hyperlane-monorepo/solidity/contracts/token/README.md

# Hyperlane Tokens and Warp Routes

This repo contains contracts and SDK tooling for Hyperlane-connected ERC20 and ERC721 tokens. The contracts herein can be used to create [Hyperlane Warp Routes](https://docs.hyperlane.xyz/docs/reference/applications/warp-routes) across different chains.

For instructions on deploying Warp Routes, see [the deployment documentation](https://docs.hyperlane.xyz/docs/deploy-hyperlane#deploy-a-warp-route) and the [Hyperlane CLI](https://www.npmjs.com/package/@hyperlane-xyz/cli).

## Warp Route Architecture

A Warp Route is a collection of [`TokenRouter`](./libs/TokenRouter.sol) contracts deployed across a set of Hyperlane chains. These contracts leverage the `Router` pattern to implement access control and routing logic for remote token transfers. These contracts send and receive [`Messages`](./libs/TokenMessage.sol) which encode payloads containing a transfer `amount` and `recipient` address.

```mermaid
%%{ init: {
  "theme": "neutral",
  "themeVariables": {
    "mainBkg": "#025AA1",
    "textColor": "white",
    "clusterBkg": "white"
  },
  "themeCSS": ".edgeLabel { color: black }"
}}%%

graph LR
    subgraph "Ethereum"
        HYP_E[TokenRouter]
        style HYP_E fill:orange
        Mailbox_E[(Mailbox)]
    end

    subgraph "Polygon"
        HYP_P[TokenRouter]
        style HYP_P fill:orange
        Mailbox_P[(Mailbox)]
    end


    subgraph "Gnosis"
        HYP_G[TokenRouter]
        style HYP_G fill:orange
        Mailbox_G[(Mailbox)]
    end

    HYP_E -. "TokenMessage" .- HYP_P -. "TokenMessage" .- HYP_G

```

The Token Router contract comes in several flavors and a warp route can be composed of a combination of these flavors.

- [`Native`](./contracts/HypNative.sol) - for warping native assets (e.g. ETH) from the canonical chain
- [`Collateral`](./contracts/HypERC20Collateral.sol) - for warping tokens, ERC20 or ERC721, from the canonical chain
- [`Synthetic`](./contracts/HypERC20.sol) - for representing tokens, Native/ERC20 or ERC721, on a non-canonical chain

## Interchain Security Models

Warp routes are unique amongst token bridging solutions because they provide modular security. Because the `TokenRouter` implements the `IMessageRecipient` interface, it can be configured with a custom interchain security module. Please refer to the relevant guide to specifying interchain security modules on the [Messaging API receive docs](https://docs.hyperlane.xyz/docs/reference/messaging/messaging-interface).

## Remote Transfer Lifecycle Diagrams

To initiate a remote transfer, users call the `TokenRouter.transferRemote` function with the `destination` chain ID, `recipient` address, and transfer `amount`.

```solidity
interface TokenRouter {
  function transferRemote(
    uint32 destination,
    bytes32 recipient,
    uint256 amount
  ) public returns (bytes32 messageId);
}
```

**NOTE:** The [Relayer](https://docs.hyperlane.xyz/docs/operate/relayer/run-relayer) shown below must be compensated. Please refer to the details on [paying for interchain gas](https://docs.hyperlane.xyz/docs/protocol/interchain-gas-payment).

Depending on the flavor of TokenRouter on the source and destination chain, this flow looks slightly different. The following diagrams illustrate these differences.

### Transfer Alice's `amount` native ETH from Ethereum to Bob on Polygon

```mermaid
%%{ init: {
  "theme": "neutral",
  "themeVariables": {
    "mainBkg": "#025AA1",
    "textColor": "white",
    "clusterBkg": "white"
  },
  "themeCSS": ".edgeLabel { color: black }"
}}%%

graph TB
    Bob((Bob))
    style Bob fill:black
    Alice((Alice))
    style Alice fill:black

    Relayer([Relayer])

    subgraph "Ethereum"
        HYP_E[NativeTokenRouter]
        style HYP_E fill:orange
        Mailbox_E[(Mailbox)]
    end

    Alice == "transferRemote(Polygon, Bob, amount)\n{value: amount}" ==> HYP_E
    linkStyle 0 color:green;
    HYP_E -- "dispatch(Polygon, (Bob, amount))" --> Mailbox_E

    subgraph "Polygon"
        HYP_P[SyntheticTokenRouter]
        style HYP_P fill:orange
        Mailbox_P[(Mailbox)]
    end

    Mailbox_E -. "indexing" .-> Relayer

    Relayer == "process(Ethereum, (Bob, amount))" ==> Mailbox_P
    Mailbox_P -- "handle(Ethereum, (Bob, amount))" --> HYP_P

    HYP_E -. "router" .- HYP_P

    HYP_P -- "mint(Bob, amount)" --> Bob
    linkStyle 6 color:green;
```

