fix(utils): support auto fields

When fields marked as `auto` are passed to kong without a value
they are auto generated by the gateway. In that case, comparing with
"defaults" doesn't work, so in order to compute a correct diff they must
be copied from Kong's configuration.

This commit addS a new FillPluginsDefaultsAutoFields utils function that
in addition to default fields, adds auto fields to the configuration.
It takes an additional parameter: oldConfig, which represents the config
from Kong: auto fields are just copied from it so that they don't show
up as differences in the diff.

kong/utils.go

@@ -278,7 +278,7 @@ func backfillResultConfigMap(res Configuration, path []string, configValue inter
 	return nil
 }
 
-func fillConfigRecord(schema gjson.Result, config Configuration) Configuration {
+func fillConfigRecord(schema gjson.Result, config Configuration, kongConfig Configuration) Configuration {
 	res := config.DeepCopy()
 	configFields := schema.Get("fields")
 	// Fetch deprecated fields
@@ -295,7 +295,7 @@ func fillConfigRecord(schema gjson.Result, config Configuration) Configuration {
 		}
 
 		if fname == "config" {
-			newConfig := fillConfigRecord(value.Get(fname), config)
+			newConfig := fillConfigRecord(value.Get(fname), config, kongConfig)
 			res = newConfig
 			return true
 		}
@@ -348,7 +348,7 @@ func fillConfigRecord(schema gjson.Result, config Configuration) Configuration {
 			default:
 				fieldConfig = subConfig.(map[string]interface{})
 			}
-			newSubConfig := fillConfigRecord(value.Get(fname), fieldConfig)
+			newSubConfig := fillConfigRecord(value.Get(fname), fieldConfig, kongConfig)
 			res[fname] = map[string]interface{}(newSubConfig)
 			return true
 		}
@@ -368,7 +368,7 @@ func fillConfigRecord(schema gjson.Result, config Configuration) Configuration {
 						for i, configRecord := range subConfigArray {
 							// Check if element is of type record, if it is, set default values by recursively calling `fillConfigRecord`
 							if configRecordMap, ok := configRecord.(map[string]interface{}); ok {
-								processedConfigRecord := fillConfigRecord(value.Get(fname).Get("elements"), configRecordMap)
+								processedConfigRecord := fillConfigRecord(value.Get(fname).Get("elements"), configRecordMap, kongConfig)
 								processedSubConfigArray[i] = processedConfigRecord
 								continue
 							}
@@ -382,6 +382,19 @@ func fillConfigRecord(schema gjson.Result, config Configuration) Configuration {
 			}
 		}
 
+		// handle `auto` fields by copying them from kongConfig if they don't have
+		// a value. When fields marked as `auto` are passed to kong without a value
+		// they are auto generated by the gateway. In that case, comparing with
+		// "defaults" doesn't work, so in order to compute a correct diff they must
+		// be copied from the kongConfig.
+		auto := value.Get(fname + ".auto")
+		if auto.Exists() && auto.Bool() && kongConfig != nil {
+			if v, ok := kongConfig[fname]; ok {
+				res[fname] = v
+				return true
+			}
+		}
+
 		// 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() {
@@ -665,9 +678,7 @@ func FillEntityDefaults(entity interface{}, schema Schema) error {
 	return nil
 }
 
-// FillPluginsDefaults ingests plugin's defaults from its schema.
-// Takes in a plugin struct and mutate it in place.
-func FillPluginsDefaults(plugin *Plugin, schema Schema) error {
+func fillConfigRecordDefaultsAutoFields(plugin *Plugin, schema map[string]interface{}, oldPlugin *Plugin) error {
 	jsonb, err := json.Marshal(&schema)
 	if err != nil {
 		return err
@@ -680,7 +691,12 @@ func FillPluginsDefaults(plugin *Plugin, schema Schema) error {
 	if plugin.Config == nil {
 		plugin.Config = make(Configuration)
 	}
-	plugin.Config = fillConfigRecord(configSchema, plugin.Config)
+
+	var oldConfig Configuration
+	if oldPlugin != nil {
+		oldConfig = oldPlugin.Config
+	}
+	plugin.Config = fillConfigRecord(configSchema, plugin.Config, oldConfig)
 	if plugin.Protocols == nil {
 		plugin.Protocols = getDefaultProtocols(gjsonSchema)
 	}
@@ -689,3 +705,15 @@ func FillPluginsDefaults(plugin *Plugin, schema Schema) error {
 	}
 	return nil
 }
+
+// FillPluginsDefaults ingests plugin's defaults from its schema.
+// Takes in a plugin struct and mutate it in place.
+func FillPluginsDefaults(plugin *Plugin, schema Schema) error {
+	return fillConfigRecordDefaultsAutoFields(plugin, schema, nil)
+}
+
+// same as FillPluginsDefaults but also fills auto fields
+// keeping both for compatibility: these utils are public
+func FillPluginsDefaultsAutoFields(plugin *Plugin, schema map[string]interface{}, oldPlugin *Plugin) error {
+	return fillConfigRecordDefaultsAutoFields(plugin, schema, oldPlugin)
+}