strings: Follow latest advice on PRECIS regarding string stabilizing

irc/strings.go

@@ -17,13 +17,31 @@ const (
 )
 
 var (
+	errCouldNotStabilize = errors.New("Could not stabilize string while casefolding")
 	errInvalidCharacter  = errors.New("Invalid character")
 	errEmpty             = errors.New("String is empty")
 )
 
 // Casefold returns a casefolded string, without doing any name or channel character checks.
 func Casefold(str string) (string, error) {
-	return precis.UsernameCaseMapped.CompareKey(str)
+	var err error
+	oldStr := str
+	// follow the stabilizing rules laid out here:
+	// https://tools.ietf.org/html/draft-ietf-precis-7564bis-10.html#section-7
+	for i := 0; i < 4; i++ {
+		str, err = precis.UsernameCaseMapped.CompareKey(str)
+		if err != nil {
+			return "", err
+		}
+		if oldStr == str {
+			break
+		}
+		oldStr = str
+	}
+	if oldStr != str {
+		return "", errCouldNotStabilize
+	}
+	return str, nil
 }
 
 // CasefoldChannel returns a casefolded version of a channel name.

irc/strings_test.go

@@ -1,4 +1,5 @@
 // Copyright (c) 2017 Euan Kemp
+// Copyright (c) 2017 Daniel Oaks
 // released under the MIT license
 
 package irc
@@ -50,14 +51,16 @@ func TestCasefoldChannel(t *testing.T) {
 	for i, tt := range testCases {
 		t.Run(fmt.Sprintf("case %d: %s", i, tt.channel), func(t *testing.T) {
 			res, err := CasefoldChannel(tt.channel)
-			if tt.err {
+			if tt.err && err == nil {
-				if err == nil {
+				t.Errorf("expected error when casefolding [%s], but did not receive one", tt.channel)
-					t.Errorf("expected error")
+				return
 			}
+			if !tt.err && err != nil {
+				t.Errorf("unexpected error while casefolding [%s]: %s", tt.channel, err.Error())
 				return
 			}
 			if tt.folded != res {
-				t.Errorf("expected %v to be %v", tt.folded, res)
+				t.Errorf("expected [%v] to be [%v]", res, tt.folded)
 			}
 		})
 	}
@@ -91,14 +94,16 @@ func TestCasefoldName(t *testing.T) {
 	for i, tt := range testCases {
 		t.Run(fmt.Sprintf("case %d: %s", i, tt.name), func(t *testing.T) {
 			res, err := CasefoldName(tt.name)
-			if tt.err {
+			if tt.err && err == nil {
-				if err == nil {
+				t.Errorf("expected error when casefolding [%s], but did not receive one", tt.name)
-					t.Errorf("expected error")
+				return
 			}
+			if !tt.err && err != nil {
+				t.Errorf("unexpected error while casefolding [%s]: %s", tt.name, err.Error())
 				return
 			}
 			if tt.folded != res {
-				t.Errorf("expected %v to be %v", tt.folded, res)
+				t.Errorf("expected [%v] to be [%v]", res, tt.folded)
 			}
 		})
 	}