@ai-sdk/provider-utils/src/uint8-utils.ts

// btoa and atob need to be invoked as a function call, not as a method call.
// Otherwise CloudFlare will throw a
// "TypeError: Illegal invocation: function called with incorrect this reference"
const { btoa, atob } = globalThis;

export function convertBase64ToUint8Array(base64String: string) {
  const base64Url = base64String.replace(/-/g, '+').replace(/_/g, '/');
  const latin1string = atob(base64Url);
  return Uint8Array.from(latin1string, byte => byte.codePointAt(0)!);
}

export function convertUint8ArrayToBase64(array: Uint8Array): string {
  let latin1string = '';

  // Note: regular for loop to support older JavaScript versions that
  // do not support for..of on Uint8Array
  for (let i = 0; i < array.length; i++) {
    latin1string += String.fromCodePoint(array[i]);
  }

  return btoa(latin1string);
}

export function convertToBase64(value: string | Uint8Array): string {
  return value instanceof Uint8Array ? convertUint8ArrayToBase64(value) : value;
}