docs/CHANGELOG.md: support empty command-line flag values in short array notation

For example, -fooDuration=',10s,' is now supported - it sets three command-line flag values:

- the first and the last one are set to the default value for `-fooDuration`
- the second one is set to 10s

docs/CHANGELOG.md

@@ -31,6 +31,7 @@ The sandbox cluster installation is running under the constant load generated by
 * SECURITY: upgrade Go builder from Go1.21.6 to Go1.21.7. See [the list of issues addressed in Go1.21.7](https://github.com/golang/go/issues?q=milestone%3AGo1.21.7+label%3ACherryPickApproved).
 
 * FEATURE: all VictoriaMetrics components: add support for TLS client certificate verification at `-httpListenAddr` (aka [mTLS](https://en.wikipedia.org/wiki/Mutual_authentication)). See [these docs](https://docs.victoriametrics.com/#mtls-protection). See [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5458).
+* FEATURE: all VictoriaMetrics components: add support for empty command flag values in short array notation. For example, `-remoteWrite.sendTimeout=',20s,'` specifies three `-remoteWrite.sendTimeout` values - the first and the last ones are default values (`30s` in this case), while the second one is `20s`.
 * FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html) and [single-node VictoriaMetrics](https://docs.victoriametrics.com): add support for data ingestion via [DataDog lambda extension](https://docs.datadoghq.com/serverless/libraries_integrations/extension/) aka `/api/beta/sketches` endpoint. See [these docs](https://docs.victoriametrics.com/#how-to-send-data-from-datadog-agent) and [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3091). Thanks to @AndrewChubatiuk for [the pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/5584).
 * FEATURE: [VictoriaMetrics cluster](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html): add `-disableReroutingOnUnavailable` command-line flag, which can be used for reducing resource usage spikes at `vmstorage` nodes during rolling restart. Thanks to @Muxa1L for [the pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/5713).
 * FEATURE: [dashboards/vmagent](https://grafana.com/grafana/dashboards/12683): add `Targets scraped/s` stat panel showing the number of targets scraped by the vmagent per-second.

lib/flagutil/array.go

@@ -21,6 +21,7 @@ func NewArrayString(name, description string) *ArrayString {
 func NewArrayDuration(name string, defaultValue time.Duration, description string) *ArrayDuration {
 	description += fmt.Sprintf(" (default %s)", defaultValue)
 	description += "\nSupports `array` of values separated by comma or specified via multiple flags."
+	description += "\nEmpty values are set to default value."
 	a := &ArrayDuration{
 		defaultValue: defaultValue,
 	}
@@ -31,6 +32,7 @@ func NewArrayDuration(name string, defaultValue time.Duration, description strin
 // NewArrayBool returns new ArrayBool with the given name and description.
 func NewArrayBool(name, description string) *ArrayBool {
 	description += "\nSupports `array` of values separated by comma or specified via multiple flags."
+	description += "\nEmpty values are set to false."
 	var a ArrayBool
 	flag.Var(&a, name, description)
 	return &a
@@ -40,6 +42,7 @@ func NewArrayBool(name, description string) *ArrayBool {
 func NewArrayInt(name string, defaultValue int, description string) *ArrayInt {
 	description += fmt.Sprintf(" (default %d)", defaultValue)
 	description += "\nSupports `array` of values separated by comma or specified via multiple flags."
+	description += "\nEmpty values are set to default value."
 	a := &ArrayInt{
 		defaultValue: defaultValue,
 	}
@@ -52,6 +55,7 @@ func NewArrayBytes(name string, defaultValue int64, description string) *ArrayBy
 	description += "\nSupports the following optional suffixes for size values: KB, MB, GB, TB, KiB, MiB, GiB, TiB."
 	description += fmt.Sprintf(" (default %d)", defaultValue)
 	description += "\nSupports `array` of values separated by comma or specified via multiple flags."
+	description += "\nEmpty values are set to default value."
 	a := &ArrayBytes{
 		defaultValue: defaultValue,
 	}
@@ -241,6 +245,9 @@ func (a *ArrayBool) String() string {
 func (a *ArrayBool) Set(value string) error {
 	values := parseArrayValues(value)
 	for _, v := range values {
+		if v == "" {
+			v = "false"
+		}
 		b, err := strconv.ParseBool(v)
 		if err != nil {
 			return err
@@ -284,6 +291,9 @@ func (a *ArrayDuration) String() string {
 func (a *ArrayDuration) Set(value string) error {
 	values := parseArrayValues(value)
 	for _, v := range values {
+		if v == "" {
+			v = a.defaultValue.String()
+		}
 		b, err := time.ParseDuration(v)
 		if err != nil {
 			return err
@@ -332,6 +342,9 @@ func (a *ArrayInt) String() string {
 func (a *ArrayInt) Set(value string) error {
 	values := parseArrayValues(value)
 	for _, v := range values {
+		if v == "" {
+			v = fmt.Sprintf("%d", a.defaultValue)
+		}
 		n, err := strconv.Atoi(v)
 		if err != nil {
 			return err
@@ -376,6 +389,9 @@ func (a *ArrayBytes) Set(value string) error {
 	values := parseArrayValues(value)
 	for _, v := range values {
 		var b Bytes
+		if v == "" {
+			v = fmt.Sprintf("%d", a.defaultValue)
+		}
 		if err := b.Set(v); err != nil {
 			return err
 		}

