feat: add structured metadata to the promtail push API (#14153)

Signed-off-by: Edward Welch <edward.welch@grafana.com>

clients/pkg/promtail/targets/lokipush/pushtarget.go

@@ -153,7 +153,8 @@ func (t *PushTarget) handleLoki(w http.ResponseWriter, r *http.Request) {
 			e := api.Entry{
 				Labels: filtered.Clone(),
 				Entry: logproto.Entry{
-					Line: entry.Line,
+					Line:               entry.Line,
+					StructuredMetadata: entry.StructuredMetadata,
 				},
 			}
 			if t.config.KeepTimestamp {

clients/pkg/promtail/targets/lokipush/pushtarget_test.go

@@ -20,6 +20,8 @@ import (
 	"github.com/prometheus/prometheus/model/relabel"
 	"github.com/stretchr/testify/require"
 
+	"github.com/grafana/loki/pkg/push"
+
 	"github.com/grafana/loki/v3/clients/pkg/promtail/api"
 	"github.com/grafana/loki/v3/clients/pkg/promtail/client"
 	"github.com/grafana/loki/v3/clients/pkg/promtail/client/fake"
@@ -101,6 +103,10 @@ func TestLokiPushTarget(t *testing.T) {
 			Entry: logproto.Entry{
 				Timestamp: time.Unix(int64(i), 0),
 				Line:      "line" + strconv.Itoa(i),
+				StructuredMetadata: push.LabelsAdapter{
+					{Name: "i", Value: strconv.Itoa(i)},
+					{Name: "anotherMetaData", Value: "val"},
+				},
 			},
 		}
 	}
@@ -123,6 +129,13 @@ func TestLokiPushTarget(t *testing.T) {
 	// Spot check the first value in the result to make sure relabel rules were applied properly
 	require.Equal(t, expectedLabels, eh.Received()[0].Labels)
 
+	expectedStructuredMetadata := push.LabelsAdapter{
+		{Name: "i", Value: strconv.Itoa(0)},
+		{Name: "anotherMetaData", Value: "val"},
+	}
+	// Spot check the first value in the result to make sure structured metadata was received properly
+	require.Equal(t, expectedStructuredMetadata, eh.Received()[0].StructuredMetadata)
+
 	// With keep timestamp enabled, verify timestamp
 	require.Equal(t, time.Unix(99, 0).Unix(), eh.Received()[99].Timestamp.Unix())