[confmap] Automatically invoke Validate() during Conf.Unmarshal

.chloggen/tyler.confmap-configvalidator.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confmap
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add ability for confmap to invoke `ConfigValidator.Validate` as part of `conf.Unmarshal`.
+
+# One or more tracking issues or pull requests related to the change
+issues: [12031]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

confmap/confmap.go

@@ -15,6 +15,7 @@
 	"github.com/knadh/koanf/maps"
 	"github.com/knadh/koanf/providers/confmap"
 	"github.com/knadh/koanf/v2"
+	"go.uber.org/multierr"
 
 	encoder "go.opentelemetry.io/collector/confmap/internal/mapstructure"
 )
@@ -59,7 +60,8 @@
 }
 
 type unmarshalOption struct {
-	ignoreUnused bool
+	ignoreUnused   bool
+	invokeValidate bool
 }
 
 // WithIgnoreUnused sets an option to ignore errors if existing
@@ -71,20 +73,109 @@
 	})
 }
 
+// WithInvokeValidate sets an option to invoke the Validate method
+// of unmarshalled types that implement ConfigValidator.
+// When used, config validation with be executed automatically
+// as part of unmarshalling.
+func WithInvokeValidate() UnmarshalOption {
+	return unmarshalOptionFunc(func(uo *unmarshalOption) {
+		uo.invokeValidate = true
+	})
+}
+
 type unmarshalOptionFunc func(*unmarshalOption)
 
 func (fn unmarshalOptionFunc) apply(set *unmarshalOption) {
 	fn(set)
 }
 
+// ConfigValidator defines an optional interface for configurations to implement to do validation.
+type ConfigValidator interface {
+	// Validate the configuration and returns an error if invalid.
+	Validate() error
+}
+
+// As interface types are only used for static typing, a common idiom to find the reflection Type
+// for an interface type Foo is to use a *Foo value.
+var configValidatorType = reflect.TypeOf((*ConfigValidator)(nil)).Elem()
+
+func validate(v reflect.Value) error {
+	// Validate the value itself.
+	k := v.Kind()
+	switch k {
+	case reflect.Invalid:
+		return nil
+	case reflect.Ptr, reflect.Interface:
+		return validate(v.Elem())
+	case reflect.Struct:
+		var errs error
+		errs = multierr.Append(errs, callValidateIfPossible(v))
+		// Reflect on the pointed data and check each of its fields.
+		for i := 0; i < v.NumField(); i++ {
+			if !v.Type().Field(i).IsExported() {
+				continue
+			}
+			errs = multierr.Append(errs, validate(v.Field(i)))
+		}
+		return errs
+	case reflect.Slice, reflect.Array:
+		var errs error
+		errs = multierr.Append(errs, callValidateIfPossible(v))
+		// Reflect on the pointed data and check each of its fields.
+		for i := 0; i < v.Len(); i++ {
+			errs = multierr.Append(errs, validate(v.Index(i)))
+		}
+		return errs
+	case reflect.Map:
+		var errs error
+		errs = multierr.Append(errs, callValidateIfPossible(v))
+		iter := v.MapRange()
+		for iter.Next() {
+			errs = multierr.Append(errs, validate(iter.Key()))
+			errs = multierr.Append(errs, validate(iter.Value()))
+		}
+		return errs
+	default:
+		return callValidateIfPossible(v)
+	}
+}
+
+func callValidateIfPossible(v reflect.Value) error {
+	// If the value type implements ConfigValidator just call Validate
+	if v.Type().Implements(configValidatorType) {
+		return v.Interface().(ConfigValidator).Validate()
+	}
+
+	// If the pointer type implements ConfigValidator call Validate on the pointer to the current value.
+	if reflect.PointerTo(v.Type()).Implements(configValidatorType) {
+		// If not addressable, then create a new *V pointer and set the value to current v.
+		if !v.CanAddr() {
+			pv := reflect.New(reflect.PointerTo(v.Type()).Elem())
+			pv.Elem().Set(v)
+			v = pv.Elem()
+		}
+		return v.Addr().Interface().(ConfigValidator).Validate()
+	}
+
+	return nil
+}
+
 // Unmarshal unmarshalls the config into a struct using the given options.
 // Tags on the fields of the structure must be properly set.
 func (l *Conf) Unmarshal(result any, opts ...UnmarshalOption) error {
 	set := unmarshalOption{}
 	for _, opt := range opts {
 		opt.apply(&set)
 	}
-	return decodeConfig(l, result, !set.ignoreUnused, l.skipTopLevelUnmarshaler)
+	err := decodeConfig(l, result, !set.ignoreUnused, l.skipTopLevelUnmarshaler)
+	if err != nil {
+		return err
+	}
+
+	if set.invokeValidate {
+		return validate(reflect.ValueOf(result))
+	}
+	return nil
 }
 
 type marshalOption struct{}

confmap/confmap_test.go

@@ -964,3 +964,108 @@ func TestStringyTypes(t *testing.T) {
 		assert.Equal(t, tt.isStringy, isStringyStructure(to))
 	}
 }
+
+type validateConfig struct {
+	String      string                          `mapstructure:"string"`
+	Nested      nestedValidateConfig            `mapstructure:"nested"`
+	SliceNested []nestedValidateConfig          `mapstructure:"slice"`
+	MapNested   map[string]nestedValidateConfig `mapstructure:"map"`
+}
+
+func (c *validateConfig) Validate() error {
+	if c.String == "error" {
+		return errors.New("error in validateConfig because String")
+	}
+	return nil
+}
+
+type nestedValidateConfig struct {
+	String string `mapstructure:"string"`
+}
+
+func (c *nestedValidateConfig) Validate() error {
+	if c.String == "error" {
+		return errors.New("error in nestedValidateConfig because String")
+	}
+	return nil
+}
+
+func TestUnmarshalInvokesValidate(t *testing.T) {
+	tests := []struct {
+		name  string
+		input map[string]any
+		err   error
+	}{
+		{
+			name: "Validation passes",
+			input: map[string]any{
+				"string": "value",
+				"nested": nestedValidateConfig{
+					String: "value",
+				},
+				"slice": []nestedValidateConfig{
+					{
+						String: "value",
+					},
+				},
+				"map": map[string]nestedValidateConfig{
+					"key": {
+						String: "value",
+					},
+				},
+			},
+			err: nil,
+		},
+		{
+			name: "Validation fails because String",
+			input: map[string]any{
+				"string": "error",
+			},
+			err: errors.New("error in validateConfig because String"),
+		},
+		{
+			name: "Validation fails because nested String",
+			input: map[string]any{
+				"nested": nestedValidateConfig{
+					String: "error",
+				},
+			},
+			err: errors.New("error in nestedValidateConfig because String"),
+		},
+		{
+			name: "Validation fails because nested slice String",
+			input: map[string]any{
+				"slice": []nestedValidateConfig{
+					{
+						String: "error",
+					},
+				},
+			},
+			err: errors.New("error in nestedValidateConfig because String"),
+		},
+		{
+			name: "Validation fails because nested map String",
+			input: map[string]any{
+				"map": map[string]nestedValidateConfig{
+					"key": {
+						String: "error",
+					},
+				},
+			},
+			err: errors.New("error in nestedValidateConfig because String"),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			conf := NewFromStringMap(tt.input)
+			c := &validateConfig{}
+			err := conf.Unmarshal(c, WithInvokeValidate())
+			if tt.err == nil {
+				require.NoError(t, err)
+			} else {
+				require.Equal(t, tt.err, err)
+			}
+		})
+	}
+}