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