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

   1 package main
   2
   3 import (
   4         "archive/tar"
   5         "compress/gzip"
   6         "context"
   7         "errors"
   8         "fmt"
   9         "io"
  10         "io/fs"
  11         "os"
  12         "path/filepath"
  13         "strings"
  14 )
  15
  16 // backupArchive writes the files in root to path through a private temporary
  17 // file and a rename. Only directories and regular files enter the archive.
  18 func backupArchive(ctx context.Context, root, path string) (size int64, err error) {
  19         file, err := os.CreateTemp(filepath.Dir(path), ".onechat-backup-*")
  20         if err != nil {
  21                 return 0, fmt.Errorf("create archive: %w", err)
  22         }
  23
  24         defer func() {
  25                 err = errors.Join(err, file.Close())
  26                 removeErr := os.Remove(file.Name())
  27                 if !errors.Is(removeErr, os.ErrNotExist) {
  28                         err = errors.Join(err, removeErr)
  29                 }
  30         }()
  31
  32         compressed := gzip.NewWriter(file)
  33         archive := tar.NewWriter(compressed)
  34         err = filepath.WalkDir(root, func(path string, entry fs.DirEntry, err error) error {
  35                 if err != nil {
  36                         return fmt.Errorf("walk backup: %w", err)
  37                 }
  38
  39                 if ctx.Err() != nil {
  40                         return ctx.Err()
  41                 }
  42
  43                 if path == root {
  44                         return nil
  45                 }
  46
  47                 name, err := filepath.Rel(root, path)
  48                 if err != nil {
  49                         return fmt.Errorf("name archive entry: %w", err)
  50                 }
  51
  52                 info, err := entry.Info()
  53                 if err != nil {
  54                         return fmt.Errorf("read backup entry: %w", err)
  55                 }
  56
  57                 if !info.IsDir() && !info.Mode().IsRegular() {
  58                         return fmt.Errorf("unsupported backup entry %q", name)
  59                 }
  60
  61                 header, err := tar.FileInfoHeader(info, "")
  62                 if err != nil {
  63                         return fmt.Errorf("make archive header: %w", err)
  64                 }
  65
  66                 header.Name = filepath.ToSlash(name)
  67                 header.Uid, header.Gid = 0, 0
  68                 header.Uname, header.Gname = "", ""
  69                 err = archive.WriteHeader(header)
  70                 if err != nil {
  71                         return fmt.Errorf("write archive header: %w", err)
  72                 }
  73
  74                 if info.IsDir() {
  75                         return nil
  76                 }
  77
  78                 err = backupCopyFile(ctx, archive, path, info.Size())
  79                 if err != nil {
  80                         return fmt.Errorf("archive file: %w", err)
  81                 }
  82
  83                 return nil
  84         })
  85         err = errors.Join(err, archive.Close(), compressed.Close())
  86         if err != nil {
  87                 return 0, fmt.Errorf("write archive: %w", err)
  88         }
  89
  90         err = file.Sync()
  91         if err != nil {
  92                 return 0, fmt.Errorf("sync archive: %w", err)
  93         }
  94
  95         info, err := file.Stat()
  96         if err != nil {
  97                 return 0, fmt.Errorf("read archive size: %w", err)
  98         }
  99
 100         err = os.Rename(file.Name(), path)
 101         if err != nil {
 102                 return 0, fmt.Errorf("install archive: %w", err)
 103         }
 104
 105         return info.Size(), nil
 106 }
 107
 108 // backupExtract restores regular files and directories in an empty staging
 109 // directory. Links, duplicate entries, unsafe names, and special modes fail.
 110 // Directory modes apply last so a read-only directory can hold files.
