address.go

/*
 * Flow Go SDK
 *
 * Copyright Flow Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package flow

import (
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"strings"
)

// Address represents the 8 byte address of an account.
type Address [AddressLength]byte

// An AddressGenerator uses a deterministic algorithm to generate Flow addresses.
type AddressGenerator struct {
	chainID ChainID
	state   addressState
}

// NewAddressGenerator creates a new address generator for the given chain ID,
// starting from the zero address state.
//
// Addresses are generated for a specific network (Flow mainnet, testnet, etc).
//
// Each addressing state is mapped to exactly one address, meaning there are as
// many addresses as states. State values are incremented from 0 to 2^k-1.
func NewAddressGenerator(chainID ChainID) *AddressGenerator {
	return &AddressGenerator{
		chainID: chainID,
		state:   zeroAddressState,
	}
}

func newAddressGeneratorAtState(chainID ChainID, state addressState) *AddressGenerator {
	return &AddressGenerator{
		chainID: chainID,
		state:   state,
	}
}

// Address generates an account address at the current addressing state.
func (gen *AddressGenerator) Address() Address {
	return generateAddress(gen.chainID, gen.state)
}

// NextAddress increments the addressing state and generates an account address.
func (gen *AddressGenerator) NextAddress() Address {
	gen.Next()
	return generateAddress(gen.chainID, gen.state)
}

// Next increments the addressing state.
//
// State values are incremented from 0 to 2^k-1.
func (gen *AddressGenerator) Next() *AddressGenerator {
	if uint64(gen.state) > maxState {
		panic(
			fmt.Sprintf("addressing state must be less than or equal to %d", maxState),
		)
	}

	gen.state  

	return gen
}

// SetIndex fast-forwards or rewinds the addressing state to the given index.
func (gen *AddressGenerator) SetIndex(i uint) *AddressGenerator {
	gen.state = addressState(i)
	return gen
}

// addressState represents the internal state of the address generation mechanism
type addressState uint64

// AddressLength is the size of an account address in bytes.
const AddressLength = (linearCodeN   7) >> 3

const (
	// zeroAddressState is the addressing state when Flow is bootstrapped
	zeroAddressState = addressState(0)
	// serviceAddressState is the initial addressing state for account creations
	serviceAddressState = addressState(1)
)

// chainCustomizer derives the constant used to generate addresses for
// the given chain.
func chainCustomizer(chain ChainID) uint64 {
	switch chain {
	case Mainnet:
		return 0
	case Testnet:
		return invalidCodeTestNetwork
	case Emulator, Localnet, Benchnet, BftTestnet:
		return invalidCodeTransientNetwork
	default:
		panic(fmt.Sprintf("chain ID [%s] is invalid or does not support linear code address generation", chain))
	}
}

// EmptyAddress is the empty address (0x0000000000000000).
var EmptyAddress = Address{}

// ServiceAddress is the first generated account address.
func ServiceAddress(chain ChainID) Address {
	return generateAddress(chain, serviceAddressState)
}

// zeroAddress represents the "zero address" (account that no one owns).
func zeroAddress(chain ChainID) Address {
	return generateAddress(chain, zeroAddressState)
}

// HexToAddress converts a hex string to an Address.
func HexToAddress(h string) Address {
	trimmed := strings.TrimPrefix(h, "0x")
	if len(trimmed)%2 == 1 {
		trimmed = "0"   trimmed
	}
	b, _ := hex.DecodeString(trimmed)
	return BytesToAddress(b)
}

// BytesToAddress returns Address with value b.
//
// If b is larger than 8, b will be cropped from the left.
// If b is smaller than 8, b will be appended by zeroes at the front.
func BytesToAddress(b []byte) Address {
	var a Address
	if len(b) > AddressLength {
		b = b[len(b)-AddressLength:]
	}
	copy(a[AddressLength-len(b):], b)
	return a
}

// Bytes returns the byte representation of the address.
func (a Address) Bytes() []byte { return a[:] }

// Hex returns the hex string representation of the address.
func (a Address) Hex() string {
	return hex.EncodeToString(a.Bytes())
}

// Hex returns the address as hex string with "0x" prefix.
func (a Address) HexWithPrefix() string {
	return fmt.Sprintf("0x%s", a.Hex())
}

// String returns the string representation of the address.
func (a Address) String() string {
	return a.Hex()
}

func (a Address) MarshalJSON() ([]byte, error) {
	return []byte(fmt.Sprintf("\"%s\"", a.Hex())), nil
}

func (a *Address) UnmarshalJSON(data []byte) error {
	*a = HexToAddress(strings.Trim(string(data), "\""))
	return nil
}

const (
	// [n,k,d]-Linear code parameters
	// The linear code used in the account addressing is a [64,45,7]
	// It generates a [64,45]-code, which is the space of Flow account addresses.
	//
	// n is the size of the code words in bits,
	// which is also the size of the account addresses in bits.
	linearCodeN = 64
	// k is size of the words in bits.
	// 2^k is the total number of possible account addresses.
	linearCodeK = 45
	// p is the number of code parity bits.
	// p = n - k
	//
	// d is the distance of the linear code.
	// It is the minimum hamming distance between any two Flow account addresses.
	// This means any pair of Flow addresses have at least 7 different bits, which
	// minimizes the mistakes of typing wrong addresses.
	// d is also the minimum hamming weight of all account addresses (the zero address is not an account address).
	linearCodeD = 7

	// the maximum value of the internal state, 2^k.
	maxState = (1 << linearCodeK) - 1
)

