38 lines
1.1 KiB
TypeScript
38 lines
1.1 KiB
TypeScript
export function estimateBase64DecodedBytes(base64: string): number {
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// Avoid `trim()`/`replace()` here: they allocate a second (potentially huge) string.
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// We only need a conservative decoded-size estimate to enforce budgets before Buffer.from(..., "base64").
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let effectiveLen = 0;
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for (let i = 0; i < base64.length; i += 1) {
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const code = base64.charCodeAt(i);
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// Treat ASCII control + space as whitespace; base64 decoders commonly ignore these.
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if (code <= 0x20) {
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continue;
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}
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effectiveLen += 1;
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}
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if (effectiveLen === 0) {
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return 0;
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}
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let padding = 0;
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// Find last non-whitespace char(s) to detect '=' padding without allocating/copying.
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let end = base64.length - 1;
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while (end >= 0 && base64.charCodeAt(end) <= 0x20) {
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end -= 1;
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}
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if (end >= 0 && base64[end] === "=") {
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padding = 1;
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end -= 1;
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while (end >= 0 && base64.charCodeAt(end) <= 0x20) {
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end -= 1;
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}
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if (end >= 0 && base64[end] === "=") {
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padding = 2;
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}
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}
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const estimated = Math.floor((effectiveLen * 3) / 4) - padding;
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return Math.max(0, estimated);
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}
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