1 files changed, 105 insertions, 0 deletions
diff --git a/swarm/storage/feed/topic.go b/swarm/storage/feed/topic.go
new file mode 100644
index 000000000..43a7b4ba4
--- /dev/null
+++ b/swarm/storage/feed/topic.go
@@ -0,0 +1,105 @@
+// 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 feed
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common/bitutil"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/swarm/storage"
+)
+
+// TopicLength establishes the max length of a topic string
+const TopicLength = storage.AddressLength
+
+// Topic represents what a feed is about
+type Topic [TopicLength]byte
+
+// ErrTopicTooLong is returned when creating a topic with a name/related content too long
+var ErrTopicTooLong = fmt.Errorf("Topic is too long. Max length is %d", TopicLength)
+
+// NewTopic creates a new topic from a provided name and "related content" byte array,
+// merging the two together.
+// If relatedContent or name are longer than TopicLength, they will be truncated and an error returned
+// name can be an empty string
+// relatedContent can be nil
+func NewTopic(name string, relatedContent []byte) (topic Topic, err error) {
+	if relatedContent != nil {
+		contentLength := len(relatedContent)
+		if contentLength > TopicLength {
+			contentLength = TopicLength
+			err = ErrTopicTooLong
+		}
+		copy(topic[:], relatedContent[:contentLength])
+	}
+	nameBytes := []byte(name)
+	nameLength := len(nameBytes)
+	if nameLength > TopicLength {
+		nameLength = TopicLength
+		err = ErrTopicTooLong
+	}
+	bitutil.XORBytes(topic[:], topic[:], nameBytes[:nameLength])
+	return topic, err
+}
+
+// Hex will return the topic encoded as an hex string
+func (t *Topic) Hex() string {
+	return hexutil.Encode(t[:])
+}
+
+// FromHex will parse a hex string into this Topic instance
+func (t *Topic) FromHex(hex string) error {
+	bytes, err := hexutil.Decode(hex)
+	if err != nil || len(bytes) != len(t) {
+		return NewErrorf(ErrInvalidValue, "Cannot decode topic")
+	}
+	copy(t[:], bytes)
+	return nil
+}
+
+// Name will try to extract the topic name out of the Topic
+func (t *Topic) Name(relatedContent []byte) string {
+	nameBytes := *t
+	if relatedContent != nil {
+		contentLength := len(relatedContent)
+		if contentLength > TopicLength {
+			contentLength = TopicLength
+		}
+		bitutil.XORBytes(nameBytes[:], t[:], relatedContent[:contentLength])
+	}
+	z := bytes.IndexByte(nameBytes[:], 0)
+	if z < 0 {
+		z = TopicLength
+	}
+	return string(nameBytes[:z])
+
+}
+
+// UnmarshalJSON implements the json.Unmarshaller interface
+func (t *Topic) UnmarshalJSON(data []byte) error {
+	var hex string
+	json.Unmarshal(data, &hex)
+	return t.FromHex(hex)
+}
+
+// MarshalJSON implements the json.Marshaller interface
+func (t *Topic) MarshalJSON() ([]byte, error) {
+	return json.Marshal(t.Hex())
+}