psbt: move bip32 structs into new file

psbt/bip32.go

@@ -0,0 +1,77 @@
+package psbt
+
+import (
+	"bytes"
+	"encoding/binary"
+)
+
+// Bip32Derivation encapsulates the data for the input and output
+// Bip32Derivation key-value fields.
+//
+// TODO(roasbeef): use hdkeychain here instead?
+type Bip32Derivation struct {
+	// PubKey is the raw pubkey serialized in compressed format.
+	PubKey []byte
+
+	// MasterKeyFingerprint is the finger print of the master pubkey.
+	MasterKeyFingerprint uint32
+
+	// Bip32Path is the BIP 32 path with child index as a distinct integer.
+	Bip32Path []uint32
+}
+
+// checkValid ensures that the PubKey in the Bip32Derivation struct is valid.
+func (pb *Bip32Derivation) checkValid() bool {
+	return validatePubkey(pb.PubKey)
+}
+
+// Bip32Sorter implements sort.Interface for the Bip32Derivation struct.
+type Bip32Sorter []*Bip32Derivation
+
+func (s Bip32Sorter) Len() int { return len(s) }
+
+func (s Bip32Sorter) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+
+func (s Bip32Sorter) Less(i, j int) bool {
+	return bytes.Compare(s[i].PubKey, s[j].PubKey) < 0
+}
+
+// readBip32Derivation deserializes a byte slice containing chunks of 4 byte
+// little endian encodings of uint32 values, the first of which is the
+// masterkeyfingerprint and the remainder of which are the derivation path.
+func readBip32Derivation(path []byte) (uint32, []uint32, error) {
+
+	if len(path)%4 != 0 || len(path)/4-1 < 1 {
+		return 0, nil, ErrInvalidPsbtFormat
+	}
+
+	masterKeyInt := binary.LittleEndian.Uint32(path[:4])
+
+	var paths []uint32
+	for i := 4; i < len(path); i += 4 {
+		paths = append(paths, binary.LittleEndian.Uint32(path[i:i+4]))
+	}
+
+	return masterKeyInt, paths, nil
+}
+
+// SerializeBIP32Derivation takes a master key fingerprint as defined in BIP32,
+// along with a path specified as a list of uint32 values, and returns a
+// bytestring specifying the derivation in the format required by BIP174: //
+// master key fingerprint (4) || child index (4) || child index (4) || ....
+func SerializeBIP32Derivation(masterKeyFingerprint uint32,
+	bip32Path []uint32) []byte {
+
+	var masterKeyBytes [4]byte
+	binary.LittleEndian.PutUint32(masterKeyBytes[:], masterKeyFingerprint)
+
+	derivationPath := make([]byte, 0, 4+4*len(bip32Path))
+	derivationPath = append(derivationPath, masterKeyBytes[:]...)
+	for _, path := range bip32Path {
+		var pathbytes [4]byte
+		binary.LittleEndian.PutUint32(pathbytes[:], path)
+		derivationPath = append(derivationPath, pathbytes[:]...)
+	}
+
+	return derivationPath
+}