// uint64ToAddress returns an address with value v
// The value v fits into the address as the address size is 8
func uint64ToAddress(v uint64) Address {
	var b [AddressLength]byte
	binary.BigEndian.PutUint64(b[:], v)
	return b
}

// uint64 converts an address into a uint64
func (a *Address) uint64() uint64 {
	v := binary.BigEndian.Uint64(a[:])
	return v
}

// generateAddress returns an account address given an addressing state.
// (network) specifies the network to generate the address for (Flow Mainnet, testent..)
// The function assumes the state is valid (<2^k) which means
// a check on the state should be done before calling this function.
func generateAddress(chain ChainID, state addressState) Address {
	index := uint64(state)

	// Multiply the index GF(2) vector by the code generator matrix
	address := uint64(0)
	for i := 0; i < linearCodeK; i   {
		if index&1 == 1 {
			address ^= generatorMatrixRows[i]
		}
		index >>= 1
	}

	// customize the code word for a specific network
	address ^= chainCustomizer(chain)
	return uint64ToAddress(address)
}

// IsValid returns true if a given address is a valid account address,
// and false otherwise.
//
// This is an off-chain check that only tells whether the address format is
// valid. If the function returns true, this does not mean a Flow account with
// this address has been generated. Such a test would require an on-chain check.
func (a *Address) IsValid(chain ChainID) bool {
	codeWord := a.uint64()
	codeWord ^= chainCustomizer(chain)

	if codeWord == 0 {
		return false
	}

	// Multiply the code word GF(2)-vector by the parity-check matrix
	parity := uint(0)
	for i := 0; i < linearCodeN; i   {
		if codeWord&1 == 1 {
			parity ^= parityCheckMatrixColumns[i]
		}
		codeWord >>= 1
	}
	return parity == 0
}

// invalid code-words in the [64,45] code
// these constants are used to generate non-Flow-Mainnet addresses
const (
	// invalidCodeTestNetwork is the invalid codeword used for long-lived test networks.
	invalidCodeTestNetwork = uint64(0x6834ba37b3980209)

	// invalidCodeTransientNetwork  is the invalid codeword used for transient test networks.
	invalidCodeTransientNetwork = uint64(0x1cb159857af02018)
)

// Rows of the generator matrix G of the [64,45]-code used for Flow addresses.
// G is a (k x n) matrix with coefficients in GF(2), each row is converted into
// a big endian integer representation of the GF(2) raw vector.
// G is used to generate the account addresses
var generatorMatrixRows = [linearCodeK]uint64{
	0xe467b9dd11fa00df, 0xf233dcee88fe0abe, 0xf919ee77447b7497, 0xfc8cf73ba23a260d,
	0xfe467b9dd11ee2a1, 0xff233dcee888d807, 0xff919ee774476ce6, 0x7fc8cf73ba231d10,
	0x3fe467b9dd11b183, 0x1ff233dcee8f96d6, 0x8ff919ee774757ba, 0x47fc8cf73ba2b331,
	0x23fe467b9dd27f6c, 0x11ff233dceee8e82, 0x88ff919ee775dd8f, 0x447fc8cf73b905e4,
	0xa23fe467b9de0d83, 0xd11ff233dce8d5a7, 0xe88ff919ee73c38a, 0x7447fc8cf73f171f,
	0xba23fe467b9dcb2b, 0xdd11ff233dcb0cb4, 0xee88ff919ee26c5d, 0x77447fc8cf775dd3,
	0x3ba23fe467b9b5a1, 0x9dd11ff233d9117a, 0xcee88ff919efa640, 0xe77447fc8cf3e297,
	0x73ba23fe467fabd2, 0xb9dd11ff233fb16c, 0xdcee88ff919adde7, 0xee77447fc8ceb196,
	0xf73ba23fe4621cd0, 0x7b9dd11ff2379ac3, 0x3dcee88ff91df46c, 0x9ee77447fc88e702,
	0xcf73ba23fe4131b6, 0x67b9dd11ff240f9a, 0x33dcee88ff90f9e0, 0x19ee77447fcff4e3,
	0x8cf73ba23fe64091, 0x467b9dd11ff115c7, 0x233dcee88ffdb735, 0x919ee77447fe2309,
	0xc8cf73ba23fdc736}

// Columns of the parity-check matrix H of the [64,45]-code used for Flow addresses.
// H is a (n x p) matrix with coefficients in GF(2), each column is converted into
// a big endian integer representation of the GF(2) column vector.
// H is used to verify a code word is a valid account address.
var parityCheckMatrixColumns = [linearCodeN]uint{
	0x00001, 0x00002, 0x00004, 0x00008,
	0x00010, 0x00020, 0x00040, 0x00080,
	0x00100, 0x00200, 0x00400, 0x00800,
	0x01000, 0x02000, 0x04000, 0x08000,
	0x10000, 0x20000, 0x40000, 0x7328d,
	0x6689a, 0x6112f, 0x6084b, 0x433fd,
	0x42aab, 0x41951, 0x233ce, 0x22a81,
	0x21948, 0x1ef60, 0x1deca, 0x1c639,
	0x1bdd8, 0x1a535, 0x194ac, 0x18c46,
	0x1632b, 0x1529b, 0x14a43, 0x13184,
	0x12942, 0x118c1, 0x0f812, 0x0e027,
	0x0d00e, 0x0c83c, 0x0b01d, 0x0a831,
	0x0982b, 0x07034, 0x0682a, 0x05819,
	0x03807, 0x007d2, 0x00727, 0x0068e,
	0x0067c, 0x0059d, 0x004eb, 0x003b4,
	0x0036a, 0x002d9, 0x001c7, 0x0003f,
}