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The naive approach to creating a ReadableStream from a Buffer is to use the ReadableStream constructor and enqueue the entire array as a single chunk. For a large buffer, this may be undesirable as this approach does not “streaming” the data in smaller chunks. 
const buf = Buffer.from('hello world');
const stream = new ReadableStream({
	start(controller) {
		controller.enqueue(buf);
		controller.close();
	},
});
To stream the data in smaller chunks, first create a Blob instance from the Buffer. Then use the Blob.stream() method to create a ReadableStream that streams the data in chunks of a specified size. 
const buf = Buffer.from('hello world');
const blob = new Blob([buf]);
const stream = blob.stream();
The chunk size can be set by passing a number to the .stream() method. 
const buf = Buffer.from('hello world');
const blob = new Blob([buf]);

// set chunk size of 1024 bytes
const stream = blob.stream(1024);
See Docs > API > Binary Data for complete documentation on manipulating binary data with Bun.