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hashring.go
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hashring.go
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package shard
import (
"encoding/json"
"fmt"
"regexp"
"strconv"
"github.com/gojekfarm/hashring"
"github.com/gojektech/weaver"
"github.com/pkg/errors"
)
func NewHashRingStrategy(data json.RawMessage) (weaver.Sharder, error) {
cfg := HashRingStrategyConfig{}
if err := json.Unmarshal(data, &cfg); err != nil {
return nil, err
}
if err := cfg.Validate(); err != nil {
return nil, err
}
hashRing, backends, err := hashringBackends(cfg)
if err != nil {
return nil, err
}
return &HashRingStrategy{
hashRing: hashRing,
backends: backends,
}, nil
}
type HashRingStrategy struct {
hashRing *hashring.HashRingCluster
backends map[string]*weaver.Backend
}
func (rs HashRingStrategy) Shard(key string) (*weaver.Backend, error) {
serverName := rs.hashRing.GetServer(key)
return rs.backends[serverName], nil
}
type HashRingStrategyConfig struct {
TotalVirtualBackends *int `json:"totalVirtualBackends"`
Backends map[string]BackendDefinition `json:"backends"`
}
func (hrCfg HashRingStrategyConfig) Validate() error {
if hrCfg.Backends == nil || len(hrCfg.Backends) == 0 {
return fmt.Errorf("No Shard Backends Specified Or Specified Incorrectly")
}
for _, backend := range hrCfg.Backends {
if err := backend.Validate(); err != nil {
return errors.Wrapf(err, "failed to validate backendDefinition for backend: %s", backend.BackendName)
}
}
return nil
}
func hashringBackends(cfg HashRingStrategyConfig) (*hashring.HashRingCluster, map[string]*weaver.Backend, error) {
if cfg.TotalVirtualBackends == nil || *cfg.TotalVirtualBackends < 0 {
defaultBackends := 1000
cfg.TotalVirtualBackends = &defaultBackends
}
backendDetails := map[string]*weaver.Backend{}
hashRingCluster := hashring.NewHashRingCluster(*cfg.TotalVirtualBackends)
virtualNodesFound := map[int]bool{}
maxValue := 0
rangeRegexp := regexp.MustCompile("^([\\d]+)-([\\d]+)$")
for k, v := range cfg.Backends {
matches := rangeRegexp.FindStringSubmatch(k)
if len(matches) != 3 {
return nil, nil, fmt.Errorf("Invalid range key format: %s", k)
}
end, _ := strconv.Atoi(matches[2])
start, _ := strconv.Atoi(matches[1])
if end <= start {
return nil, nil, fmt.Errorf("Invalid range key %d-%d for backends", start, end)
}
for i := start; i <= end; i++ {
if _, ok := virtualNodesFound[i]; ok {
return nil, nil, fmt.Errorf("Overlap seen in range key %d", i)
}
virtualNodesFound[i] = true
if maxValue < i {
maxValue = i
}
}
backend, err := parseBackend(v)
if err != nil {
return nil, nil, err
}
backendDetails[backend.Name] = backend
hashRingCluster.AddServer(backend.Name, k)
}
if maxValue != *cfg.TotalVirtualBackends-1 {
return nil, nil, fmt.Errorf("Shard is out of bounds Max %d found %d", *cfg.TotalVirtualBackends-1, maxValue)
}
for i := 0; i < *cfg.TotalVirtualBackends; i++ {
if _, ok := virtualNodesFound[i]; !ok {
return nil, nil, fmt.Errorf("Shard is missing coverage for %d", i)
}
}
return hashRingCluster, backendDetails, nil
}