use ergochat/irc-go instead of goshuirc/irc-go

vendor/github.com/ergochat/irc-go/ircutils/hostnames.go

@@ -0,0 +1,41 @@
+// written by Daniel Oaks <daniel@danieloaks.net>
+// released under the ISC license
+
+package ircutils
+
+import "strings"
+
+var allowedHostnameChars = "abcdefghijklmnopqrstuvwxyz1234567890-."
+
+// HostnameIsValid provides a way for servers to check whether a looked-up client
+// hostname is valid (see InspIRCd #1033 for why this is required).
+//
+// This function shouldn't be called by clients since they don't need to validate
+// hostnames for IRC use, just by servers that need to confirm hostnames of incoming
+// clients.
+//
+// In addition to this function, servers should impose their own limits on max
+// hostname length -- this function limits it to 200 but most servers will probably
+// want to make it smaller than that.
+func HostnameIsValid(hostname string) bool {
+	// IRC hostnames specifically require a period, rough limit of 200 chars
+	if !strings.Contains(hostname, ".") || len(hostname) < 1 || len(hostname) > 200 {
+		return false
+	}
+
+	// ensure each part of hostname is valid
+	for _, part := range strings.Split(hostname, ".") {
+		if len(part) < 1 || len(part) > 63 || strings.HasPrefix(part, "-") || strings.HasSuffix(part, "-") {
+			return false
+		}
+	}
+
+	// ensure all chars of hostname are valid
+	for _, char := range strings.Split(strings.ToLower(hostname), "") {
+		if !strings.Contains(allowedHostnameChars, char) {
+			return false
+		}
+	}
+
+	return true
+}