perf: replace the ipv6 map by an array of struct (#20)

That replace a 20ms spent in init, with 0.005ms.

asn.go

@@ -52,14 +52,14 @@ func (a *asnStore) AsnForIPv6(ip net.IP) (string, error) {
 func newAsnStore() (*asnStore, error) {
 	cr := cidranger.NewPCTrieRanger()
 
-	for k, v := range ipv6CidrToAsnMap {
-		_, nn, err := net.ParseCIDR(k)
+	for _, v := range ipv6CidrToAsnPairList {
+		_, nn, err := net.ParseCIDR(v.cidr)
 		if err != nil {
-			return nil, fmt.Errorf("failed to parse CIDR %s: %w", k, err)
+			return nil, fmt.Errorf("failed to parse CIDR %s: %w", v.cidr, err)
 		}
 
-		if err := cr.Insert(&networkWithAsn{*nn, v}); err != nil {
-			return nil, fmt.Errorf("failed to insert CIDR %s in Trie store: %w", k, err)
+		if err := cr.Insert(&networkWithAsn{*nn, v.asn}); err != nil {
+			return nil, fmt.Errorf("failed to insert CIDR %s in Trie store: %w", v.cidr, err)
 		}
 	}
 

generate/main.go

@@ -18,7 +18,7 @@ import (
 const (
 	pkgName        = "asnutil"
 	ipv6OutputFile = "ipv6_asn_map.gen.go"
-	ipv6MapName    = "ipv6CidrToAsnMap"
+	ipv6listName   = "ipv6CidrToAsnPairList"
 )
 
 const defaultFile = "https://iptoasn.com/data/ip2asn-v6.tsv.gz"
@@ -45,10 +45,10 @@ func main() {
 		panic(err)
 	}
 	defer f.Close()
-	writeMappingToFile(f, ipv6CidrToAsnMap, ipv6MapName)
+	writeMappingToFile(f, ipv6CidrToAsnMap, ipv6listName)
 }
 
-func writeMappingToFile(f *os.File, m map[string]string, mapName string) {
+func writeMappingToFile(f *os.File, m map[string]string, listName string) {
 	printf := func(s string, args ...interface{}) {
 		_, err := fmt.Fprintf(f, s, args...)
 		if err != nil {
@@ -57,11 +57,11 @@ func writeMappingToFile(f *os.File, m map[string]string, mapName string) {
 	}
 	printf("package %s\n\n", pkgName)
 	printf("// Code generated by generate/main.go DO NOT EDIT\n")
-	printf("var %s = map[string]string {", mapName)
+	printf("var %s = [...]struct{ cidr, asn string }{", listName)
 	for k, v := range m {
-		printf("\n\t \"%s\": \"%s\",", k, v)
+		printf("\n\t{\"%s\", \"%s\"},", k, v)
 	}
-	printf("\n}")
+	printf("\n}\n")
 }
 
 func readMappingFile(path string) map[string]string {