improve response from backend when there are different fields returns

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## tip
 
+* BUGFIX: fix bug with displaying responses with a custom set of fields. See [this issue](https://github.com/VictoriaMetrics/victorialogs-datasource/issues/23).
+
 ## v0.2.1
 
 * BUGFIX: change the `metrics` flag from `false` to `true` in `plugin.json` to ensure the plugin appears in the Grafana datasource selection list.

pkg/plugin/response.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"time"
 
 	"github.com/VictoriaMetrics/metricsql"
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
@@ -84,6 +85,19 @@ func parseStreamResponse(reader io.Reader) backend.DataResponse {
 			return newResponseError(err, backend.StatusInternal)
 		}
 		labelsField.Append(d)
+
+		// Grafana expects lineField to be always non-empty.
+		if timeFd.Len() == 0 {
+			lineField.Append(string(d))
+		}
+	}
+
+	// Grafana expects time field to be always non-empty.
+	if timeFd.Len() == 0 {
+		now := time.Now()
+		for i := 0; i < lineField.Len(); i++ {
+			timeFd.Append(now)
+		}
 	}
 
 	frame := data.NewFrame("", timeFd, lineField, labelsField)

pkg/plugin/response_test.go

@@ -127,6 +127,77 @@ func Test_parseStreamResponse(t *testing.T) {
 				frame.Meta = &data.FrameMeta{}
 				rsp.Frames = append(rsp.Frames, frame)
 
+				return rsp
+			},
+		},
+		{
+			name: "response with different labels and without standard fields",
+			response: `{"stream":"stderr","count(*)":"394"}
+{"stream":"stdout","count(*)":"21"}`,
+			want: func() backend.DataResponse {
+				labelsField := data.NewFieldFromFieldType(data.FieldTypeJSON, 0)
+				labelsField.Name = gLabelsField
+
+				timeFd := data.NewFieldFromFieldType(data.FieldTypeTime, 0)
+				timeFd.Name = gTimeField
+
+				lineField := data.NewFieldFromFieldType(data.FieldTypeString, 0)
+				lineField.Name = gLineField
+
+				lineField.Append(`{"count(*)":"394","stream":"stderr"}`)
+				lineField.Append(`{"count(*)":"21","stream":"stdout"}`)
+
+				labels := data.Labels{
+					"count(*)": "394",
+					"stream":   "stderr",
+				}
+
+				b, _ := labelsToJSON(labels)
+				labelsField.Append(b)
+
+				labels = data.Labels{
+					"count(*)": "21",
+					"stream":   "stdout",
+				}
+				b, _ = labelsToJSON(labels)
+				labelsField.Append(b)
+				frame := data.NewFrame("", timeFd, lineField, labelsField)
+
+				rsp := backend.DataResponse{}
+				frame.Meta = &data.FrameMeta{}
+				rsp.Frames = append(rsp.Frames, frame)
+
+				return rsp
+			},
+		},
+		{
+			name:     "response with different labels only one label",
+			response: `{"level":""}`,
+			want: func() backend.DataResponse {
+				labelsField := data.NewFieldFromFieldType(data.FieldTypeJSON, 0)
+				labelsField.Name = gLabelsField
+
+				timeFd := data.NewFieldFromFieldType(data.FieldTypeTime, 0)
+				timeFd.Name = gTimeField
+
+				lineField := data.NewFieldFromFieldType(data.FieldTypeString, 0)
+				lineField.Name = gLineField
+
+				lineField.Append(`{"level":""}`)
+
+				labels := data.Labels{
+					"level": "",
+				}
+
+				b, _ := labelsToJSON(labels)
+				labelsField.Append(b)
+
+				frame := data.NewFrame("", timeFd, lineField, labelsField)
+
+				rsp := backend.DataResponse{}
+				frame.Meta = &data.FrameMeta{}
+				rsp.Frames = append(rsp.Frames, frame)
+
 				return rsp
 			},
 		},
@@ -135,8 +206,41 @@ func Test_parseStreamResponse(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			r := io.NopCloser(bytes.NewBuffer([]byte(tt.response)))
 			w := tt.want()
-			if got := parseStreamResponse(r); !reflect.DeepEqual(got, w) {
-				t.Errorf("parseStreamResponse() = %#v, want %#v", got, w)
+			resp := parseStreamResponse(r)
+			if w.Error != nil {
+				if !reflect.DeepEqual(w, resp) {
+					t.Errorf("parseStreamResponse() = %#v, want %#v", resp, w)
+				}
+				return
+			}
+
+			if len(resp.Frames) != 1 {
+				t.Fatalf("expected for response to always contain 1 Frame; got %d", len(resp.Frames))
+			}
+			got := resp.Frames[0]
+			want := w.Frames[0]
+			expFieldsLen := got.Fields[0].Len()
+			for j, field := range want.Fields {
+				// if time field is empty, fill it with the value from the response
+				// because time field in the parseStreamResponse generated as time.Now()
+				if field.Name == gTimeField && field.Len() == 0 {
+					for _, f := range got.Fields {
+						if f.Name == gTimeField {
+							want.Fields[j] = f
+						}
+					}
+				}
+
+				// all fields within response should have equal length
+				gf := got.Fields[j]
+				if gf.Len() != expFieldsLen {
+					t.Fatalf("expected all fields to have equal length %d; got %d instead for field %q",
+						expFieldsLen, gf.Len(), gf.Name)
+				}
+			}
+
+			if !reflect.DeepEqual(got, want) {
+				t.Errorf("parseStreamResponse() = %#v, want %#v", got, want)
 			}
 		})
 	}