This @zingle/stream-spigot module exports the Spigot class, which can be used to read a large Readable stream into a series of Writable buckets. The Spigot writes to one bucket at a time, and has a shutoff valve to detect when the bucket is full and provide an opportunity to start filling a new bucket.

Spigot class

The Spigot class extends EventEmitter and implements PassThrough. The constructor takes a shutoff valve function that should return true if the shutoff valve should be triggered. When the shutoff valve is triggered, the Spigot will emit the "shutoff" event and close the current Writable bucket.

Data that passes through the Spigot will be written to the bucket In addition, the Spigot class has a .pipe(Writable) method which can be used similarly to Readable.pipe(Writable). Once data starts writing to a bucket in this manner, each chunk is passed to the shutoff valve to determine if the bucket is filled yet.

Example - Write Multiple Files

The following example reads an input stream and splits it into multiple files, each under 10MiB in size.

const {createWriteStream} = require("fs");
const bytesized = require("bytesized");
const {Spigot} = require("@zingle/stream-spigot");

const readable = getReadableStreamSomehow();
const spigot = new Spigot(shutoff);

let num = 0;    // file number for naming file
let size = 0;   // size of file so far

spigot.on("shutoff", () => {
  const bucket = createWriteStream(`file-${++num}`)
  spigot.fill(bucket);
  size = 0;
});

readable.pipe(spigot);

function shutoff(chunk) {
  size += chunk.length;
  return size > bytesized("10 MiB");
}