Consider the CASEMAPPING isupport token

Using RFC1459 as a default since servers not advertising this token are
likely to be pre-IRCv2, thus following the casemapping described in the
RFCs.

2 files changed, 25 insertions, 2 deletions

diff --git a/irc/states.go b/irc/states.go
index 650c0e1..da5d582 100644
--- a/irc/states.go
+++ b/irc/states.go
@@ -265,8 +265,11 @@ func (s *Session) IsChannel(name string) bool {
 }
 
 func (s *Session) Casemap(name string) string {
-	// TODO use CASEMAPPING
-	return CasemapASCII(name)
+	if s.features["CASEMAPPING"] == "ascii" {
+		return CasemapASCII(name)
+	} else {
+		return CasemapRFC1459(name)
+	}
 }
 
 func (s *Session) Users() []string {
diff --git a/irc/tokens.go b/irc/tokens.go
index 7ad5738..f4ec3c7 100644
--- a/irc/tokens.go
+++ b/irc/tokens.go
@@ -20,6 +20,26 @@ func CasemapASCII(name string) string {
 	return sb.String()
 }
 
+func CasemapRFC1459(name string) string {
+	var sb strings.Builder
+	sb.Grow(len(name))
+	for _, r := range name {
+		if 'A' <= r && r <= 'Z' {
+			r += 'a' - 'A'
+		} else if r == '[' {
+			r = '{'
+		} else if r == ']' {
+			r = '}'
+		} else if r == '\\' {
+			r = '|'
+		} else if r == '~' {
+			r = '^'
+		}
+		sb.WriteRune(r)
+	}
+	return sb.String()
+}
+
 func word(s string) (w, rest string) {
 	split := strings.SplitN(s, " ", 2)