What is a "unexpected EOF during chunk size line" error in Deno?

I'm developing an Edge Function from Supabase locally. It runs on Deno. When I execute the code below, the following error appears:

CPU time limit reached. isolate: 16597602940236451129
CPU time used: 560ms
hyper::Error(User(Body), hyper::Error(Body, Custom { kind: UnexpectedEof, error: "unexpected EOF during chunk size line" }))

This is the code:

import { serve } from "https://deno.land/std@0.168.0/http/server.ts";
import { corsHeaders } from "../_shared/cors.ts";

function fetchArtistPage(artistName: string): Promise<string> {
  return new Promise((resolve, reject) => {
    setTimeout(async () => {
      try {
        const response = await fetch("https://www.last.fm/music/" + artistName.replace(" ", "+"));
        const page = await response.text();
        resolve(page);
      } catch (error) {
        reject(error);
      }
    }, 1000);
  });
}

serve(async (req) => {
  if (req.method === "OPTIONS") return new Response("ok", { headers: corsHeaders });

  const textEncoder = new TextEncoder();
  const artistsNames = await req.json();
  const body = new ReadableStream({
    async start(controller) {
      for (const artistName of artistsNames) {
        controller.enqueue(textEncoder.encode("START_OF_JSON "));
        const artistsData = {
          name: artistName,
          page: await fetchArtistPage(artistName),
        };
        controller.enqueue(textEncoder.encode(JSON.stringify(artistsData)));
        controller.enqueue(textEncoder.encode("END_OF_JSON "));
      }
      controller.close();
    },
  });
  return new Response(body, {
    headers: {
      ...corsHeaders,
      "Content-Type": "text/event-stream",
    },
  });
});

Context

The artistsNames variable will hold an array containing a maximum of 50 strings, where each string represent an artist name. I will fetch the artist last.fm page and send it back in the response inside the artistsData object.

When I run this code, the error appears near the 35-40th artist. If I use just 10 artists, the error doesn't appear. I just tried so many things and nothing works. If I just return text and not the page, it works. But if I parse the html page and return the text content of a tag, it doesn't work.

Edit: I have tried using the data and event fields as the Server Side Events documentations tells to do but I didn't solve the problem.

As @Bergi mentioned, the real issue is CPU time limit reached after which the isolate is destroyed, which triggers the Hyper (Server) error you're seeing, since the server is shutdown.

You can see the Deno Deploy limits here https://deno.com/deploy/docs/pricing-and-limits

> During the initial public beta, the following hard limits apply. If
> any runtime limits are exceeded, all related requests will be
> immediately terminated, and a warning will be logged to the
> deployment’s logs.

You could implement a limit/paging mechanism to avoid the timeout since you mention that you don't get the error when fetching 10 artists.

Make your server only return 1-10 artists on each request.