1 files changed, 121 insertions, 0 deletions
diff --git a/contracts/ens/cid.go b/contracts/ens/cid.go
new file mode 100644
index 000000000..fae9bfd0a
--- /dev/null
+++ b/contracts/ens/cid.go
@@ -0,0 +1,121 @@
+// Copyright 2016 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 ens
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+const (
+	cidv1 = 0x1
+
+	nsIpfs  = 0xe3
+	nsSwarm = 0xe4
+
+	swarmTypecode = 0xfa //swarm manifest, see https://github.com/multiformats/multicodec/blob/master/table.csv
+	swarmHashtype = 0xd6 // BMT, see https://github.com/multiformats/multicodec/blob/master/table.csv
+
+	hashLength = 32
+)
+
+// deocodeEIP1577ContentHash decodes a chain-stored content hash from an ENS record according to EIP-1577
+// a successful decode will result the different parts of the content hash in accordance to the CID spec
+// Note: only CIDv1 is supported
+func decodeEIP1577ContentHash(buf []byte) (storageNs, contentType, hashType, hashLength uint64, hash []byte, err error) {
+	if len(buf) < 10 {
+		return 0, 0, 0, 0, nil, errors.New("buffer too short")
+	}
+
+	storageNs, n := binary.Uvarint(buf)
+
+	buf = buf[n:]
+	vers, n := binary.Uvarint(buf)
+
+	if vers != 1 {
+		return 0, 0, 0, 0, nil, fmt.Errorf("expected cid v1, got: %d", vers)
+	}
+	buf = buf[n:]
+	contentType, n = binary.Uvarint(buf)
+
+	buf = buf[n:]
+	hashType, n = binary.Uvarint(buf)
+
+	buf = buf[n:]
+	hashLength, n = binary.Uvarint(buf)
+
+	hash = buf[n:]
+
+	if len(hash) != int(hashLength) {
+		return 0, 0, 0, 0, nil, errors.New("hash length mismatch")
+	}
+	return storageNs, contentType, hashType, hashLength, hash, nil
+}
+
+func extractContentHash(buf []byte) (common.Hash, error) {
+	storageNs, _ /*contentType*/, _ /* hashType*/, decodedHashLength, hashBytes, err := decodeEIP1577ContentHash(buf)
+
+	if err != nil {
+		return common.Hash{}, err
+	}
+
+	if storageNs != nsSwarm {
+		return common.Hash{}, errors.New("unknown storage system")
+	}
+
+	//todo: for the time being we implement loose enforcement for the EIP rules until ENS manager is updated
+	/*if contentType != swarmTypecode {
+		return common.Hash{}, errors.New("unknown content type")
+	}
+
+	if hashType != swarmHashtype {
+		return common.Hash{}, errors.New("unknown multihash type")
+	}*/
+
+	if decodedHashLength != hashLength {
+		return common.Hash{}, errors.New("odd hash length, swarm expects 32 bytes")
+	}
+
+	if len(hashBytes) != int(hashLength) {
+		return common.Hash{}, errors.New("hash length mismatch")
+	}
+
+	return common.BytesToHash(buf), nil
+}
+
+func EncodeSwarmHash(hash common.Hash) ([]byte, error) {
+	var cidBytes []byte
+	var headerBytes = []byte{
+		nsSwarm,       //swarm namespace
+		cidv1,         // CIDv1
+		swarmTypecode, // swarm hash
+		swarmHashtype, // swarm bmt hash
+		hashLength,    //hash length. 32 bytes
+	}
+
+	varintbuf := make([]byte, binary.MaxVarintLen64)
+	for _, v := range headerBytes {
+		n := binary.PutUvarint(varintbuf, uint64(v))
+		cidBytes = append(cidBytes, varintbuf[:n]...)
+	}
+
+	cidBytes = append(cidBytes, hash[:]...)
+	return cidBytes, nil
+}