Keep the gateway connection alive and resume hosted queues after reconnecting

The client doesn't ping while it's sending, so when the proxy answers its frames itself (everything it
sends in a hosted room), IMVU's gateway saw an idle connection and closed it after about a minute. A
ping now goes to the gateway in place of each answered frame. And after a reconnect, hosted rooms'
queues are taken out of C2gOpenFloodgates and answered here (the gateway never answered them, so the
client gave up and closed the room).

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

internal/imq/messages.go

@@ -4,15 +4,17 @@ import "errors"
 
 // Message types the proxy reads or writes.
 const (
-	C2gSendMessage = 1304
-	C2gUnsubscribe = 1308
-	C2gSubscribe   = 1309
-	G2cResult      = 3102
-	G2cSendMessage = 3104
-	G2cStateChange = 3105
-	G2cJoinedQueue = 3106
-	G2cLeftQueue   = 3107
-	G2cCreateMount = 3108
+	C2gPing           = 1301
+	C2gSendMessage    = 1304
+	C2gOpenFloodgates = 1306
+	C2gUnsubscribe    = 1308
+	C2gSubscribe      = 1309
+	G2cResult         = 3102
+	G2cSendMessage    = 3104
+	G2cStateChange    = 3105
+	G2cJoinedQueue    = 3106
+	G2cLeftQueue      = 3107
+	G2cCreateMount    = 3108
 )
 
 // Mount types (G2cCreateMount).
@@ -314,3 +316,42 @@ func StateChange(opID uint64, userID, queue, mount string, props []Property, seq
 	b = appendBytesField(appendBytesField(appendBytesField(b, 2, []byte(userID)), 3, []byte(queue)), 4, []byte(mount))
 	return appendVarintField(appendProperties(b, 5, props), 6, sequence)
 }
+
+// ParseFloodgates reads a C2gOpenFloodgates's data (after reconnecting, the queues to resume): each queue's state
+// as a QueueOp (its op ID for a result), keeping the entry as sent.
+func ParseFloodgates(data []byte) ([]QueueOp, error) {
+	fs, err := fields(data)
+	if err != nil {
+		return nil, err
+	}
+	var out []QueueOp
+	for _, f := range fs {
+		if f.num != 1 || !f.isLen {
+			return nil, errors.New("imq: unexpected field in C2gOpenFloodgates")
+		}
+		sub, err := fields(f.bytes)
+		if err != nil {
+			return nil, err
+		}
+		q := QueueOp{raw: f.bytes}
+		for _, sf := range sub {
+			switch {
+			case sf.num == 1 && sf.isLen:
+				q.Queue = string(sf.bytes)
+			case sf.num == 3 && !sf.isLen:
+				q.OpID = sf.varint
+			}
+		}
+		out = append(out, q)
+	}
+	return out, nil
+}
+
+// MarshalFloodgates encodes a C2gOpenFloodgates's data from queue states read by ParseFloodgates.
+func MarshalFloodgates(states []QueueOp) []byte {
+	var b []byte
+	for _, q := range states {
+		b = appendBytesField(b, 1, q.raw)
+	}
+	return b
+}