diff options
Diffstat (limited to 'vendor/github.com/Microsoft/go-winio/backuptar/tar.go')
| -rw-r--r-- | vendor/github.com/Microsoft/go-winio/backuptar/tar.go | 74 |
1 files changed, 51 insertions, 23 deletions
diff --git a/vendor/github.com/Microsoft/go-winio/backuptar/tar.go b/vendor/github.com/Microsoft/go-winio/backuptar/tar.go index cb461ca31..689e4da6b 100644 --- a/vendor/github.com/Microsoft/go-winio/backuptar/tar.go +++ b/vendor/github.com/Microsoft/go-winio/backuptar/tar.go @@ -5,7 +5,6 @@ package backuptar import ( "archive/tar" "encoding/base64" - "errors" "fmt" "io" "io/ioutil" @@ -42,19 +41,14 @@ const ( hdrCreationTime = "LIBARCHIVE.creationtime" ) -func writeZeroes(w io.Writer, count int64) error { - buf := make([]byte, 8192) - c := len(buf) - for i := int64(0); i < count; i += int64(c) { - if int64(c) > count-i { - c = int(count - i) - } - _, err := w.Write(buf[:c]) - if err != nil { - return err - } +// zeroReader is an io.Reader that always returns 0s. +type zeroReader struct{} + +func (zr zeroReader) Read(b []byte) (int, error) { + for i := range b { + b[i] = 0 } - return nil + return len(b), nil } func copySparse(t *tar.Writer, br *winio.BackupStreamReader) error { @@ -71,16 +65,26 @@ func copySparse(t *tar.Writer, br *winio.BackupStreamReader) error { return fmt.Errorf("unexpected stream %d", bhdr.Id) } + // We can't seek backwards, since we have already written that data to the tar.Writer. + if bhdr.Offset < curOffset { + return fmt.Errorf("cannot seek back from %d to %d", curOffset, bhdr.Offset) + } // archive/tar does not support writing sparse files // so just write zeroes to catch up to the current offset. - err = writeZeroes(t, bhdr.Offset-curOffset) + if _, err := io.CopyN(t, zeroReader{}, bhdr.Offset-curOffset); err != nil { + return fmt.Errorf("seek to offset %d: %s", bhdr.Offset, err) + } if bhdr.Size == 0 { + // A sparse block with size = 0 is used to mark the end of the sparse blocks. break } n, err := io.Copy(t, br) if err != nil { return err } + if n != bhdr.Size { + return fmt.Errorf("copied %d bytes instead of %d at offset %d", n, bhdr.Size, bhdr.Offset) + } curOffset = bhdr.Offset + n } return nil @@ -221,20 +225,44 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size } } + // The logic for copying file contents is fairly complicated due to the need for handling sparse files, + // and the weird ways they are represented by BackupRead. A normal file will always either have a data stream + // with size and content, or no data stream at all (if empty). However, for a sparse file, the content can also + // be represented using a series of sparse block streams following the data stream. Additionally, the way sparse + // files are handled by BackupRead has changed in the OS recently. The specifics of the representation are described + // in the list at the bottom of this block comment. + // + // Sparse files can be represented in four different ways, based on the specifics of the file. + // - Size = 0: + // Previously: BackupRead yields no data stream and no sparse block streams. + // Recently: BackupRead yields a data stream with size = 0. There are no following sparse block streams. + // - Size > 0, no allocated ranges: + // BackupRead yields a data stream with size = 0. Following is a single sparse block stream with + // size = 0 and offset = <file size>. + // - Size > 0, one allocated range: + // BackupRead yields a data stream with size = <file size> containing the file contents. There are no + // sparse block streams. This is the case if you take a normal file with contents and simply set the + // sparse flag on it. + // - Size > 0, multiple allocated ranges: + // BackupRead yields a data stream with size = 0. Following are sparse block streams for each allocated + // range of the file containing the range contents. Finally there is a sparse block stream with + // size = 0 and offset = <file size>. + if dataHdr != nil { // A data stream was found. Copy the data. - if (dataHdr.Attributes & winio.StreamSparseAttributes) == 0 { + // We assume that we will either have a data stream size > 0 XOR have sparse block streams. + if dataHdr.Size > 0 || (dataHdr.Attributes&winio.StreamSparseAttributes) == 0 { if size != dataHdr.Size { return fmt.Errorf("%s: mismatch between file size %d and header size %d", name, size, dataHdr.Size) } - _, err = io.Copy(t, br) - if err != nil { - return err + if _, err = io.Copy(t, br); err != nil { + return fmt.Errorf("%s: copying contents from data stream: %s", name, err) } - } else { - err = copySparse(t, br) - if err != nil { - return err + } else if size > 0 { + // As of a recent OS change, BackupRead now returns a data stream for empty sparse files. + // These files have no sparse block streams, so skip the copySparse call if file size = 0. + if err = copySparse(t, br); err != nil { + return fmt.Errorf("%s: copying contents from sparse block stream: %s", name, err) } } } @@ -279,7 +307,7 @@ func WriteTarFileFromBackupStream(t *tar.Writer, r io.Reader, name string, size } else { // Unsupported for now, since the size of the alternate stream is not present // in the backup stream until after the data has been read. - return errors.New("tar of sparse alternate data streams is unsupported") + return fmt.Errorf("%s: tar of sparse alternate data streams is unsupported", name) } case winio.BackupEaData, winio.BackupLink, winio.BackupPropertyData, winio.BackupObjectId, winio.BackupTxfsData: // ignore these streams |