Encode and decode CBOR

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CBOR is a binary serialization format standardized as RFC 8949. It backs WebAuthn, IoT protocols and many other systems that need compact self-describing messages. Unlike JSON it has native support for binary data and dates. The Standard Library implements it in jsr:@std/cbor.

import { decodeCbor, encodeCbor } from "jsr:@std/cbor";

The value contains a Uint8Array and a Date. Neither would survive JSON.stringify, which has no representation for them.

const value = {
  name: "Deno",
  version: 2,
  active: true,
  signature: new Uint8Array([222, 173, 190, 239]),
  released: new Date("2020-05-13T00:00:00Z"),
};

To encode, pass the value to the encodeCbor function. The result is a Uint8Array.

const bytes = encodeCbor(value);
console.log(bytes.length); // 58

To decode, pass the bytes to the decodeCbor function. It returns the broad CborType, so cast the result to the shape you expect.

const decoded = decodeCbor(bytes) as typeof value;

The binary payload and the date both come back as their real types.

console.log(decoded.signature); // Uint8Array(4) [ 222, 173, 190, 239 ]
console.log(decoded.released instanceof Date); // true
console.log(decoded.released.toISOString()); // 2020-05-13T00:00:00.000Z

CBOR is also more compact than JSON text. For this small object the encoding saves about a third of the bytes.

const small = { name: "Deno", version: 2, active: true };
console.log(JSON.stringify(small).length); // 41
console.log(encodeCbor(small).length); // 28

Supported value types are undefined, null, boolean, number, bigint, string, Uint8Array, Date, arrays and plain objects of those, plus CborTag for the remaining tagged values from the specification.

Run this example locally using the Deno CLI:

deno run https://docs.deno.com/examples/scripts/cbor_encoding.ts

Encode and decode CBOR

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