Azure blob存储下载流返回“”asp.net

Question

I am currently trying to download a file from Azure blob storage using the DownloadToStream method to download the contents of a blob as a text string. However I am not getting anything back but an empty string.

Here is my code that I use to connect to the azure blob container and retrieve the blob file.

    public static string DownLoadFroalaImageAsString(string blobStorageName, string companyID)
    {
        // Retrieve storage account from connection string.
        CloudStorageAccount storageAccount = CloudStorageAccount.Parse(
            CloudConfigurationManager.GetSetting("StorageConnectionString"));

        // Create the blob client.
        CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();

        // Retrieve reference to a previously created container.
        CloudBlobContainer container = blobClient.GetContainerReference(companyID.ToLower());

        //retrieving the actual filename of the blob
        string removeString = "BLOB/";
        string trimmedString = blobStorageName.Remove(blobStorageName.IndexOf(removeString), removeString.Length);

        // Retrieve reference to a blob named "trimmedString"
        CloudBlockBlob blockBlob2 = container.GetBlockBlobReference(trimmedString);

        string text;
        using (var memoryStream = new MemoryStream())
        {
            blockBlob2.DownloadToStream(memoryStream);
            text = System.Text.Encoding.UTF8.GetString(memoryStream.ToArray());
        }
        return text;
    }

I was following along this documentation however I cannot seem to get it to work. Any help would be greatly appreciated.

Answer 1

However I am not getting anything back but an empty string.

I test your supplied code on my side, it works correctly. I assume that the test blob content is empty in your case. We could trouble shooting with following ways:

1.please have a try to check the Length of memoryStream. If length equal 0 we could know that the blob content is empty.

using (var memoryStream = new MemoryStream())
{
    blockBlob2.DownloadToStream(memoryStream);
    var length = memoryStream.Length;
    text = System.Text.Encoding.UTF8.GetString(memoryStream.ToArray());
 }

2.We could upload a blob with content to container, we could do that with Azure portal or Microsoft Azure storage explorer easily. And please have a try test it with uploaded blob.

Answer 2

If you want to get the text from the blob, you can use DownloadTextAsync()

var text = await blockBlob2.DownloadTextAsync();

If you want to return file stream back to an API respoinse, you can use FileStreamResult which is IActionResult.

var stream = await blockBlob2.OpenReadAsync();
return File(stream, blockBlob2.Properties.ContentType, "name");