1 files changed, 70 insertions, 0 deletions
diff --git a/whisper/whisperv5/topic.go b/whisper/whisperv5/topic.go
new file mode 100644
index 000000000..c29c344be
--- /dev/null
+++ b/whisper/whisperv5/topic.go
@@ -0,0 +1,70 @@
+// 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/>.
+
+// Contains the Whisper protocol Topic element. For formal details please see
+// the specs at https://github.com/ethereum/wiki/wiki/Whisper-PoC-1-Protocol-Spec#topics.
+
+package whisperv5
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+// Topic represents a cryptographically secure, probabilistic partial
+// classifications of a message, determined as the first (left) 4 bytes of the
+// SHA3 hash of some arbitrary data given by the original author of the message.
+type TopicType [TopicLength]byte
+
+func BytesToTopic(b []byte) (t TopicType) {
+	sz := TopicLength
+	if x := len(b); x < TopicLength {
+		sz = x
+	}
+	for i := 0; i < sz; i++ {
+		t[i] = b[i]
+	}
+	return t
+}
+
+// String converts a topic byte array to a string representation.
+func (topic *TopicType) String() string {
+	return string(common.ToHex(topic[:]))
+}
+
+// UnmarshalJSON parses a hex representation to a topic.
+func (t *TopicType) UnmarshalJSON(input []byte) error {
+	length := len(input)
+	if length >= 2 && input[0] == '"' && input[length-1] == '"' {
+		input = input[1 : length-1]
+	}
+	// strip "0x" for length check
+	if len(input) > 1 && strings.ToLower(string(input[:2])) == "0x" {
+		input = input[2:]
+	}
+	// validate the length of the input
+	if len(input) != TopicLength*2 {
+		return fmt.Errorf("unmarshalJSON failed: topic must be exactly %d bytes", TopicLength)
+	}
+	b := common.FromHex(string(input))
+	if b == nil {
+		return fmt.Errorf("unmarshalJSON failed: wrong topic format")
+	}
+	*t = BytesToTopic(b)
+	return nil
+}