1 files changed, 61 insertions, 0 deletions
diff --git a/whisper/topic.go b/whisper/topic.go
new file mode 100644
index 000000000..a965c7cc2
--- /dev/null
+++ b/whisper/topic.go
@@ -0,0 +1,61 @@
+// 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 whisper
+
+import "github.com/ethereum/go-ethereum/crypto"
+
+// 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 Topic [4]byte
+
+// NewTopic creates a topic from the 4 byte prefix of the SHA3 hash of the data.
+func NewTopic(data []byte) Topic {
+	prefix := [4]byte{}
+	copy(prefix[:], crypto.Sha3(data)[:4])
+	return Topic(prefix)
+}
+
+// NewTopics creates a list of topics from a list of binary data elements, by
+// iteratively calling NewTopic on each of them.
+func NewTopics(data ...[]byte) []Topic {
+	topics := make([]Topic, len(data))
+	for i, element := range data {
+		topics[i] = NewTopic(element)
+	}
+	return topics
+}
+
+// NewTopicFromString creates a topic using the binary data contents of the
+// specified string.
+func NewTopicFromString(data string) Topic {
+	return NewTopic([]byte(data))
+}
+
+// NewTopicsFromStrings creates a list of topics from a list of textual data
+// elements, by iteratively calling NewTopicFromString on each of them.
+func NewTopicsFromStrings(data ...string) []Topic {
+	topics := make([]Topic, len(data))
+	for i, element := range data {
+		topics[i] = NewTopicFromString(element)
+	}
+	return topics
+}
+
+// String converts a topic byte array to a string representation.
+func (self *Topic) String() string {
+	return string(self[:])
+}
+
+// TopicSet represents a hash set to check if a topic exists or not.
+type topicSet map[string]struct{}
+
+// NewTopicSet creates a topic hash set from a slice of topics.
+func newTopicSet(topics []Topic) topicSet {
+	set := make(map[string]struct{})
+	for _, topic := range topics {
+		set[topic.String()] = struct{}{}
+	}
+	return topicSet(set)
+}