contracts.go

This file is responsible for executing smart contracts on the EVM.

Imports

The following imports are used:

• Package sha256 from the crypto project implements the SHA224 and SHA256 hash algorithms as defined in FIPS 180-4.
• errors, the Go language simple error handling primitives, such as error.
• math/big implements arbitrary-precision arithmetic (big numbers).

• Other packages in this project (go-ethereum):

  "github.com/ethereum/go-ethereum/common"
  "github.com/ethereum/go-ethereum/common/math"
  "github.com/ethereum/go-ethereum/crypto"
  "github.com/ethereum/go-ethereum/crypto/bn256"
  "github.com/ethereum/go-ethereum/params"
  

  Suggestion: Again, I think the above imports would have been better specified as relative imports:

  "../../common"
  "../../common/math"
  "../../crypto"
  "../../crypto/bn256"
  "../../params"
  

• ripemd160 implements the RIPEMD-160 hash algorithm, a secure replacement for the MD4 and MD5 hash functions. These hashes are also termed RIPE message digests.

Type PrecompiledContract

PrecompiledContract is the interface for native Go smart contracts. This interface is used by precompiled contracts, as we will see next. Contract is a struct defined in contract.go.

Pre-Compiled Contract Maps

These maps specify various types of cryptographic hashes and utility functions, accessed via their address.

PrecompiledContractsHomestead contains the default set of pre-compiled contract addresses used in the Frontier and Homestead releases of Ethereum: ecrecover, sha256hash, ripemd160hash and dataCopy.

PrecompiledContractsByzantium contains the default set of pre-compiled contract addresses used in the Byzantium Ethereum release. All of the previously defined pre-compiled contract addresses are provided in Byzantium, plus: bigModExp, bn256Add, bn256ScalarMul and bn256Pairing.

Suggestion: Some code is duplicated, whereby the contents of PrecompiledContractsHomestead are incorporated into PrecompiledContractsByzantium by listing the values again; this would be better expressed by referencing the values of PrecompiledContractsHomestead instead of duplicating them.

Contract Evaluator Function

The RunPrecompiledContract function runs and evaluates the output of a precompiled contract. It accepts three parameters:

• A PrecompiledContract instance.
• A byte array of input data.
• A reference to a Contract, defined in contract.go, discussed above.

The function returns:

• A byte array containing the output of the contract.
• An error value, which could be nil.

Other Functions

• RunPrecompiledContract – runs and evaluates the output of a precompiled contract; returns the output as a byte array and an error.
• RequiredGas (overloaded) – Computes the gas required for input data, specified as a byte array and returns a uint64.
• Run (overloaded) – Computes the smart contract for input data, specified as a byte array and returns the result as a left-padded byte array and an error.
• newCurvePoint – Unmarshals a binary blob into a bn256 elliptic curve point. BN-curves are an elliptic curves suitable for cryptographic pairings that provide high security and efficiency cryptographic schemes. See the IETF paper on Barreto-Naehrig Curves for more information.