WebAssembly Smart Contracts

Overview

ArthaChain employs WebAssembly (WASM) as its smart contract runtime environment, providing a secure, efficient, and language-agnostic approach to contract development. The WASM VM offers significant advantages over traditional blockchain VMs, including enhanced performance, formal verification capabilities, and quantum resistance.

Architecture

The WASM smart contract system is implemented across several modules in blockchain_node/src/wasm/:

blockchain_node/src/wasm/
├── abi.rs              # Contract ABI definitions
├── context.rs          # Execution context
├── debug.rs            # Debugging infrastructure
├── engine.rs           # Core VM engine
├── executor.rs         # Contract execution logic
├── gas.rs              # Gas metering
├── host.rs             # Host environment
├── host_functions.rs   # Functions callable from contracts
├── mod.rs              # Module entry point
├── rpc.rs              # RPC interface
├── runtime.rs          # Runtime environment
├── standards.rs        # Contract standards
├── storage.rs          # Contract storage
├── types.rs            # Common type definitions
├── upgrade.rs          # Contract upgrade mechanisms
├── verification.rs     # Formal verification
└── vm.rs               # VM implementation

WASM Virtual Machine

The core VM implementation in vm.rs provides the execution environment for contracts:

pub struct WasmVm {
    /// VM configuration
    config: WasmVmConfig,
    /// Cached modules
    modules: HashMap<String, wasmer::Module>,
    /// Wasmer store
    store: wasmer::Store,
}

Key features include:

• Memory-Safe Execution: Sandboxed runtime with strict memory boundaries (100 pages/6.4MB max)
• Deterministic Execution: Guaranteed identical results across all validators
• JIT Compilation: Just-in-time compilation for optimized performance
• Bytecode Validation: Strict validation of contract bytecode
• Metered Execution: Fine-grained gas metering for resource accounting

VM Configuration

The VM is highly configurable through the WasmVmConfig structure:

pub struct WasmVmConfig {
    /// Maximum memory pages (64KB each)
    pub max_memory_pages: u32,
    /// Maximum gas limit per execution
    pub default_gas_limit: u64,
    /// Timeout in milliseconds
    pub execution_timeout_ms: u64,
    /// Maximum WASM module size in bytes
    pub max_module_size: usize,
    /// Features enabled for WASM execution
    pub features: WasmFeatures,
}

Default configuration values:

impl Default for WasmVmConfig {
    fn default() -> Self {
        Self {
            max_memory_pages: 100, // 6.4MB (64KB per page)
            default_gas_limit: 10_000_000,
            execution_timeout_ms: 5000,       // 5 seconds
            max_module_size: 2 * 1024 * 1024, // 2MB
            features: WasmFeatures::default(),
        }
    }
}

Contract Execution Environment

The execution environment provides the contract with access to blockchain state and functions:

pub struct WasmEnv {
    /// Storage access for the contract
    pub storage: Arc<dyn Storage>,
    /// Memory for the contract
    pub memory: RefCell<Vec<u8>>,
    /// Gas meter for metered execution
    pub gas_meter: GasMeter,
    /// Call context (caller, block info, etc.)
    pub context: CallContext,
    /// Contract address
    pub contract_address: Address,
    /// Caller address
    pub caller: Address,
    /// State access
    pub state: Arc<State>,
    /// Current caller
    pub caller_str: String,
    /// Current contract address
    pub contract_address_str: String,
    /// Value sent with call
    pub value: u64,
    /// Contract call data
    pub call_data: Vec<u8>,
    /// Execution logs
    pub logs: Vec<String>,
}

Host Functions

Contracts interact with the blockchain through host functions defined in host_functions.rs:

// Re-exported in mod.rs
pub use host_functions::{
    crypto_verify, get_block_number, get_caller, storage_delete, storage_read, storage_write,
};

These functions provide capabilities like:

• Storage Access: Read, write and delete contract state
• Blockchain Context: Access to block information, transaction details
• Cryptographic Operations: Hash computation, signature verification
• Caller Information: Details about the transaction sender
• Contract Interaction: Ability to call other contracts

Smart Contract Development

Supported Languages

The WASM VM supports multiple programming languages for contract development:

Rust

Rust is the primary recommended language for ArthaChain smart contracts due to its memory safety guarantees, performance, and rich type system.

Example Rust Contract:

use artha_sdk::prelude::*;

#[artha_contract]
pub struct TokenContract {
    total_supply: u64,
    balances: Map<Address, u64>,
}

#[artha_methods]
impl TokenContract {
    pub fn new(initial_supply: u64) -> Self {
        let mut contract = Self {
            total_supply: initial_supply,
            balances: Map::new(),
        };
        let deployer = env::caller();
        contract.balances.insert(deployer, initial_supply);
        contract
    }
    
    pub fn transfer(&mut self, to: Address, amount: u64) -> Result<(), String> {
        let from = env::caller();
        let from_balance = self.balances.get(&from).unwrap_or(0);
        
        if from_balance < amount {
            return Err("Insufficient balance".to_string());
        }
        
        self.balances.insert(from, from_balance - amount);
        let to_balance = self.balances.get(&to).unwrap_or(0);
        self.balances.insert(to, to_balance + amount);
        
        Ok(())
    }
    
    pub fn balance_of(&self, account: Address) -> u64 {
        self.balances.get(&account).unwrap_or(0)
    }
}

AssemblyScript

AssemblyScript provides a TypeScript-like experience targeting WebAssembly.

