ircmap: Add RFC3454 mappings

ircmap/istring.go

@@ -3,7 +3,11 @@
 
 package ircmap
 
-import "strings"
+import (
+	"strings"
+
+	"github.com/DanielOaks/go-idn/idna2003/stringprep"
+)
 
 // MappingType values represent the types of IRC casemapping we support.
 type MappingType int
@@ -15,9 +19,18 @@ const (
 	// RFC1459 represents the casemapping defined by "rfc1459"
 	RFC1459
 
-	// RFC3454 represents the UTF-8 casefolding defined by mammon.io and
-	// ircv3-harmony. Not supported yet due to no appropriate libs to do it.
-	// RFC3454
+	// RFC3454 represents the UTF-8 nameprep casefolding as used by mammon.io
+	// and ircv3-harmony.
+	RFC3454
+)
+
+var (
+	// Mappings is a mapping of ISUPPORT CASEMAP value to our MappingTypes.
+	Mappings = map[string]MappingType{
+		"ascii":   ASCII,
+		"rfc1459": RFC1459,
+		"rfc3454": RFC3454,
+	}
 )
 
 // rfc1459Fold casefolds only the special chars defined by RFC1459 -- the
@@ -30,19 +43,23 @@ func rfc1459Fold(r rune) rune {
 }
 
 // Casefold returns a string, lowercased/casefolded according to the given
-// mapping, as defined by this package.
-func Casefold(mapping MappingType, in string) string {
+// mapping as defined by this package (or an error if the given string is not
+// valid in the chosen mapping).
+func Casefold(mapping MappingType, input string) (string, error) {
 	var out string
+	var err error
 
 	if mapping == ASCII || mapping == RFC1459 {
 		// strings.ToLower ONLY replaces a-z, no unicode stuff so we're safe
 		// to use that here without any issues.
-		out = strings.ToLower(in)
+		out = strings.ToLower(input)
 
 		if mapping == RFC1459 {
 			out = strings.Map(rfc1459Fold, out)
 		}
+	} else if mapping == RFC3454 {
+		out, err = stringprep.Nameprep(input)
 	}
 
-	return out
+	return out, err
 }