Stream created with ZipWriter is not read by Response

[sntran]

Using the Hello World with Streams example, I try to write a server that responds with zip file, but it does not work.

The minimal code for such server is below:

import { serve } from "https://deno.land/[email protected]/http/server.ts";

import {
  ZipWriter,
} from "https://deno.land/x/[email protected]/index.js";

serve(async (req: Request) => {
  // Creates a TransformStream object, the zip content will be written in the
  // `writable` property. The `readable` property is responded to client.
  const { readable, writable } = new TransformStream();
  const zipWriter = new ZipWriter(writable);
  const entry = await zipWriter.add("hello.txt", new Blob(["Hello world!"]).stream());
  console.log(entry);
  await zipWriter.close();

  const headers = new Headers();
  headers.set("Content-Disposition", `attachment; filename="hello.zip"`);

  return new Response(readable, {
    // headers,
  });
});

You can also see it in action on Deno Deploy Playground: https://dash.deno.com/playground/zipjs

The console.log(entry) is never called. The whole process just hangs.

[gildas-lormeau]

This is due to the usage of await. Here's an example showing how to make it work: https://dash.deno.com/playground/bitter-kingfisher-23

[gildas-lormeau]

The problem is that zip.js cannot write to the writable stream because the readable stream is not consumed. An alternative is to define the highWaterMarkof the writable stream to the desired size (if known), see https://dash.deno.com/playground/interesting-oyster-43.

[sntran]

This is due to the usage of await. Here's an example showing how to make it work: https://dash.deno.com/playground/bitter-kingfisher-23

That was it. I did try not to use await on add, but forgot about the close too. Thanks a lot!

[sntran]

The problem is that zip.js cannot write to the writable stream because the readable stream is not consumed. An alternative is to define the highWaterMarkof the writable stream to the desired size (if known), see https://dash.deno.com/playground/interesting-oyster-43.

It should not be a problem for my case, since the readable stream will be immediately consumed by the client, but good to know!

[gildas-lormeau]

The usage of await blocks the Response object to read the readable, and thus it prevents zip.js to write in to the writable. Defining the highWaterMarkvalue prevents zip.js to be blocked.