feature/s3/manager: Suppress WriterAt which can bypass Windows optimizations. (#1791)

Fixes issue with Go 1.19 discovered in the S3 transfer manager's windows upload and downloader buffer pools. It looks like the update to Go 1.19 changes the code path that is used by the pool because io.NopCloser was updated to forward WriterTo if the underlying Writer implemented it. Looks likes we'd made some assumptions about this behavior not being present. This PR suppresses the WriterTo of the buffer pool to prevent the unexpected usage.

Author: skmcgrail

feature/s3/manager/download.go

@@ -100,7 +100,8 @@ func WithDownloaderClientOptions(opts ...func(*s3.Options)) func(*Downloader) {
 // interface.
 //
 // Example:
-// 	// Load AWS Config
+//
+//	// Load AWS Config
 //	cfg, err := config.LoadDefaultConfig(context.TODO())
 //	if err != nil {
 //		panic(err)
@@ -153,6 +154,7 @@ func NewDownloader(c DownloadAPIClient, options ...func(*Downloader)) *Downloade
 // and GC runs.
 //
 // Example:
+//
 //	// pre-allocate in memory buffer, where headObject type is *s3.HeadObjectOutput
 //	buf := make([]byte, int(headObject.ContentLength))
 //	// wrap with aws.WriteAtBuffer
@@ -397,7 +399,11 @@ func (d *downloader) tryDownloadChunk(params *s3.GetObjectInput, w io.Writer) (i
 	}
 	d.setTotalBytes(resp) // Set total if not yet set.
 
-	n, err := io.Copy(w, resp.Body)
+	var src io.Reader = resp.Body
+	if d.cfg.BufferProvider != nil {
+		src = &suppressWriterAt{suppressed: src}
+	}
+	n, err := io.Copy(w, src)
 	resp.Body.Close()
 	if err != nil {
 		return n, &errReadingBody{err: err}

feature/s3/manager/writer_read_from.go

@@ -73,3 +73,11 @@ func (p *PooledBufferedReadFromProvider) GetReadFrom(writer io.Writer) (r Writer
 	}
 	return r, cleanup
 }
+
+type suppressWriterAt struct {
+	suppressed io.Reader
+}
+
+func (s *suppressWriterAt) Read(p []byte) (n int, err error) {
+	return s.suppressed.Read(p)
+}