A simple Asset Swap smart contract

This smart contract is designed to be used in a peer-to-peer exchange scenario where two parties agree to exchange assets. The contract ensures that the assets are locked up until it is accepted by the other party. At any point before it is accepted, one can cancel the swap to retrieve the assets.

This contract is just for academic purposes because of its limitations. It assumes that both parties are dealing with the same asset type. It lacks the ability to handle multiple asset types or interact with token standards (e.g., ERC-20 or PSP-22 for Polkadot).

Key Features

Feature	Description
Atomic Swaps	Either both parties get their assets or the swap is canceled
Authorization Checks	Strict permission controls for swap operations
Reentrancy Protection	Prevents recursive call attacks
Event Logging	Track all swap lifecycle changes
Detailed Error Codes	Clear failure reasons for debugging
Storage Efficiency	Optimized mapping structure for swap storage

Data Structures

Structure	Fields	Description
Swap	initiator: AccountId counterparty: AccountId initiator_asset: Balance counterparty_asset: Balance	Represents a single swap agreement
SwapContract	swaps: Mapping<u32, Swap> next_swap_id: u32 reentrancy_guard: bool	Main contract storage with security features

Functions Overview

initiate_swap() - Creates new swap agreement

• Key Points:
  • Validate initiator's deposit > 0
  • Generate incremental swap ID
  • Store terms in mapping
  • Emit SwapInitiated event

accept_swap() - Execute asset exchange

• Key Points:
  • Activate reentrancy guard
  • Verify counterparty identity
  • Validate transferred amount
  • Transfer assets atomically
  • Clean storage & emit event

cancel_swap() - Abort swap and refund

• Key Points:
  • Verify initiator identity
  • Return locked funds
  • Remove swap record
  • Emit cancellation event

State Diagram

stateDiagram
    [*] --> Idle
    Idle --> Initiated: initiate_swap()
    Initiated --> Accepted: accept_swap()
    Initiated --> Canceled: cancel_swap()
    Accepted --> [*]
    Canceled --> [*]

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Sequence Diagram

sequenceDiagram
    participant I as Initiator
    participant C as Contract
    participant R as Counterparty

    I->>C: initiate_swap(counterparty, amount)
    C-->>I: swap_id
    
    R->>C: accept_swap(swap_id) with funds
    C->>I: Transfer counterparty_asset
    C->>R: Transfer initiator_asset
    C-->>R: SwapAccepted event
    
    alt Cancel
    I->>C: cancel_swap(swap_id)
    C->>I: Return initiator_asset
    C-->>I: SwapCancelled event
    end

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