hono/deno_dist/utils/encode.ts

export const decodeBase64Url = (str: string): Uint8Array => {
  return decodeBase64(str.replace(/_|-/g, (m) => ({ _: '/', '-': '+' }[m] ?? m)))
}

export const encodeBase64Url = (buf: ArrayBufferLike): string =>
  encodeBase64(buf).replace(/\/|\+/g, (m) => ({ '/': '_', '+': '-' }[m] ?? m))

// This approach is written in MDN.
// btoa does not support utf-8 characters. So we need a little bit hack.
export const encodeBase64 = (buf: ArrayBufferLike): string => {
  const binary = String.fromCharCode(...new Uint8Array(buf))
  return btoa(binary)
}

// atob does not support utf-8 characters. So we need a little bit hack.
export const decodeBase64 = (str: string): Uint8Array => {
  const binary = atob(str)
  const bytes = new Uint8Array(new ArrayBuffer(binary.length))
  const half = binary.length / 2
  for (let i = 0, j = binary.length - 1; i <= half; i++, j--) {
    bytes[i] = binary.charCodeAt(i)
    bytes[j] = binary.charCodeAt(j)
  }
  return bytes
}