如何正确使用流通过 discordbot 检索、编辑、保存和发送图像

Question

I am writing a discord bot using DSharp plus library.

The command I am currently writing gets an image from the discord chat I then edit the image and send the edited image back as a single frame gif.

I retrieve the image from the image url by using:

HttpClient client = new HttpClient();
Stream stream = await client.GetStreamAsync(attachments[0].Url);
Bitmap image = new Bitmap(System.Drawing.Image.FromStream(stream));

I then call my edit function and edit the image. I then save the image to my files using:

using (var stream = new FileStream("Images/output.gif", FileMode.Create))
{
   imgToGif.SaveAsGif(stream);
}

where .SaveAsGif() is a function from the KGySoft.Drawing library I found online.

To send the edited image back I use:

FileStream file = new FileStream("Images/output.gif", FileMode.Open);

DiscordMessageBuilder messagefile = new DiscordMessageBuilder();

messagefile.AddFile(file);

ctx.RespondAsync(messagefile);

But this throws a "The process cannot access the file "Image/output.gif" because it is being used by another process." error.

After some googling I tried to close the FileStream which saves my image to my files using stream.close() or stream.dispose() . The problem however is that I cannot acces the stream again because it will throw the "Cannot acces closed stream error".

I also tried using FileShare.read, FileShare.ReadWrite .

Tried closing both stream and tried to use 1 stream only. So I kept the stream open and used it to send the message in discord chat but that would send a file with 0 bytes in the discord chat.

Answer 1

I think you closed the stream too early while sending the gif

you need to call file.Close() after you call RespondAsync() and you need to change ctx.RespondAsync(messagefile); to await ctx.RespondAsync(messagefile); because RespondAsync() is an asynchronous method if you dont use await rest of the code will continue running so the stream will close while ctx.RespondAsync(messagefile); is still running and it will give an error.

sending a gif part should look like this:

FileStream file = new FileStream("Images/output.gif", FileMode.Open);
DiscordMessageBuilder messagefile = new DiscordMessageBuilder();
messagefile.AddFile(file);
await ctx.RespondAsync(messagefile);
file.Close();

if you have done the rest of the code correct this should work.