sia: parallel download block pieces

sia/store.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"sync"
 	"time"
 
 	"github.com/gogo/protobuf/proto"
@@ -43,20 +44,48 @@ func (bs *RenterdBlockStore) Has(ctx context.Context, c cid.Cid) (bool, error) {
 
 func (bs *RenterdBlockStore) downloadBlock(ctx context.Context, cm Block) (blocks.Block, error) {
 	var data, metadata []byte
-	var err error
 
+	ctx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	var wg sync.WaitGroup
+	errCh := make(chan error, 2)
 	if cm.Data.BlockSize != 0 {
-		data, err = downloadPartialData(ctx, bs.renterd, cm.Data.Bucket, cm.Data.Key, cm.Data.Offset, cm.Data.BlockSize)
-		if err != nil {
-			return nil, fmt.Errorf("failed to download data: %w", err)
-		}
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+
+			var err error
+			data, err = downloadPartialData(ctx, bs.renterd, cm.Data.Bucket, cm.Data.Key, cm.Data.Offset, cm.Data.BlockSize)
+			if err != nil {
+				bs.log.Error("failed to download block data", zap.Error(err), zap.Stringer("cid", cm.CID))
+				errCh <- fmt.Errorf("failed to download block data: %w", err)
+			}
+		}()
 	}
 
 	if cm.Metadata.Length != 0 {
-		metadata, err = downloadPartialData(ctx, bs.renterd, cm.Metadata.Bucket, cm.Metadata.Key, cm.Metadata.Offset, cm.Metadata.Length)
-		if err != nil {
-			return nil, fmt.Errorf("failed to download object: %w", err)
-		}
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+
+			var err error
+			metadata, err = downloadPartialData(ctx, bs.renterd, cm.Metadata.Bucket, cm.Metadata.Key, cm.Metadata.Offset, cm.Metadata.Length)
+			if err != nil {
+				bs.log.Error("failed to download block metadata", zap.Error(err), zap.Stringer("cid", cm.CID))
+				errCh <- fmt.Errorf("failed to download block metadata: %w", err)
+			}
+		}()
+	}
+
+	// Wait for all downloads to complete.
+	go func() {
+		wg.Wait()
+		close(errCh)
+	}()
+
+	for err := range errCh {
+		return nil, err
 	}
 
 	if n := len(data); n != int(cm.Data.BlockSize) {