otelmap: handle conversion of struct types (#45234)

The otelmap package does not handle struct types properly, the
convertion of a struct results in a string error.

To follow the libbeat behavior, handle struct types the same way, by
serializing to json and back, resulting in a map of keys and values.

Author: mauri870

libbeat/otelbeat/otelmap/otelmap.go

@@ -19,6 +19,8 @@
 package otelmap
 
 import (
+	"encoding"
+	"encoding/json"
 	"fmt"
 	"reflect"
 	"time"
@@ -86,6 +88,13 @@ func ConvertNonPrimitive[T mapstrOrMap](m T) {
 				s = append(s, time.Time(i).UTC().Format("2006-01-02T15:04:05.000Z"))
 			}
 			m[key] = s
+		case encoding.TextMarshaler:
+			text, err := x.MarshalText()
+			if err != nil {
+				m[key] = fmt.Sprintf("error converting %T to string: %s", x, err)
+				continue
+			}
+			m[key] = string(text)
 		case []bool, []string, []float32, []float64, []int, []int8, []int16, []int32, []int64,
 			[]uint, []uint8, []uint16, []uint32, []uint64:
 			ref := reflect.ValueOf(x)
@@ -97,6 +106,17 @@ func ConvertNonPrimitive[T mapstrOrMap](m T) {
 		case nil, string, int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64, bool:
 		default:
 			ref := reflect.ValueOf(x)
+			if ref.Kind() == reflect.Struct {
+				var im map[string]any
+				err := marshalUnmarshal(x, &im)
+				if err != nil {
+					m[key] = fmt.Sprintf("error encoding struct to map: %s", err)
+					continue
+				}
+				ConvertNonPrimitive(im)
+				m[key] = im
+				break
+			}
 			if ref.Kind() == reflect.Slice || ref.Kind() == reflect.Array {
 				s := make([]any, ref.Len())
 				for i := 0; i < ref.Len(); i++ {
@@ -114,8 +134,24 @@ func ConvertNonPrimitive[T mapstrOrMap](m T) {
 				m[key] = s
 				break // we figured out the type, so we don't need the unknown type case
 			}
-
 			m[key] = fmt.Sprintf("unknown type: %T", x)
 		}
 	}
 }
+
+// marshalUnmarshal converts an interface to a mapstr.M by marshalling to JSON
+// then unmarshalling the JSON object into a mapstr.M.
+// Copied from libbeat/common/event.go
+func marshalUnmarshal(in interface{}, out interface{}) error {
+	// Decode and encode as JSON to normalize the types.
+	marshaled, err := json.Marshal(in)
+	if err != nil {
+		return fmt.Errorf("error marshalling to JSON: %w", err)
+	}
+	err = json.Unmarshal(marshaled, out)
+	if err != nil {
+		return fmt.Errorf("error unmarshalling from JSON: %w", err)
+	}
+
+	return nil
+}

libbeat/otelbeat/otelmap/otelmap_test.go

@@ -273,12 +273,28 @@ func TestFromMapstrSliceCommonTime(t *testing.T) {
 	assert.Equal(t, want, inputMap)
 }
 
+type structWithTextMarshaler struct {
+	Value string `json:"value"`
+}
+
+func (s *structWithTextMarshaler) MarshalText() ([]byte, error) {
+	return []byte("marshalled:" + s.Value), nil
+}
+
 func TestFromMapstrWithNestedData(t *testing.T) {
 	input := mapstr.M{
 		"any_array":  [3]any{1, "string", 3},
 		"any_slice":  []any{5.1, 6.2},
 		"bool_array": [2]bool{true, false},
 		"bool_slice": []bool{false, true},
+		"struct": struct {
+			Value string `json:"value"`
+		}{
+			Value: "string",
+		},
+		"struct_with_text_marshaler": &structWithTextMarshaler{
+			Value: "string",
+		},
 		"inner": []mapstr.M{
 			{
 				"inner_int":       42,
@@ -287,6 +303,14 @@ func TestFromMapstrWithNestedData(t *testing.T) {
 					{"string": "string"},
 					{"number": 12.3},
 				},
+				"inner_struct": struct {
+					Value string `json:"value"`
+				}{
+					Value: "string",
+				},
+				"inner_struct_with_text_marshaler": &structWithTextMarshaler{
+					Value: "string",
+				},
 			},
 			{
 				"inner_int": 43,
@@ -306,6 +330,10 @@ func TestFromMapstrWithNestedData(t *testing.T) {
 		"any_slice":  []any{5.1, 6.2},
 		"bool_array": []any{true, false},
 		"bool_slice": []any{false, true},
+		"struct": map[string]any{
+			"value": "string",
+		},
+		"struct_with_text_marshaler": "marshalled:string",
 		"inner": []any{
 			map[string]any{
 				"inner_int":       42,
@@ -314,6 +342,10 @@ func TestFromMapstrWithNestedData(t *testing.T) {
 					map[string]any{"string": "string"},
 					map[string]any{"number": 12.3},
 				},
+				"inner_struct": map[string]any{
+					"value": "string",
+				},
+				"inner_struct_with_text_marshaler": "marshalled:string",
 			},
 			map[string]any{
 				"inner_int": 43,
@@ -363,24 +395,12 @@ func TestToMapstr(t *testing.T) {
 	assert.Equal(t, want, got)
 }
 
-type unknown struct {
-	Value int `json:"value"`
-}
-
 func TestUnknownType(t *testing.T) {
 	inputMap := mapstr.M{
-		"unknown": unknown{42},
-		"nested": mapstr.M{
-			"unknown": unknown{43},
-		},
 		"unknown_map": map[string]int{"key": 42},
 	}
 
 	expected := mapstr.M{
-		"unknown": "unknown type: otelmap.unknown",
-		"nested": map[string]any{
-			"unknown": "unknown type: otelmap.unknown",
-		},
 		"unknown_map": "unknown type: map[string]int",
 	}