a streamlined interface, they can be integrated into scripts and bots trivially. Because they are composable, they can be used together in applications enabling arbitrage between different protocols trivially, or entire new user experiences to be developed without having to understand how each and every supported headless dApp works at it's core.

Headless dApps are the future for enabling newer devs who have limited experience in developing smart contract protocols to still have a real impact on the dApp sphere. The separation of concerns allows building on top of headless dApps without requiring the substantial time sink in understanding the nitty gritty details that made the dApp possible.

Furthermore, headless dApps open up the ecosystem for a whole new business model. Rather than the smart contact protocol creators sucking up all potential profit/value from the success of the protocol, headless dApps uncover an as-of-yet untapped revenue stream for front-end devs. By decentralizing the potential profit from solely the protocol creators to now encompass each and every frontend that is developed, we take a step back from the centralizing effect that we have today with popular dApps with a single hosted frontend. Instead we can incentivize a robust ecosystem of numerous independent frontends built by various devs/companies which all can profit from improving the ecosystem as a whole.

Headless dApps enable all of this, while further enhancing the developer experience at the exact same time.

Project Goals

1. Enable developers to write their off-chain logic once using the HDF to create their own headless dApps, thereby targeting all platforms (desktop, web, mobile).

2. Provide developers with an easy experience to go from Ergo dApp Specifications to headless dApp with greater assurance and a straightforward path of implementation.

3. Separating the dApp off-chain logic from any front-end logic, thereby allowing reusability no matter what application or front-end is attempting to integrate your headless dApp.

4. Providing easy-to-use methods for front-end implementors to easily access current state of the dApp protocol without having to understand how any of it works.

5. Abstracting the concept of defining and acquiring input UTXOs for your headless dApp by using a novel design pattern in specifying BoxSpecs for the required input UTXOs.

6. Enabling scripts, (arbitrage) bots, and other software to be trivially built on top multiple headless dApps built using the HDF, thus offering a standardized interface and a level of composability.

Understanding The Ergo Headless dApp Framework

Before you get started using the HDF, there are a number of terms and concepts that are important to understand. The overarching design of the HDF is based off of EIP-6: Ergo Smart Contract Protocol Specification Format.

What this means is that at the highest level, your dApp is defined as a smart contract protocol. If your dApp only has a single stage, then it is defined as a "single-stage smart contract protocol". If your dApp has multiple stages, then it is a "multi-stage smart contract protocol. The HDF supports building both single and multi-stage protocol dApps.

Each stage can be considered a state in the protocol where a UTXO with Ergs, tokens, and data (within registers) is at in a given point in time. There may be a single box(UTXO) which moves from one stage to the next throughout the entire protocol, multiple boxes which go through all of the stages in parallel, or a variety of boxes asynchronously moving through certain sub-sets of stages.

No matter the specific design/complexity of your given smart contract protocol, each of these stages require "Actions". Actions are the state transitions (transaction logic) which allow:

1. Ergs/tokens/data to enter the protocol (aka. a bootstrap action)
2. Ergs/tokens/data to go from one stage in the protocol to another stage (or exiting the protocol).
3. Ergs/tokens/data to leave the protocol.

Each of these actions is made up of two key parts in the context of your headless dApp:

1. Acquiring inputs (UTXOs/user input/external data from the outside world)
2. Creating output UTXOs with the result of the state transition

Thus to restate the above, your dApp may either be a single or multi-stage smart contract protocol. Each stage in your dApp's protocol may have one or more actions. These actions are then defined by you the developer via specifying the required inputs required for a given action, and encoding the required state transition logic in order to create output UTXOs which are embedded within a newly created UnsignedTx.

The HDF provides you with the required tools to specify each of these building blocks in order to build your headless dApp from the ground-up. In the sections below, we will go through further details about how the HDF is built, and how you yourself can get started using it today.

Modules Of The Ergo Headless dApp Framework

Box Spec

This module exposes the BoxSpec struct, which allows you to create a specification of a UTXO. This is used for defining the boxes which are required for the actions of your protocol.

/// A specification which specifies parameters of an `ErgoBox`.
/// This spec is used as a "source of truth" to both verify and find
/// `ErgoBox`es which match the spec. This is often used for defining
/// Stages in multi-stage smart contract protocols, but can also be used
/// to define input boxes for Actions.
/// All fields are wrapped in `Option`s to allow ignoring specifying
/// the field.
#[wasm_bindgen]
#[derive(Clone)]
pub struct BoxSpec {
    /// The address of the box
    address: Option<ErgoAddressString>,
    /// The allowed range of nanoErgs
    value_range: Option<Range<NanoErg>>,
    /// A sorted list of `Constant`s which define registers
    /// of an `ErgoBox`.
    /// First element is treated as R4, second as R5, and so on.
    registers: Vec<Option<Constant>>,
    /// A sorted list of `TokenSpec`s which define tokens
    /// of an `ErgoBox`.
    tokens: Vec<Option<TokenSpec>>,
    /// An optional predicate which allows for defining custom
    /// specification logic which gets processed when verifying
    /// the box.
    predicate: Option<fn(&ErgoBox) -> bool>,
}

Once you've constructed a BoxSpec, you have a number of essential methods that simplify the experience of writing off-chain code for dApps.

