Allow labelFromKey field

Allow `labelFromKey` field for the following types:
* Gauge: Done.
* Info: Done.
* StateSet: N/A (redundant use case, see doc changes for more info).

Signed-off-by: Pranshu Srivastava <rexagod@gmail.com>

Author: rexagod

docs/customresourcestate-metrics.md

@@ -146,6 +146,7 @@ spec:
               path: [status, sub]
 
               # if path targets an object, the object key will be used as label value
+              # This is not supported for StateSet type as all values will be truthy, which is redundant.
               labelFromKey: type
               # label values can be resolved specific to this path 
               labelsFromPath:

pkg/customresourcestate/config_metrics_types.go

@@ -51,6 +51,8 @@ type MetricGauge struct {
 // Ref: https://github.com/OpenObservability/OpenMetrics/blob/main/specification/OpenMetrics.md#info
 type MetricInfo struct {
 	MetricMeta `yaml:",inline" json:",inline"`
+	// LabelFromKey adds a label with the given name if Path is an object. The label value will be the object key.
+	LabelFromKey string `yaml:"labelFromKey" json:"labelFromKey"`
 }
 
 // MetricStateSet is a metric which represent a series of related boolean values, also called a bitset.

pkg/customresourcestate/registry_factory.go

@@ -157,6 +157,7 @@ func newCompiledMetric(m Metric) (compiledMetric, error) {
 			compiledCommon: *cc,
 			ValueFrom:      valueFromPath,
 			NilIsZero:      m.Gauge.NilIsZero,
+			labelFromKey:   m.Gauge.LabelFromKey,
 		}, nil
 	case MetricTypeInfo:
 		if m.Info == nil {
@@ -168,6 +169,7 @@ func newCompiledMetric(m Metric) (compiledMetric, error) {
 		}
 		return &compiledInfo{
 			compiledCommon: *cc,
+			labelFromKey:   m.Info.LabelFromKey,
 		}, nil
 	case MetricTypeStateSet:
 		if m.StateSet == nil {
@@ -195,23 +197,8 @@ func newCompiledMetric(m Metric) (compiledMetric, error) {
 type compiledGauge struct {
 	compiledCommon
 	ValueFrom    valuePath
-	LabelFromKey string
 	NilIsZero    bool
-}
-
-func newCompiledGauge(m *MetricGauge) (*compiledGauge, error) {
-	cc, err := compileCommon(m.MetricMeta)
-	if err != nil {
-		return nil, fmt.Errorf("compile common: %w", err)
-	}
-	valueFromPath, err := compilePath(m.ValueFrom)
-	if err != nil {
-		return nil, fmt.Errorf("compile path ValueFrom: %w", err)
-	}
-	return &compiledGauge{
-		compiledCommon: *cc,
-		ValueFrom:      valueFromPath,
-	}, nil
+	labelFromKey string
 }
 
 func (c *compiledGauge) Values(v interface{}) (result []eachValue, errs []error) {
@@ -227,8 +214,8 @@ func (c *compiledGauge) Values(v interface{}) (result []eachValue, errs []error)
 				onError(fmt.Errorf("[%s]: %w", key, err))
 				continue
 			}
-			if key != "" && c.LabelFromKey != "" {
-				ev.Labels[c.LabelFromKey] = key
+			if key != "" && c.labelFromKey != "" {
+				ev.Labels[c.labelFromKey] = key
 			}
 			addPathLabels(it, c.LabelFromPath(), ev.Labels)
 			result = append(result, *ev)
@@ -257,22 +244,54 @@ func (c *compiledGauge) Values(v interface{}) (result []eachValue, errs []error)
 
 type compiledInfo struct {
 	compiledCommon
+	labelFromKey string
 }
 
 func (c *compiledInfo) Values(v interface{}) (result []eachValue, errs []error) {
-	if vs, isArray := v.([]interface{}); isArray {
-		for _, obj := range vs {
+	onError := func(err ...error) {
+		errs = append(errs, fmt.Errorf("%s: %v", c.Path(), err))
+	}
+
+	switch iter := v.(type) {
+	case []interface{}:
+		for _, obj := range iter {
 			ev, err := c.values(obj)
 			if len(err) > 0 {
-				errs = append(errs, err...)
+				onError(err...)
 				continue
 			}
 			result = append(result, ev...)
 		}
-		return
+	default:
+		value, err := c.values(v)
+		if err != nil {
+			onError(err...)
+			break
+		}
+		// labelFromKey logic
+		if vv, ok := v.(map[string]interface{}); ok {
+			for key, val := range vv {
+				if key != "" && c.labelFromKey != "" {
+					n, err := toFloat64(val, false)
+					if err != nil {
+						onError(err)
+						continue
+					}
+					result = append(result, eachValue{
+						Labels: map[string]string{
+							c.labelFromKey: key,
+						},
+						Value: n,
+					})
+				}
+			}
+		}
+		if len(result) == 0 {
+			result = value
+		}
 	}
 
