Fix incorrect downloaded file size when size of the file is not a mul…

…tiple of the block size (#22036)

* convert apply method of SourceContentValidation to private

* fixed buffer length while batch download

* add another test case and fixed typos

* Fixing buffer size

* PR comment

---------

Co-authored-by: Sourav Gupta <souravgupta@microsoft.com>

sdk/storage/azblob/CHANGELOG.md

@@ -14,6 +14,7 @@
 * Fixed SharedKeyMissingError when using client.BlobClient().GetSASURL() method
 * Fixed an issue that would cause metadata keys with empty values to be omitted when enumerating blobs.
 * Fixed an issue where passing empty map to set blob tags API was causing panic. Fixes [#21869](https://github.com/Azure/azure-sdk-for-go/issues/21869).
+* Fixed an issue where downloaded file has incorrect size when not a multiple of block size. Fixes [#21995](https://github.com/Azure/azure-sdk-for-go/issues/21995).
 
 ### Other Changes
 

sdk/storage/azblob/blob/client.go

@@ -464,7 +464,7 @@ func (b *Client) downloadFile(ctx context.Context, writer io.Writer, o downloadO
 
 	buffers := shared.NewMMBPool(int(o.Concurrency), o.BlockSize)
 	defer buffers.Free()
-	aquireBuffer := func() ([]byte, error) {
+	acquireBuffer := func() ([]byte, error) {
 		select {
 		case b := <-buffers.Acquire():
 			// got a buffer
@@ -489,21 +489,23 @@ func (b *Client) downloadFile(ctx context.Context, writer io.Writer, o downloadO
 	/*
 	 * We have created as many channels as the number of chunks we have.
 	 * Each downloaded block will be sent to the channel matching its
-	 * sequece number, i.e. 0th block is sent to 0th channel, 1st block
+	 * sequence number, i.e. 0th block is sent to 0th channel, 1st block
 	 * to 1st channel and likewise. The blocks are then read and written
 	 * to the file serially by below goroutine. Do note that the blocks
-	 * blocks are still downloaded parallelly from n/w, only serailized
+	 * are still downloaded parallelly from n/w, only serialized
 	 * and written to file here.
 	 */
 	writerError := make(chan error)
+	writeSize := int64(0)
 	go func(ch chan error) {
 		for _, block := range blocks {
 			select {
 			case <-ctx.Done():
 				return
 			case block := <-block:
-				_, err := writer.Write(block)
-				buffers.Release(block)
+				n, err := writer.Write(block)
+				writeSize += int64(n)
+				buffers.Release(block[:cap(block)])
 				if err != nil {
 					ch <- err
 					return
@@ -521,7 +523,7 @@ func (b *Client) downloadFile(ctx context.Context, writer io.Writer, o downloadO
 		NumChunks:     numChunks,
 		Concurrency:   o.Concurrency,
 		Operation: func(ctx context.Context, chunkStart int64, count int64) error {
-			buff, err := aquireBuffer()
+			buff, err := acquireBuffer()
 			if err != nil {
 				return err
 			}
@@ -538,8 +540,8 @@ func (b *Client) downloadFile(ctx context.Context, writer io.Writer, o downloadO
 				return err
 			}
 
-			blockIndex := (chunkStart / o.BlockSize)
-			blocks[blockIndex] <- buff
+			blockIndex := chunkStart / o.BlockSize
+			blocks[blockIndex] <- buff[:count]
 			return nil
 		},
 	})
@@ -551,7 +553,7 @@ func (b *Client) downloadFile(ctx context.Context, writer io.Writer, o downloadO
 	if err = <-writerError; err != nil {
 		return 0, err
 	}
-	return count, nil
+	return writeSize, nil
 }
 
 // DownloadStream reads a range of bytes from a blob. The response also includes the blob's properties and metadata.

sdk/storage/azblob/blob/client_test.go

@@ -289,7 +289,7 @@ func (s *BlobUnrecordedTestsSuite) TestUploadDownloadBlockBlob() {
 		_, err = srcBlob.Upload(context.Background(), body, nil)
 		_require.NoError(err)
 
-		// downlod to a temp file and verify contents
+		// download to a temp file and verify contents
 		tmp, err := os.CreateTemp("", "")
 		_require.NoError(err)
 		defer tmp.Close()
@@ -299,6 +299,10 @@ func (s *BlobUnrecordedTestsSuite) TestUploadDownloadBlockBlob() {
 		_require.NoError(err)
 		_require.Equal(int64(contentSize), n)
 
+		stat, err := tmp.Stat()
+		_require.NoError(err)
+		_require.Equal(int64(contentSize), stat.Size())
+
 		// Compute md5 of file, and verify it against stored value.
 		_, _ = tmp.Seek(0, io.SeekStart)
 		buff := make([]byte, contentSize)
@@ -327,6 +331,10 @@ func (s *BlobUnrecordedTestsSuite) TestUploadDownloadBlockBlob() {
 
 	// 199 MB file, more blocks than threads
 	testUploadDownload(199 * MiB)
+
+	testUploadDownload(7 * MiB)
+
+	testUploadDownload(8241066)
 }
 
 func (s *BlobRecordedTestsSuite) TestBlobStartCopyDestEmpty() {