WebClient.DownloadData throws an exception in Bot Framework

问题

I am uploading an image and using WebClient with DownloadData to get the byte array, but now it throws me an exception:

Exception: State size exceeded configured limit.
[File of type 'text/plain']

I haven't noticed such behaviour before with the exact same image. What might have gone wrong?

private async Task SendPhoto_ActivityReceivedAsync(IDialogContext context, IAwaitable<object> result)
    {
        Activity activity = await result as Activity;
        Activity activityReply = activity.CreateReply();

        if (0 < activity.Attachments?.Count)
        {
            if (activity.Attachments.FirstOrDefault().ContentType.Equals("image/jpg") ||
                activity.Attachments.FirstOrDefault().ContentType.Equals("image/jpeg") ||
                activity.Attachments.FirstOrDefault().ContentType.Equals("image/png") ||
                activity.Attachments.FirstOrDefault().ContentType.Equals("image/tiff"))
            {
                picImage = activity.Attachments.FirstOrDefault().Name;

                HttpClient httpClient= new HttpClient();
                picImageFile = await httpClient.GetByteArrayAsync(activity.Attachments.FirstOrDefault().ContentUrl);

                await context.PostAsync("Want to send another?");

                context.Wait(SendAnotherImage_ActivityReceivedAsync);
            }
        }
    }

UPDATE: Changed the WebClient to HttpClient.GetByteArrayAsync and the problem remains. The exception is shown in the Bot Emulator right after the PostAsync is executed

回答1:

The problem is that picImageFile is a variable inside of your dialog, and so it's being saved in the state because the dialog is serialized. Two options

1. Download the image and process it in that method, without saving it in memory
2. Save the byte array in an external storage.

来源：https://stackoverflow.com/questions/46645806/webclient-downloaddata-throws-an-exception-in-bot-framework