Question: Best way to load and save files from a buffer when file type is not known

[avin-kavish]

I'm loading images from the IFormFile container. I'm not sure what the best way is to find the image type so that I can save the images in the original format they were uploaded in. IFormFile.ContentType might not be reliable. I'm aware that libvips sniffs the first few bytes when loading a file from disk, is there a way to replicate that behaviour in this library? Perhaps to sniff from the intermediary buffer I'm using to load the image.

[kleisauke]

libvips has two useful functions to quickly identify the image type:

• vips_foreign_find_load
• vips_foreign_find_load_buffer

I just made these functions available in NetVips with commit 3fffefc.

Note that these functions will not detect truncated images, it just performs some basic verification of image metadata. For example, reading a buffer with GIF89a will result in VipsForeignLoadGifBuffer.

If you also want to detect broken images, you can use this:

net-vips/samples/NetVips.Samples/Samples/IdentifyExtension.cs

Lines 40 to 63 in 3fffefc

	public string GetExtensionNonTruncated(byte[] buffer)
	{
	try
	{
	// The fail option makes NetVips throw an exception on a file format error
	var image = Image.NewFromBuffer(buffer, fail: true, access: Enums.Access.Sequential);
	// Calculate the average pixel value. That way you are guaranteed to read every pixel
	// and the operation is cheap.
	var avg = image.Avg();
	// Unfortunately, vips-loader is the operation nickname, rather
	// than the canonical name returned by vips_foreign_find_load().
	var vipsLoader = (string) image.Get("vips-loader");
	var suffixLength = vipsLoader.EndsWith("load_buffer") ? 11 : 4;
	return vipsLoader.Substring(0, vipsLoader.Length - suffixLength);
	}
	catch (VipsException e)
	{
	Console.WriteLine($"Couldn't identify image extension: {e.Message}");
	return null;
	}
	}

[avin-kavish]

Thanks for the prompt attention, when is this shipping on nuget?

[kleisauke]

I'm a bit busy with college and other side projects these days, but I hope to release NetVips 1.1.0 a few days after libvips 8.8.1 is released (libvips 8.8.1 will be released within a few days). Version 1.1.0 is more or less ready to be shipped (:shipit:). NetVips.Native takes most of the time, because I try to keep the dependencies up-to-date (where possible).

If you want to test this earlier, you can use the nightly version of NetVips. Add the https://ci.appveyor.com/nuget/net-vips feed in the <packageSources> section of your NuGet.config:

<packageSources>
  <add key="netvips-nightly" value="https://ci.appveyor.com/nuget/net-vips" />
</packageSources>

And update NetVips to version 1.1.0.140-develop.

[kleisauke]

NetVips 1.1.0-rc3 is released on NuGet. If there's nothing reported for a week, this will become 1.1.0 final.

[avin-kavish]

FindLoadBuffer seems stable so far. Closing as resolved.

[kleisauke]

NetVips v1.1.0 is now available.