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v3 Planning & Objectives #194
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As I began to understand the OpenMcdf code better and more generally the CFB format while investigating #184, I was thinking that it might be quite difficult to add the features I've previously mentioned to v2. So, at the end of last week I took the liberty and started some proof of concept work for a new approach for version 3. I've adapted/written code to parse headers and directory entries, enumerate FAT sectors, traverse sector chains and read the contents of a stream. There's obviously quite a lot of functionality missing (substorage traversal, reading mini FAT, any kind of writing), but it is at least enough to spin up the equivalent of the "InMemory" benchmark: Windows Structured Storage (ILockBytes over a MemoryStream)
OpenMcdf v2.3.1
OpenMcdf v3 Proof of Concept
So, there's some pretty big performance (400x faster for short reads) and memory reduction (Gen0 GCs are drastically reduced, and Gen1/2 GCs are eliminated) wins to be had on reading, while also enforcing reasonably strict validation. In the proof of concept, BinaryReader and BinaryWriter are extended to handle CFB types, and there is only one reader and one writer stored in a context (along with the header) that is shared across objects that need access to it. Sectors are lightweight structs mostly to record their ID and map to their position within the CFB stream/file. There are a couple of enumerators that do the main work: Although I haven't done any code to write data yet, I'm thinking the enumerators might be converted to mutable iterators which should also be reasonably fast/efficient. I'll share some code when I've cleaned it up and progressed a bit further! |
Honestly speaking... it's a perfect summary. |
@ironfede Yesterday, I added a dedicated enumerator for directory entries in a FAT chain and another enumerator for the directory tree, so it can now traverse storages and streams as part of a tree (it could only traverse them as a list before) . I also improved the enumerators so they're a bit easier to follow and improved validation (enumerators and sector offsets throw if you try to access something that's invalid/out of bounds). I'll have a look at implementing support for mini FAT sectors today, then I think I'll be to the point where I'll have something worth sharing for comments and feedback. But essentially, aside from some clean-up and further validation/testing, I think the POC already meets the following objectives:
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@Numpsy Looks like you might have a particular interest in the OLE Property Set Data Structures? Do you have anything you'd like to see for v3? I can't say I know too much about it, so aside from some nit-pick refactoring work my only real comment is that perhaps OpenMcdf.Extensions should be renamed to OpenMcdf.Ole (i.e. explicitly about OLE only). Especially since we probably won't require a decorator for streams in v3. |
My current use case is reading and writing metadata (summary information etc) in Office documents, so things like really massive files aren't really an issue. As far as the API goes, I think it would be nice to review how it presents the different property sets - as well as SummaryInformation/DocumentSummaryInformation, there is some amound of support for others, but it's not clear how far the intended support goes. |
There's also scope for a more complete set of functions for adding/updating/deleting properties (e.g. #190) - that's a higher level API than the changes to the storage part. |
My use case is similar to @Numpsy but on Solid Edge (CAD) documents, besides the standard SummaryInformation/DocumentSummaryInformation, some more app-specific metadata streams need to be accessed. Regular documents contain one part per file however some documents may contain more than one part; this means the file's structure becomes multilevel and each part has its own SummaryInformation/DocumentSummaryInformation and so on. If needed I can provide example files with an explanation of their structure. |
@jeremy-visionaid that's great, let me know where to upload the files besides a brief descriptions of them |
@farfilli Maybe you could push them with on a branch of a fork and put some descriptions in the commit message? |
@jeremy-visionaid done in 0c8fc18 |
Okeydoke, I think I've progressed with the v3 proof of concept far enough that I'm happy to push it for some early feedback. There are some notable things still missing:
I'll at least try and add some comments tomorrow, and see if I can add some additional features as above through the week, but comments and feedback would be appreciated! |
I've pushed some changes with some refactoring, improved terminology, filled out the summary comments and improved validation for corrupt CFBs. The reading part at least should be in pretty good shape if anyone wants to take it for a spin and try it out. I could bring the structured storage explorer across if it's of interest? Otherwise it's just unit tests right now. |
Thank you @jeremy-visionaid for all your work. I'm already working on a base v3, including some deep structural changes in manipulation of sector chains and streams in general to set a background to evolve in a future for a SWMR scenario and for a performance enhancement in write operations. I hope to put a draft online in short time since I understand that there's (correctly) a little bit of pressure on this... :-) |
Now that v2.4 looks like it's coming together. I was wondering what folks thoughts were for objectives for v3?
If I understand correctly, the values/objectives for v2 are:
There are some goals I have in mind for v3:
Other thoughts:
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