implement metadata before-connect (#2281)

* metadata spec update: disallow colon entirely

* refactor key validation

* implement metadata before-connect

* play the metadata in reg burst to all clients with the cap

* bump irctest

* remove all case normalization for keys

From spec discussion, we will most likely either require keys to be lowercase,
or else treat them as case-opaque, similar to message tag keys.

irc/getters.go

@@ -839,6 +839,8 @@ func (session *Session) isSubscribedTo(key string) bool {
 }
 
 func (session *Session) SubscribeTo(keys ...string) ([]string, error) {
+	maxSubs := session.client.server.Config().Metadata.MaxSubs
+
 	session.client.stateMutex.Lock()
 	defer session.client.stateMutex.Unlock()
 
@@ -848,8 +850,6 @@ func (session *Session) SubscribeTo(keys ...string) ([]string, error) {
 
 	var added []string
 
-	maxSubs := session.client.server.Config().Metadata.MaxSubs
-
 	for _, k := range keys {
 		if !session.metadataSubscriptions.Has(k) {
 			if len(session.metadataSubscriptions) > maxSubs {
@@ -980,6 +980,30 @@ func (client *Client) SetMetadata(key string, value string, limit int) (updated
 	return updated, nil
 }
 
+func (client *Client) UpdateMetadataFromPrereg(preregData map[string]string, limit int) (updates map[string]string) {
+	updates = make(map[string]string, len(preregData))
+
+	client.stateMutex.Lock()
+	defer client.stateMutex.Unlock()
+
+	if client.metadata == nil {
+		client.metadata = make(map[string]string)
+	}
+
+	for k, v := range preregData {
+		// do not overwrite any existing keys
+		_, ok := client.metadata[k]
+		if ok {
+			continue
+		}
+		if len(client.metadata) >= limit {
+			return // we know this is a new key
+		}
+		client.metadata[k] = v
+	}
+	return
+}
+
 func (client *Client) ListMetadata() map[string]string {
 	client.stateMutex.RLock()
 	defer client.stateMutex.RUnlock()