无法使用 SAS 从 Azure Blob 存储检索文件

Question

We have a web based application that allows users to send emails. Every email body contains an image which represents the signature block. The image is stored in Azure Blob storage in a private container. To pull the image from storage and place it in the email body, as the email is being constructed by the user, we generate a Uri using the following C# function:

public string GenerateBlobDownloadUri(string containerName, string blobName)
        {
            var policy = new SharedAccessBlobPolicy();

            // Get a reference to a container if it exists.
            var container = GetContainer(containerName, false);
            if (container == null)
                return string.Empty;

            // Retrieve reference to the blob
            CloudBlockBlob blockBlob = container.GetBlockBlobReference(blobName);
            if (!blockBlob.Exists())
                return string.Empty;

            policy.SharedAccessExpiryTime = DateTime.Now.AddYears(10);
            policy.Permissions = SharedAccessBlobPermissions.Read;

            var token = blockBlob.GetSharedAccessSignature(policy);

            return blockBlob.Uri + token;
        }

Using this function, we're able to successfully pull the image from Azure into our email body as the email is being constructed and have it display correctly.

However, if I were to look at the underlying HTML code of the email, copy the Uri generated and paste it into the browser, the image will not display or download. I just get a Json message saying the image couldn't be found.

The actualy Uri being generated by the above function is this:

https://xxxxx.blob.core.windows.net/winterscontainer/55-Email Signature Block.png?sv=2018-03-28&sr=b&sig=8zkwcK7naE%2BPZRfo6GtBYVfHJLzlCBLR6IaYymTIOGo%3D&se=2030-10-17T12%3A30%3A56Z&sp=r

Again, this Uri works from within our application and correctly pulls in the image and displays correctly while the email is being created. However, when the email is sent, the recipient just sees a placeholder for the image.

If I paste the Uri into my browser, I get this:

<Error>
<Code>ResourceNotFound</Code>
<Message>The specified resource does not exist. RequestId:4ca4e68b-b01e-0130-5781-a4a67e000000 Time:2020-10-17T12:33:33.0601864Z</Message>
</Error>

Answer 1

If you check your Uri you will notice something a bit "strange" on the query part, ampersands are being converted to HTML entities, instead of & you are receiving & . Something in the chain that process the message until it arrives to your clients (your api, mail server, web browser, mail client... there is a lot of possibilities) is encoding it (it could be that you already received it encoded but I doubt it, I also use Azure blob storage and never received it encoded).

If you manually decode those escaped chars you will notice that the Uri works fine, so now you must find where in the chain is being encoded, it's a totally different scenario.