arc: gerund-form errors, time column guard, and lint fixes

- Update fmt.Errorf messages to project gerund-form convention
  (creating HTTP client, encoding msgpack, compressing, interpolating
  measurement, mapping tags, reading tags mapping result)
- Always skip "time" key in message fields regardless of
  timestamp_field value (the "time" column is reserved for the
  extracted timestamp; a literal "time" field in data would otherwise
  collide in both columnar and row paths)
- Fix golangci-lint issues: unused receiver on Connect, unused
  request params in test handlers, testify GreaterOrEqual for
  length check

Author: Ignacio Van Droogenbroeck

internal/impl/arc/output.go

@@ -213,13 +213,13 @@ func newArcOutput(conf *service.ParsedConfig, mgr *service.Resources) (*arcOutpu
 	httpCfg.MetricPrefix = "arc_http"
 
 	if o.client, err = httpclient.NewClient(httpCfg, mgr); err != nil {
-		return nil, fmt.Errorf("create HTTP client: %w", err)
+		return nil, fmt.Errorf("creating HTTP client: %w", err)
 	}
 
 	return o, nil
 }
 
-func (o *arcOutput) Connect(_ context.Context) error {
+func (*arcOutput) Connect(_ context.Context) error {
 	return nil
 }
 
@@ -245,12 +245,12 @@ func (o *arcOutput) WriteBatch(ctx context.Context, batch service.MessageBatch)
 
 	data, err := msgpack.Marshal(payload)
 	if err != nil {
-		return fmt.Errorf("msgpack encoding: %w", err)
+		return fmt.Errorf("encoding msgpack: %w", err)
 	}
 
 	compressed, encoding, err := o.compress(data)
 	if err != nil {
-		return fmt.Errorf("compression: %w", err)
+		return fmt.Errorf("compressing: %w", err)
 	}
 
 	return o.sendRequest(ctx, compressed, encoding)
@@ -270,7 +270,7 @@ func (o *arcOutput) buildColumnarPayload(batch service.MessageBatch) (any, error
 	for i, msg := range batch {
 		measName, err := measExec.TryString(i)
 		if err != nil {
-			return nil, fmt.Errorf("measurement interpolation: %w", err)
+			return nil, fmt.Errorf("interpolating measurement: %w", err)
 		}
 
 		data, err := msg.AsStructuredMut()
@@ -294,7 +294,7 @@ func (o *arcOutput) buildColumnarPayload(batch service.MessageBatch) (any, error
 
 		rec.columns["time"] = append(rec.columns["time"], ts)
 		for k, v := range dataMap {
-			if k == o.timestampField || (o.timestampField == "" && k == "time") {
+			if k == o.timestampField || k == "time" {
 				continue
 			}
 			rec.columns[k] = append(rec.columns[k], v)
@@ -329,7 +329,7 @@ func (o *arcOutput) buildRowPayload(batch service.MessageBatch) (any, error) {
 	for i, msg := range batch {
 		measName, err := measExec.TryString(i)
 		if err != nil {
-			return nil, fmt.Errorf("measurement interpolation: %w", err)
+			return nil, fmt.Errorf("interpolating measurement: %w", err)
 		}
 
 		data, err := msg.AsStructuredMut()
@@ -347,7 +347,7 @@ func (o *arcOutput) buildRowPayload(batch service.MessageBatch) (any, error) {
 		// Remove timestamp field from fields if present
 		fields := make(map[string]any, len(dataMap))
 		for k, v := range dataMap {
-			if k == o.timestampField || (o.timestampField == "" && k == "time") {
+			if k == o.timestampField || k == "time" {
 				continue
 			}
 			fields[k] = v
@@ -363,12 +363,12 @@ func (o *arcOutput) buildRowPayload(batch service.MessageBatch) (any, error) {
 		if tagsExec != nil {
 			tagMsg, err := tagsExec.Query(i)
 			if err != nil {
-				return nil, fmt.Errorf("tags mapping: %w", err)
+				return nil, fmt.Errorf("mapping tags: %w", err)
 			}
 			if tagMsg != nil {
 				tagResult, err := tagMsg.AsStructured()
 				if err != nil {
-					return nil, fmt.Errorf("tags mapping result: %w", err)
+					return nil, fmt.Errorf("reading tags mapping result: %w", err)
 				}
 				if tagMap, ok := tagResult.(map[string]any); ok {
 					tags := make(map[string]string, len(tagMap))

internal/impl/arc/output_test.go

@@ -269,7 +269,7 @@ compression: gzip
 	defer mu.Unlock()
 
 	assert.Equal(t, "gzip", headers.Get("Content-Encoding"))
-	require.True(t, len(*received) >= 2)
+	require.GreaterOrEqual(t, len(*received), 2)
 	assert.Equal(t, byte(0x1f), (*received)[0])
 	assert.Equal(t, byte(0x8b), (*received)[1])
 
@@ -308,7 +308,7 @@ compression: none
 }
 
 func TestArcOutput_ErrorResponse(t *testing.T) {
-	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		w.WriteHeader(http.StatusBadRequest)
 		_ = json.NewEncoder(w).Encode(map[string]string{"error": "invalid measurement name"})
@@ -342,7 +342,7 @@ compression: none
 func TestArcOutput_EmptyBatch(t *testing.T) {
 	var mu sync.Mutex
 	called := false
-	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
 		mu.Lock()
 		called = true
 		mu.Unlock()