estimateDataURLDecodedBytes.jsβ’2.06 kB
/**
* Estimate decoded byte length of a data:// URL *without* allocating large buffers.
* - For base64: compute exact decoded size using length and padding;
* handle %XX at the character-count level (no string allocation).
* - For non-base64: use UTF-8 byteLength of the encoded body as a safe upper bound.
*
* @param {string} url
* @returns {number}
*/
export default function estimateDataURLDecodedBytes(url) {
if (!url || typeof url !== 'string') return 0;
if (!url.startsWith('data:')) return 0;
const comma = url.indexOf(',');
if (comma < 0) return 0;
const meta = url.slice(5, comma);
const body = url.slice(comma + 1);
const isBase64 = /;base64/i.test(meta);
if (isBase64) {
let effectiveLen = body.length;
const len = body.length; // cache length
for (let i = 0; i < len; i++) {
if (body.charCodeAt(i) === 37 /* '%' */ && i + 2 < len) {
const a = body.charCodeAt(i + 1);
const b = body.charCodeAt(i + 2);
const isHex =
((a >= 48 && a <= 57) || (a >= 65 && a <= 70) || (a >= 97 && a <= 102)) &&
((b >= 48 && b <= 57) || (b >= 65 && b <= 70) || (b >= 97 && b <= 102));
if (isHex) {
effectiveLen -= 2;
i += 2;
}
}
}
let pad = 0;
let idx = len - 1;
const tailIsPct3D = (j) =>
j >= 2 &&
body.charCodeAt(j - 2) === 37 && // '%'
body.charCodeAt(j - 1) === 51 && // '3'
(body.charCodeAt(j) === 68 || body.charCodeAt(j) === 100); // 'D' or 'd'
if (idx >= 0) {
if (body.charCodeAt(idx) === 61 /* '=' */) {
pad++;
idx--;
} else if (tailIsPct3D(idx)) {
pad++;
idx -= 3;
}
}
if (pad === 1 && idx >= 0) {
if (body.charCodeAt(idx) === 61 /* '=' */) {
pad++;
} else if (tailIsPct3D(idx)) {
pad++;
}
}
const groups = Math.floor(effectiveLen / 4);
const bytes = groups * 3 - (pad || 0);
return bytes > 0 ? bytes : 0;
}
return Buffer.byteLength(body, 'utf8');
}