feat(storage): Add WebFileSystemStore

packages/storage/src/web-fs.ts

@@ -0,0 +1,64 @@
+import type { AbsolutePath, AsyncReadable } from "./types.js";
+
+/**
+ * Get a file handle to a file in a directory.
+ *
+ * @param root - A root directory from the Web File System API.
+ * @param path - A key to a file in the root directory.
+ * @returns A file handle to the file.
+ */
+async function resolveFileHandleForPath(root: FileSystemDirectoryHandle, path: string): Promise<FileSystemFileHandle> {
+	const dirs = path.split("/");
+	const fname = dirs.pop();
+	if (!fname) {
+		throw new Error("Invalid path");
+	}
+	for (const dir of dirs) {
+		root = await root.getDirectoryHandle(dir);
+	}
+	return root.getFileHandle(fname);
+}
+
+/**
+ * A store for zarrita based on the Web File System API.
+ *
+ * Note: usage requires prompting the user to select a directory to grant
+ * access to the Web File System API.
+ *
+ * @see {@link https://developer.mozilla.org/en-US/docs/Web/API/File_System_API}
+ *
+ * @example
+ * ```js
+ * import * as zarr from "zarrita";
+ * import WebFileSystemStore from "@zarrita/storage/web-fs";
+ *
+ * let directoryHandle = await globalThis.showDirectoryPicker();
+ * let store = new WebFileSystemStore(directoryHandle);
+ * let root = await zarr.root(store);
+ * let arr = await zarr.open(root.resolve("/foo"), { kind: "array" });
+ * ```
+ */
+class WebFileSystemStore implements AsyncReadable {
+	#root: FileSystemDirectoryHandle;
+
+	constructor(root: FileSystemDirectoryHandle) {
+		this.#root = root;
+	}
+
+	async get(key: AbsolutePath): Promise<Uint8Array | undefined> {
+		let fh = await resolveFileHandleForPath(this.#root, key.slice(1)).catch(() => {
+			// TODO: better error handling
+			// I believe a missing file will trigger an error here, which we should explicitly
+			// catch and return `undefined`
+			return undefined;
+		});
+		if (!fh) {
+			return undefined;
+		};
+		let file = await fh.getFile();
+		let buffer = await file.arrayBuffer();
+		return new Uint8Array(buffer);
+	}
+}
+
+export default WebFileSystemStore;