Buffer.copy() Method in Node.js

Working with raw binary data is a core aspect of Node.js, and the Buffer class provides several useful methods for handling this. One such method is Buffer.copy(), which allows you to copy the contents of one buffer into another. This method is particularly useful when you want to manipulate data in memory efficiently.

What is Buffer.copy()?

The Buffer.copy() method is used to copy data from one buffer to another. It gives you control over where the data is copied from and to, including how many bytes to copy and the exact start positions in both the source and target buffers.

Syntax of Buffer.copy()

Here’s how the method is structured:

sourceBuffer.copy(targetBuffer, targetStart, sourceStart, sourceEnd);

• targetBuffer: The buffer you want to copy data into.
• targetStart (optional): Index in the target buffer where copying should begin. Defaults to 0.
• sourceStart (optional): Index in the source buffer where copying starts. Defaults to 0.
• sourceEnd (optional): Index in the source buffer where copying ends (non-inclusive). Defaults to the end of the buffer.

Basic Example

Let’s take a look at a simple usage of the Buffer.copy() method:

const source = Buffer.from('Node.js');
const target = Buffer.alloc(10);

source.copy(target);

console.log(target.toString()); // Outputs: 'Node.js'

In this example, the contents of the source buffer are copied into the target buffer starting from index 0.

Copying a Specific Range

You can also copy only a portion of the source buffer into a specific section of the target buffer:

const source = Buffer.from('JavaScript');
const target = Buffer.alloc(10);

// Copy characters from index 4 to 10 ('Script')
source.copy(target, 0, 4, 10);

console.log(target.toString()); // Outputs: 'Script'

Here, only the substring "Script" is copied from the source buffer into the target buffer.

Overlapping Buffers

It’s important to note that Buffer.copy() works properly even if the source and target buffers share memory. Node.js ensures the copy happens without corrupting data.

const buffer = Buffer.from('123456789');
buffer.copy(buffer, 0, 3, 6); // Moves '456' to the beginning

console.log(buffer.toString()); // Outputs: '456456789'

Use Cases

• Copying raw data between memory segments
• Preparing binary data before sending it over a network
• Combining or slicing buffers while optimizing performance

Conclusion

The Buffer.copy() method is a powerful tool when working with low-level binary data in Node.js. It allows precise and performant manipulation of buffer content and is an essential method for developers working with files, network streams, or custom binary formats.