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

   1 package main
   2
   3 import (
   4         "errors"
   5         "fmt"
   6         "os"
   7         "path/filepath"
   8 )
   9
  10 // writeFileAtomic replaces the file at path with data through a temporary file
  11 // and a rename. A reader or a crash of the process sees the old file or the new
  12 // file, never a part of one.
  13 func writeFileAtomic(path string, data []byte) error {
  14         file, err := os.CreateTemp(filepath.Dir(path), "."+filepath.Base(path)+".*")
  15         if err != nil {
  16                 return fmt.Errorf("create temporary file: %w", err)
  17         }
  18
  19         _, err = file.Write(data)
  20         err = errors.Join(err, file.Close())
  21         if err == nil {
  22                 err = os.Rename(file.Name(), path)
  23         }
  24
  25         if err != nil {
  26                 return errors.Join(fmt.Errorf("replace file: %w", err), os.Remove(file.Name()))
  27         }
  28
  29         return nil
  30 }
  31
  32 // writeFileDurable replaces path only after syncing its private temporary file.
  33 // It syncs the directory after rename before it reports success. An error after
  34 // rename has an uncertain outcome, so callers must stop writes until recovery.
  35 func writeFileDurable(path string, data []byte) (err error) {
  36         file, err := os.CreateTemp(filepath.Dir(path), "."+filepath.Base(path)+".*")
  37         if err != nil {
  38                 return fmt.Errorf("create durable temporary file: %w", err)
  39         }
  40
  41         defer func() {
  42                 removeErr := os.Remove(file.Name())
  43                 if removeErr != nil && !errors.Is(removeErr, os.ErrNotExist) {
  44                         err = errors.Join(err, fmt.Errorf("remove durable temporary file: %w", removeErr))
  45                 }
  46         }()
  47
  48         _, err = file.Write(data)
  49         if err == nil {
  50                 err = file.Sync()
  51         }
  52
  53         err = errors.Join(err, file.Close())
  54         if err != nil {
  55                 return fmt.Errorf("write durable temporary file: %w", err)
  56         }
  57
  58         err = os.Rename(file.Name(), path)
  59         if err != nil {
  60                 return fmt.Errorf("publish durable file: %w", err)
  61         }
  62
  63         directory, err := os.Open(filepath.Dir(path))
  64         if err != nil {
  65                 return fmt.Errorf("open durable directory: %w", err)
  66         }
  67
  68         err = errors.Join(directory.Sync(), directory.Close())
  69         if err != nil {
  70                 return fmt.Errorf("sync durable directory: %w", err)
  71         }
  72
  73         return nil
  74 }