For example, verify_box allows you to test whether an ErgoBox you provide as input matches the specification you created with your BoxSpec.

pub fn verify_box(&self, ergo_box: &ErgoBox) -> Result<()> {

Box Traits

This module exposes two traits:

1. WrappedBox
2. SpecifiedBox
3. ExplorerFindable

All ExplorerFindable structs are also SpecifiedBoxes which are all WrappedBoxes. In your off-chain code you will be defining all of your inputs UTXOs to actions as structs that implement SpecifiedBox, while automatically deriving WrappedBox and ExplorerFindable without any extra work.

WrappedBoxes provide a simplified interface for interacting with ErgoBoxes. SpecifiedBoxes on the other hand specify that a given WrappedBox also implements a BoxSpec via the box_spec() method. And lastly ExplorerFindable provides an interface on top of the SpecifiedBox trait for finding boxes that match the BoxSpec from an Ergo Explorer API instance.

Specified Boxes

This module exposes generic "Specified Box" structs that implement the SpecifiedBox/WrappedBox/ExplorerFindable traits. These boxes can be used as inputs for Actions in your off-chain protocol code, while also enabling front-end devs to easily gain access to on-chain data, such as Oracle Pool data.

Currently Implemented Specified Boxes:

1. ErgsBox
2. ErgUsdOraclePoolBox
3. AdaUsdOraclePoolBox

ErgsBox are used for acquiring inputs that hold Ergs inside of them which can be used within your smart contract protocol actions.

ErgUsdOraclePoolBox & AdaUsdOraclePoolBox provide an extremely simplified interface for both headless dApp developers as well as front-end implementors to utilize data from the two currently running Oracle Pools. These two specified boxes can even be used by wallets/any off-chain application that needs to read the current rates from the Oracle Pool boxes.

The code block below shows how in 4 lines you can read the current Erg-USD oracle pool rate from your preferred Ergo Explorer API instance:

let url = ErgUsdOraclePoolBox::explorer_endpoint("https://api.ergoplatform.com/api").unwrap();
let response = get(&url).unwrap().text().unwrap();
let oracle_pool_box =
    ErgUsdOraclePoolBox::process_explorer_response(&response).unwrap()[0].clone();
println!(
    "Erg-USD Oracle Pool: {} nanoErgs per USD",
    oracle_pool_box.datapoint()
);

Output Builders

This module exposes structs which provide you with a basic interface for creating common output UTXOs within your Actions. These are often used for creating outputs that hold a user's change or pay a tx fee.

Example Output Builders:

1. ChangeBox

2. TokensChangeBox

3. TxFeeBox

Tx Creation

This module exposes a few basic functions for making your life easier when building UnsignedTransactions inside of your Actions.

Encoding

This module exposes a number of helpful functions related to encoding/decoding/wrapping/unwrapping values from one form into another.

Examples:

pub fn erg_to_nano_erg(erg_amount: f64) -> u64;
pub fn nano_erg_to_erg(nanoerg_amount: u64) -> f64;
pub fn unwrap_long(c: &Constant) -> Result<i64>;
pub fn serialize_p2s_from_ergo_tree(ergo_tree: ErgoTree) -> P2SAddressString;

Procedural Macros

This crate exposes three procedural macros to make the life of devs much simpler:

1. WrapBox
2. SpecBox
3. WASMBox

WrapBox simply implements the WrappedBox trait for you, SpecBox implements a customized new() method that uses your BoxSpec + implements the ExplorerFindable trait for you, and WASMBox implements the two basic required methods to enable WASM support for your struct (w_new() and w_box_struct()).

Getting Started

The Math Bounty Headless dApp tutorial series has been created to guide you through using the Ergo Headless dApp Framework. You will be lead step-by-step in developing your own headless dApp from project creation all the way to implementing a command line based interface.

Currently available parts:

1. Math Bounty Headless dApp - Getting Started Writing Your First Action

2. Math Bounty Headless dApp - Finishing The Headless dApp

3. Math Bounty Headless dApp - Writing A CLI Frontend For Creating Bounties

Documentation

To read the documentation for the HDF run the command below:

cargo doc --open