-void *mutt_hcache_open(const char *path, const char *folder);
-void mutt_hcache_close(void *db);
-HEADER *mutt_hcache_restore(const unsigned char *d, HEADER **oh);
-void *mutt_hcache_fetch(void *db, const char *filename,
+typedef struct hcache_t hcache_t;
+
+hcache_t *mutt_hcache_open(const char *folder);
+void mutt_hcache_close(hcache_t **db);
+
+HEADER *mutt_hcache_restore(const void *d, HEADER **oh);
+void *mutt_hcache_fetch(hcache_t *db, const char *filename,