-	return c.values(v)
+	return
 }
 
 func (c *compiledInfo) values(v interface{}) (result []eachValue, err []error) {
@@ -355,7 +374,7 @@ func less(a, b map[string]string) bool {
 
 func (c compiledGauge) value(it interface{}) (*eachValue, error) {
 	labels := make(map[string]string)
-	value, err := getNum(c.ValueFrom.Get(it), c.NilIsZero)
+	value, err := toFloat64(c.ValueFrom.Get(it), c.NilIsZero)
 	if err != nil {
 		return nil, fmt.Errorf("%s: %w", c.ValueFrom, err)
 	}
@@ -478,7 +497,7 @@ func compilePath(path []string) (out valuePath, _ error) {
 				return nil, fmt.Errorf("invalid list lookup: %s", part)
 			}
 			key, val := eq[0], eq[1]
-			num, notNum := getNum(val, false)
+			num, notNum := toFloat64(val, false)
 			boolVal, notBool := strconv.ParseBool(val)
 			out = append(out, pathOp{
 				part: part,
@@ -496,7 +515,7 @@ func compilePath(path []string) (out valuePath, _ error) {
 								}
 
 								if notNum == nil {
-									if i, err := getNum(candidate, false); err == nil && num == i {
+									if i, err := toFloat64(candidate, false); err == nil && num == i {
 										return m
 									}
 								}
@@ -522,13 +541,14 @@ func compilePath(path []string) (out valuePath, _ error) {
 					} else if s, ok := m.([]interface{}); ok {
 						i, err := strconv.Atoi(part)
 						if err != nil {
-							return nil
+							return fmt.Errorf("invalid list index: %s", part)
 						}
 						if i < 0 {
+							// negative index
 							i += len(s)
 						}
 						if !(0 <= i && i < len(s)) {
-							return nil
+							return fmt.Errorf("list index out of range: %s", part)
 						}
 						return s[i]
 					}
@@ -544,6 +564,7 @@ func famGen(f compiledFamily) generator.FamilyGenerator {
 	errLog := klog.V(f.ErrorLogV)
 	return generator.FamilyGenerator{
 		Name: f.Name,
+		// TODO(@rexagod): This should be dynamic.
 		Type: metric.Gauge,
 		Help: f.Help,
 		GenerateFunc: func(obj interface{}) *metric.Family {
@@ -585,8 +606,8 @@ func scrapeValuesFor(e compiledEach, obj map[string]interface{}) ([]eachValue, [
 	return result, errs
 }
 
-// getNum converts the value to a float64 which is the value type for any metric.
-func getNum(value interface{}, nilIsZero bool) (float64, error) {
+// toFloat64 converts the value to a float64 which is the value type for any metric.
+func toFloat64(value interface{}, nilIsZero bool) (float64, error) {
 	var v float64
 	// same as bool==false but for bool pointers
 	if value == nil {

pkg/customresourcestate/registry_factory_test.go

@@ -155,7 +155,7 @@ func Test_values(t *testing.T) {
 			compiledCommon: compiledCommon{
 				path: mustCompilePath(t, "status", "active"),
 			},
-			LabelFromKey: "type",
+			labelFromKey: "type",
 		}, wantResult: []eachValue{
 			newEachValue(t, 1, "type", "type-a"),
 			newEachValue(t, 3, "type", "type-b"),
@@ -167,7 +167,7 @@ func Test_values(t *testing.T) {
 					"active": mustCompilePath(t, "active"),
 				},
 			},
-			LabelFromKey: "type",
+			labelFromKey: "type",
 			ValueFrom:    mustCompilePath(t, "ready"),
 		}, wantResult: []eachValue{
 			newEachValue(t, 2, "type", "type-a", "active", "1"),
@@ -201,7 +201,7 @@ func Test_values(t *testing.T) {
 			newEachValue(t, 0),
 		}},
 		{name: "info", each: &compiledInfo{
-			compiledCommon{
+			compiledCommon: compiledCommon{
 				labelFromPath: map[string]valuePath{
 					"version": mustCompilePath(t, "spec", "version"),
 				},
@@ -210,10 +210,19 @@ func Test_values(t *testing.T) {
 			newEachValue(t, 1, "version", "v0.0.0"),
 		}},
 		{name: "info nil path", each: &compiledInfo{
-			compiledCommon{
+			compiledCommon: compiledCommon{
 				path: mustCompilePath(t, "does", "not", "exist"),
 			},
 		}, wantResult: nil},
+		{name: "info label from key", each: &compiledInfo{
+			compiledCommon: compiledCommon{
+				path: mustCompilePath(t, "status", "active"),
+			},
+			labelFromKey: "type",
+		}, wantResult: []eachValue{
+			newEachValue(t, 1, "type", "type-a"),
+			newEachValue(t, 3, "type", "type-b"),
+		}},
 		{name: "stateset", each: &compiledStateSet{
 			compiledCommon: compiledCommon{
 				path: mustCompilePath(t, "status", "phase"),