multiShardCoordinator.go

package sharding

import (
	"bytes"
	"math"

	"github.com/subrahamanyam341/andes-core-go/core"
)

// multiShardCoordinator struct defines the functionality for handling transaction dispatching to
// the corresponding shards. The number of shards is currently passed as a constructor
// parameter and later it should be calculated by this structure
type multiShardCoordinator struct {
	maskHigh       uint32
	maskLow        uint32
	selfId         uint32
	numberOfShards uint32
}

// NewMultiShardCoordinator returns a new multiShardCoordinator and initializes the masks
func NewMultiShardCoordinator(numberOfShards, selfId uint32) (*multiShardCoordinator, error) {
	if numberOfShards < 1 {
		return nil, ErrInvalidNumberOfShards
	}
	if selfId >= numberOfShards && selfId != core.MetachainShardId {
		return nil, ErrInvalidShardId
	}

	sr := &multiShardCoordinator{}
	sr.selfId = selfId
	sr.numberOfShards = numberOfShards
	sr.maskHigh, sr.maskLow = calculateMasks(numberOfShards)

	return sr, nil
}

// calculateMasks will create two numbers who's binary form is composed from as many
// ones needed to be taken into consideration for the shard assignment. The result
// of a bitwise AND operation of an address with this mask will result in the
// shard id where a transaction from that address will be dispatched
func calculateMasks(numOfShards uint32) (uint32, uint32) {
	n := math.Ceil(math.Log2(float64(numOfShards)))
	return (1 << uint(n)) - 1, (1 << uint(n-1)) - 1
}

// ComputeId calculates the shard for a given address container
func (msc *multiShardCoordinator) ComputeId(address []byte) uint32 {
	return msc.ComputeIdFromBytes(address)
}

// ComputeShardID will compute shard id of the given address based on the number of shards parameter
func ComputeShardID(address []byte, numberOfShards uint32) uint32 {
	maskHigh, maskLow := calculateMasks(numberOfShards)

	return computeIdBasedOfNrOfShardAndMasks(address, numberOfShards, maskHigh, maskLow)
}

// ComputeIdFromBytes calculates the shard for a given address
func (msc *multiShardCoordinator) ComputeIdFromBytes(address []byte) uint32 {
	if core.IsEmptyAddress(address) {
		return msc.selfId
	}

	return computeIdBasedOfNrOfShardAndMasks(address, msc.numberOfShards, msc.maskHigh, msc.maskLow)
}

func computeIdBasedOfNrOfShardAndMasks(address []byte, numberOfShards, maskHigh, maskLow uint32) uint32 {
	var bytesNeed int
	if numberOfShards <= 256 {
		bytesNeed = 1
	} else if numberOfShards <= 65536 {
		bytesNeed = 2
	} else if numberOfShards <= 16777216 {
		bytesNeed = 3
	} else {
		bytesNeed = 4
	}

	startingIndex := 0
	if len(address) > bytesNeed {
		startingIndex = len(address) - bytesNeed
	}

	buffNeeded := address[startingIndex:]
	if core.IsSmartContractOnMetachain(buffNeeded, address) {
		return core.MetachainShardId
	}

	addr := uint32(0)
	for i := 0; i < len(buffNeeded); i++ {
		addr = addr<<8 + uint32(buffNeeded[i])
	}

	shard := addr & maskHigh
	if shard > numberOfShards-1 {
		shard = addr & maskLow
	}

	return shard
}

// NumberOfShards returns the number of shards
func (msc *multiShardCoordinator) NumberOfShards() uint32 {
	return msc.numberOfShards
}

// SelfId gets the shard id of the current node
func (msc *multiShardCoordinator) SelfId() uint32 {
	return msc.selfId
}

// SameShard returns weather two addresses belong to the same shard
func (msc *multiShardCoordinator) SameShard(firstAddress, secondAddress []byte) bool {
	if core.IsEmptyAddress(firstAddress) || core.IsEmptyAddress(secondAddress) {
		return true
	}

	if bytes.Equal(firstAddress, secondAddress) {
		return true
	}

	return msc.ComputeId(firstAddress) == msc.ComputeId(secondAddress)
}

// CommunicationIdentifier returns the identifier between current shard ID and destination shard ID
// identifier is generated such as the first shard from identifier is always smaller or equal than the last
func (msc *multiShardCoordinator) CommunicationIdentifier(destShardID uint32) string {
	return core.CommunicationIdentifierBetweenShards(msc.selfId, destShardID)
}

// IsInterfaceNil returns true if there is no value under the interface
func (msc *multiShardCoordinator) IsInterfaceNil() bool {
	return msc == nil
}