Add resumable downloads, download paths, queue controls and history

internal/fetch/worker.go

@@ -0,0 +1,107 @@
+package fetch
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+const (
+	maxRetriesWithoutProgress = 8
+	retryBaseDelay            = 2 * time.Second
+	retryMaxDelay             = 30 * time.Second
+)
+
+type segmentWorker struct {
+	session        *session
+	segment        *liveSegment
+	failedAttempts int
+}
+
+func (worker *segmentWorker) run(ctx context.Context, response *http.Response) error {
+	var err error
+	if response == nil {
+		response, err = worker.open(ctx)
+	}
+	for {
+		if err != nil {
+			response, err = worker.reconnect(ctx, err)
+			if err != nil {
+				return err
+			}
+		}
+
+		doneBefore := worker.segment.done.Load()
+		err = worker.copyFrom(response)
+		if err == nil {
+			return nil
+		}
+		if worker.segment.done.Load() > doneBefore {
+			worker.failedAttempts = 0
+		}
+	}
+}
+
+func (worker *segmentWorker) open(ctx context.Context) (*http.Response, error) {
+	return worker.session.downloader.open(ctx, worker.session.source, worker.segment.position(), worker.segment.end)
+}
+
+func (worker *segmentWorker) copyFrom(response *http.Response) error {
+	defer response.Body.Close()
+	writer := io.NewOffsetWriter(worker.session.file, worker.segment.position())
+	if err := copyBody(writer, response.Body, worker.segment.remaining(), worker.record); err != nil {
+		return err
+	}
+	if worker.segment.bounded() && !worker.segment.complete() {
+		return ErrIncomplete
+	}
+	return nil
+}
+
+func (worker *segmentWorker) record(count int64) error {
+	worker.segment.done.Add(count)
+	return worker.session.record(count)
+}
+
+func (worker *segmentWorker) reconnect(ctx context.Context, cause error) (*http.Response, error) {
+	progress := worker.session.request.Progress
+	for {
+		worker.failedAttempts++
+		if ctx.Err() != nil || !isRetryable(cause) || worker.failedAttempts > maxRetriesWithoutProgress {
+			return nil, cause
+		}
+		progress.SetNotice(fmt.Sprintf("Connection lost, reconnecting (attempt %d of %d)", worker.failedAttempts, maxRetriesWithoutProgress))
+		if err := waitBeforeRetry(ctx, worker.failedAttempts); err != nil {
+			return nil, err
+		}
+
+		response, err := worker.open(ctx)
+		if err == nil {
+			progress.SetNotice("")
+			return response, nil
+		}
+		cause = err
+	}
+}
+
+func isRetryable(err error) bool {
+	return errors.Is(err, errConnectionFailed) ||
+		errors.Is(err, errServerUnavailable) ||
+		errors.Is(err, ErrStalled) ||
+		errors.Is(err, ErrIncomplete)
+}
+
+func waitBeforeRetry(ctx context.Context, attempt int) error {
+	delay := min(retryBaseDelay*time.Duration(attempt), retryMaxDelay)
+	timer := time.NewTimer(delay)
+	defer timer.Stop()
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case <-timer.C:
+		return nil
+	}
+}