lib/flagutil/array_test.go

@@ -165,6 +165,7 @@ func TestArrayDuration_Set(t *testing.T) {
 	f := func(s, expectedResult string) {
 		t.Helper()
 		var a ArrayDuration
+		a.defaultValue = 42 * time.Second
 		if err := a.Set(s); err != nil {
 			t.Fatalf("unexpected error: %s", err)
 		}
@@ -176,6 +177,7 @@ func TestArrayDuration_Set(t *testing.T) {
 	f("", "")
 	f(`1m`, `1m0s`)
 	f(`5m,1s,1h`, `5m0s,1s,1h0m0s`)
+	f(`5m,,1h`, `5m0s,42s,1h0m0s`)
 }
 
 func TestArrayDuration_GetOptionalArg(t *testing.T) {
@@ -238,6 +240,7 @@ func TestArrayBool_Set(t *testing.T) {
 	f("", "")
 	f(`true`, `true`)
 	f(`false,True,False`, `false,true,false`)
+	f(`1,,False`, `true,false,false`)
 }
 
 func TestArrayBool_GetOptionalArg(t *testing.T) {
@@ -289,6 +292,7 @@ func TestArrayInt_Set(t *testing.T) {
 	f := func(s, expectedResult string, expectedValues []int) {
 		t.Helper()
 		var a ArrayInt
+		a.defaultValue = 42
 		if err := a.Set(s); err != nil {
 			t.Fatalf("unexpected error: %s", err)
 		}
@@ -304,6 +308,7 @@ func TestArrayInt_Set(t *testing.T) {
 	f("", "", nil)
 	f(`1`, `1`, []int{1})
 	f(`-2,3,-64`, `-2,3,-64`, []int{-2, 3, -64})
+	f(`,,-64,`, `42,42,-64,42`, []int{42, 42, -64, 42})
 }
 
 func TestArrayInt_GetOptionalArg(t *testing.T) {
@@ -357,6 +362,7 @@ func TestArrayBytes_Set(t *testing.T) {
 	f := func(s, expectedResult string) {
 		t.Helper()
 		var a ArrayBytes
+		a.defaultValue = 42
 		if err := a.Set(s); err != nil {
 			t.Fatalf("unexpected error: %s", err)
 		}
@@ -368,6 +374,7 @@ func TestArrayBytes_Set(t *testing.T) {
 	f("", "")
 	f(`1`, `1`)
 	f(`-2,3,10kb`, `-2,3,10KB`)
+	f(`,,10kb`, `42,42,10KB`)
 }
 
 func TestArrayBytes_GetOptionalArg(t *testing.T) {

lib/flagutil/bytes.go

@@ -47,6 +47,11 @@ func (b *Bytes) String() string {
 
 // Set implements flag.Value interface
 func (b *Bytes) Set(value string) error {
+	if value == "" {
+		b.N = 0
+		b.valueString = ""
+		return nil
+	}
 	value = normalizeBytesString(value)
 	switch {
 	case strings.HasSuffix(value, "KB"):

lib/flagutil/bytes_test.go

@@ -12,7 +12,6 @@ func TestBytesSetFailure(t *testing.T) {
 			t.Fatalf("expecting non-nil error in b.Set(%q)", value)
 		}
 	}
-	f("")
 	f("foobar")
 	f("5foobar")
 	f("aKB")
@@ -39,6 +38,7 @@ func TestBytesSetSuccess(t *testing.T) {
 			t.Fatalf("unexpected valueString; got %q; want %q", valueString, valueExpected)
 		}
 	}
+	f("", 0)
 	f("0", 0)
 	f("1", 1)
 	f("-1234", -1234)

lib/flagutil/duration.go

@@ -49,6 +49,11 @@ func (d *Duration) String() string {
 
 // Set implements flag.Value interface
 func (d *Duration) Set(value string) error {
+	if value == "" {
+		d.msecs = 0
+		d.valueString = ""
+		return nil
+	}
 	// An attempt to parse value in months.
 	months, err := strconv.ParseFloat(value, 64)
 	if err == nil {

lib/flagutil/duration_test.go

@@ -14,7 +14,6 @@ func TestDurationSetFailure(t *testing.T) {
 			t.Fatalf("expecting non-nil error in d.Set(%q)", value)
 		}
 	}
-	f("")
 	f("foobar")
 	f("5foobar")
 	f("ah")
@@ -51,6 +50,7 @@ func TestDurationSetSuccess(t *testing.T) {
 			t.Fatalf("unexpected valueString; got %q; want %q", valueString, valueExpected)
 		}
 	}
+	f("", 0)
 	f("0", 0)
 	f("1", msecsPer31Days)
 	f("123.456", 123.456*msecsPer31Days)