perf: asynchronously move the ipv6 initialisation

asn.go

@@ -52,6 +52,8 @@ func (a *asnStore) AsnForIPv6(ip net.IP) (string, error) {
 func newAsnStore() (*asnStore, error) {
 	cr := cidranger.NewPCTrieRanger()
 
+	loadipv6CidrToAsnMap()
+
 	for k, v := range ipv6CidrToAsnMap {
 		_, nn, err := net.ParseCIDR(k)
 		if err != nil {

generate/main.go

@@ -56,12 +56,24 @@ func writeMappingToFile(f *os.File, m map[string]string, mapName string) {
 		}
 	}
 	printf("package %s\n\n", pkgName)
+	printf("import \"sync\"\n\n")
 	printf("// Code generated by generate/main.go DO NOT EDIT\n")
-	printf("var %s = map[string]string {", mapName)
+	printf("// %s is only valid after calling load%s and it returned\n", mapName, mapName)
+	printf("var %s map[string]string\n\n", mapName)
+	printf("// Code generated by generate/main.go DO NOT EDIT\n")
+	printf("var %sOnce sync.Once\n\n", mapName)
+	printf("// Code generated by generate/main.go DO NOT EDIT\n")
+	printf("func init() { go load%s() }\n\n", mapName)
+	printf("// Code generated by generate/main.go DO NOT EDIT\n")
+	printf("func load%s() {\n", mapName)
+	printf("\t%sOnce.Do(func(){\n", mapName)
+	printf("\t\t%s = map[string]string {", mapName)
 	for k, v := range m {
-		printf("\n\t \"%s\": \"%s\",", k, v)
+		printf("\n\t\t\t\"%s\": \"%s\",", k, v)
 	}
-	printf("\n}")
+	printf("\n\t\t}\n")
+	printf("\t})\n")
+	printf("}\n\n")
 }
 
 func readMappingFile(path string) map[string]string {