MagickImage.Read() should raise an exception when specifying an invalid FrameIndex

[martinkoch-geniebelt]

First, thanks for maintaining this - it's great!

Prerequisites

• I have written a descriptive issue title
• I have verified that I am using the latest version of Magick.NET
• I have searched open and closed issues to ensure it has not already been reported

Description

When trying to read a specific frame past the last frame from e.g. a PDF, a MagicImage is disposed, and

   No pages will be processed (FirstPage > LastPage).

is written on stdout.

Instead, I think an exception should be raised so that this situation can be dealt with in a nicer way than the sample below.

var magickReadSettings = new MagickReadSettings {FrameIndex = 42};
using (MagickImage mi = new MagickImage())
{
    try 
    {
        mi.Read("onePagePdf.pdf", magickReadSettings);
        // after reading, mi is _disposed_ if we have read past end. Try to access a field to 
        // see if this is the case (and if it is, catch the exception)
        var dummy = mi.Width;
    }
    catch (System.ObjectDisposedException)
    {
        Console.WriteLine("read past the last frame.");
    }
}

An additional nice-to-have would be a fast way of determining the number of pages in a PDF without having to load the whole thing :)

System Configuration

ios, linux.

• Magick.NET version: 7.22.2.2
• Environment (Operating system, version and so on): seen on mac, dockerized ubuntu
• Additional information:

[dlemstra]

This looks like a "duplicate" of what was requested in #268

[martinkoch-geniebelt]

Thanks for a fast response!

There are two parts to this, and, yes, I agree that the 'fast pagecount' is a duplicate, as you say.

However, this bug is about the object being disposed when (IMO :) ) it ought to raise an exception instead.

[dlemstra]

Can you share the PDF file so I can reproduce it?

[martinkoch-geniebelt]

In this example, any pdf with fewer than 42 pages will do. For example, this one

[dlemstra]

I am unable to reproduce your issue. Is it possible to create a small sample project with a DockerFile that uses ubuntu that demonstrates this issue?

[martinkoch-geniebelt]

Thanks again!
I am indeed unable to reproduce this on ubuntu and on windows.

On mac catalina 10.15.7, however, I observe this behavior.

[dlemstra]

Is it possible to reproduce the issue in GitHub actions?

p.s. Getting a fast page count will become available in the next release.

[martinkoch-geniebelt]

I'll look into creating a GHA to build on mac

[dlemstra]

We made some changes in the PDF reading, can you give it another try with the latest release @martinkoch-geniebelt? And I would advise you to use the new PdfInfo class to get the page count.