coil-kt/coil

Support saving images to the origin private file system on Js and wasmJs.

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#1951 opened on Dec 13, 2023

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 (1 comment) (0 reactions) (0 assignees)Kotlin (11,779 stars) (757 forks)batch import
enhancementhelp wanted

Description

This is out of date. See below.

Is your feature request related to a problem? Please describe. One of the downsides of running Kotlin Multiplatform code on browser-based Javascript is that it's not possible to read from or write to the device's file system. Currently, that means NetworkFetcher can't cache images on disk and can only store them in memory.

Describe the solution you'd like Due to the nature of browser-based Javascript, it's not possible to write a FileSystem implementation for Javascript. As such it's not possible to write a Ktor response body to disk. This means we need to write a separate fetcher since we can't rely on Ktor or Okio.

The <img> tag in Javascript has special privileges to write to a disk cache on browsers. Using this tag we may be able to fetch the image data using a hidden <img> tag and then read and wrap its binary data as an ImageSource. Ideally, we would avoid the <img> tag decoding the image into memory, but I'm not sure if that's possible.

Additional context This may or may not happen as there might be blockers or performance issues. I'm not very familiar with the web's APIs and their constraints.

Contributor guide

Tech stack
javascriptwasm
Domain
frontend
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
unclear
Prerequisites
Kotlin/JS knowledgeBrowser file system APICoil library internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
The issue is a feature request for saving images to the origin private file system on JS and wasmJs targets, but the original description is outdated and strikethrough. A first step is to check the issue comments for any updated direction from maintainers. Then, study the File System Access API and how Kotlin/JS can use it. Look at existing fetcher implementations in Coil's multiplatform module for patterns. Finally, prototype a solution using browser's file system methods and test it.