fm: store file to OPFS temporarily (#413)

resource/static/file.js

@@ -0,0 +1,70 @@
+let receivedLength = 0;
+let expectedLength = 0;
+let root;
+let draftHandle;
+let accessHandle;
+
+const Operation = Object.freeze({
+    WriteHeader: 1,
+    WriteChunks: 2,
+    DeleteFiles: 3
+});
+
+onmessage = async function (event) {
+    try {
+        const { operation, arrayBuffer, fileName } = event.data;
+
+        switch (operation) {
+            case Operation.WriteHeader: {
+                const dataView = new DataView(arrayBuffer);
+                expectedLength = Number(dataView.getBigUint64(4, false));
+                receivedLength = 0;
+
+                // Create a new temporary file
+                root = await navigator.storage.getDirectory();
+                draftHandle = await root.getFileHandle(fileName, { create: true });
+                accessHandle = await draftHandle.createSyncAccessHandle();
+
+                // Inform that file handle is created
+                const dataChunk = arrayBuffer.slice(12);
+                receivedLength += dataChunk.byteLength;
+                accessHandle.write(dataChunk, { at: 0 });
+                const progress = 'got handle';
+                postMessage({ type: 'progress', progress: progress });
+                break;
+            }
+            case Operation.WriteChunks: {
+                if (!accessHandle) {
+                    throw new Error('accessHandle is undefined');
+                }
+
+                const dataChunk = arrayBuffer;
+                accessHandle.write(dataChunk, { at: receivedLength });
+                receivedLength += dataChunk.byteLength;
+
+                if (receivedLength === expectedLength) {
+                    accessHandle.flush();
+                    accessHandle.close();
+
+                    const fileBlob = await draftHandle.getFile();
+                    const blob = new Blob([fileBlob], { type: 'application/octet-stream' });
+
+                    postMessage({ type: 'result', blob: blob, fileName: fileName });
+                }
+                break;
+            }
+            case Operation.DeleteFiles: {
+                for await (const [name, handle] of root.entries()) {
+                    if (handle.kind === 'file') {
+                        await root.removeEntry(name);
+                    } else if (handle.kind === 'directory') {
+                        await root.removeEntry(name, { recursive: true });
+                    }
+                }
+                break;
+            }
+        }
+    } catch (error) {
+        postMessage({ error: error.message });
+    }
+};