fix(das): Clarify logs for historic headers that are skipped (#3380)

Fix is kind of ugly but there needs to be a way to bubble up to worker
that the header is skipped vs being sampled successfully.

Resolves #3194

Author: renaynay

das/daser.go

@@ -21,6 +21,11 @@ import (
 
 var log = logging.Logger("das")
 
+// errOutsideSamplingWindow is an error used to inform
+// the caller of Sample that the given header is outside
+// the sampling window.
+var errOutsideSamplingWindow = fmt.Errorf("skipping header outside of sampling window")
+
 // DASer continuously validates availability of data committed to headers.
 type DASer struct {
 	params Parameters
@@ -160,7 +165,7 @@ func (d *DASer) sample(ctx context.Context, h *header.ExtendedHeader) error {
 	if !d.isWithinSamplingWindow(h) {
 		log.Debugw("skipping header outside sampling window", "height", h.Height(),
 			"time", h.Time())
-		return nil
+		return errOutsideSamplingWindow
 	}
 
 	err := d.da.SharesAvailable(ctx, h)

das/worker.go

@@ -75,12 +75,18 @@ func (w *worker) run(ctx context.Context, timeout time.Duration, resultCh chan<-
 	jobStart := time.Now()
 	log.Debugw("start sampling worker", "from", w.state.from, "to", w.state.to)
 
+	skipped := 0
+
 	for curr := w.state.from; curr <= w.state.to; curr++ {
 		err := w.sample(ctx, timeout, curr)
 		if errors.Is(err, context.Canceled) {
 			// sampling worker will resume upon restart
 			return
 		}
+		if errors.Is(err, errOutsideSamplingWindow) {
+			skipped++
+			err = nil
+		}
 		w.setResult(curr, err)
 	}
 
@@ -91,6 +97,7 @@ func (w *worker) run(ctx context.Context, timeout time.Duration, resultCh chan<-
 			"from", w.state.from,
 			"to", w.state.curr,
 			"errors", len(w.state.failed),
+			"# of headers skipped as outside of sampling window", skipped,
 			"finished (s)", time.Since(jobStart),
 		)
 	}
@@ -112,6 +119,12 @@ func (w *worker) sample(ctx context.Context, timeout time.Duration, height uint6
 	defer cancel()
 
 	err = w.sampleFn(ctx, h)
+	if errors.Is(err, errOutsideSamplingWindow) {
+		// if header is outside sampling window, do not log
+		// or record it.
+		return err
+	}
+
 	w.metrics.observeSample(ctx, h, time.Since(start), w.state.jobType, err)
 	if err != nil {
 		if !errors.Is(err, context.Canceled) {