cbor2

Encode and parse data in the Concise Binary Object Representation (CBOR) data format (RFC8949).

This package supersedes node-cbor, with the following goals:

• Web-first. Usable in Node and Deno.
• Simpler where possible. Remove non-core features in favor of extensibility.
• Synchronous decoding. Removes streaming capabilities that are rarely used.
• Complete break of API compatibility, allowing use of newer JavaScript constructs.
• No work-arounds for older environments.

Start playing with cbor2 now

Visit the web playground for an interactive view of how the library works.

Supported Node.js versions

This project now only supports versions of Node.js that the Node team is currently supporting. Currently, that means Node 20+ is required.

Installation

npm install --save cbor2

Documentation

See the full API documentation.

Example:

import {decode, diagnose, encode} from 'cbor2';

const encoded = encode(true); // Returns Uint8Array(1) [ 245 ]
decode(encoded); // Returns true

// Use integers as keys:
const m = new Map();
m.set(1, 25);
encode(m); // Returns Uint8Array(3) [ 161, 1, 24, 25 ]
diagnose(encode(m)); // {1: 25_0}

Supported types

If you load cbor2 using import {decode, encode} from 'cbor2';, all of the type converters will be loaded automatically. If you import only pieces of the API and you want the type converters loaded, please also do import 'cbor2/types';.

The following types are supported for encoding:

• boolean
• number (including -0, NaN, and ±Infinity)
• string (Set the wtf8 option to enable encoding invalid UTF-16 strings to tag 273)
• bigint
• Array
• Set
• Object (including null)
• Map
• undefined
• Date,
• RegExp
• URL
• TypedArrays: Uint8Array is mapped to a CBOR byte array, others are tagged
• Boxed primitive types: String, Number, BigInt, Boolean
• cbor2.Simple
• cbor2.Tag

Decoding supports the above types, including the following CBOR tag numbers:

Adding new Encoders

There are several ways to add a new encoder:

toCBOR method

This is the easiest approach, if you can modify the class being encoded. Add a toCBOR() method to your class, which should return a two-element array containing the tag number and data item that encodes your class. If the tag number is NaN, no tag will be written. If you return undefined, nothing will be written. In this case you will likely write custom bytes to the Writer instance that is passed in, perhaps using the encoding options.

For example:

class Foo {
  constructor(one, two) {
    this.one = one;
    this.two = two;
  }

  toCBOR(_writer, _options) {
    return [64000, [this.one, this.two]];
  }
}

You can also modify an existing type by monkey-patching a toCBOR function onto its prototype, but this isn't recommended.

toJSON() method

If your object does not have a toCBOR() method, but does have a toJSON() method, the value returned from toJSON() will be used to serialize the object.

registerEncoder

Sometimes, you want to support an existing type without modification to that type. In this case, call registerEncoder(type, encodeFunction). The encodeFunction takes an object instance and returns the same type as toCBOR above:

import {Buffer} from 'node:buffer';
import {registerEncoder} from 'cbor2/encoder';

registerEncoder(Buffer, b => [
  // Don't write a tag
  NaN,
  // New view on the ArrayBuffer, without copying bytes
  new Uint8Array(b.buffer, b.byteOffset, b.byteLength),
]);

If you want to have different encoders for different calls to encode, you can pass a types parameter to encode:

import {TypeEncoderMap, encode} from 'cbor2';
import {Buffer} from 'node:buffer';

const types = new TypeEncoderMap();
types.registerEncoder(Buffer, b => [
  // Don't write a tag
  NaN,
  // New view on the ArrayBuffer, without copying bytes
  new Uint8Array(b.buffer, b.byteOffset, b.byteLength),
]);
encode(Buffer.from('foo'), {types});

Adding new decoders

Most of the time, you will want to add support for decoding a new tag type. If the Decoder class encounters a tag it doesn't support, it will generate a Tag instance that you can handle or ignore as needed. To have a specific type generated instead, call Tag.registerDecoder() with the tag number and a function that will convert the tags value to the appropriate type. For the Foo example above, this might look like:

import {Tag} from 'cbor2/tag';

Tag.registerDecoder(64000, tag => new Foo(tag.contents[0], tag.contents[1]));

You can also replace the default decoders by passing in an appropriate tag function. For example:

// Tag 0 is Date/Time as an ISO-8601 string
import 'cbor2/types';
import {Tag} from 'cbor2/tag';

Tag.registerDecoder(0, ({contents}) => Temporal.Instant.from(contents));

Finally, you can pass a tags parameter to decode to specify tag decoding for a single call to decode:

const tags = new Map([
  [64000, ({contents}) => new Foo(contents[0], contents[1])],
]);
decode('d9fa00820102', {tags});

Boxed Types

JavaScript "boxed" types, such as those created with new Number(3), are object wrappers around JavaScript primitives. These objects can be used in most places that a primitive value would be used, but since they are objects they can have associated properties. This library can decode CBOR values into boxed types if desired, such that the original CBOR encoding of that value is stored as a hidden property on the value, ensuring that round-tripping between decoding and encoding will produce the original CBOR value, no matter which of the many legal CBOR encodings were used for a given value. For example:

import {decode, encode} from 'cbor';

const val = decode('fa40800000', {boxed: true}); // [Number: 4]
encode(4); // 0x04
encode(new Number(4)); // 0x04
encode(val); // 0xfa40800000, the original encoding
encode(val, {ignoreOriginalEncoding: true}); // 0x04

When pedantic protocols are strict about the types they will accept, and you want to force a particular numeric encoding, you can use the encodedNumber function to create a boxed number with the desired encoding attached:

import {encode, encodedNumber} from 'cbor';

const val = encodedNumber(4, 'i64'); // [Number: 4]
encode(val); // 0x1b0000000000000004
encode(encodedNumber(4)); // 0xf94400

Note that the default format for encodedNumber is the preferred floating point representation, which can be explicitly selected with an encoding of 'f'.

CBOR Sequences

If you would like to decode a CBOR Sequence, use the decodeSequence method, which returns an iterator:

import {decodeSequence} from 'cbor';

for (const item of decodeSequence('0102')) {
  console.log(item); // First 1, then 2
}
// Or
const seq = [...decodeSequence('0102')]; // [1, 2]

Developers

The tests for this package use a set of test vectors from RFC 8949 appendix A by importing a machine readable version of them from https://github.com/cbor/test-vectors. For these tests to work, you will need to use the command git submodule update --init after cloning or pulling this code. See the git docs for more information.