 111 func backupExtract(ctx context.Context, path, root string) (err error) {
 112         file, err := os.Open(path)
 113         if err != nil {
 114                 return fmt.Errorf("open archive: %w", err)
 115         }
 116
 117         defer func() {
 118                 err = errors.Join(err, file.Close())
 119         }()
 120
 121         compressed, err := gzip.NewReader(file)
 122         if err != nil {
 123                 return fmt.Errorf("open compressed archive: %w", err)
 124         }
 125
 126         defer func() {
 127                 err = errors.Join(err, compressed.Close())
 128         }()
 129
 130         archive := tar.NewReader(BackupReader{
 131                 ctx:    ctx,
 132                 reader: compressed,
 133         })
 134         seen := make(map[string]bool)
 135
 136         var directories []*tar.Header
 137
 138         for {
 139                 var header *tar.Header
 140
 141                 header, err = archive.Next()
 142                 if errors.Is(err, io.EOF) {
 143                         break
 144                 }
 145
 146                 if err != nil {
 147                         return fmt.Errorf("read archive entry: %w", err)
 148                 }
 149
 150                 name := strings.TrimSuffix(header.Name, "/")
 151                 if !filepath.IsLocal(name) || strings.Contains(name, "\\") || filepath.Clean(name) != name || backupExcluded(name) {
 152                         return fmt.Errorf("unsafe archive path %q", header.Name)
 153                 }
 154
 155                 if seen[name] {
 156                         return fmt.Errorf("duplicate archive path %q", name)
 157                 }
 158
 159                 seen[name] = true
 160                 if header.Mode & ^int64(0o777) != 0 {
 161                         return fmt.Errorf("unsafe archive mode for %q", name)
 162                 }
 163
 164                 target := filepath.Join(root, name)
 165                 switch header.Typeflag {
 166                 case tar.TypeDir:
 167                         err = os.MkdirAll(target, 0o700)
 168                         directories = append(directories, header)
 169                 case tar.TypeReg:
 170                         err = os.MkdirAll(filepath.Dir(target), 0o700)
 171                         if err == nil {
 172                                 err = backupExtractFile(archive, target, os.FileMode(header.Mode))
 173                         }
 174                 default:
 175                         return fmt.Errorf("unsupported archive entry %q", name)
 176                 }
 177
 178                 if err != nil {
 179                         return fmt.Errorf("restore archive entry %q: %w", name, err)
 180                 }
 181         }
 182
 183         // Read through the gzip trailer to check its checksum.
 184         _, err = io.Copy(io.Discard, compressed)
 185         if err != nil {
 186                 return fmt.Errorf("check archive checksum: %w", err)
 187         }
 188
 189         for i := len(directories) - 1; i >= 0; i-- {
 190                 header := directories[i]
 191                 err = os.Chmod(filepath.Join(root, header.Name), os.FileMode(header.Mode))
 192                 if err != nil {
 193                         return fmt.Errorf("restore directory mode: %w", err)
 194                 }
 195         }
 196
 197         return nil
 198 }
 199
 200 // BackupReader checks cancellation between reads of an archive or file.
 201 type BackupReader struct {
 202         ctx    context.Context
 203         reader io.Reader
 204 }
 205
 206 func (r BackupReader) Read(data []byte) (int, error) {
 207         if r.ctx.Err() != nil {
 208                 return 0, r.ctx.Err()
 209         }
 210
 211         count, err := r.reader.Read(data)
 212         if err != nil {
 213                 return count, fmt.Errorf("read backup data: %w", err)
 214         }
 215
 216         return count, nil
 217 }
 218
 219 // backupCopyFile copies the size fixed at the snapshot of path. Growth after
 220 // that point is not part of the copy, and a shorter file is an error.
 221 func backupCopyFile(ctx context.Context, out io.Writer, path string, size int64) (err error) {
 222         file, err := os.Open(path)
 223         if err != nil {
 224                 return fmt.Errorf("open backup file: %w", err)
 225         }
 226
 227         defer func() {
 228                 err = errors.Join(err, file.Close())
 229         }()
 230
 231         _, err = io.CopyN(out, BackupReader{
 232                 ctx:    ctx,
 233                 reader: file,
 234         }, size)
 235         if err != nil {
 236                 return fmt.Errorf("copy backup file: %w", err)
 237         }
 238
 239         return nil
 240 }
 241
 242 func backupExtractFile(in io.Reader, path string, mode os.FileMode) (err error) {
 243         file, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
 244         if err != nil {
 245                 return fmt.Errorf("create restored file: %w", err)
 246         }
 247
 248         defer func() {
 249                 err = errors.Join(err, file.Close())
 250         }()
 251
 252         _, err = io.Copy(file, in)
 253         if err != nil {
 254                 return fmt.Errorf("write restored file: %w", err)
 255         }
 256
 257         err = file.Chmod(mode)
 258         if err != nil {
 259                 return fmt.Errorf("restore file mode: %w", err)
 260         }
 261
 262         return nil
 263 }
 264
 265 // backupExcluded keeps runtime locks, sockets, probe files, and import copies
 266 // out of the snapshot.
 267 func backupExcluded(name string) bool {
 268         first, _, _ := strings.Cut(filepath.ToSlash(name), "/")
 269         if first == socketFileName || first == tokenLockFileName || first == "probe" || strings.HasPrefix(first, "agent-backup-") {
 270                 return true
 271         }
 272
 273         if filepath.Base(name) == "lock" {
 274                 return true
 275         }
 276
 277         return false
 278 }