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hash.go
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hash.go
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package ring
import (
"hash/crc32"
"sort"
"strconv"
)
type Hash func(data []byte) uint32
type Map struct {
hash Hash
replicas int
keys []int // Sorted
hashMap map[int]string
}
// New returns a new ConsistentHashMap
func New(replicas int, fn Hash) *Map {
m := &Map{
replicas: replicas,
hash: fn,
hashMap: make(map[int]string),
}
if m.hash == nil {
m.hash = crc32.ChecksumIEEE
}
return m
}
// IsEmpty returns true if there are no items available.
func (m *Map) IsEmpty() bool {
return len(m.keys) == 0
}
// Add adds some nodes to the hash.
func (m *Map) Add(nodes ...string) {
for _, key := range nodes {
for i := 0; i < m.replicas; i++ {
hash := int(m.hash([]byte(strconv.Itoa(i) + key)))
m.keys = append(m.keys, hash)
m.hashMap[hash] = key
}
}
sort.Ints(m.keys)
}
// Remove nodes from hash
func (m *Map) Remove(nodes ...string) {
for _, key := range nodes {
for i := 0; i < m.replicas; i++ {
hash := int(m.hash([]byte(strconv.Itoa(i) + key)))
idx := sort.SearchInts(m.keys, hash)
if idx >= 0 {
copy(m.keys[idx:], m.keys[idx+1:])
m.keys = m.keys[:len(m.keys)-1]
}
delete(m.hashMap, hash)
}
}
}
// Get gets the closest item in the hash to the provided key.
func (m *Map) Get(key string) string {
if m.IsEmpty() {
return ""
}
hash := int(m.hash([]byte(key)))
// Binary search for appropriate replica.
idx := sort.Search(len(m.keys), func(i int) bool { return m.keys[i] >= hash })
// Means we have cycled back to the first replica.
if idx == len(m.keys) {
idx = 0
}
return m.hashMap[m.keys[idx]]
}