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topic.go
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topic.go
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package types
import (
"github.com/ethereum/go-ethereum/common/hexutil"
)
const (
// TopicLength is the expected length of the topic, in bytes
TopicLength = 4
// BloomFilterSize is the expected length of a bloom filter byte array, in bytes
BloomFilterSize = 64
)
// TopicType 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
// BytesToTopic converts from the byte array representation of a topic
// into the TopicType type.
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 (t *TopicType) String() string {
return EncodeHex(t[:])
}
// MarshalText returns the hex representation of t.
func (t TopicType) MarshalText() ([]byte, error) {
return HexBytes(t[:]).MarshalText()
}
// UnmarshalText parses a hex representation to a topic.
func (t *TopicType) UnmarshalText(input []byte) error {
return UnmarshalFixedText("Topic", input, t[:])
}
// TopicToBloom converts the topic (4 bytes) to the bloom filter (64 bytes)
func TopicToBloom(topic TopicType) []byte {
b := make([]byte, BloomFilterSize)
var index [3]int
for j := 0; j < 3; j++ {
index[j] = int(topic[j])
if (topic[3] & (1 << uint(j))) != 0 {
index[j] += 256
}
}
for j := 0; j < 3; j++ {
byteIndex := index[j] / 8
bitIndex := index[j] % 8
b[byteIndex] = (1 << uint(bitIndex))
}
return b
}
// BloomFilterMatch returns true if a sample matches a bloom filter
func BloomFilterMatch(filter, sample []byte) bool {
if filter == nil {
return true
}
for i := 0; i < BloomFilterSize; i++ {
f := filter[i]
s := sample[i]
if (f | s) != f {
return false
}
}
return true
}
// MakeFullNodeBloom returns a bloom filter which matches all topics
func MakeFullNodeBloom() []byte {
bloom := make([]byte, BloomFilterSize)
for i := 0; i < BloomFilterSize; i++ {
bloom[i] = 0xFF
}
return bloom
}
func StringToTopic(s string) (t TopicType) {
str, _ := hexutil.Decode(s)
return BytesToTopic(str)
}
func TopicTypeToByteArray(t TopicType) []byte {
topic := make([]byte, 4)
for i, b := range t {
topic[i] = b
}
return topic
}