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writer: split embedded data into chunks #13

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merged 1 commit into from
Mar 2, 2023
Merged

writer: split embedded data into chunks #13

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54 changes: 47 additions & 7 deletions relayer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,24 @@ var (
internalPrivateKey = "5JGgKfRy6vEcWBpLJV5FXUfMGNXzvdWzQHUM1rVLEUJfvZUSwvS"
)

// chunkSlice splits input slice into max chunkSize length slices
func chunkSlice(slice []byte, chunkSize int) [][]byte {
var chunks [][]byte
for i := 0; i < len(slice); i += chunkSize {
end := i + chunkSize

// necessary check to avoid slicing beyond
// slice capacity
if end > len(slice) {
end = len(slice)
}

chunks = append(chunks, slice[i:end])
}

return chunks
}

// createTaprootAddress returns an address committing to a Taproot script with
// a single leaf containing the spend path with the script:
// <embedded data> OP_DROP <pubkey> OP_CHECKSIG
Expand All @@ -38,8 +56,13 @@ func createTaprootAddress(embeddedData []byte) (string, error) {

// Step 1: Construct the Taproot script with one leaf.
builder := txscript.NewScriptBuilder()
builder.AddData(embeddedData)
builder.AddOp(txscript.OP_DROP)
builder.AddOp(txscript.OP_0)
builder.AddOp(txscript.OP_IF)
chunks := chunkSlice(embeddedData, 520)
for _, chunk := range chunks {
builder.AddData(chunk)
}
builder.AddOp(txscript.OP_ENDIF)
builder.AddData(schnorr.SerializePubKey(pubKey))
builder.AddOp(txscript.OP_CHECKSIG)
pkScript, err := builder.Script()
Expand Down Expand Up @@ -153,8 +176,13 @@ func (r Relayer) revealTx(embeddedData []byte, commitHash *chainhash.Hash) (*cha
// Our script will be a simple <embedded-data> OP_DROP OP_CHECKSIG as the
// sole leaf of a tapscript tree.
builder := txscript.NewScriptBuilder()
builder.AddData(embeddedData)
builder.AddOp(txscript.OP_DROP)
builder.AddOp(txscript.OP_0)
builder.AddOp(txscript.OP_IF)
chunks := chunkSlice(embeddedData, 520)
for _, chunk := range chunks {
builder.AddData(chunk)
}
builder.AddOp(txscript.OP_ENDIF)
builder.AddData(schnorr.SerializePubKey(pubKey))
builder.AddOp(txscript.OP_CHECKSIG)
pkScript, err := builder.Script()
Expand Down Expand Up @@ -266,10 +294,22 @@ func (r Relayer) Read(height uint64) ([][]byte, error) {
var data [][]byte
for _, tx := range block.Transactions {
if len(tx.TxIn[0].Witness) > 1 {
// FIXME: UGLY HACK
// ideally we should template match the script and extract
// see: txscript.ExtractAtomicSwapDataPushes
witness := tx.TxIn[0].Witness[1]
size := uint(witness[0])
if bytes.HasPrefix(witness[1:], PROTOCOL_ID) {
data = append(data, witness[1:size+1])
start := bytes.Index(witness, PROTOCOL_ID)
// script template:
// < --------- 35 bytes --------->
// OP_FALSE OP_IF + "roll" marker + <data> + canonical int + 32 bytes pubkey + OP_CHECKSIG
// ^ ^
// start ------------ ^
// end -------------------------------------
if start > 0 && len(witness) > start+35 {
end := len(witness) - 35
if end > start {
data = append(data, witness[start:end])
}
}
}
}
Expand Down