Add detailed download progress

utils/progress_readable.ts

@@ -0,0 +1,60 @@
+type EventMap = {
+    "finished": number;
+    "progress": number;
+};
+
+export class ProgressReadable extends EventTarget {
+    readable: ReadableStream<Uint8Array>;
+    readed: number;
+    constructor(readable: ReadableStream<Uint8Array>) {
+        super();
+        this.readed = 0;
+        const reader = readable.getReader();
+        this.readable = new ReadableStream({
+            pull: async (c) => {
+                if (c.byobRequest) {
+                    throw Error("Unimplemented.");
+                } else {
+                    const v = await reader.read();
+                    if (v.done) {
+                        this.dispatchEvent("finished", this.readed);
+                        c.close();
+                        return;
+                    } else {
+                        this.readed += v.value.byteLength;
+                        this.dispatchEvent("progress", this.readed);
+                        c.enqueue(v.value);
+                    }
+                }
+            },
+            cancel: (reason) => {
+                readable.cancel(reason);
+            },
+            type: "bytes",
+        });
+    }
+    // @ts-ignore Checked type
+    addEventListener<T extends keyof EventMap>(
+        type: T,
+        callback: (e: CustomEvent<EventMap[T]>) => void | Promise<void>,
+        options?: boolean | AddEventListenerOptions,
+    ): void {
+        super.addEventListener(type, <EventListener> callback, options);
+    }
+    // @ts-ignore Checked type
+    dispatchEvent<T extends keyof EventMap>(type: T, detail: EventMap[T]) {
+        return super.dispatchEvent(new CustomEvent(type, { detail }));
+    }
+    // @ts-ignore Checked type
+    removeEventListener<T extends keyof EventMap>(
+        type: T,
+        callback: (e: CustomEvent<EventMap[T]>) => void | Promise<void>,
+        options?: boolean | EventListenerOptions,
+    ): void {
+        super.removeEventListener(
+            type,
+            <EventListener> callback,
+            options,
+        );
+    }
+}