SendGrid：如何从 Azure blob 存储附加文件？

Question

I have blobs in Windows Azure blob storage that I'd like to attach to emails sent with SendGrid. I'd like to specify the file name for the attachment (real file names are just mumbo jumbo) which afaik forces me to add the attachment as a stream.

My code looks like this:

var msg = SendGrid.GetInstance();
// Code for adding sender, recipient etc...
var storageAccount = CloudStorageAccount.Parse(ConfigurationManager.ConnectionStrings["storage"].ConnectionString);
var blobClient = storageAccount.CreateCloudBlobClient();
var container = blobClient.GetContainerReference(typeName);
var blob = container.GetBlockBlobReference("somefile.png");
var ms = new MemoryStream();
blob.DownloadToStream(ms);
msg.AddAttachment(ms, "originalfilename.png");

The file gets read from the storage to the memory stream and adding the attachment seems to work fine but after receiving the email the attached file is 0 bytes.

Thank you in advance.

Answer 1

This has probably already been solved, but you need to make sure that you 'rewind' the stream back to the beginning using Seek. Sample code below.

stream.Seek(0, SeekOrigin.Begin);
sendGrid.AddAttachment(stream, "name");

Answer 2

Even though I am not sure how AddAttachment API works, please note that your MemoryStream's position will be set to its length at the end of the download. Hence, you might need to seek it to the beginning before calling AddAttachment.

var ms = new MemoryStream();
blob.DownloadToStream(ms);
ms.Position = 0;
msg.AddAttachment(ms, "originalfilename.png");

Answer 3

I found a way to stream the file directly from Azure into the SendGrid email message object. Here's the relevant snippet:

var client = new SendGridClient(apiKey);
var mailFrom = new EmailAddress(from.Email, from.Name);
var mailTo = new EmailAddress(to.Email, to.Name);
var msg = MailHelper.CreateSingleEmail(mailFrom, mailTo, subject, bodyText, bodyHtml);
    
// Attach file from Azure if fileName is set
if (fileName != null) {
    // Initialize the Azure blob client
    var container = new BlobContainerClient(_azureConnectionString, _azureContainerName);
    var blob = container.GetBlobClient(fileName);
    
    // Validate the file exists in Azure
    if (!await blob.ExistsAsync()) return NotFound("File not found");
                
    // Stream the file directly from Azure into the email attachment
    await msg.AddAttachmentAsync(fileName, blob.OpenRead());
}
    
var response = await client.SendEmailAsync(msg);