git.giacomolli.uk - onechat/blob - lock.go

   1 package main
   2
   3 import (
   4         "errors"
   5         "fmt"
   6         "os"
   7         "path/filepath"
   8         "syscall"
   9 )
  10
  11 // tokenLockFileName is the lock file of the token file in the data directory.
  12 const tokenLockFileName = "auth.lock"
  13
  14 // errTokensInUse tells that another onechat process uses the token file.
  15 var errTokensInUse = errors.New("another onechat process uses the token file, such as the daemon")
  16
  17 // errLocked tells that another process owns the chat.
  18 var errLocked = errors.New("another process owns the chat")
  19
  20 // lockTokens takes the lock of the token file in dir. Each process that reads
  21 // or refreshes the tokens holds it, because a refresh in one process rotates
  22 // the refresh token of the other and logs it out.
  23 func lockTokens(dir string) (*os.File, error) {
  24         lock, err := lockFile(filepath.Join(dir, tokenLockFileName))
  25         if errors.Is(err, errLocked) {
  26                 return nil, errTokensInUse
  27         }
  28
  29         return lock, err
  30 }
  31
  32 // lockFile opens the file at path and takes an exclusive lock on it. The lock
  33 // stays until the file closes or the process ends.
  34 func lockFile(path string) (*os.File, error) {
  35         file, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR, 0o600)
  36         if err != nil {
  37                 return nil, fmt.Errorf("open lock file: %w", err)
  38         }
  39
  40         err = syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
  41         if errors.Is(err, syscall.EWOULDBLOCK) {
  42                 err = errLocked
  43         }
  44
  45         if err != nil {
  46                 return nil, errors.Join(fmt.Errorf("lock chat: %w", err), file.Close())
  47         }
  48
  49         return file, nil
  50 }