Stats: improve JSON support, add missing structs

- Fix json marshalling of stats containing enums
- Add UnmarshalStatsJSON helper
- Add marshalling/unmarshalling tests
- Add missing AudioSourceStats, VideoSourceStats AudioPlayoutStats
  defined in https://www.w3.org/TR/webrtc-stats
- Deprecate ICECandidateStats' NetworkType, use plain string
  instead of enum which does not suite the definition:
  https://clck.ru/354H9r

AUTHORS.txt

@@ -12,6 +12,7 @@ Adrian Cable <adrian.cable@gmail.com>
 adwpc <adwpc@hotmail.com>
 aggresss <aggresss@163.com>
 akil <akil@everycrave.me>
+Aleksandr Alekseev <alekseev-dev@yandex-team.ru>
 Aleksandr Razumov <ar@gortc.io>
 aler9 <46489434+aler9@users.noreply.github.com>
 Alex Browne <stephenalexbrowne@gmail.com>

datachannelstate.go

@@ -62,3 +62,14 @@ func (t DataChannelState) String() string {
 		return ErrUnknownType.Error()
 	}
 }
+
+// MarshalText implements encoding.TextMarshaler
+func (t DataChannelState) MarshalText() ([]byte, error) {
+	return []byte(t.String()), nil
+}
+
+// UnmarshalText implements encoding.TextUnmarshaler
+func (t *DataChannelState) UnmarshalText(b []byte) error {
+	*t = newDataChannelState(string(b))
+	return nil
+}

dtlstransportstate.go

@@ -72,3 +72,14 @@ func (t DTLSTransportState) String() string {
 		return ErrUnknownType.Error()
 	}
 }
+
+// MarshalText implements encoding.TextMarshaler
+func (t DTLSTransportState) MarshalText() ([]byte, error) {
+	return []byte(t.String()), nil
+}
+
+// UnmarshalText implements encoding.TextUnmarshaler
+func (t *DTLSTransportState) UnmarshalText(b []byte) error {
+	*t = newDTLSTransportState(string(b))
+	return nil
+}

icecandidatetype.go

@@ -95,3 +95,15 @@ func getCandidateType(candidateType ice.CandidateType) (ICECandidateType, error)
 		return ICECandidateType(Unknown), err
 	}
 }
+
+// MarshalText implements the encoding.TextMarshaler interface.
+func (t ICECandidateType) MarshalText() ([]byte, error) {
+	return []byte(t.String()), nil
+}
+
+// UnmarshalText implements the encoding.TextUnmarshaler interface.
+func (t *ICECandidateType) UnmarshalText(b []byte) error {
+	var err error
+	*t, err = NewICECandidateType(string(b))
+	return err
+}

icegatherer.go

@@ -347,7 +347,6 @@ func (g *ICEGatherer) collectStats(collector *statsReportCollector) {
 				Timestamp:     statsTimestampFrom(candidateStats.Timestamp),
 				ID:            candidateStats.ID,
 				Type:          StatsTypeLocalCandidate,
-				NetworkType:   networkType,
 				IP:            candidateStats.IP,
 				Port:          int32(candidateStats.Port),
 				Protocol:      networkType.Protocol(),
@@ -376,7 +375,6 @@ func (g *ICEGatherer) collectStats(collector *statsReportCollector) {
 				Timestamp:     statsTimestampFrom(candidateStats.Timestamp),
 				ID:            candidateStats.ID,
 				Type:          StatsTypeRemoteCandidate,
-				NetworkType:   networkType,
 				IP:            candidateStats.IP,
 				Port:          int32(candidateStats.Port),
 				Protocol:      networkType.Protocol(),

icerole.go

@@ -46,3 +46,14 @@ func (t ICERole) String() string {
 		return ErrUnknownType.Error()
 	}
 }
+
+// MarshalText implements encoding.TextMarshaler
+func (t ICERole) MarshalText() ([]byte, error) {
+	return []byte(t.String()), nil
+}
+
+// UnmarshalText implements encoding.TextUnmarshaler
+func (t *ICERole) UnmarshalText(b []byte) error {
+	*t = newICERole(string(b))
+	return nil
+}