pdf-lib/src/utils/base64.ts

Create and modify PDF files with JavaScript

/*
 * The `chars`, `lookup`, `encode`, and `decode` members of this file are
 * licensed under the following:
 *
 *     base64-arraybuffer
 *     https://github.com/niklasvh/base64-arraybuffer
 *
 *     Copyright (c) 2012 Niklas von Hertzen
 *     Licensed under the MIT license.
 *
 */

const chars =
  'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

// Use a lookup table to find the index.
const lookup = new Uint8Array(256);
for (let i = 0; i < chars.length; i++) {
  lookup[chars.charCodeAt(i)] = i;
}

export const encodeToBase64 = (bytes: Uint8Array): string => {
  let base64 = '';
  const len = bytes.length;
  for (let i = 0; i < len; i += 3) {
    base64 += chars[bytes[i] >> 2];
    base64 += chars[((bytes[i] & 3) << 4) | (bytes[i + 1] >> 4)];
    base64 += chars[((bytes[i + 1] & 15) << 2) | (bytes[i + 2] >> 6)];
    base64 += chars[bytes[i + 2] & 63];
  }

  if (len % 3 === 2) {
    base64 = base64.substring(0, base64.length - 1) + '=';
  } else if (len % 3 === 1) {
    base64 = base64.substring(0, base64.length - 2) + '==';
  }

  return base64;
};

export const decodeFromBase64 = (base64: string): Uint8Array => {
  let bufferLength = base64.length * 0.75;
  const len = base64.length;
  let i;
  let p = 0;
  let encoded1;
  let encoded2;
  let encoded3;
  let encoded4;

  if (base64[base64.length - 1] === '=') {
    bufferLength--;
    if (base64[base64.length - 2] === '=') {
      bufferLength--;
    }
  }

  const bytes = new Uint8Array(bufferLength);

  for (i = 0; i < len; i += 4) {
    encoded1 = lookup[base64.charCodeAt(i)];
    encoded2 = lookup[base64.charCodeAt(i + 1)];
    encoded3 = lookup[base64.charCodeAt(i + 2)];
    encoded4 = lookup[base64.charCodeAt(i + 3)];

    bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
    bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
    bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
  }

  return bytes;
};

// This regex is designed to be as flexible as possible. It will parse certain
// invalid data URIs.
const DATA_URI_PREFIX_REGEX = /^(data)?:?([\w\/\+]+)?;?(charset=[\w-]+|base64)?.*,/i;

/**
 * If the `dataUri` input is a data URI, then the data URI prefix must not be
 * longer than 100 characters, or this function will fail to decode it.
 *
 * @param dataUri a base64 data URI or plain base64 string
 * @returns a Uint8Array containing the decoded input
 */
export const decodeFromBase64DataUri = (dataUri: string): Uint8Array => {
  const trimmedUri = dataUri.trim();

  const prefix = trimmedUri.substring(0, 100);
  const res = prefix.match(DATA_URI_PREFIX_REGEX);

  // Assume it's not a data URI - just a plain base64 string
  if (!res) return decodeFromBase64(trimmedUri);

  // Remove the data URI prefix and parse the remainder as a base64 string
  const [fullMatch] = res;
  const data = trimmedUri.substring(fullMatch.length);

  return decodeFromBase64(data);
};