fix: Return error 422 (Unprocessable Content) when push request does not contain any streams

pkg/distributor/distributor.go

@@ -429,7 +429,7 @@ func (d *Distributor) Push(ctx context.Context, req *logproto.PushRequest) (*log
 
 	// Return early if request does not contain any streams
 	if len(req.Streams) == 0 {
-		return &logproto.PushResponse{}, nil
+		return &logproto.PushResponse{}, httpgrpc.Errorf(http.StatusUnprocessableEntity, validation.MissingStreamsErrorMsg)
 	}
 
 	// First we flatten out the request into a list of samples.

pkg/distributor/distributor_test.go

@@ -629,6 +629,16 @@ func Test_DiscardEmptyStreamsAfterValidation(t *testing.T) {
 		topVal := ingester.Peek()
 		require.Nil(t, topVal)
 	})
+
+	t.Run("it returns unprocessable entity error if the streams is empty", func(t *testing.T) {
+		limits, ingester := setup()
+		distributors, _ := prepare(t, 1, 5, limits, func(_ string) (ring_client.PoolClient, error) { return ingester, nil })
+
+		_, err := distributors[0].Push(ctx, makeWriteRequestWithLabels(1, 1, []string{}))
+		require.Equal(t, err, httpgrpc.Errorf(http.StatusUnprocessableEntity, validation.MissingStreamsErrorMsg))
+		topVal := ingester.Peek()
+		require.Nil(t, topVal)
+	})
 }
 
 func TestStreamShard(t *testing.T) {

pkg/validation/validate.go

@@ -11,7 +11,9 @@ import (
 )
 
 const (
-	ReasonLabel = "reason"
+	ReasonLabel            = "reason"
+	MissingStreamsErrorMsg = "error at least one valid stream is required for ingestion"
+
 	// InvalidLabels is a reason for discarding log lines which have labels that cannot be parsed.
 	InvalidLabels = "invalid_labels"
 	MissingLabels = "missing_labels"