Kevin Parsons 33a480106a backuptar: Fix sparse file handling ...

A recent OS change altered how sparse files are represented in backup
streams. This caused backuptar to no longer work with certain files. The
specific behavior that changed is as follows:
- Empty sparse files (size = 0), previously did not have any data or
  sparse block streams in the backup stream. Now, they will have a
  data stream with size = 0, and no sparse block streams.
- Sparse files with a single allocated range (e.g. a normal file that
  has the sparse attribute set) previously would not show as sparse in
  the backup stream. Now, they will show as sparse.

The old backuptar behavior assumed that if the sparse flag was set on
the data stream, then there would always be a set of sparse blocks
following. These changes break this assumption, and so require special
handling.

It is unsupported to have a data stream, marked sparse, that contains
file content AND a series of sparse block streams following. As far as
I can tell this is not a valid case for backup streams.

This change also cleans up some code and error messages, and expands on
the test coverage for backuptar.

For more information on backup stream format see: https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-bkup/f67950c8-d583-469a-83dd-c4ff4cedf533

Signed-off-by: Kevin Parsons <kevpar@microsoft.com>

2021-09-23 11:13:05 -07:00

..

noop.go

Include build tags to allow go get on non-Windows platforms. Fixes #30

2016-10-06 18:00:50 -03:00

strconv.go

Replace archive/tar fork with use of archive/tar

2020-07-17 00:45:58 +10:00

tar_test.go

backuptar: Fix sparse file handling

2021-09-23 11:13:05 -07:00

tar.go

backuptar: Fix sparse file handling

2021-09-23 11:13:05 -07:00