New common unarchive code.

archival/libunarchive/check_header_gzip.c

@@ -0,0 +1,75 @@
+#include <stdlib.h>
+#include <unistd.h>
+#include "libbb.h"
+
+extern void check_header_gzip(int src_fd)
+{
+	union {
+		unsigned char raw[10];
+		struct {
+			unsigned char magic[2];
+			unsigned char method;
+			unsigned char flags;
+			unsigned int mtime;
+			unsigned char xtra_flags;
+			unsigned char os_flags;
+		} formated;
+	} header;
+
+	xread_all(src_fd, header.raw, 10);
+
+   /* Magic header for gzip files, 1F 8B = \037\213 */
+	if ((header.formated.magic[0] != 0x1F)
+		|| (header.formated.magic[1] != 0x8b)) {
+		error_msg_and_die("Invalid gzip magic");
+	}
+
+   /* Check the compression method */
+	if (header.formated.method != 8) {
+		error_msg_and_die("Unknown compression method %d",
+						  header.formated.method);
+	}
+
+	if (header.formated.flags & 0x04) {
+		/* bit 2 set: extra field present */
+		unsigned char extra_short;
+
+		extra_short = xread_char(src_fd);
+		extra_short += 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.formated.flags & 0x08) {
+	   /* bit 3 set: original file name present */
+		char tmp;
+
+		do {
+			read(src_fd, &tmp, 1);
+		} while (tmp != 0);
+	}
+
+   /* Discard file comment if any */
+	if (header.formated.flags & 0x10) {
+	   /* bit 4 set: file comment present */
+		char tmp;
+
+		do {
+			read(src_fd, &tmp, 1);
+		} while (tmp != 0);
+	}
+
+   /* Read the header checksum */
+	if (header.formated.flags & 0x02) {
+		char tmp;
+
+		read(src_fd, &tmp, 1);
+		read(src_fd, &tmp, 1);
+	}
+
+	return;
+}