core/Base64

Module for Base64 encoding of byte sequences.

Base64 encoding converts binary data to an ASCII string using 64 printable characters, as specified in RFC 4648. It is widely used for HTTP Basic Authentication, encoding binary data in JSON payloads, and data URIs.

This module uses the standard Base64 alphabet (A–Z, a–z, 0–9, +, /) and pads output to a multiple of 4 characters using =.

Original version authored by Claude Sonnet (claude-sonnet-4-6) for use in generated Motoko API clients. The module received subsequent manual performance improvements.

Import from the core package to use this module.

import Base64 "mo:core/Base64";

Function encode

func encode(data : Blob) : Text

Encodes a Blob as a Base64 Text string (RFC 4648 §4).

Output length is always a multiple of 4, padded with = as needed. An empty Blob encodes to an empty Text.

Example:

assert Base64.encode("" : Blob) == "";
assert Base64.encode("f" : Blob) == "Zg==";
assert Base64.encode("fo" : Blob) == "Zm8=";
assert Base64.encode("foo" : Blob) == "Zm9v";
assert Base64.encode("foobar" : Blob) == "Zm9vYmFy";

Typical use — embedding text in a data URI:

let payload = "Hello" : Blob;
let uri = "data:text/plain;base64," # Base64.encode(payload);
assert uri == "data:text/plain;base64,SGVsbG8=";