[core] add const to some etag prototypes

src/etag.c

@@ -6,7 +6,7 @@
 #include <sys/stat.h>
 #include <string.h>
 
-int etag_is_equal(buffer *etag, const char *line, int weak_ok) {
+int etag_is_equal(const buffer *etag, const char *line, int weak_ok) {
 	enum {
 		START = 0,
 		CHECK,
@@ -143,7 +143,7 @@ int etag_is_equal(buffer *etag, const char *line, int weak_ok) {
 	return 0;
 }
 
-int etag_create(buffer *etag, struct stat *st,etag_flags_t flags) {
+int etag_create(buffer *etag, const struct stat *st, etag_flags_t flags) {
 	if (0 == flags) return 0;
 
 	buffer_clear(etag);

src/etag.h

@@ -8,8 +8,8 @@ struct stat;            /* declaration */
 
 typedef enum { ETAG_USE_INODE = 1, ETAG_USE_MTIME = 2, ETAG_USE_SIZE = 4 } etag_flags_t;
 
-int etag_is_equal(buffer *etag, const char *matches, int weak_ok);
-int etag_create(buffer *etag, struct stat *st, etag_flags_t flags);
+int etag_is_equal(const buffer *etag, const char *matches, int weak_ok);
+int etag_create(buffer *etag, const struct stat *st, etag_flags_t flags);
 int etag_mutate(buffer *mut, buffer *etag);