stream: add writable.writeAhead()

[KhooHaoYit]

This PR add a new function called writeAhead to writable

The main reason I feel like it should belong to nodejs is because its hard to do first in last out using stream which my code needs to do

Example use case:

queue = new stream.Writable({
  objectMode: true,
  writev(chunks, cb){
    // Assuming that it could only process 2 chunk at a time
    console.log([chunks.shift(), chunks.shift()]);
    // Any write before returning would be cleared soo .nextTick is needed
    process.nextTick(() => {
      this.cork();
      for(let index = chunks.length; index--; ){
        const { chunk, encoding, callback } = chunks[index];
        // Callback needs to be cleared due to that `cb()` would call them automatically
        chunks[index].callback = () => {};
        this.writeAhead(chunk, encoding, callback); // Quite hard to achieve
      }
      process.nextTick(() => this.uncork());
    });
    cb();
  },
});
queue.cork();
queue.write({ a: 1 });
queue.write({ b: 2 });
queue.write({ c: 3 });
queue.write({ d: 4 });
queue.write({ e: 5 });
queue.uncork(); // Assuming the stream never .end()

Any suggestion/improvement is welcomed

[nodejs-github-bot]

Review requested:

• @nodejs/streams

[ronag]

I don't believe this belongs in streams. What's wrong with unshift?

[KhooHaoYit]

Assuming you are talking about readable.unshift, no, there's nothing wrong with unshift

But for writable, you can only add data behind (.write), while readable can add data behind and in front (.push and .unshift)

This PR gives the ability to do something similar to .unshift for readable in writable

[benjamingr]

unshift (which I don't like tbh) is used for "read then regret if the chunk doesn't match" cases, typically streams go in one direction - I'm also -1 about having this in core although a userland subclass is free to add this.