Save CFSTR_FILECONTENTS to file

[Alex4SSB]

Hi, I'm trying to read FileContents from a Drag&Drop, but I get "Cannot access a closed stream" exception on CopyTo:

// dataObject here is System.Windows.IDataObject received from DragEventArgs Data
var shdo = new ShellDataObject(dataObject);

var contents = shdo.GetData("CFSTR_FILECONTENTS", 0);

using (var fileStream = new FileStream("E:\\Downloads\\file", FileMode.Create, FileAccess.Write))
{
    ((Stream)contents).CopyTo(fileStream);
}

So my questions are am I missing something and is there a better way of saving a file to disk from FileContents? (I omitted FileGroupDescriptorW here, but it is used)

[dahall]

I think this test has a pretty good example. Effectively, ShellDataObject gets the COM IStream values and puts them into a .NET Stream[].

There is some good detail on StackOverflow on writing those streams to file.

[Alex4SSB]

Thanks for the reply, but the test you mentioned doesn't actually read the data (or copy it).

[dahall]

I'm not sure I follow. The test creates a data object from a Word doc and confirms that both the CFSTR_FILEDESCRIPTORW and CFSTR_FILECONTENTS clipboard formats are supported. It then extracts the document as an array of Stream and asserts there is only the single stream and then asserts the length of the stream matches the length of the file. Since it sits in a stream, you can then use the StackOverflow options for extracting that to a new file. What am I missing?

[Alex4SSB]

Yes, the test indeed verifies the stream count and the length (of the only stream), but it doesn't read the bytes (and compare to the source). StackOverflow suggests exactly what I'm trying to do - CopyTo(), but when I try it using Vanara it throws an exception.

The data is from a zip file opened in File Explorer (I know it also has Shell ID List which Vanara supports perfectly).

[dahall]

Do these additions answer your question?

	[Test]
	public void GetDataTest()
	{
		const int cnt = 512;

		byte[] orig;
		using (var fs = File.OpenRead(TestCaseSources.WordDoc))
			orig = GetFileBytes(fs, cnt);
		var obj = new ShellDataObject([new ShellItem(TestCaseSources.WordDoc)]);

		Assert.That(obj.GetDataPresent(ShellClipboardFormat.CFSTR_FILEDESCRIPTORW));
		var fd = obj.GetData(ShellClipboardFormat.CFSTR_FILEDESCRIPTORW, true);
		Assert.That(fd is ShellFileDescriptor[]);
		Assert.That((ShellFileDescriptor[])fd, Has.Exactly(1).Items);
		Assert.That(((ShellFileDescriptor[])fd)[0].Info.Name, Is.EqualTo(Path.GetFileName(TestCaseSources.WordDoc)));

		Assert.That(obj.GetDataPresent(ShellClipboardFormat.CFSTR_FILECONTENTS));
		var fc = obj.GetData(ShellClipboardFormat.CFSTR_FILECONTENTS, true);
		if (fc is not Stream[] fcs) { Assert.Fail(); return; }
		Assert.That(fcs, Has.Exactly(1).Items);
		Assert.That(fcs[0].Length, Is.EqualTo(new FileInfo(TestCaseSources.WordDoc).Length));

		byte[] found = GetFileBytes(fcs[0], cnt);
		Assert.That(found, Is.EquivalentTo(orig));

		static byte[] GetFileBytes(Stream fs, int count)
		{
			var ret = new byte[count];
			fs.Read(ret, 0, count);
			return ret;
		}
	}

[Alex4SSB]

Yes, thanks, looks like this works. Its just bizarre that CopyTo() doesn't work.

[dahall]

So, in the example above, you're saying that fcs[0].CopyTo(newFileStream) fails with an exception?

[Alex4SSB]

Yes, but I only tried it on FileContents from File Explorer, though it wouldn't surprise me if the CopyTo function just doesn't support COM streams.