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channel_id.go
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channel_id.go
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package lnwire
import (
"encoding/binary"
"encoding/hex"
"math"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/wire"
)
const (
// MaxFundingTxOutputs is the maximum number of allowed outputs on a
// funding transaction within the protocol. This is due to the fact
// that we use 2-bytes to encode the index within the funding output
// during the funding workflow. Funding transaction with more outputs
// than this are considered invalid within the protocol.
MaxFundingTxOutputs = math.MaxUint16
)
// ChannelID is a series of 32-bytes that uniquely identifies all channels
// within the network. The ChannelID is computed using the outpoint of the
// funding transaction (the txid, and output index). Given a funding output the
// ChannelID can be calculated by XOR'ing the big-endian serialization of the
// txid and the big-endian serialization of the output index, truncated to
// 2 bytes.
type ChannelID [32]byte
// ConnectionWideID is an all-zero ChannelID, which is used to represent a
// message intended for all channels to specific peer.
var ConnectionWideID = ChannelID{}
// String returns the string representation of the ChannelID. This is just the
// hex string encoding of the ChannelID itself.
func (c ChannelID) String() string {
return hex.EncodeToString(c[:])
}
// NewChanIDFromOutPoint converts a target OutPoint into a ChannelID that is
// usable within the network. In order to convert the OutPoint into a ChannelID,
// we XOR the lower 2-bytes of the txid within the OutPoint with the big-endian
// serialization of the Index of the OutPoint, truncated to 2-bytes.
func NewChanIDFromOutPoint(op *wire.OutPoint) ChannelID {
// First we'll copy the txid of the outpoint into our channel ID slice.
var cid ChannelID
copy(cid[:], op.Hash[:])
// With the txid copied over, we'll now XOR the lower 2-bytes of the
// partial channelID with big-endian serialization of output index.
xorTxid(&cid, uint16(op.Index))
return cid
}
// xorTxid performs the transformation needed to transform an OutPoint into a
// ChannelID. To do this, we expect the cid parameter to contain the txid
// unaltered and the outputIndex to be the output index
func xorTxid(cid *ChannelID, outputIndex uint16) {
var buf [32]byte
binary.BigEndian.PutUint16(buf[30:], outputIndex)
cid[30] = cid[30] ^ buf[30]
cid[31] = cid[31] ^ buf[31]
}
// GenPossibleOutPoints generates all the possible outputs given a channel ID.
// In order to generate these possible outpoints, we perform a brute-force
// search through the candidate output index space, performing a reverse
// mapping from channelID back to OutPoint.
func (c *ChannelID) GenPossibleOutPoints() [MaxFundingTxOutputs]wire.OutPoint {
var possiblePoints [MaxFundingTxOutputs]wire.OutPoint
for i := uint32(0); i < MaxFundingTxOutputs; i++ {
cidCopy := *c
xorTxid(&cidCopy, uint16(i))
possiblePoints[i] = wire.OutPoint{
Hash: chainhash.Hash(cidCopy),
Index: i,
}
}
return possiblePoints
}
// IsChanPoint returns true if the OutPoint passed corresponds to the target
// ChannelID.
func (c ChannelID) IsChanPoint(op *wire.OutPoint) bool {
candidateCid := NewChanIDFromOutPoint(op)
return candidateCid == c
}