MQTT: publish the forecast as a single JSON message (#32710)

server/mqtt.go

@@ -84,6 +84,16 @@ func mqttTagAttribute(attr string, f reflect.StructField) bool {
 }
 
 func (m *MQTT) publishComplex(topic string, retained bool, payload any) {
+	// unwrap first so the wrapped value is still checked for the marshalers below
+	if mm, ok := payload.(api.StructMarshaler); ok {
+		d, err := mm.MarshalStruct()
+		if err != nil {
+			m.log.ERROR.Printf("marshal struct: %v", err)
+			return
+		}
+		payload = d
+	}
+
 	if _, ok := payload.(fmt.Stringer); ok || payload == nil {
 		m.publishSingleValue(topic, retained, payload)
 		return
@@ -98,16 +108,6 @@ func (m *MQTT) publishComplex(topic string, retained bool, payload any) {
 		return
 	}
 
-	if mm, ok := payload.(api.StructMarshaler); ok {
-		if d, err := mm.MarshalStruct(); err != nil {
-			m.log.ERROR.Printf("marshal struct: %v", err)
-			return
-		} else {
-			payload = d
-			// fallthrough
-		}
-	}
-
 	switch typ := reflect.TypeOf(payload); typ.Kind() {
 	case reflect.Slice:
 		// publish count

server/mqtt_test.go

@@ -1,6 +1,7 @@
 package server
 
 import (
+	"encoding/json"
 	"math"
 	"slices"
 	"strconv"
@@ -8,6 +9,7 @@ import (
 	"time"
 
 	"github.com/evcc-io/evcc/core/types"
+	"github.com/evcc-io/evcc/util"
 	"github.com/samber/lo"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/suite"
@@ -97,6 +99,22 @@ func (suite *mqttSuite) TestSlice() {
 	suite.Equal([]string{"2", "10", "20"}, suite.payloads, "payloads")
 }
 
+type jsonPayload struct {
+	Foo [][]float64 `json:"foo,omitempty"`
+}
+
+func (p jsonPayload) MarshalBytes() ([]byte, error) {
+	return json.Marshal(p)
+}
+
+// a BytesMarshaler wrapped in a Sharder must still publish as a single message
+func (suite *mqttSuite) TestShardedBytesMarshaler() {
+	p := jsonPayload{Foo: [][]float64{{1, 2, 3}, {4, 5, 6}}}
+	suite.publish("test", false, util.NewSharder("test", p))
+	suite.Equal([]string{"test"}, suite.topics, "topics")
+	suite.Equal([]string{`{"foo":[[1,2,3],[4,5,6]]}`}, suite.payloads, "payloads")
+}
+
 func (suite *mqttSuite) TestNilInterface() {
 	var ptr *time.Time
 	suite.publish("test", false, ptr)