ms2k
e4b84d9802
Resume goals after transient API failures with persisted exponential backoff while respecting pauses and interruptions.
78 lines
1.6 KiB
Go
78 lines
1.6 KiB
Go
package main
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import (
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"encoding/json"
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"errors"
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"fmt"
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"os"
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"path/filepath"
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"syscall"
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)
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type store struct {
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path string
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lock *os.File
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Watches map[string]*watch `json:"watches"`
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}
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func openStore(path string) (*store, error) {
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if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
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return nil, err
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}
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lock, err := os.OpenFile(path+".lock", os.O_CREATE|os.O_RDWR, 0600)
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if err != nil {
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return nil, err
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}
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if err := syscall.Flock(int(lock.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
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return nil, fmt.Errorf("checkpoint is already in use: %w", errors.Join(err, lock.Close()))
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}
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s := &store{path: path, lock: lock, Watches: make(map[string]*watch)}
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data, err := os.ReadFile(path)
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if errors.Is(err, os.ErrNotExist) {
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return s, nil
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}
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if err == nil {
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err = json.Unmarshal(data, s)
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}
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if err == nil && s.Watches == nil {
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err = errors.New("checkpoint has no watches")
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}
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if err != nil {
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return nil, errors.Join(err, s.close())
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}
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return s, nil
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}
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func (s *store) close() error { return s.lock.Close() }
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func (s *store) save() error {
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data, err := json.Marshal(s)
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if err != nil {
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return err
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}
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f, err := os.CreateTemp(filepath.Dir(s.path), ".state-*")
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if err != nil {
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return err
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}
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defer func() { _ = os.Remove(f.Name()) }()
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if _, err = f.Write(data); err == nil {
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err = f.Sync()
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}
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closeErr := f.Close()
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if err != nil {
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return err
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}
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if closeErr != nil {
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return closeErr
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}
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return os.Rename(f.Name(), s.path)
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}
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func (s *store) watch(id string) *watch {
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w := s.Watches[id]
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if w == nil {
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w = &watch{}
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s.Watches[id] = w
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}
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return w
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}
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