This is a simple journey that explores the nature of the NodeJS Buffer. After reading the docs there are a still a few things that remain a mystery around buffers.
For instance:
- Which operations create new copies of existing buffers, vs which ops create buffers that reference the original memory. The documentation is pretty clear when it comes to slice but not so clear with other methods.
Through experimentation and examples we will explore the core node buffers (and some useful additional modules from userland).
The following exercises have been created organically as I have had questions that needed answering. Apologies for them not being in any order that makes sense...
While the documentation is pretty clear about this, let's check for ourselves.
var a = new Buffer([0x00, 0x01, 0x02, 0x03]);
var b = a.slice(1, 3);
console.log(a);
// => <Buffer 00 01 02 03>
console.log(b);
// => <Buffer 01 02>
// update the contents of a
a[1] = 0xFF;
console.log(a);
// => <Buffer 00 ff 02 03>
console.log(b);
// => ?var a = new Buffer([0x00, 0x01, 0x02, 0x03]);
var b = new Buffer([0x04, 0x05, 0x06, 0x07]);
var c = Buffer.concat([a, b]);
console.log(a);
// => <Buffer 00 01 02 03>
console.log(b);
// => <Buffer 04 05 06 07>
console.log(c);
// => <Buffer 00 01 02 03 04 05 06 07>
// update the contents of a
a[0] = 0x10;
console.log(a);
// => <Buffer 10 01 02 03>
console.log(c);
// => ?Yes, using the bl module you can.
var buffers = require('bl');
// create our test buffers
var a = new Buffer([0x00, 0x01, 0x02, 0x03]);
var b = new Buffer([0x04, 0x05, 0x06, 0x07]);
// group a + b in logical group c
var c = buffers([a, b]);
console.log(a);
// => <Buffer 00 01 02 03>
console.log(b);
// => <Buffer 04 05 06 07>
console.log(c);
// => { _bufs: [ <Buffer 00 01 02 03>, <Buffer 04 05 06 07> ], ... }
/* slice and dice */
// slice within the first buffer boundary
var d = c.slice(1, 4);
// slice across the boundary
var e = c.slice(3, 7);
console.log(d);
// => <Buffer 01 02 03>
console.log(e);
// => <Buffer 03 04 05 06>
/* update a and check impact to existing buffers */
// update a
a[3] = 0xFF;
console.log(a);
// => <Buffer 00 01 02 ff>
console.log(d);
// => <Buffer 01 02 ff>
console.log(e);
// => <Buffer 03 04 05 06>As outlined in the bl module docs for the
slice method, slice
will return a reference to the original buffer if the slice operation
remains within the boundary of the original buffer. If, however, it crosses
a buffer boundary then a copy operation will need to occur.
For an example of this compare the console output of d and e after
modifying the original buffer a.
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