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id.go
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id.go
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package main
import (
"encoding/json"
"hash/fnv"
"math/rand"
"os"
"path"
"time"
"github.com/oklog/ulid"
"github.com/pkg/errors"
)
var Clock = time.Now
// RunState describe configuration key generated at runtime we do not want to change when a restart occurs
type RunState struct {
ID uint64 `json:"id"`
}
func loadID(datadir string) (uint64, error) {
state := RunState{}
filename := path.Join(datadir, "run_state.json")
fd, err := os.Open(filename)
defer fd.Close()
if err != nil {
if os.IsNotExist(err) {
state, err = initRunState(datadir)
if err != nil {
return 0, errors.Wrap(err, "failed to create run state")
}
return state.ID, nil
}
return 0, err
}
err = json.NewDecoder(fd).Decode(&state)
if err != nil {
return 0, err
}
return state.ID, nil
}
func saveRunState(state RunState, datadir string) error {
fd, err := os.Create(path.Join(datadir, "run_state.json"))
if err != nil {
return err
}
defer fd.Close()
return json.NewEncoder(fd).Encode(&state)
}
func hashID(id string) uint64 {
h := fnv.New64()
h.Write([]byte(id))
return h.Sum64()
}
func initRunState(datadir string) (RunState, error) {
t := Clock().UTC()
entropy := rand.New(rand.NewSource(t.UnixNano()))
id, err := ulid.New(ulid.Timestamp(t), entropy)
if err != nil {
return RunState{}, err
}
state := RunState{ID: hashID(id.String())}
return state, saveRunState(state, datadir)
}