Room channel: other T5DE users' community products on their avatars

The proxy follows the client's IMQ chat subscriptions and tells the hub which chats it's in (and the room, from
chat.getOrMakeChat). For the other T5DE users the hub says are in a chat, it gives the client the community
products it has packs for, as *use and *remove lines from them, and adds them to the whole outfits they send.
It also takes community products out of the outfit the client posts to IMVU's chat participant endpoint, which
had been sending them to IMVU.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

internal/imq/messages.go

@@ -5,7 +5,10 @@ import "errors"
 // Message types the proxy reads or writes.
 const (
 	C2gSendMessage = 1304
+	C2gUnsubscribe = 1308
+	C2gSubscribe   = 1309
 	G2cResult      = 3102
+	G2cSendMessage = 3104
 )
 
 // SendMessage is a C2gSendMessage: a message the client sends to a queue's mount.
@@ -118,3 +121,84 @@ func appendBytesField(b []byte, num uint64, v []byte) []byte {
 	b = appendVarint(appendVarint(b, num<<3|2), uint64(len(v)))
 	return append(b, v...)
 }
+
+// ParseSubscription reads a C2gSubscribe's or C2gUnsubscribe's data: the queues (listed plainly, or with an op ID
+// for a result).
+func ParseSubscription(data []byte) ([]string, error) {
+	fs, err := fields(data)
+	if err != nil {
+		return nil, err
+	}
+	var queues []string
+	for _, f := range fs {
+		switch {
+		case f.num == 1 && f.isLen:
+			queues = append(queues, string(f.bytes))
+		case f.num == 2 && f.isLen:
+			sub, err := fields(f.bytes)
+			if err != nil {
+				return nil, err
+			}
+			for _, sf := range sub {
+				if sf.num == 1 && sf.isLen {
+					queues = append(queues, string(sf.bytes))
+				}
+			}
+		default:
+			return nil, errors.New("imq: unexpected field in a subscription")
+		}
+	}
+	return queues, nil
+}
+
+// Delivered is a G2cSendMessage: a message the gateway delivers to the client, from a user (user_id).
+type Delivered struct {
+	UserID   string
+	Queue    string
+	Mount    string
+	Message  []byte
+	Sequence uint64 // 0: none (the client only tracks sequences it's given)
+}
+
+// ParseDelivered reads a G2cSendMessage's data.
+func ParseDelivered(data []byte) (Delivered, error) {
+	fs, err := fields(data)
+	if err != nil {
+		return Delivered{}, err
+	}
+	var m Delivered
+	seen := 0
+	for _, f := range fs {
+		switch {
+		case f.num == 1 && f.isLen:
+			m.UserID, seen = string(f.bytes), seen|1
+		case f.num == 2 && f.isLen:
+			m.Queue, seen = string(f.bytes), seen|2
+		case f.num == 3 && f.isLen:
+			m.Mount, seen = string(f.bytes), seen|4
+		case f.num == 4 && f.isLen:
+			m.Message, seen = f.bytes, seen|8
+		case f.num == 5 && !f.isLen:
+			m.Sequence = f.varint
+		default:
+			return Delivered{}, errors.New("imq: unexpected field in G2cSendMessage")
+		}
+	}
+	if seen != 15 {
+		return Delivered{}, errors.New("imq: G2cSendMessage is missing fields")
+	}
+	return m, nil
+}
+
+// Marshal encodes the message's data, fields in the gateway's order.
+func (m Delivered) Marshal() []byte {
+	var b []byte
+	b = appendBytesField(b, 1, []byte(m.UserID))
+	b = appendBytesField(b, 2, []byte(m.Queue))
+	b = appendBytesField(b, 3, []byte(m.Mount))
+	b = appendBytesField(b, 4, m.Message)
+	if m.Sequence != 0 {
+		b = appendVarintField(b, 5, m.Sequence)
+	}
+	return b
+}