topic.go

// Copyright 2019 The Waku Library Authors.
//
// The Waku 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 Waku library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty off
// 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 Waku library. If not, see <http://www.gnu.org/licenses/>.
//
// This software uses the go-ethereum library, which is licensed
// under the GNU Lesser General Public Library, version 3 or any later.

package common

import (
	"github.com/ethereum/go-ethereum/common/hexutil"
)

// TopicType represents a cryptographically secure, probabilistic partial
// classifications of a message, determined as the first (leftmost) 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 hexutil.Encode(t[:])
}

// MarshalText returns the hex representation of t.
func (t TopicType) MarshalText() ([]byte, error) {
	return hexutil.Bytes(t[:]).MarshalText()
}

// UnmarshalText parses a hex representation to a topic.
func (t *TopicType) UnmarshalText(input []byte) error {
	return hexutil.UnmarshalFixedText("Topic", input, t[:])
}

// ToBloom converts the topic (4 bytes) to the bloom filter (64 bytes)
func (t TopicType) ToBloom() []byte {
	b := make([]byte, BloomFilterSize)
	var index [3]int
	for j := 0; j < 3; j++ {
		index[j] = int(t[j])
		if (t[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
}