2 files changed, 61 insertions, 0 deletions
diff --git a/packages/backend/src/misc/FileWriterStream.ts b/packages/backend/src/misc/FileWriterStream.ts
new file mode 100644
index 0000000000..828851df0e
--- /dev/null
+++ b/packages/backend/src/misc/FileWriterStream.ts
@@ -0,0 +1,31 @@
+import * as fs from 'node:fs/promises';
+import type { PathLike } from 'node:fs';
+
+/**
+ * `fs.createWriteStream()`相当のことを行う`WritableStream` (Web標準)
+ */
+export class FileWriterStream extends WritableStream<Uint8Array> {
+	constructor(path: PathLike) {
+		let file: fs.FileHandle | null = null;
+
+		super({
+			start: async () => {
+				file = await fs.open(path, 'a');
+			},
+			write: async (chunk, controller) => {
+				if (file === null) {
+					controller.error();
+					throw new Error();
+				}
+
+				await file.write(chunk);
+			},
+			close: async () => {
+				await file?.close();
+			},
+			abort: async () => {
+				await file?.close();
+			},
+		});
+	}
+}
diff --git a/packages/backend/src/misc/JsonArrayStream.ts b/packages/backend/src/misc/JsonArrayStream.ts
new file mode 100644
index 0000000000..ad35bb3a79
--- /dev/null
+++ b/packages/backend/src/misc/JsonArrayStream.ts
@@ -0,0 +1,30 @@
+import { TransformStream } from 'node:stream/web';
+
+/**
+ * ストリームに流れてきた各データについて`JSON.stringify()`した上で、それらを一つの配列にまとめる
+ */
+export class JsonArrayStream extends TransformStream<unknown, string> {
+	constructor() {
+		/** 最初の要素かどうかを変数に記録 */
+		let isFirst = true;
+
+		super({
+			start(controller) {
+				controller.enqueue('[');
+			},
+			flush(controller) {
+				controller.enqueue(']');
+			},
+			transform(chunk, controller) {
+				if (isFirst) {
+					isFirst = false;
+				} else {
+					// 妥当なJSON配列にするためには最初以外の要素の前に`,`を挿入しなければならない
+					controller.enqueue(',\n');
+				}
+
+				controller.enqueue(JSON.stringify(chunk));
+			},
+		});
+	}
+}