Stream writable.cork() Method in Node.js

The writable.cork() method in Node.js allows you to temporarily buffer all writes to a writable stream. This is useful when you want to batch multiple write operations and flush them together for better performance, particularly in situations involving complex or high-volume data writes.

Purpose of writable.cork()

Normally, every write() call on a writable stream is processed individually. With cork(), these calls are queued instead of being sent right away. You can later call uncork() to flush the buffered data. This can reduce system load by minimizing the number of write operations.

Syntax

writable.cork()

The method doesn't take any arguments and doesn't return anything. It simply tells the stream to start buffering any written data.

How It Works

1. Call writable.cork() to start buffering.
2. Call writable.write() one or more times. These will be queued internally.
3. Call writable.uncork() to flush the queued data to the destination.

Example: Using cork() and uncork()

Here’s a practical example showing how corking can help buffer writes to a file stream.

const fs = require('fs');

// Create a writable stream
const stream = fs.createWriteStream('example.txt');

// Start buffering writes
stream.cork();

// Write multiple chunks (they'll be buffered)
stream.write('Line 1\n');
stream.write('Line 2\n');
stream.write('Line 3\n');

// Flush the buffered data
process.nextTick(() => {
    stream.uncork(); // Now all writes happen together
});
    

Why Use cork()?

• Performance Boost: Reduces the number of system calls by batching writes.
• Better Control: Gives you more control over when data is actually flushed.
• Efficient Output: Useful when writing many small chunks of data quickly.

Important Notes

• If you call uncork() multiple times, each call will flush the current buffer.
• writable.cork() is especially helpful in performance-sensitive environments.
• It works only with streams that implement the writable stream interface.

Conclusion

The writable.cork() method in Node.js provides a simple way to buffer write operations and improve I/O efficiency. By using it with writable.uncork(), you can reduce system overhead and gain more precise control over data flow in writable streams. It’s a small but powerful feature for optimizing stream-based operations.