Intent to Extend Origin Trial: Origin Private File System extension: AccessHandle

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Austin Sullivan

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Jan 20, 2022, 12:42:39 PM1/20/22

to blink-dev, Marijn Kruisselbrink, Richard Stotz, Emanuel Krivoy

Contact emails

asu...@chromium.org, five...@chromium.org, m...@chromium.org, rs...@chromium.org

Explainer

https://github.com/WICG/file-system-access/blob/main/AccessHandle.md

Specification

Summary

The Origin Private File System (OPFS, part of the File System Access API) is augmented with a new surface that brings very performant access to data. This new surface differs from existing ones by offering in-place and exclusive write access to a file’s content. This change, along with the ability to consistently read unflushed modifications and the availability of a synchronous variant on dedicated workers, significantly improves performance and unblocks new use cases.

Included in this origin trial is also a version of the FileSystemHandle::move() method, currently limited to files in the OPFS only. The move() method will be shipped separately with its own intent (https://chromestatus.com/feature/5640802622504960), but this limited subset is included in this origin trial because it significantly improves the performance and ease of use of the OPFS.

Blink component

Blink>Storage>FileSystem

TAG review

https://github.com/w3ctag/design-reviews/issues/664

TAG review status

Pending

Risks

Interoperability and Compatibility

The feature has to be compatible with existing ways to access data on OPFS i.e., createWritable() and getFile(). The use of write locks and care for backwards compatibility should mean that the risk here is low. In order to ease compatibility concerns in the future, we've added an optional 'mode' parameter to createAccessHandle()/createSyncAccessHandle(). This allows us to eventually extend AccessHandle functionality to non-OPFS file systems without necessarily taking the OPFS behaviour as default (more details here: https://github.com/WICG/file-system-access/blob/main/AccessHandle.md#exposing-accesshandles-on-all-filesystems). There is a risk of interoperability between vendors, pending the position on implementing this surface. This design is the result of feedback from Gecko and WebKit, who reviewed previous iterations of this functionality and gave feedback that it should integrate more strongly with OPFS. We believe that the new design, when paired with a separate streams-based extension to OPFS, meets these goals. However, we have not yet received work back as to whether they agree with our assessment.

Gecko: No signal on official Request for Position (https://github.com/mozilla/standards-positions/issues/562), but supportive of migrating the spec to whatwg (https://github.com/whatwg/sg/issues/176).

WebKit: In development (https://lists.webkit.org/pipermail/webkit-dev/2021-August/031934.html) Request for position was not answered, but the feature is being implemented and is available in TP. See reference bug: https://bugs.webkit.org/show_bug.cgi?id=231185

Web developers: No signals

Other signals:

Goals for experimentation

In general, we want to validate the new surface against "real world" use cases from our partners and developers at large. In particular, we are interested in the relative usage between the sync and async methods, since this could have an impact on performance when using Asyncify. We also would like to receive qualitative feedback on the ease of use of the API from within Wasm.

Reason this experiment is being extended

We're working with a partner, but they need more time to test and give feedback on the API.

Ongoing technical constraints

None

Debuggability

Basic tooling: Autocomplete works as described in "New WebIDL/DOM interfaces and attributes". Extended tooling: we'll eventually want to be able to explore files stored in OPFS. There are two tracking bugs related to this: crbug.com/256067 and crbug.com/735618. This API doesn't really add new storage backends, just new ways to interact with files, so we'd be covered by those as well.