Proving that Golang, as of Go1.5.1 does not maintain sparse files during file compression with compress/tar.

Steps to reproduce:

vagrant up

During Vagrant Provision, Vagrant will perform the following steps:

• Install Go1.5.1

• Create a Sparse file on the Linux Filesystem by:

# truncate -s 512M sparse.img

• Verify that the created file has an apparent size of 512M, but an actual size of 0M

# ls -lash sparse.img
0 -rw-r--r-- 1 root root 512M Nov 30 21:29 sparse.img

• Run compress.go, which uses archive/tar to compress the sparse file both with and without the sparse type set in the archive header. This creates directories of non_sparse/ and sparse/ for non-sparse and sparse compression, named respectively.

• Extract both of the archives created from compress.go.

# tar -C non_sparse/ -xf non_sparse/non_sparse.tar
# tar -C sparse/ -xf sparse/sparse.tar

• Verifies that Go did NOT keep file sparseness regardless of whether the GNUSparse type was set in the archive header or not.

# ls -lash non_sparse/sparse.img
512M -rw-r--r-- 1 root root 512M Nov 30 21:29 non_sparse/sparse.img
# ls -lash sparse/sparse.img
513M -rw-r--r-- 1 root root 512M Nov 30 21:29 sparse/sparse.img

• Compresses the sparse file using GNU Tar, maintaining the sparseness of the file

tar -Scf tar/sparse.tar sparse.img

• Extract the archive created from GNU Tar.

tar -C tar/ -xf tar/sparse.tar

• Verify that compression via Tar, maintains the sparse file.

ls -lash tar/sparse.img
0 -rw-r--r-- 1 root root 512M Nov 30 21:29 tar/sparse.img