Contract Runtime

The Contract Runtime on OP_NET, powered by @btc-vision/btc-runtime/runtime, provides developers with tools to interact with the blockchain environment. This guide explains the key features of the Blockchain class and its associated components, enabling advanced contract functionality.

---

Blockchain Documentation

The Blockchain object is essential for executing smart contracts within the OP_NET runtime. It provides the necessary context, such as the transaction origin, sender, block details, and contract-specific information.

---

Public Properties

1. tx.origin

Property Details

• Type: Address
• Description: Represents the initial sender of the transaction. (equivalent to tx.origin in Solidity)
• Usage Example:

  let txOrigin: Address = Blockchain.tx.origin;
  Blockchain.log(`Transaction Origin: ${txOrigin}`);

2. tx.sender

Property Details

• Type: Address
• Description: Refers to the immediate caller of the transaction. (equivalent to msg.sender in Solidity)
• Usage Example:

  let txSender: Address = Blockchain.tx.sender;
  Blockchain.log(`Transaction Sender: ${txSender}`);

3. block.medianTimestamp

Property Details

• Type: u64
• Description: Timestamp of the block in which the transaction is executed.
• Usage Example:

  let blockTimestamp: u64 = Blockchain.block.medianTimestamp;
  Blockchain.log(`Block Timestamp: ${blockTimestamp}`);

4. contract

Property Details

• Type: OP_NET
• Description: Accesses the current contract instance.
• Usage Example:

  let currentContract: OP_NET = Blockchain.contract;

5. nextPointer

Property Details

• Type: u16
• Description: Manages dynamic storage pointers.
• Usage Example:

  let pointer: u16 = Blockchain.nextPointer;
  Blockchain.log(`Next Pointer: ${pointer}`);

6. contractDeployer

Property Details

• Type: Address
• Description: The contract deployer's address.
• Usage Example:

  let contractDeployer: Address = Blockchain.contractDeployer;
  Blockchain.log(`Contract Deployer: ${contractDeployer}`);

7. contractAddress

Property Details

• Type: Address
• Description: The deployed address of the contract.
• Usage Example:

  let deployedAddress: Address = Blockchain.contractAddress;
  Blockchain.log(`Deployed Contract Address: ${deployedAddress}`);

8. block.number

Property Details

• Type: u256
• Description: The current block number as a 256-bit unsigned integer.
• Usage Example:

  let currentBlockNum: u256 = Blockchain.block.number;
  Blockchain.log(`Current Block Number: ${currentBlockNum}`);

9. block.numberU64

Property Details

• Type: u64
• Description: The current block number as a 64-bit unsigned integer.
• Usage Example:

  let currentBlockNum: u64 = Blockchain.block.numberU64;
  Blockchain.log(`Current Block Number: ${currentBlockNum}`);

---

Public Methods

1. call(destinationContract: Address, calldata: BytesWriter)

Method Details

• Returns: BytesReader
• Description: Executes a call to another contract.
• Usage Example:

  let destination: Address = ...;
  let calldata = new BytesWriter(length);
  calldata.writeString('methodName');
  let response = Blockchain.call(destination, calldata);
  Blockchain.log(`Response: ${response}`);

2. log(data: string)

Method Details

• Description: Logs string data for debugging or tracking. (only available in the development environment)
• Usage Example:

  Blockchain.log("Execution started.");

3. deployContract(hash: u256, bytecode: Uint8Array)

Method Details

• Returns: DeployContractResponse
• Description: Deploys a contract using a hash and bytecode.
• Usage Example:

  let contractHash = u256.fromU64(0x1234567890); // Your contract hash.
  let bytecode: Uint8Array = ...; // Your contract bytecode.
  let deployResponse = Blockchain.deployContract(contractHash, bytecode);
  Blockchain.log(`Deployed Address: ${deployResponse.contractAddress}`);

4. encodeVirtualAddress(virtualAddress: u8[])

Method Details

• Returns: Address
• Description: Encodes a virtual address into a standard format.
• Usage Example:

  let virtualAddr: u8[] = ...;
  let encodedAddr: Address = Blockchain.encodeVirtualAddress(virtualAddr);
  Blockchain.log(`Encoded Address: ${encodedAddr}`);

---

Loading and Storing Pointers

1. Encoding and Hashing Process

Storage on OP_NET uses a combination of pointers (u16) and sub-pointers (u256) for efficient data management. These are encoded and hashed into a MemorySlotPointer.

Encoding Example

export function encodePointerHash(pointer: u16, sub: u256): MemorySlotPointer {
  const buffer = new Uint8Array(34);
  const mergedKey = [u8(pointer & 0xff), u8((pointer >> 8) & 0xff)];
  buffer.set(mergedKey, 0);
  buffer.set(sub.toUint8Array(), 2);

  return bytes32(Sha256.hash(buffer));
}

---

2. Usage Example in a Contract

Let's consider a simple contract that stores and retrieves data using pointers.

Contract Implementation

class MyContract {
  private pointer: u16;
  private subPointer: MemorySlotPointer;

  constructor(pointer: u16, subKey: string) {
    this.pointer = pointer;
    this.subPointer = encodePointer(
      this.pointer,
      Uint8Array.wrap(String.UTF8.encode(subKey))
    );
  }

  public storeData(value: u256): void {
    const storageKey = encodePointerHash(this.pointer, this.subPointer);
    Blockchain.setStorageAt(storageKey, value);
  }

  public retrieveData(): u256 {
    const storageKey = encodePointerHash(this.pointer, this.subPointer);
    return Blockchain.getStorageAt(storageKey, u256.Zero);
  }
}