1 files changed, 53 insertions, 0 deletions
diff --git a/lib/fstream/uncompress/autodetect.c b/lib/fstream/uncompress/autodetect.c
new file mode 100644
index 0000000..4ffe078
--- /dev/null
+++ b/lib/fstream/uncompress/autodetect.c
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-3.0-or-later */
+/*
+ * autodetect.c
+ *
+ * Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
+ */
+#include "../internal.h"
+
+static const struct {
+	int id;
+	const sqfs_u8 *value;
+	size_t len;
+} magic[] = {
+	{ FSTREAM_COMPRESSOR_GZIP, (const sqfs_u8 *)"\x1F\x8B\x08", 3 },
+	{ FSTREAM_COMPRESSOR_XZ, (const sqfs_u8 *)("\xFD" "7zXZ"), 6 },
+};
+
+int istream_detect_compressor(istream_t *strm,
+			      int (*probe)(const sqfs_u8 *data, size_t size))
+{
+	size_t i;
+	int ret;
+
+	ret = istream_precache(strm);
+	if (ret != 0)
+		return ret;
+
+	if (probe != NULL) {
+		ret = probe(strm->buffer + strm->buffer_offset,
+			    strm->buffer_used - strm->buffer_offset);
+		if (ret < 0)
+			return ret;
+
+		/* XXX: this means the data is uncompressed. We do this check
+		   first since it might be perfectly OK for the uncompressed
+		   data to contain a magic number from the table. */
+		if (ret > 0)
+			return 0;
+	}
+
+	for (i = 0; i < sizeof(magic) / sizeof(magic[0]); ++i) {
+		if ((strm->buffer_used - strm->buffer_offset) < magic[i].len)
+			continue;
+
+		ret = memcmp(strm->buffer + strm->buffer_offset,
+			     magic[i].value, magic[i].len);
+
+		if (ret == 0)
+			return magic[i].id;
+	}
+
+	return 0;
+}