Raise netlink buffers for large batches; restore snapshot when try apply fails

internal/nftables/engine_test.go

@@ -0,0 +1,59 @@
+package nftables
+
+import (
+	"os"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/mdlayher/netlink"
+	"golang.org/x/sys/unix"
+)
+
+func TestLargeBuffersRaisesSocketBuffers(t *testing.T) {
+	c, err := netlink.Dial(unix.NETLINK_NETFILTER, nil)
+	if err != nil {
+		t.Skipf("netlink unavailable: %v", err)
+	}
+	defer c.Close()
+	if err := largeBuffers(c); err != nil {
+		t.Fatal(err)
+	}
+	// Without CAP_NET_ADMIN the kernel caps at the sysctl max; it doubles either way.
+	for opt, sysctl := range map[int]string{unix.SO_RCVBUF: "rmem_max", unix.SO_SNDBUF: "wmem_max"} {
+		want := 2 * min(batchBufSize, procInt(t, "/proc/sys/net/core/"+sysctl))
+		if got := sockBuf(t, c, opt); got < want {
+			t.Errorf("%s-bounded buffer = %d, want >= %d", sysctl, got, want)
+		}
+	}
+}
+
+func procInt(t *testing.T, path string) int {
+	t.Helper()
+	b, err := os.ReadFile(path)
+	if err != nil {
+		t.Skipf("reading %s: %v", path, err)
+	}
+	v, err := strconv.Atoi(strings.TrimSpace(string(b)))
+	if err != nil {
+		t.Fatal(err)
+	}
+	return v
+}
+
+func sockBuf(t *testing.T, c *netlink.Conn, opt int) int {
+	t.Helper()
+	rc, err := c.SyscallConn()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var v int
+	var serr error
+	if err := rc.Control(func(fd uintptr) { v, serr = unix.GetsockoptInt(int(fd), unix.SOL_SOCKET, opt) }); err != nil {
+		t.Fatal(err)
+	}
+	if serr != nil {
+		t.Fatal(serr)
+	}
+	return v
+}