fix #2307

Add METADATA to the response for new subscriptions; generation of this
response is throttled, even though subscription itself is not, so if
you're throttled the subscription will succeed but you won't get
METADATA lines.

irc/client.go

@@ -823,7 +823,7 @@ func (client *Client) applyPreregMetadata(session *Session) {
 		return
 	}
 
-	// TODO this is expensive
+	// note: this is expensive but it's comparable to destroy(), OK to do once per session
 	friends := client.FriendsMonitors(caps.Metadata)
 	for _, s := range client.Sessions() {
 		if s != session {

irc/getters.go

@@ -895,6 +895,23 @@ func (channel *Channel) GetMetadata(key string) (string, bool) {
 	return val, ok
 }
 
+type MetadataPair struct {
+	Key   string
+	Value string
+}
+
+func (channel *Channel) GetMetadataBulk(keys []string) (result []MetadataPair) {
+	channel.stateMutex.RLock()
+	defer channel.stateMutex.RUnlock()
+
+	for _, k := range keys {
+		if val, ok := channel.metadata[k]; ok {
+			result = append(result, MetadataPair{Key: k, Value: val})
+		}
+	}
+	return result
+}
+
 func (channel *Channel) SetMetadata(key string, value string, limit int) (updated bool, err error) {
 	defer channel.MarkDirty(IncludeAllAttrs)
 
@@ -962,6 +979,18 @@ func (client *Client) GetMetadata(key string) (string, bool) {
 	return val, ok
 }
 
+func (client *Client) GetMetadataBulk(keys []string) (result []MetadataPair) {
+	client.stateMutex.RLock()
+	defer client.stateMutex.RUnlock()
+
+	for _, k := range keys {
+		if val, ok := client.metadata[k]; ok {
+			result = append(result, MetadataPair{Key: k, Value: val})
+		}
+	}
+	return result
+}
+
 func (client *Client) SetMetadata(key string, value string, limit int) (updated bool, err error) {
 	var alwaysOn bool
 	defer func() {

irc/handlers.go

@@ -3375,6 +3375,12 @@ func metadataSubsHandler(client *Client, subcommand string, params []string, rb
 			rb.Add(nil, server.name, RPL_METADATASUBOK, params...)
 		}
 
+		if client.registered && len(added) != 0 {
+			if throttled, _ := client.checkMetadataThrottle(); !throttled {
+				processMetadataNewSubscriptions(client, rb, added)
+			}
+		}
+
 	case "unsub":
 		keys := params[2:]
 		removed := rb.session.UnsubscribeFrom(keys...)

irc/metadata.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/ergochat/ergo/irc/caps"
 	"github.com/ergochat/ergo/irc/modes"
+	"github.com/ergochat/ergo/irc/utils"
 )
 
 const (
@@ -35,7 +36,6 @@ func notifySubscribers(server *Server, session *Session, targetObj MetadataHaver
 
 	switch target := targetObj.(type) {
 	case *Client:
-		// TODO this case is expensive and might warrant rate-limiting
 		friends := target.FriendsMonitors(caps.Metadata)
 		// broadcast metadata update to other connected sessions
 		for _, s := range target.Sessions() {
@@ -126,6 +126,40 @@ func playMetadataVerbBatch(rb *ResponseBuffer, target string, values map[string]
 	}
 }
 
+func processMetadataNewSubscriptions(client *Client, rb *ResponseBuffer, subs []string) {
+	// "When subscribing to a key, clients SHOULD receive the current value
+	// of that key for channels/users they are receiving updates for."
+	// note that this is expensive because we need to compute the friends
+	visibility := "*"
+	friendsSeen := make(utils.HashSet[*Client])
+	for _, channel := range client.Channels() {
+		chname := channel.Name()
+		for _, pair := range channel.GetMetadataBulk(subs) {
+			rb.Add(nil, client.server.name, "METADATA", chname, pair.Key, visibility, pair.Value)
+		}
+		for _, friend := range channel.Members() {
+			if friendsSeen.Has(friend) {
+				continue
+			}
+			friendsSeen.Add(friend)
+			for _, pair := range friend.GetMetadataBulk(subs) {
+				rb.Add(nil, client.server.name, "METADATA", friend.Nick(), pair.Key, visibility, pair.Value)
+			}
+		}
+	}
+
+	for _, friendNick := range client.server.monitorManager.List(rb.session) {
+		friend := client.server.clients.Get(friendNick)
+		if friend == nil || friendsSeen.Has(friend) {
+			continue
+		}
+		friendsSeen.Add(friend)
+		for _, pair := range friend.GetMetadataBulk(subs) {
+			rb.Add(nil, client.server.name, "METADATA", friend.Nick(), pair.Key, visibility, pair.Value)
+		}
+	}
+}
+
 var validMetadataKeyRegexp = regexp.MustCompile("^[a-z0-9_./-]+$")
 
 func metadataKeyIsEvil(key string) bool {