feat: limit max connection count (#2701)

server/middlewares/limit.go

@@ -0,0 +1,16 @@
+package middlewares
+
+import (
+	"github.com/gin-gonic/gin"
+)
+
+func MaxAllowed(n int) gin.HandlerFunc {
+	sem := make(chan struct{}, n)
+	acquire := func() { sem <- struct{}{} }
+	release := func() { <-sem }
+	return func(c *gin.Context) {
+		acquire()
+		defer release()
+		c.Next()
+	}
+}