BlockBlobClient.UploadAsync fails when trying to modify the incoming WatchableReadStream object - azure

Question

I hope you're having some advice because I'm pretty much out of options. What I'm trying to do:
upload an image to a blobcontainer via the azure portal
when doing that, the blobtrigger below fires.
I want to resize the incoming image which is a Microsoft.Azure.WebJobs.Host.Blobs.WatchableReadStream object.
I want to upload the result to a new blob container.
The issue is, when I am passing any other Stream, e.g. a MemoryStream than the unmodified myBlob object the UploadAsync method seems to silently fail and the BlobTrigger fires again, starting an endless loop. Writing to the current myBlob object also silently fails. Only thing which works is passing the myBlob object in BlockBlobClient.UploadAsync without ANY modification whatsoever, which is useless. I am doing a remote debugging session in Azure.
Also, when I try to feed a MemoryStream object to the UploadAsync method the same problem occurs. The method below is the blob trigger:
public async Task UploadImage([BlobTrigger("mediafullsizecontainer/{name}", Connection = "AzureWebJobsStorage")]Stream myBlob, string name, ILogger log)
{
BlockBlobClient fullsizeBlobClient = _mediaFullsizeContainerClient.GetBlockBlobClient(name);
Response<BlobProperties> blobPropertiesResponse = await fullsizeBlobClient.GetPropertiesAsync(null, default);
BlobProperties blobProperties = blobPropertiesResponse.Value;
//Only process blobs when the correct metadata properties are set
if (blobProperties.Metadata.Any(property => property.Key == "category" & property.Value != String.Empty))
{
string category = blobProperties.Metadata["category"];
Stream s = await ResizeImage(myBlob);
BlockBlobClient thumbnailBlobclient = _mediaThumbnailContainerClient.GetBlockBlobClient(name);
Response<BlobContentInfo> uploadResponse = await thumbnailBlobclient.UploadAsync(s, new BlobUploadOptions(), default);
BlobContentInfo blobContentInfo = uploadResponse.Value;
}
}
The ResizeImage method uses the SixLabors.ImageSharp image processing library.
public async Task<Stream> ResizeImage(Stream inputStream)
{
(Image image, IImageFormat imageFormat) imageWithFormat = await Image.LoadWithFormatAsync(inputStream);
int height = imageWithFormat.image.Height;
int width = imageWithFormat.image.Width;
imageWithFormat.image.Mutate(operation => {
operation.Resize(width / 4, height / 4);
});
MemoryStream outputStream = new MemoryStream();
imageWithFormat.image.Save(outputStream, imageWithFormat.imageFormat);
return outputStream;
}
So when I do a mock change on the myBlob object like this, myBlob.Write(buffer) fails:
byte[] buffer = new byte[myBlob.Length];
myBlob.Read(buffer, 0, (int)myBlob.Length);
myBlob.Position = 0;
myBlob.Write(buffer);
When I copy the myBlob contents to a MemoryStream and pass the memoryStream to UploadAsync, UploadAsync fails:
MemoryStream ms = new MemoryStream();
myBlob.CopyTo(ms);
BlockBlobClient thumbnailBlobclient = _mediaThumbnailContainerClient.GetBlockBlobClient(name);
Response<BlobContentInfo> uploadResponse = await thumbnailBlobclient.UploadAsync(ms, new BlobUploadOptions(), default);
Only thing which works is passing the myBlob object without any modification to UploadAsync which is useless since I need to modify the incoming stream:
public async Task UploadImage([BlobTrigger("mediafullsizecontainer/{name}", Connection = "AzureWebJobsStorage")]Stream myBlob, string name, ILogger log)
{
BlockBlobClient fullsizeBlobClient = _mediaFullsizeContainerClient.GetBlockBlobClient(name);
Response<BlobProperties> blobPropertiesResponse = await fullsizeBlobClient.GetPropertiesAsync(null, default);
BlobProperties blobProperties = blobPropertiesResponse.Value;
//Only process blobs when the correct metadata properties are set
if (blobProperties.Metadata.Any(property => property.Key == "category" & property.Value != String.Empty))
{
string category = blobProperties.Metadata["category"];
BlockBlobClient thumbnailBlobclient = _mediaThumbnailContainerClient.GetBlockBlobClient(name);
Response<BlobContentInfo> uploadResponse = await thumbnailBlobclient.UploadAsync(myBlob, new BlobUploadOptions(), default);
BlobContentInfo blobContentInfo = uploadResponse.Value;
}
}
How can I pass a custom stream to the UploadAsync method? The documentation on https://learn.microsoft.com/en-us/dotnet/api/azure.storage.blobs.specialized.blockblobclient.uploadasync?view=azure-dotnet says you just need a stream object - but this does not work. Thanks in advance.

Answer 1

Ok looks like I found the answer myself, I got rid of the dreaded UploadAsync method and did it like this by reading the outputStream of the resized image into a buffer then opening a Stream for writing to the thumbnailBlobclient object and passing the buffer to the stream object. It makes sense that trying to modify the incoming myBlob object which came with the trigger, fires the trigger again and creating a loop.
Stream outputStream = await ResizeAndCropImage(myBlob);
byte[] buffer = new byte[outputStream.Length];
outputStream.Read(buffer);
BlockBlobClient thumbnailBlobclient = _mediaThumbnailContainerClient.GetBlockBlobClient(name);
Stream s = thumbnailBlobclient.OpenWrite(true, new BlockBlobOpenWriteOptions { HttpHeaders = new BlobHttpHeaders { ContentType = "image/jpg" } }, default); //set http headers here as well?
await s.WriteAsync(buffer);
s.Close();
I will set the content type in a more generic way but this concept is working.