refactor: TS

src/helper.ts

@@ -0,0 +1,52 @@
+import { Stats } from "fs";
+import { ReadStream } from "fs";
+import mrmime from "mrmime";
+
+/**
+ * Create a simple ETag.
+ */
+export async function getEtag(stat: Stats): Promise<string> {
+  const mtime = stat.mtime.getTime().toString(16);
+  const size = stat.size.toString(16);
+
+  return `W/"${size}-${mtime}"`;
+}
+
+export function createReadStreamOrReadFileSync(
+  filename: string,
+  outputFileSystem: {
+    createReadStream: (
+      path: string,
+      options: { start: number; end: number },
+    ) => Buffer | ReadStream;
+  },
+  start: number,
+  end: number,
+): { bufferOrStream: Buffer | ReadStream; byteLength: number } {
+  const bufferOrStream = outputFileSystem.createReadStream(filename, {
+    start,
+    end,
+  });
+  // Handle files with zero bytes
+  const byteLength = end === 0 ? 0 : end - start + 1;
+
+  return { bufferOrStream, byteLength };
+}
+
+/**
+ * Create a full Content-Type header given a MIME type or extension.
+ */
+export function getContentType(str: string): false | string {
+  let mime = mrmime.lookup(str);
+  if (!mime) {
+    return false;
+  }
+  if (
+    mime.startsWith("text/") ||
+    mime === "application/json" ||
+    mime === "application/manifest+json"
+  ) {
+    mime += `; charset=utf-8`;
+  }
+  return mime;
+}