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- /*
- Copyright 2013 Google Inc.
-
- Licensed under the Apache License, Version 2.0 (the "License");
- you may not use this file except in compliance with the License.
- You may obtain a copy of the License at
-
- http://www.apache.org/licenses/LICENSE-2.0
-
- Unless required by applicable law or agreed to in writing, software
- distributed under the License is distributed on an "AS IS" BASIS,
- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- See the License for the specific language governing permissions and
- limitations under the License.
- */
-
- // Package consistenthash provides an implementation of a ring hash.
- package consistenthash
-
- 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
- }
-
- 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
- }
-
- // Returns true if there are no items available.
- func (m *Map) IsEmpty() bool {
- return len(m.keys) == 0
- }
-
- // Adds some keys to the hash.
- func (m *Map) Add(keys ...string) {
- for _, key := range keys {
- 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)
- }
-
- // 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]]
- }
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