Add TestGetMessageSize

nftables_test.go

@@ -7396,3 +7396,77 @@ func TestSetElementComment(t *testing.T) {
 		}
 	}
 }
+
+func TestGetMessageSize(t *testing.T) {
+	// Use generous socket buffer sizes
+	writeBufSize := 1 * 1024 * 1024
+	readBufSize := 1 * 1024 * 1024
+	_, newNS := nftest.OpenSystemConn(t, *enableSysTests)
+	conn, err := nftables.New(nftables.WithNetNSFd(int(newNS)), nftables.WithSockOptions(func(conn *netlink.Conn) error {
+		if err := conn.SetWriteBuffer(writeBufSize); err != nil {
+			return err
+		}
+		if err := conn.SetReadBuffer(readBufSize); err != nil {
+			return err
+		}
+		return nil
+	}))
+	if err != nil {
+		t.Fatalf("nftables.New() failed: %v", err)
+	}
+	defer nftest.CleanupSystemConn(t, newNS)
+	conn.FlushRuleset()
+	defer conn.FlushRuleset()
+
+	want := uint32(20)
+	size := conn.GetMessageSize()
+	if size != want {
+		t.Fatalf("got message size %d, want %d", size, want)
+	}
+
+	table := conn.AddTable(&nftables.Table{
+		Family: nftables.TableFamilyIPv4,
+		Name:   "test-table",
+	})
+	want += 44 // Table adds 44 bytes
+	size = conn.GetMessageSize()
+	if size != want {
+		t.Fatalf("got message size %d, want %d", size, want)
+	}
+
+	chain := conn.AddChain(&nftables.Chain{
+		Name:  "test-message",
+		Table: table,
+	})
+	want += 56 // Chain adds 56 bytes
+	size = conn.GetMessageSize()
+	if size != want {
+		t.Fatalf("got message size %d, want %d", size, want)
+	}
+
+	for i := 0; i < 2048; i++ {
+		conn.AddRule(&nftables.Rule{
+			Table: table,
+			Chain: chain,
+			Exprs: []expr.Any{
+				&expr.Verdict{
+					Kind: expr.VerdictAccept,
+				},
+			},
+		})
+		want += 116 // Rule adds 116 bytes
+		size = conn.GetMessageSize()
+		if size != want {
+			t.Fatalf("got message size %d, want %d", size, want)
+		}
+
+		// Do not use over half of the buffer before flushing
+		if size > 32768/2 {
+			want = 0
+			err := conn.Flush()
+			if err != nil {
+				t.Fatalf("failed to flush: %v", err)
+			}
+		}
+	}
+}