Clean up instance map name generation (#5704)

Put the instance map name generation in a seperate function
Fix some compiler warnings
Fixes #5691
Thanks @RadianFord

src/char/char_clif.cpp

@@ -822,7 +822,7 @@ int chclif_parse_charselect(int fd, struct char_session_data* sd,uint32 ipl){
 			WFIFOHEAD(fd, 24);
 			WFIFOW(fd, 0) = 0x840;
 			WFIFOW(fd, 2) = 24;
-			memcpy(WFIFOP(fd, 4), "0", 20); // we can't send it empty (otherwise the list will pop up)
+			strncpy(WFIFOCP(fd, 4), "0", 20); // we can't send it empty (otherwise the list will pop up)
 			WFIFOSET(fd, 24);
 			return 1;
 		}

src/map/instance.cpp

@@ -4,6 +4,7 @@
 #include "instance.hpp"
 
 #include <stdlib.h>
+#include <math.h>
 #include <yaml-cpp/yaml.h>
 
 #include "../common/cbasetypes.hpp"
@@ -708,6 +709,26 @@ int instance_addmap(int instance_id) {
 	return idata->map.size();
 }
 
+/**
+ * Fills outname with the name of the instance map name
+ * @param map_id: Mapid to use
+ * @param instance_id: Instance id
+ * @param outname: Pointer to allocated memory that will be filled in
+ */
+void instance_generate_mapname(int map_id, int instance_id, char outname[MAP_NAME_LENGTH]) {
+
+#if MAX_MAP_PER_SERVER > 9999
+	#error This algorithm is only safe for up to 9999 maps, change at your own risk.
+#endif
+	// Safe up to 9999 maps per map-server
+	static const int prefix_length = 4;
+	// Full map name length - prefix length - seperator character - zero termination
+	static const int suffix_length = MAP_NAME_LENGTH - prefix_length - 1 - 1;
+	static const int prefix_limit = pow(10, prefix_length);
+	static const int suffix_limit = pow(10, suffix_length);
+	safesnprintf(outname, MAP_NAME_LENGTH, "%0*u#%0*u", prefix_length, map_id % prefix_limit, suffix_length, instance_id % suffix_limit);
+}
+
 /**
  * Returns an instance map ID
  * @param m: Source map ID
@@ -730,15 +751,8 @@ int16 instance_mapid(int16 m, int instance_id)
 
 	for (const auto &it : idata->map) {
 		if (it.src_m == m) {
-			char iname[MAP_NAME_LENGTH], alt_name[MAP_NAME_LENGTH];
-
-			strcpy(iname, name);
-
-			if (!(strchr(iname, '@')) && strlen(iname) > 8) {
-				memmove(iname, iname + (strlen(iname) - 9), strlen(iname));
-				snprintf(alt_name, sizeof(alt_name), "%d#%s", (instance_id % 1000), iname);
-			} else
-				snprintf(alt_name, sizeof(alt_name), "%.3d%s", (instance_id % 1000), iname);
+			char alt_name[MAP_NAME_LENGTH];
+			instance_generate_mapname(m, instance_id, alt_name);
 			return map_mapname2mapid(alt_name);
 		}
 	}

src/map/instance.hpp

@@ -118,6 +118,7 @@ e_instance_enter instance_enter(struct map_session_data *sd, int instance_id, co
 bool instance_reqinfo(struct map_session_data *sd, int instance_id);
 bool instance_addusers(int instance_id);
 bool instance_delusers(int instance_id);
+void instance_generate_mapname(int map_id, int instance_id, char outname[MAP_NAME_LENGTH]);
 int16 instance_mapid(int16 m, int instance_id);
 int instance_addmap(int instance_id);
 

src/map/map.cpp

@@ -2724,19 +2724,10 @@ int map_addinstancemap(int src_m, int instance_id)
 
 	struct map_data *src_map = map_getmapdata(src_m);
 	struct map_data *dst_map = map_getmapdata(dst_m);
-	char iname[MAP_NAME_LENGTH];
-
-	strcpy(iname, name);
 
 	// Alter the name
-	// Due to this being custom we only worry about preserving as many characters as necessary for accurate map distinguishing
 	// This also allows us to maintain complete independence with main map functions
-	if ((strchr(iname, '@') == nullptr) && strlen(iname) > 8) {
-		memmove(iname, iname + (strlen(iname) - 9), strlen(iname));
-		snprintf(dst_map->name, sizeof(dst_map->name), "%d#%s", (instance_id % 1000), iname);
-	} else
-		snprintf(dst_map->name, sizeof(dst_map->name), "%.3d%s", (instance_id % 1000), iname);
-	dst_map->name[MAP_NAME_LENGTH - 1] = '\0';
+	instance_generate_mapname(src_m, instance_id, dst_map->name);
 
 	dst_map->m = dst_m;
 	dst_map->instance_id = instance_id;