Implement bnUSD

[CyrusVorwald]

Overview

bnUSD is a token contract that burns instead of locks on the source chain when sending cross-chain.

Example Usage

Alice has 1000 bnUSD on Stacks and wants to send 500 bnUSD to Bob's Ethereum address.

(cross-transfer "0x1.eth/0x742d35Cc6634C0532925a3b844Bc454e4438f44e" u500000000 none)

500 bnUSD is burned from Alice's account on Stacks and the following RLP-encoded cross-chain message is sent to Ethereum via xCall.

{
  "method": "xCrossTransfer",
  "from": "0x1.stx/SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7",  // Alice's Stacks address
  "to": "0x1.eth/0x742d35Cc6634C0532925a3b844Bc454e4438f44e",  // Bob's Ethereum address
  "amount": 500000000,
  "data": null  // No additional data
}

On Ethereum, the bnUSD contract receives this message and mints 500 bnUSD to Bob's address.

If the transfer fails on Ethereum for any reason, a revert message would be sent back to Stacks to mint 500 bnUSD back to Alice's address:

{
  "method": "xCrossTransferRevert",
  "to": "SP2J6ZY48GV1EZ5V2V5RB9MP66SW86PYKKNRV9EJ7",  // Alice's Stacks address
  "amount": 500000000
}

Requirements

Implement RLP encoding/decoding for the following cross-chain messages:

;; Asset Transfer Message
;; For sending assets to other chains
(define-data-var transfer-message
  (tuple
    (method (string-ascii 13))      ;; "xCrossTransfer"
    (from (string-ascii 42))
    (to (string-ascii 42))
    (amount uint)
    (data (optional (buff 256)))
  )
)

;; Asset Transfer Revert Message
;; For handling failed transfers
(define-data-var transfer-revert-message
  (tuple
    (method (string-ascii 19))      ;; "xCrossTransferRevert"
    (to principal)
    (amount uint)
  )
)

Implement handle-call-message:

(define-public (handle-call-message (from (string-ascii 64)) (data (buff 1024)) (protocols (list 10 (string-ascii 64))))
  (begin
    ;; Implementation
    ;; 1. Verify the message source and protocols
    ;; 2. Decode the message data
    ;; 3. Route to the appropriate function (transfer or revert)
    (ok true)
  )
)

Implement cross-transfer:

(define-public (cross-transfer (to (string-ascii 42)) (amount uint) (data (optional (buff 256))))
  (begin
    ;; Implementation
    ;; 1. Burn tokens from sender
    ;; 2. Prepare cross-chain message
    ;; 3. Call xCall service to send the message
    (ok true)
  )
)