Trying to return a stream-buffer from a function-CodePudding

I am attempting to create a zip file containing a csv file and return it from a function as a buffer. The code I have is as follows:

const archiver = require('archiver');
const streamBuffers = require("stream-buffers");

createZipFromCsv(csv) {

  var myWritableStreamBuffer = new streamBuffers.WritableStreamBuffer({
    initialSize: (100 * 1024),   // start at 100 kilobytes.
    incrementAmount: (10 * 1024) // grow by 10 kilobytes each time buffer overflows.
  });

  myWritableStreamBuffer.on('finish', () => {
    console.log(myWritableStreamBuffer.getContents())
    return Promise.resolve(myWritableStreamBuffer.getContents());
  });

  const archive = archiver('zip');
  archive.pipe(myWritableStreamBuffer);
  archive.append(csv, { name: 'csvName.csv' });
  archive.finalize();

}

And the function call:

const buffer = await createZipFromCsv("some,csv,data");
console.log(buffer)

however, the buffer console log after the function call is undefined. The console log inside the on finish returns a good buffer, but only after the console log after the function call. I'm confused why the function is returning before the buffer has finished writing.

Any help appreciated!

CodePudding user response：

You need to wrap your code in a promise that you return and then resolve/reject appropriately. Here's one way to do that:

const archiver = require('archiver');
const streamBuffers = require("stream-buffers");

createZipFromCsv(csv) {

    return new Promise((resolve, reject) => {
        const myWritableStreamBuffer = new streamBuffers.WritableStreamBuffer({
            initialSize: (100 * 1024), // start at 100 kilobytes.
            incrementAmount: (10 * 1024) // grow by 10 kilobytes each time buffer overflows.
        });

        myWritableStreamBuffer.on('finish', () => {
            resolve(myWritableStreamBuffer.getContents());
        });

        myWritableStreamBuffer.on('error', reject);

        const archive = archiver('zip');
        archive.pipe(myWritableStreamBuffer);
        archive.append(csv, { name: 'csvName.csv' });
        archive.finalize();

    });
}