C/C++

For advanced use cases requiring maximum performance or specific optimizations.

Contract ABI

Contracts expose their interface through a standardized ABI:

pub struct ContractABI {
    /// Contract name
    pub name: String,
    /// Contract version
    pub version: String,
    /// Contract methods
    pub methods: Vec<ABIMethod>,
    /// Contract events
    pub events: Vec<ABIEvent>,
    /// Contract constructor
    pub constructor: Option<ABIConstructor>,
}

Contract Execution

Loading and Execution

Contract execution follows a well-defined lifecycle:

1. Loading: Contract bytecode is loaded and validated

   pub fn load_module(
       &mut self,
       contract_address: &str,
       bytecode: &[u8],
   ) -> Result<(), WasmError>

2. Instantiation: An instance is created with the appropriate environment

   let instance = wasmer::Instance::new(module, &import_object)
       .map_err(|e| WasmError::InstantiationError(e.to_string()))?;

3. Execution: The specified function is called with provided arguments

   pub fn execute(
       &self,
       contract_address: &str,
       env: WasmEnv,
       function: &str,
       args: &[wasmer::Value],
   ) -> Result<WasmExecutionResult, WasmError>

Gas Metering

Execution is metered to ensure fair resource usage:

const GAS_PER_INSTRUCTION: u64 = 1;
const MAX_EXECUTION_STEPS: u64 = 10_000_000; // 10 million steps

Gas is charged for:

• Instruction Execution: Basic computational operations
• Memory Operations: Allocation, reads, and writes
• Storage Access: Reading from and writing to persistent storage
• Host Function Calls: Interactions with the blockchain

Security Features

Memory Safety

The VM enforces strict memory isolation:

// From vm.rs
// Add memory
let memory = wasmer::Memory::new(
    &self.store,
    wasmer::MemoryType::new(1, Some(self.config.max_memory_pages)),
)
.map_err(|e| WasmError::InstantiationError(e.to_string()))?;

Key security features:

• Memory bounds checking
• Stack depth limitations
• Maximum module size enforcement
• Execution timeout protection

Validation

All WASM bytecode undergoes rigorous validation before execution:

// From vm.rs
let mut validator = Validator::new_with_features(self.config.features);

// Parse and validate the module
for payload in Parser::new(0).parse_all(bytecode) {
    let payload = payload.map_err(|e| WasmError::ValidationError(e.to_string()))?;
    validator
        .payload(&payload)
        .map_err(|e| WasmError::ValidationError(e.to_string()))?;
}

Formal Verification

The system includes tools for formal verification of contracts:

// From mod.rs
pub use verification::{ContractVerifier, LivenessProperty, SafetyProperty, VerificationResult};

Verification capabilities include:

• Safety Properties: Ensuring contracts behave as expected
• Liveness Properties: Guaranteeing progress under fair conditions
• Model Checking: Verifying against formally specified requirements

Contract Standards

The system supports standardized interfaces for common contract types:

// From mod.rs
pub use standards::{
    ContractStandard, GovernanceStandard, SecurityStandard, StandardRegistry, StandardType,
    TokenStandard,
};

Available standards include:

• Token Standards: Fungible and non-fungible token interfaces
• Governance Standards: Decentralized governance protocols
• Security Standards: Enhanced security compliance requirements

Upgradeability

Contracts can be designed for upgradeability:

// From mod.rs
pub use upgrade::{ContractVersion, StorageLayout, UpgradeManager, UpgradePattern};

Upgrade patterns include:

• Proxy Pattern: Delegating calls to implementation contracts
• Diamond Pattern: Multi-facet upgradeable contracts
• Storage Migration: Upgrading while preserving state

Debugging Tools

The system includes comprehensive debugging capabilities:

// From mod.rs
pub use debug::{Breakpoint, DebugManager, DebugSession, StackFrame, StackTrace};

Debugging features include:

• Breakpoints: Pausing execution at specific points
• Stack Traces: Viewing call history
• State Inspection: Examining contract memory and storage
• Gas Profiling: Analyzing gas usage

AI Integration

ArthaChain uniquely integrates AI capabilities with smart contracts:

Neural Network Interface

Contracts can access pre-trained models for:

• Fraud Detection: Identifying suspicious transaction patterns
• Data Classification: Categorizing on-chain data
• Anomaly Detection: Flagging unusual contract behaviors
• Pattern Recognition: Identifying patterns in blockchain data

Model Integration

The AI integration follows a strict versioning and verification pattern:

1. Models are deployed to the blockchain with versioning
2. Contracts specify required model versions
3. Runtime ensures model compatibility and integrity
4. Execution provides secure, metered model inference

Performance Characteristics

The WASM VM is optimized for blockchain execution:

• Execution Speed: Near-native performance through JIT compilation
• Memory Efficiency: Minimal memory footprint with explicit allocation
• Startup Time: Fast instantiation through module caching
• Determinism: Guaranteed identical execution across all nodes
• Scalability: Linear scaling with hardware capabilities

Conclusion

ArthaChain's WebAssembly Smart Contract system provides a secure, flexible, and efficient environment for developing and executing blockchain applications. By leveraging the power of WASM with blockchain-specific optimizations, it enables complex decentralized applications with strong security guarantees.