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naive.go
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naive.go
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package hyperbloom
import (
"bufio"
"bytes"
"errors"
"fmt"
"io"
"log"
"os"
"sync"
)
/*
NaiveBloomFilter is a bloomfilter backed by a byte vector rather than a bitvector. As a result, lookups are faster although at an 8x space penalty. It uses central locking via a RWMutex
*/
type NaiveBloomFilter struct {
bv []byte //bytevector
size uint64 //Size of bytevector. MUST BE A POWER OF 2.
hf int //Number of hash functions
mut *sync.RWMutex //Centralized mutex
}
/*
NewNaiveBloomfilter allocates a NaiveBloomFilter with a given size (in bytes) and using a certain number of hashes.
Size must be a power of 2 and larger than 64
*/
func NewNaiveBloomFilter(size uint64, hf int) (*NaiveBloomFilter, error) {
var bf NaiveBloomFilter
bf.size = size
if bf.size < 64 {
return nil, errors.New("Filter size must be at least 64")
} else if (bf.size & (bf.size - 1)) != 0 {
return nil, errors.New("Size must be a power of 2")
}
bf.bv = make([]byte, size)
bf.hf = int(hf)
bf.mut = &sync.RWMutex{}
for i := 0; i < len(bf.bv); i++ {
bf.bv[i] = 0
}
return &bf, nil
}
func (bf NaiveBloomFilter) setByte(idx uint64) error {
if int(idx) >= len(bf.bv) {
return errors.New("Index can't be larger than filter size")
}
bf.mut.Lock()
bf.bv[idx] = 1
bf.mut.Unlock()
return nil
}
func (bf NaiveBloomFilter) setByteAsync(idx uint64) error {
if int(idx) >= len(bf.bv) {
return errors.New("Index can't be larger than filter size")
}
bf.bv[idx] = 1
return nil
}
func (bf NaiveBloomFilter) getByte(idx uint64) (bool, error) {
if idx >= bf.size {
return false, errors.New("Index can't be larger than filter size")
}
bf.mut.RLock()
switch bf.bv[idx] {
case 1:
bf.mut.RUnlock()
return true, nil
default:
bf.mut.RUnlock()
return false, nil
}
}
func (bf NaiveBloomFilter) getByteAsync(idx uint64) (bool, error) {
if idx >= bf.size {
return false, errors.New("Index can't be larger than filter size")
}
switch bf.bv[idx] {
case 1:
return true, nil
default:
return false, nil
}
}
/*Looks up an entry into the NaiveBloomFilter. Returns true if a match is found, false otherwise. If an error occurs, will also return false.
This perform a reader lock on the filter (writers must wait until all active readers finish).
*/
func (bf NaiveBloomFilter) Lookup(entry string) (bool, error) {
hashes := hashEntry([]byte(entry), bf.hf)
for i := 0; i < bf.hf; i++ {
lookup_idx := hashes[i] & (bf.size - 1)
if exists, err := bf.getByte(lookup_idx); !exists {
if err != nil {
return false, err
}
return false, nil
}
}
return true, nil
}
/*Looks up an entry into the NaiveBloomFilter. Returns true if a match is found, false otherwise. If an error occurs, will also return false.
This won't lock the filter.
*/
func (bf NaiveBloomFilter) LookupAsync(entry string) (bool, error) {
hashes := hashEntry([]byte(entry), bf.hf)
for i := 0; i < bf.hf; i++ {
lookup_idx := hashes[i] & (bf.size - 1)
if exists, err := bf.getByteAsync(lookup_idx); !exists {
if err != nil {
return false, err
}
return false, nil
}
}
return true, nil
}
/*Inserts an entry into the NaiveBloomFilter. Locks the filter.*/
func (bf NaiveBloomFilter) Insert(entry string) error {
hashes := hashEntry([]byte(entry), bf.hf)
for i := 0; i < bf.hf; i++ {
insert_idx := hashes[i] & (bf.size - 1)
err := bf.setByte(insert_idx)
if err != nil {
return err
}
}
return nil
}
/*Inserts an entry into the NaiveBloomFilter. Does not lock the filter.*/
func (bf NaiveBloomFilter) InsertAsync(entry string) error {
hashes := hashEntry([]byte(entry), bf.hf)
for i := 0; i < bf.hf; i++ {
insert_idx := hashes[i] & (bf.size - 1)
err := bf.setByteAsync(insert_idx)
if err != nil {
return err
}
}
return nil
}
/*Writes underlying byte vector to a file.*/
func (bf NaiveBloomFilter) Write(filename string) error {
var err error
f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0777)
defer f.Close()
if err != nil {
return err
}
var b bytes.Buffer
for i := 0; i < int(bf.size); i++ {
bin := fmt.Sprintf("%d", bf.bv[i])
b.Write([]byte(bin))
}
bv := b.Bytes()
log.Println("Writing byte vector to file...")
f.Write(bv)
f.Close()
log.Printf("Successfully wrote bytevector to file: %s\n", filename)
return nil
}
/*Merges current byte vector with one loaded from a file.
This locks the filter for each nonzero byte being written.
*/
func (bf NaiveBloomFilter) Load(filename string) error {
f, err := os.Open(filename)
defer f.Close()
if err != nil {
return err
}
buf_rdr := bufio.NewReader(f)
bv, err := buf_rdr.ReadBytes('\n')
if err != nil && err != io.EOF {
return err
}
log.Println("Bytes read successfully")
if bf.size != uint64(len(bv)-1) {
return errors.New(fmt.Sprintf("File bitvector size: %d. Specified size: %d. Mismatch.", len(bv)-1, bf.size))
}
for i := 0; i < len(bv); i++ {
if bv[i] > 0 {
bf.setByte(uint64(i))
}
}
fmt.Printf("Loaded bitvector from file: %s\n", filename)
return nil
}