wasm: Fix operation not supported on std::fs. Closes #115

[iceiix]

Implementing a minimal web-based std::fs replacement for #115 wasm broken: panicked at 'called Result::unwrap() on an Err value: Custom { kind: Other, error: StringError("operation not supported on wasm yet") }

[iceiix]

Emscripten for reference: https://github.com/emscripten-core/emscripten/blob/incoming/src/library_fs.js

https://emscripten.org/docs/api_reference/Filesystem-API.html supports MEMFS (in-memory), NODEFS (node.js only), and IDBFS (browser only).

IDB = IndexedDB, https://www.w3.org/TR/IndexedDB/, seems to be the best. Supports storing Uint8Array binary keys, in contrast to localStorage https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage which only allows string values.

Is there an existing crate for IndexedDB in Rust? https://crates.io/crates/indexeddb last modified 5 months ago, 0.1.0 disclaimer "very early stages". https://docs.rs/stdweb/0.4.17/stdweb/ seems not to support it? There is an open merge request: koute/stdweb#297 from January, not merged with some pending feedback.

Emscripten's IndexedDB filesystem:

https://github.com/emscripten-core/emscripten/blob/incoming/src/IDBStore.js
https://github.com/emscripten-core/emscripten/blob/incoming/src/library_idbstore.js
https://github.com/emscripten-core/emscripten/blob/incoming/src/library_idbfs.js

Mozilla documentation: https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API/Using_IndexedDB

[iceiix]

Moved to a separate module, replaced std::fs everywhere, so far so good. Barely implemented any of the API, but that's all I'm using. However, it doesn't persist the data anywhere, yet. Would be used for configuration (conf.cfg), server list (servers.json), packet debugging (last-packet), resources (although it is disabled on wasm32 for now), and skins (ditto).

Next up, use stdweb indexeddb branch (koute/stdweb#342) to provide a persistence backend. Start out simple first, but this could be useful for others to publish as a new crate.

[iceiix]

As koute/stdweb#342 is still in review may change, and the Indexed DB API is quite complex, hacked up a quick and dirty Local Storage backend for now. Since it only stores strings, encoded the bytes as hex. This works, conf.cfg is written:

and decodes correctly, albeit ugly.