Imagesharp: Image.Load throws an ArgumentException when loading PNG

[casperOne]

Prerequisites

• [x] I have written a descriptive issue title
• [x] I have verified that I am running the latest version of ImageSharp
• [ ] I have verified if the problem exist in both DEBUG and RELEASE mode
• [x] I have searched open and closed issues to ensure it has not already been reported

Description

Loading the following PNG (from a Stream or ReadOnlyMemory<byte> instance) throws an ArgumentException.

https://user-images.githubusercontent.com/561862/54476020-e3ab4c00-47ce-11e9-9cb1-2542507bf23c.png

Which has the following message:

Offset and length were out of bounds for the array or count is greater than the number of elements from index to the end of the source collection.

Notes:

• The image renders in Chrome correctly
• According to http://www.libpng.org/pub/png/apps/pngcheck.html, there are no problems with image integrity
• There are three IDAT sections in the PNG (this shouldn't make a difference, from what I can tell in my reading of the spec)
• The images are produced out of FFMPEG, but other PNG images output from the same process/video are able to be loaded

Steps to Reproduce

Use the above image in a FileStream (or any Stream representation).

Load the image (this can be copied/pasted into a .NET Core 2.2 console app and the ImageSharp libraries referenced):

````
static async Task Main()
{
try
{
// Use http client.
var client = new HttpClient();

    // Make the request.
    using (Stream stream = await client.GetStreamAsync(
            "https://user-images.githubusercontent.com/561862/54476020-e3ab4c00-47ce-11e9-9cb1-2542507bf23c.png")
        .ConfigureAwait(false))
    {
        Image<Rgba32> image = Image.Load<Rgba32>(stream, new PngDecoder());
    }
}
catch (Exception e)
{
    Console.WriteLine(e);
    throw;
}

}
````

System Configuration

• ImageSharp version: 1.0.0-beta0006
• Other ImageSharp packages and versions: None
• Environment (Operating system, version and so on): Windows 10
• .NET Framework version: .NET Core 2.2
• Additional information:

[clintonrocksmith]

Hi there,

I did find this as an issue but had to set the decoder explicitly to being a png otherwise it failed. This was in a .NET Core solution as well whereby I loaded via a stream from Blob Storage in Azure, just giving more information to help.

[casperOne]

@clintonrocksmith Thanks for the reply, much appreciated.

That said, I didn't have any luck setting the decoder explicitly. Using HttpClient to download the link above, I still get the same error using this:

````
static async Task Main()
{
try
{
// Use http client.
var client = new HttpClient();

    // Make the request.
    using (Stream stream = await client.GetStreamAsync(
            "https://user-images.githubusercontent.com/561862/54476020-e3ab4c00-47ce-11e9-9cb1-2542507bf23c.png")
        .ConfigureAwait(false))
    {
        Image<Rgba32> image = Image.Load<Rgba32>(stream, new PngDecoder());
    }
}
catch (Exception e)
{
    Console.WriteLine(e);
    throw;
}

}
````

May I ask how you were able to get it to load?

[JimBobSquarePants]

@casperOne @clintonrocksmith The two issues are not related. There’s something about that png that causes our current decoder to fail. I fixed the issue locally today though.

The other issue sounds like it was due to the input stream being in the wrong position for us to identify the decoder.

[casperOne]

@JimBobSquarePants Thanks for the follow-up. I'll keep an eye on this to be closed when a PR gets merged. Looking forward to the next push to Nuget for the fix.

Thanks!

[JimBobSquarePants]

@casperOne Don't forget we have rock solid development releases on Myget

https://github.com/SixLabors/ImageSharp#installation

[casperOne]

@JimBobSquarePants Thanks for addressing this, I've confirmed this works, and have used the MyGet repository.