| 1 | // SPDX-License-Identifier: AGPL-3.0-or-later |
| 2 | |
| 3 | package storage |
| 4 | |
| 5 | import ( |
| 6 | "crypto/rand" |
| 7 | "encoding/hex" |
| 8 | "fmt" |
| 9 | "io" |
| 10 | "os" |
| 11 | "path/filepath" |
| 12 | ) |
| 13 | |
| 14 | // WriteAtomic writes src to path via a tempfile in the same directory, |
| 15 | // fsyncs, and renames. A crash between write and rename leaves the temp |
| 16 | // file behind (callers may sweep these on startup) but never a partial |
| 17 | // file at path. |
| 18 | // |
| 19 | // The temp file MUST live on the same mount as path so the rename is |
| 20 | // atomic — callers should not pass paths that cross mount points. |
| 21 | func WriteAtomic(path string, src io.Reader) error { |
| 22 | dir := filepath.Dir(path) |
| 23 | suffix, err := randomSuffix() |
| 24 | if err != nil { |
| 25 | return fmt.Errorf("storage: atomic: random suffix: %w", err) |
| 26 | } |
| 27 | tmp := filepath.Join(dir, "."+filepath.Base(path)+".tmp."+suffix) |
| 28 | |
| 29 | f, err := os.OpenFile(tmp, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600) |
| 30 | if err != nil { |
| 31 | return fmt.Errorf("storage: atomic: open temp: %w", err) |
| 32 | } |
| 33 | cleanup := func() { _ = os.Remove(tmp) } |
| 34 | |
| 35 | if _, err := io.Copy(f, src); err != nil { |
| 36 | _ = f.Close() |
| 37 | cleanup() |
| 38 | return fmt.Errorf("storage: atomic: copy: %w", err) |
| 39 | } |
| 40 | if err := f.Sync(); err != nil { |
| 41 | _ = f.Close() |
| 42 | cleanup() |
| 43 | return fmt.Errorf("storage: atomic: fsync: %w", err) |
| 44 | } |
| 45 | if err := f.Close(); err != nil { |
| 46 | cleanup() |
| 47 | return fmt.Errorf("storage: atomic: close: %w", err) |
| 48 | } |
| 49 | if err := os.Rename(tmp, path); err != nil { |
| 50 | cleanup() |
| 51 | return fmt.Errorf("storage: atomic: rename: %w", err) |
| 52 | } |
| 53 | return nil |
| 54 | } |
| 55 | |
| 56 | func randomSuffix() (string, error) { |
| 57 | var b [8]byte |
| 58 | if _, err := rand.Read(b[:]); err != nil { |
| 59 | return "", err |
| 60 | } |
| 61 | return hex.EncodeToString(b[:]), nil |
| 62 | } |
| 63 |