Add resumable downloads, download paths, queue controls and history

internal/fetch/copy.go

@@ -0,0 +1,55 @@
+package fetch
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"sync/atomic"
+	"time"
+)
+
+const (
+	bufferSize   = 1 << 20
+	stallTimeout = 2 * time.Minute
+)
+
+func copyBody(destination io.Writer, body io.ReadCloser, remaining int64, record func(int64) error) error {
+	var stalled atomic.Bool
+	stallTimer := time.AfterFunc(stallTimeout, func() {
+		stalled.Store(true)
+		body.Close()
+	})
+	defer stallTimer.Stop()
+
+	buffer := make([]byte, bufferSize)
+	for remaining != 0 {
+		readSize := len(buffer)
+		if remaining > 0 && remaining < int64(readSize) {
+			readSize = int(remaining)
+		}
+
+		count, readErr := body.Read(buffer[:readSize])
+		if count > 0 {
+			stallTimer.Reset(stallTimeout)
+			if _, err := destination.Write(buffer[:count]); err != nil {
+				return err
+			}
+			if err := record(int64(count)); err != nil {
+				return err
+			}
+			if remaining > 0 {
+				remaining -= int64(count)
+			}
+		}
+		if errors.Is(readErr, io.EOF) {
+			return nil
+		}
+		if readErr != nil {
+			if stalled.Load() {
+				return ErrStalled
+			}
+			return fmt.Errorf("%w: %w", errConnectionFailed, readErr)
+		}
+	}
+	return nil
+}