1 files changed, 92 insertions, 0 deletions
diff --git a/swarm/multihash/multihash.go b/swarm/multihash/multihash.go
new file mode 100644
index 000000000..3306e3a6d
--- /dev/null
+++ b/swarm/multihash/multihash.go
@@ -0,0 +1,92 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package multihash
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+)
+
+const (
+	defaultMultihashLength   = 32
+	defaultMultihashTypeCode = 0x1b
+)
+
+var (
+	multihashTypeCode uint8
+	MultihashLength   = defaultMultihashLength
+)
+
+func init() {
+	multihashTypeCode = defaultMultihashTypeCode
+	MultihashLength = defaultMultihashLength
+}
+
+// check if valid swarm multihash
+func isSwarmMultihashType(code uint8) bool {
+	return code == multihashTypeCode
+}
+
+// GetMultihashLength returns the digest length of the provided multihash
+// It will fail if the multihash is not a valid swarm mulithash
+func GetMultihashLength(data []byte) (int, int, error) {
+	cursor := 0
+	typ, c := binary.Uvarint(data)
+	if c <= 0 {
+		return 0, 0, errors.New("unreadable hashtype field")
+	}
+	if !isSwarmMultihashType(uint8(typ)) {
+		return 0, 0, fmt.Errorf("hash code %x is not a swarm hashtype", typ)
+	}
+	cursor += c
+	hashlength, c := binary.Uvarint(data[cursor:])
+	if c <= 0 {
+		return 0, 0, errors.New("unreadable length field")
+	}
+	cursor += c
+
+	// we cheekily assume hashlength < maxint
+	inthashlength := int(hashlength)
+	if len(data[c:]) < inthashlength {
+		return 0, 0, errors.New("length mismatch")
+	}
+	return inthashlength, cursor, nil
+}
+
+// FromMulithash returns the digest portion of the multihash
+// It will fail if the multihash is not a valid swarm multihash
+func FromMultihash(data []byte) ([]byte, error) {
+	hashLength, _, err := GetMultihashLength(data)
+	if err != nil {
+		return nil, err
+	}
+	return data[len(data)-hashLength:], nil
+}
+
+// ToMulithash wraps the provided digest data with a swarm mulithash header
+func ToMultihash(hashData []byte) []byte {
+	buf := bytes.NewBuffer(nil)
+	b := make([]byte, 8)
+	c := binary.PutUvarint(b, uint64(multihashTypeCode))
+	buf.Write(b[:c])
+	c = binary.PutUvarint(b, uint64(len(hashData)))
+	buf.Write(b[:c])
+	buf.Write(hashData)
+	return buf.Bytes()
+}