ui-snapshot: add support for zstd compression

This patch adds support for zstd [0] compressed snapshots (*.tar.zst).
We enable multiple working threads (-T0), but keep default compression
level. The latter can be influenced by environment variable.

[0] https://www.zstd.net/

Signed-off-by: Christian Hesse <mail@eworm.de>

cgitrc.5.txt

@@ -407,9 +407,12 @@ side-by-side-diffs::
 snapshots::
 	Text which specifies the default set of snapshot formats that cgit
 	generates links for. The value is a space-separated list of zero or
-	more of the values "tar", "tar.gz", "tar.bz2", "tar.xz", "tar.lz" and
-	"zip". The special value "all" enables all snapshot formats.
-	Default value: none.
+	more of the values "tar", "tar.gz", "tar.bz2", "tar.lz", "tar.xz",
+	"tar.zst" and "zip". The special value "all" enables all snapshot
+	formats. Default value: none.
+	All compressors use default settings. Some settings can be influenced
+	with environment variables, for example set ZSTD_CLEVEL=10 in web
+	server environment for higher (but slower) zstd compression.
 
 source-filter::
 	Specifies a command which will be invoked to format plaintext blobs

tests/setup.sh

@@ -104,7 +104,7 @@ virtual-root=/
 cache-root=$PWD/cache
 
 cache-size=1021
-snapshots=tar.gz tar.bz tar.lz tar.xz zip
+snapshots=tar.gz tar.bz tar.lz tar.xz tar.zst zip
 enable-log-filecount=1
 enable-log-linecount=1
 summary-log=5

tests/t0107-snapshot.sh

@@ -122,6 +122,48 @@ test_expect_success XZ 'verify untarred file-5' '
 	test_line_count = 1 master/file-5
 '
 
+if test -n "$(which zstd 2>/dev/null)"; then
+	test_set_prereq ZSTD
+else
+	say 'Skipping ZSTD validation tests: zstd not found'
+fi
+
+test_expect_success ZSTD 'get foo/snapshot/master.tar.zst' '
+	cgit_url "foo/snapshot/master.tar.zst" >tmp
+'
+
+test_expect_success ZSTD 'check html headers' '
+	head -n 1 tmp |
+	grep "Content-Type: application/x-zstd" &&
+
+	head -n 2 tmp |
+	grep "Content-Disposition: inline; filename=.master.tar.zst."
+'
+
+test_expect_success ZSTD 'strip off the header lines' '
+	strip_headers <tmp >master.tar.zst
+'
+
+test_expect_success ZSTD 'verify zstd format' '
+	zstd --test master.tar.zst &&
+	cp master.tar.zst /tmp/.
+'
+
+test_expect_success ZSTD 'untar' '
+	rm -rf master &&
+	tar --zstd -xf master.tar.zst
+'
+
+test_expect_success ZSTD 'count files' '
+	ls master/ >output &&
+	test_line_count = 5 output
+'
+
+test_expect_success ZSTD 'verify untarred file-5' '
+	grep "^5$" master/file-5 &&
+	test_line_count = 1 master/file-5
+'
+
 test_expect_success 'get foo/snapshot/master.zip' '
 	cgit_url "foo/snapshot/master.zip" >tmp
 '

ui-snapshot.c

@@ -91,6 +91,12 @@ static int write_tar_xz_archive(const char *hex, const char *prefix)
 	return write_compressed_tar_archive(hex, prefix, argv);
 }
 
+static int write_tar_zstd_archive(const char *hex, const char *prefix)
+{
+	char *argv[] = { "zstd", "-T0", NULL };
+	return write_compressed_tar_archive(hex, prefix, argv);
+}
+
 const struct cgit_snapshot_format cgit_snapshot_formats[] = {
 	/* .tar must remain the 0 index */
 	{ ".tar",	"application/x-tar",	write_tar_archive	},
@@ -98,6 +104,7 @@ const struct cgit_snapshot_format cgit_snapshot_formats[] = {
 	{ ".tar.bz2",	"application/x-bzip2",	write_tar_bzip2_archive	},
 	{ ".tar.lz",	"application/x-lzip",	write_tar_lzip_archive	},
 	{ ".tar.xz",	"application/x-xz",	write_tar_xz_archive	},
+	{ ".tar.zst",	"application/x-zstd",	write_tar_zstd_archive	},
 	{ ".zip",	"application/x-zip",	write_zip_archive	},
 	{ NULL }
 };