1 files changed, 62 insertions, 0 deletions
diff --git a/archival/libunarchive/check_header_gzip.c b/archival/libunarchive/check_header_gzip.c
new file mode 100644
index 000000000..3e42035b9
--- /dev/null
+++ b/archival/libunarchive/check_header_gzip.c
@@ -0,0 +1,62 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
+ */
+#include <stdlib.h>
+#include <unistd.h>
+#include "libbb.h"
+#include "unarchive.h" /* for external decl of check_header_gzip */
+
+void check_header_gzip(int src_fd)
+{
+	union {
+		unsigned char raw[8];
+		struct {
+			unsigned char method;
+			unsigned char flags;
+			unsigned int mtime;
+			unsigned char xtra_flags;
+			unsigned char os_flags;
+		} formatted;
+	} header;
+
+	xread(src_fd, header.raw, 8);
+
+	/* Check the compression method */
+	if (header.formatted.method != 8) {
+		bb_error_msg_and_die("unknown compression method %d",
+						  header.formatted.method);
+	}
+
+	if (header.formatted.flags & 0x04) {
+		/* bit 2 set: extra field present */
+		unsigned char extra_short;
+
+		extra_short = xread_char(src_fd) + (xread_char(src_fd) << 8);
+		while (extra_short > 0) {
+			/* Ignore extra field */
+			xread_char(src_fd);
+			extra_short--;
+		}
+	}
+
+	/* Discard original name if any */
+	if (header.formatted.flags & 0x08) {
+		/* bit 3 set: original file name present */
+		while(xread_char(src_fd) != 0);
+	}
+
+	/* Discard file comment if any */
+	if (header.formatted.flags & 0x10) {
+		/* bit 4 set: file comment present */
+		while(xread_char(src_fd) != 0);
+	}
+
+	/* Read the header checksum */
+	if (header.formatted.flags & 0x02) {
+		xread_char(src_fd);
+		xread_char(src_fd);
+	}
+
+	return;
+}