fix(config): serialize Duration as a flat string under YAML

config.Duration only implemented MarshalJSON, so gopkg.in/yaml.v2/v3 (which
does not honor MarshalJSON) serialized the embedded time.Duration as a nested
`duration:` map. Any config that serializes a Duration to YAML and is read
back through the viper/mapstructure config loader (TagName json +
StringToTimeDurationHookFunc, which expects a string like "30s") would fail
to decode.

This first surfaced with the connector keepalive config: the operator writes
the connector configmap with yaml.v2, emitting `time:\n  duration: 30s`,
which the connector plugin could not read back. Add MarshalYAML/UnmarshalYAML
so Duration round-trips as a flat "30s" string under YAML.

Signed-off-by: Kevin Su <pingsutw@apache.org>

Author: pingsutw

flytestdlib/config/duration.go

@@ -46,6 +46,31 @@ func (d *Duration) UnmarshalJSON(b []byte) error {
 	return nil
 }
 
+// MarshalYAML serializes the duration as a string (e.g. "30s") so that
+// gopkg.in/yaml.v2/v3 (which does not honor MarshalJSON) emits a flat value
+// instead of leaking the embedded time.Duration as a nested `duration:` map.
+func (d Duration) MarshalYAML() (interface{}, error) {
+	return d.String(), nil
+}
+
+// UnmarshalYAML parses the string form (e.g. "30s") produced by MarshalYAML.
+func (d *Duration) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var s string
+	if err := unmarshal(&s); err != nil {
+		return err
+	}
+	if len(s) == 0 {
+		d.Duration = time.Duration(0)
+		return nil
+	}
+	parsed, err := time.ParseDuration(s)
+	if err != nil {
+		return err
+	}
+	d.Duration = parsed
+	return nil
+}
+
 // Set implements PFlag's Value interface's set method to set the value of duration from string.
 func (d *Duration) Set(val string) error {
 	var err error