Move file creation to serviceworker to prevent loading everything into RAM

public/scripts/sw-file-digester.js

@@ -0,0 +1,48 @@
+self.addEventListener('message', async e => {
+    try {
+        switch (e.data.type) {
+            case "part":
+                await this.onPart(e.data.name, e.data.buffer, e.data.offset);
+                break;
+            case "get-file":
+                await this.onGetFile(e.data.name);
+                break;
+        }
+    }
+    catch (e) {
+        self.postMessage({type: "error", error: e});
+    }
+})
+
+async function getFileHandle(fileName) {
+    const root = await navigator.storage.getDirectory();
+    return await root.getFileHandle(fileName, {create: true});
+}
+
+async function getAccessHandle(fileName) {
+    const fileHandle = await getFileHandle(fileName);
+
+    // Create FileSystemSyncAccessHandle on the file.
+    return await fileHandle.createSyncAccessHandle();
+}
+
+async function onPart(fileName, buffer, offset) {
+    const accessHandle = await getAccessHandle(fileName);
+
+    // Write the message to the end of the file.
+    let encodedMessage = new DataView(buffer);
+    accessHandle.write(encodedMessage, { at: offset });
+    accessHandle.close();
+
+    self.postMessage({type: "part", part: encodedMessage});
+    encodedMessage = null;
+}
+
+async function onGetFile(fileName) {
+    const fileHandle = await getFileHandle(fileName);
+    let file = await fileHandle.getFile();
+
+    self.postMessage({type: "file", file: file});
+    file = null;
+    // Todo: delete file from storage
+}