public static async Task VerifyAvatarOrThrow(string url)
{
// List of MIME types we consider acceptable
var acceptableMimeTypes = new[]
{
"image/jpeg",
"image/gif",
"image/png"
// TODO: add image/webp once ImageSharp supports this
};
using (var client = new HttpClient())
{
Uri uri;
try
{
uri = new Uri(url);
if (!uri.IsAbsoluteUri)
{
throw Errors.InvalidUrl(url);
}
}
catch (UriFormatException)
{
throw Errors.InvalidUrl(url);
}
var response = await client.GetAsync(uri);
if (!response.IsSuccessStatusCode) // Check status code
{
throw Errors.AvatarServerError(response.StatusCode);
}
if (response.Content.Headers.ContentLength == null) // Check presence of content length
{
throw Errors.AvatarNotAnImage(null);
}
if (response.Content.Headers.ContentLength > Limits.AvatarFileSizeLimit) // Check content length
{
throw Errors.AvatarFileSizeLimit(response.Content.Headers.ContentLength.Value);
}
if (!acceptableMimeTypes.Contains(response.Content.Headers.ContentType.MediaType)) // Check MIME type
{
throw Errors.AvatarNotAnImage(response.Content.Headers.ContentType.MediaType);
}
// Parse the image header in a worker
var stream = await response.Content.ReadAsStreamAsync();
var image = await Task.Run(() => Image.Identify(stream));
if (image.Width > Limits.AvatarDimensionLimit || image.Height > Limits.AvatarDimensionLimit) // Check image size
{
throw Errors.AvatarDimensionsTooLarge(image.Width, image.Height);
}
}
}