feat: tune websocket hub backpressure

internal/transport/httpserver/hub_options.go

@@ -0,0 +1,48 @@
+package httpserver
+
+// HubOptions 是节点内 Worker/Event WebSocket Hub 的有界运行参数。
+// 这些参数只控制本节点内存和领取并发，不改变 MySQL 中的授权、租约或配额事实。
+type HubOptions struct {
+	// ConnectionLimit 是该 Hub 允许的同时连接数；超过后返回 429。
+	ConnectionLimit int
+	// DispatchWorkers 是本 Hub 同时执行数据库领取调用的 Go 协程上限。
+	DispatchWorkers int
+	// DispatchCapacity 是领取调用的有界内存排队槽位；满额时连接等待下一轮扫描。
+	DispatchCapacity int
+}
+
+const (
+	defaultHubConnectionLimit  = 128
+	defaultHubDispatchWorkers  = 4
+	defaultHubDispatchCapacity = 128
+	maxHubConnectionLimit      = 4096
+	maxHubDispatchWorkers      = 256
+	maxHubDispatchCapacity     = 65536
+)
+
+func resolveHubOptions(options []HubOptions) HubOptions {
+	out := HubOptions{
+		ConnectionLimit:  defaultHubConnectionLimit,
+		DispatchWorkers:  defaultHubDispatchWorkers,
+		DispatchCapacity: defaultHubDispatchCapacity,
+	}
+	if len(options) > 1 {
+		panic("at most one HubOptions value is allowed")
+	}
+	if len(options) == 1 {
+		in := options[0]
+		if in.ConnectionLimit != 0 {
+			out.ConnectionLimit = in.ConnectionLimit
+		}
+		if in.DispatchWorkers != 0 {
+			out.DispatchWorkers = in.DispatchWorkers
+		}
+		if in.DispatchCapacity != 0 {
+			out.DispatchCapacity = in.DispatchCapacity
+		}
+	}
+	if out.ConnectionLimit < 1 || out.ConnectionLimit > maxHubConnectionLimit || out.DispatchWorkers < 1 || out.DispatchWorkers > maxHubDispatchWorkers || out.DispatchCapacity < 1 || out.DispatchCapacity > maxHubDispatchCapacity {
+		panic("HubOptions values exceed bounded range")
+	}
+	return out
+}