internal http api: update NewDeadlineTransport() with new go http fea…

…tures

More timeouts and limits were added to http.Transport in go-1.7.
Some that were enabled in http.DefaultTransport ended up disabled
in nsq's with-custom-timeouts http.Transport.
IdleConnTimeout in particular is helpful.

internal/http_api/api_request.go

@@ -28,15 +28,17 @@ func (c *deadlinedConn) Write(b []byte) (n int, err error) {
 
 // A custom http.Transport with support for deadline timeouts
 func NewDeadlineTransport(connectTimeout time.Duration, requestTimeout time.Duration) *http.Transport {
+	// arbitrary values copied from http.DefaultTransport
 	transport := &http.Transport{
-		Dial: func(netw, addr string) (net.Conn, error) {
-			c, err := net.DialTimeout(netw, addr, connectTimeout)
-			if err != nil {
-				return nil, err
-			}
-			return &deadlinedConn{connectTimeout, c}, nil
-		},
+		DialContext: (&net.Dialer{
+			Timeout:   connectTimeout,
+			KeepAlive: 30 * time.Second,
+			DualStack: true,
+		}).DialContext,
 		ResponseHeaderTimeout: requestTimeout,
+		MaxIdleConns:          100,
+		IdleConnTimeout:       90 * time.Second,
+		TLSHandshakeTimeout:   10 * time.Second,
 	}
 	return transport
 }