### Transfer Alice's ERC20 `amount` from Ethereum to Bob on Polygon

```mermaid
%%{ init: {
  "theme": "neutral",
  "themeVariables": {
    "mainBkg": "#025AA1",
    "textColor": "white",
    "clusterBkg": "white"
  },
  "themeCSS": ".edgeLabel { color: black }"
}}%%

graph TB
    Alice((Alice))
    Bob((Bob))
    style Alice fill:black
    style Bob fill:black

    Relayer([Relayer])

    subgraph "Ethereum"
        Token_E[ERC20]
        style Token_E fill:green
        HYP_E[CollateralTokenRouter]
        style HYP_E fill:orange
        Mailbox_E[(Mailbox)]
    end

    Alice == "approve(CollateralTokenRouter, infinity)" ==> Token_E
    Alice == "transferRemote(Polygon, Bob, amount)" ==> HYP_E
    Token_E -- "transferFrom(Alice, amount)" --> HYP_E
    linkStyle 2 color:green;
    HYP_E -- "dispatch(Polygon, (Bob, amount))" --> Mailbox_E

    subgraph "Polygon"
        HYP_P[SyntheticRouter]
        style HYP_P fill:orange
        Mailbox_P[(Mailbox)]
    end

    Mailbox_E -. "indexing" .-> Relayer

    Relayer == "process(Ethereum, (Bob, amount))" ==> Mailbox_P
    Mailbox_P -- "handle(Ethereum, (Bob, amount))" --> HYP_P

    HYP_E -. "router" .- HYP_P
    HYP_P -- "mint(Bob, amount)" --> Bob
    linkStyle 8 color:green;
```

### Transfer Alice's `amount` synthetic MATIC from Ethereum back to Bob as native MATIC on Polygon

```mermaid
%%{ init: {
  "theme": "neutral",
  "themeVariables": {
    "mainBkg": "#025AA1",
    "textColor": "white",
    "clusterBkg": "white"
  },
  "themeCSS": ".edgeLabel { color: black }"
}}%%

graph TB
    Bob((Bob))
    style Bob fill:black
    Alice((Alice))
    style Alice fill:black

    Relayer([Relayer])

    subgraph "Ethereum"
        HYP_E[SyntheticTokenRouter]
        style HYP_E fill:orange
        Mailbox_E[(Mailbox)]
    end

    Alice == "transferRemote(Polygon, Bob, amount)" ==> HYP_E
    Alice -- "burn(Alice, amount)" --> HYP_E
    linkStyle 1 color:green;
    HYP_E -- "dispatch(Polygon, (Bob, amount))" --> Mailbox_E

    subgraph "Polygon"
        HYP_P[NativeTokenRouter]
        style HYP_P fill:orange
        Mailbox_P[(Mailbox)]
    end

    Mailbox_E -. "indexing" .-> Relayer

    Relayer == "process(Ethereum, (Bob, amount))" ==> Mailbox_P
    Mailbox_P -- "handle(Ethereum, (Bob, amount))" --> HYP_P

    HYP_E -. "router" .- HYP_P
    HYP_P -- "transfer(){value: amount}" --> Bob
    linkStyle 7 color:green;
```

**NOTE:** ERC721 collateral variants are assumed to [enumerable](https://docs.openzeppelin.com/contracts/4.x/api/token/erc721#IERC721Enumerable) and [metadata](https://docs.openzeppelin.com/contracts/4.x/api/token/erc721#IERC721Metadata) compliant.

## Versions

| Git Ref                  | Release Date | Notes                          |
| ------------------------ | ------------ | ------------------------------ |
| [audit-v2-remediation]() | 2023-02-15   | Hyperlane V2 Audit remediation |
| [main]()                 | ~            | Bleeding edge                  |

## Learn more

For more information, see the [Hyperlane introduction documentation](https://docs.hyperlane.xyz/docs/intro).