Export SVCB map

The mappings of the numeric SVCB key values to strings are exported, under names
consistent with the already existing exported mappings, to make it easier for
the clients of the module to validate and print SVCB keys.

Split off from miekg#1359.

svcb.go

@@ -27,7 +27,8 @@ const (
 	svcb_RESERVED SVCBKey = 65535
 )
 
-var svcbKeyToStringMap = map[SVCBKey]string{
+// SVCBKeyToString is a map of strings for each SVCB key.
+var SVCBKeyToString = map[SVCBKey]string{
 	SVCB_MANDATORY:       "mandatory",
 	SVCB_ALPN:            "alpn",
 	SVCB_NO_DEFAULT_ALPN: "no-default-alpn",
@@ -38,9 +39,11 @@ var svcbKeyToStringMap = map[SVCBKey]string{
 	SVCB_DOHPATH:         "dohpath",
 }
 
-var svcbStringToKeyMap = reverseSVCBKeyMap(svcbKeyToStringMap)
+// StringToSVCBKey is the reverse of SVCBKeyToString, needed for string
+// parsing.
+var StringToSVCBKey = reverseSVCBKey(SVCBKeyToString)
 
-func reverseSVCBKeyMap(m map[SVCBKey]string) map[string]SVCBKey {
+func reverseSVCBKey(m map[SVCBKey]string) map[string]SVCBKey {
 	n := make(map[string]SVCBKey, len(m))
 	for u, s := range m {
 		n[s] = u
@@ -52,7 +55,7 @@ func reverseSVCBKeyMap(m map[SVCBKey]string) map[string]SVCBKey {
 // Returns an empty string for reserved keys.
 // Accepts unassigned keys as well as experimental/private keys.
 func (key SVCBKey) String() string {
-	if x := svcbKeyToStringMap[key]; x != "" {
+	if x := SVCBKeyToString[key]; x != "" {
 		return x
 	}
 	if key == svcb_RESERVED {
@@ -69,12 +72,12 @@ func svcbStringToKey(s string) SVCBKey {
 		a, err := strconv.ParseUint(s[3:], 10, 16)
 		// no leading zeros
 		// key shouldn't be registered
-		if err != nil || a == 65535 || s[3] == '0' || svcbKeyToStringMap[SVCBKey(a)] != "" {
+		if err != nil || a == 65535 || s[3] == '0' || SVCBKeyToString[SVCBKey(a)] != "" {
 			return svcb_RESERVED
 		}
 		return SVCBKey(a)
 	}
-	if key, ok := svcbStringToKeyMap[s]; ok {
+	if key, ok := StringToSVCBKey[s]; ok {
 		return key
 	}
 	return svcb_RESERVED