WordprocessingDocument.Open is very slow

Description

WordprocessingDocument.Open is very very slow when reading big .docx document. i’m trying to read 10 mb sized .docx document and it takes about 1 minute just to open it.

Information

• .NET Target: .NET Core 2.2
• DocumentFormat.OpenXml Version: 2.9.0

Repro

Console.WriteLine("Creating filter")
using (var doc = WordprocessingDocument.Open(path, false))
{
        Console.WriteLine("Creating BodyReader");
        _bodyReader = OpenXmlReader.Create(doc.MainDocumentPart.Document);
}

Link to the file: https://drive.google.com/file/d/1_InQLbZ19KCUgkuePAiLXvUuLcZl6Qu7/view?usp=sharing

Uploaded to GitHub: 10mb_file.docx

Observed

I put to lines of Console.WriteLine so the time between “Creating filter” and “Creating BodyReader” is about 1 min. It doesn’t matter if i opening file from memory stream or just giving it a real path to the file.

Expected

Instant open expected 😃

[twsouthwick]

I’m going to open as I recently made a change to System.IO.Packaging that may help this and I want to verify. See https://github.com/dotnet/runtime/pull/35978

[twsouthwick]

FYI the fix that I got into System.IO.Packaging fixes this!

Before:

| Method |    Mean |    Error |   StdDev |
|------- |--------:|---------:|---------:|
|   Open | 9.167 s | 0.1791 s | 0.2265 s |

After:

| Method |     Mean |   Error |  StdDev |
|------- |---------:|--------:|--------:|
|   Open | 184.5 ms | 3.64 ms | 4.85 ms |

Since the package is still in preview, we won’t be upgrading it for the project at this time. Note, since the major version of this is changing, we won’t actually be able to bring it into the repo until v3.0 (due to semantic versioning). That’ll probably happen sometime soon, but not for a bit. However, you may manually bring in 5.0.0-preview.6.20305.6+ of the package to get the benefit (although it will only help you if you are on .NET Core)