fix(utils): support record-level default schema values (#431)

Before this change, during the process of filling default configuration
values, if a record existed in the schema with a structure similar to the
following:
```
{
	"default": {
			"some_field": "record_level_default"
	},
	"fields": [
		{
			"some_field": {
				"type": "string",
				"default": "field_level_default"
			}
		}
	]
}
```
the value `record_level_default` would be ignored and the field set to
the `field_level_default` value. Similarly, in case of no field-level
default, the field would be set to `null`.

This commit modifies the utils/fillConfigRecord logic to assign fields
with record-level default values when available.

Example of default configuration values that were previously ignored:
https://github.com/Kong/kong/blob/8fe14097a17cf904676672fc8cdaabe5e02e4a2d/kong/plugins/opentelemetry/schema.lua#L49
https://github.com/Kong/kong/blob/8fe14097a17cf904676672fc8cdaabe5e02e4a2d/kong/plugins/opentelemetry/schema.lua#L90

CHANGELOG.md

@@ -1,5 +1,6 @@
 # Table of Contents
 
+- [v0.53.0](#v0530)
 - [v0.52.0](#v0520)
 - [v0.51.0](#v0510)
 - [v0.50.0](#v0500)
@@ -64,6 +65,13 @@
 - [0.2.0](#020)
 - [0.1.0](#010)
 
+## [v0.53.0]
+
+> Release date: 
+
+- Support record-level default schema values.
+  [#431](https://github.com/Kong/go-kong/pull/431)
+
 ## [v0.52.0]
 
 > Release date: 2024/03/26
@@ -861,6 +869,8 @@ authentication credentials in Kong.
   releases of Kong since every release of Kong is introducing breaking changes
   to the Admin API.
 
+[v0.53.0]: https://github.com/Kong/go-kong/compare/v0.52.0...v0.53.0
+[v0.52.0]: https://github.com/Kong/go-kong/compare/v0.51.0...v0.52.0
 [v0.51.0]: https://github.com/Kong/go-kong/compare/v0.50.0...v0.51.0
 [v0.50.0]: https://github.com/Kong/go-kong/compare/v0.49.0...v0.50.0
 [v0.49.0]: https://github.com/Kong/go-kong/compare/v0.48.0...v0.49.0

kong/utils.go

@@ -211,6 +211,7 @@ func getConfigSchema(schema gjson.Result) (gjson.Result, error) {
 func fillConfigRecord(schema gjson.Result, config Configuration) Configuration {
 	res := config.DeepCopy()
 	value := schema.Get("fields")
+	defaultRecordValue := schema.Get("default")
 
 	value.ForEach(func(_, value gjson.Result) bool {
 		// get the key name
@@ -308,7 +309,15 @@ func fillConfigRecord(schema gjson.Result, config Configuration) Configuration {
 				}
 			}
 		}
-		value = value.Get(fname + ".default")
+
+		// Check if the record has a default value for the specified field.
+		// If so, use it. If not, fall back to the default value of the field itself.
+		if defaultRecordValue.Exists() && defaultRecordValue.Get(fname).Exists() {
+			value = defaultRecordValue.Get(fname)
+		} else {
+			value = value.Get(fname + ".default")
+		}
+
 		if value.Exists() {
 			res[fname] = value.Value()
 		} else {

kong/utils_test.go

@@ -667,6 +667,91 @@ const AcmeSchema = `{
     ]
 }`
 
+const defaultRecordSchema = `{
+	"fields": [
+			{
+					"config": {
+							"fields": [
+									{
+											"endpoint": {
+													"description": "endpoint",
+													"referenceable": true,
+													"required": true,
+													"type": "string"
+											}
+									},
+									{
+											"queue": {
+													"default": {
+															"max_batch_size": 200
+													},
+													"fields": [
+															{
+																	"max_batch_size": {
+																			"between": [
+																					1,
+																					1000000
+																			],
+																			"default": 1,
+																			"type": "integer"
+																	}
+															},
+															{
+																	"max_coalescing_delay": {
+																			"between": [
+																					0,
+																					3600
+																			],
+																			"default": 1,
+																			"type": "number"
+																	}
+															}
+													],
+													"required": true,
+													"type": "record"
+											}
+									},
+									{
+											"propagation": {
+													"default": {
+															"default_format": "w3c"
+													},
+													"fields": [
+															{
+																	"extract": {
+																			"elements": {
+																					"one_of": [
+																							"w3c",
+																							"b3"
+																					],
+																					"type": "string"
+																			},
+																			"type": "array"
+																	}
+															},
+															{
+																	"default_format": {
+																			"one_of": [
+																					"w3c",
+																					"b3"
+																			],
+																			"required": true,
+																			"type": "string"
+																	}
+															}
+													],
+													"required": true,
+													"type": "record"
+											}
+									}
+							],
+							"required": true,
+							"type": "record"
+					}
+			}
+	]
+}`
+
 func TestStringArrayToString(t *testing.T) {
 	assert := assert.New(t)
 
@@ -2213,6 +2298,81 @@ func Test_FillPluginsDefaults_Acme(t *testing.T) {
 	}
 }
 
+func Test_FillPluginsDefaults_DefaultRecord(t *testing.T) {
+	client, err := NewTestClient(nil, nil)
+	require.NoError(t, err)
+	require.NotNil(t, client)
+
+	tests := []struct {
+		name     string
+		plugin   *Plugin
+		expected *Plugin
+	}{
+		{
+			name: "record defaults take precedence over fields defaults",
+			plugin: &Plugin{
+				Config: Configuration{
+					"endpoint": "http://test.test:4317",
+				},
+			},
+			expected: &Plugin{
+				Config: Configuration{
+					"endpoint": "http://test.test:4317",
+					"propagation": map[string]interface{}{
+						"default_format": string("w3c"), // from record defaults
+						"extract":        nil,           // from field defaults
+					},
+					"queue": map[string]interface{}{
+						"max_batch_size":       float64(200), // from record defaults
+						"max_coalescing_delay": float64(1),   // from field defaults
+					},
+				},
+			},
+		},
+		{
+			name: "configured values take precedence over record defaults",
+			plugin: &Plugin{
+				Config: Configuration{
+					"endpoint": "http://test.test:4317",
+					"propagation": map[string]interface{}{
+						"default_format": "b3",
+					},
+					"queue": map[string]interface{}{
+						"max_batch_size": 123,
+					},
+				},
+			},
+			expected: &Plugin{
+				Config: Configuration{
+					"endpoint": "http://test.test:4317",
+					"propagation": map[string]interface{}{
+						"default_format": string("b3"),
+						"extract":        nil, // from field defaults
+					},
+					"queue": map[string]interface{}{
+						"max_batch_size":       float64(123),
+						"max_coalescing_delay": float64(1), // from field defaults
+					},
+				},
+			},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			plugin := tc.plugin
+			var fullSchema map[string]interface{}
+			require.NoError(t, json.Unmarshal([]byte(defaultRecordSchema), &fullSchema))
+			require.NotNil(t, fullSchema)
+			assert.NoError(t, FillPluginsDefaults(plugin, fullSchema))
+			opts := cmpopts.IgnoreFields(*plugin, "Enabled", "Protocols")
+			if diff := cmp.Diff(plugin, tc.expected, opts); diff != "" {
+				t.Errorf(diff)
+			}
+		})
+	}
+}
+
 const NonEmptyDefaultArrayFieldSchema = `{
     "fields": [
         {