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// 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 mru
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 resource 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())
}
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