From 01a5cbba6d9d9f425f045b58fa16d8c85804c29c Mon Sep 17 00:00:00 2001
From: Brenna N Epp <brennae@google.com>
Date: Mon, 8 Jul 2024 16:54:39 -0700
Subject: [PATCH] fix(storage/transfermanager): correct Attrs.StartOffset for
 sharded downloads (#10512)

Because the download is in pieces, the StartOffset may be incorrect.
---
 storage/transfermanager/downloader.go       | 6 ++++++
 storage/transfermanager/integration_test.go | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/storage/transfermanager/downloader.go b/storage/transfermanager/downloader.go
index d0694d9b75c8..b29f1ee40eb2 100644
--- a/storage/transfermanager/downloader.go
+++ b/storage/transfermanager/downloader.go
@@ -419,6 +419,12 @@ func (d *Downloader) gatherShards(in *DownloadObjectInput, outs <-chan *Download
 	if len(errs) != 0 {
 		shardOut.Err = fmt.Errorf("download shard errors:\n%w", errors.Join(errs...))
 	}
+	if shardOut.Attrs != nil {
+		shardOut.Attrs.StartOffset = 0
+		if in.Range != nil {
+			shardOut.Attrs.StartOffset = in.Range.Offset
+		}
+	}
 	d.addResult(in, shardOut)
 }
 
diff --git a/storage/transfermanager/integration_test.go b/storage/transfermanager/integration_test.go
index 815d036dd6fb..a2ab3a9dac7e 100644
--- a/storage/transfermanager/integration_test.go
+++ b/storage/transfermanager/integration_test.go
@@ -423,6 +423,10 @@ func TestIntegration_DownloaderSynchronous(t *testing.T) {
 			if got, want := got.Attrs.Size, tb.objectSizes[got.Object]; want != got {
 				t.Errorf("expected object size %d, got %d", want, got)
 			}
+
+			if got, want := got.Attrs.StartOffset, int64(0); want != got {
+				t.Errorf("expected start offset %d, got %d", want, got)
+			}
 		}
 
 		if len(results) != len(objects) {