Fix netx.Conn metrics and reduce ndt7 websocket buffer (#299)

* Guarantee conn count is decremented once on close
* Define smaller websocket buffer size
* Be explicit in comment about buffer size

ndt7/handler/handler.go

@@ -126,8 +126,8 @@ func setupConn(writer http.ResponseWriter, request *http.Request) *websocket.Con
 		CheckOrigin: func(r *http.Request) bool {
 			return true // Allow cross origin resource sharing
 		},
-		ReadBufferSize:  spec.MaxMessageSize,
-		WriteBufferSize: spec.MaxMessageSize,
+		ReadBufferSize:  spec.DefaultWebsocketBufferSize,
+		WriteBufferSize: spec.DefaultWebsocketBufferSize,
 	}
 	conn, err := upgrader.Upgrade(writer, request, headers)
 	if err != nil {

ndt7/spec/spec.go

@@ -22,6 +22,13 @@ const MaxMessageSize = 1 << 24
 // a good compromise between Go and JavaScript as seen in cloud based tests.
 const MaxScaledMessageSize = 1 << 20
 
+// DefaultWebsocketBufferSize is the read and write buffer sizes used when
+// creating a websocket connection. This size is independent of the websocket
+// message sizes defined above (which may be larger) and used to optimize read
+// and write operations. However, larger buffers will practically limit the
+// total number of concurrent connections possible. We use 1MB as a balance.
+const DefaultWebsocketBufferSize = 1 << 20
+
 // ScalingFraction sets the threshold for scaling binary messages. When
 // the current binary message size is <= than 1/scalingFactor of the
 // amount of bytes sent so far, we scale the message. This is documented

netx/net.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"net"
 	"os"
+	"sync"
 	"time"
 
 	guuid "github.com/google/uuid"
@@ -51,6 +52,7 @@ type Conn struct {
 	net.Conn
 	fp      *os.File
 	netinfo iface.NetInfo
+	once    sync.Once
 }
 
 // Addr supports the net.Addr interface and allows mediated access to operations
@@ -110,7 +112,7 @@ func (ln *Listener) Accept() (net.Conn, error) {
 // returned by LocalAddr and RemoteAddr should be released before calling Close.
 func (mc *Conn) Close() error {
 	mc.fp.Close()
-	CurrentOpenConns.Dec()
+	mc.once.Do(CurrentOpenConns.Dec)
 	return mc.Conn.Close()
 }