/** Estimates decoded bytes without allocating a cleaned copy of the base64 payload. */

export function estimateBase64DecodedBytes(base64: string): number {

// Avoid `trim()`/`replace()` here: they allocate a second (potentially huge) string.

// We only need a conservative decoded-size estimate to enforce budgets before Buffer.from(..., "base64").

let effectiveLen = 0;

for (let i = 0; i < base64.length; i += 1) {

const code = base64.charCodeAt(i);

// Treat ASCII control + space as whitespace; base64 decoders commonly ignore these.

if (code <= 0x20) {

continue;

}

effectiveLen += 1;

}

if (effectiveLen === 0) {

return 0;

}

let padding = 0;

// Find last non-whitespace char(s) to detect '=' padding without allocating/copying.

let end = base64.length - 1;

while (end >= 0 && base64.charCodeAt(end) <= 0x20) {

end -= 1;

}

if (end >= 0 && base64[end] === "=") {

padding = 1;

end -= 1;

while (end >= 0 && base64.charCodeAt(end) <= 0x20) {

end -= 1;

}

if (end >= 0 && base64[end] === "=") {

padding = 2;

}

}

const estimated = Math.floor((effectiveLen * 3) / 4) - padding;

return Math.max(0, estimated);

}

function isBase64DataChar(code: number): boolean {

return (

(code >= 0x41 && code <= 0x5a) ||

(code >= 0x61 && code <= 0x7a) ||

(code >= 0x30 && code <= 0x39) ||

code === 0x2b ||

code === 0x2f

);

}

/**

* Normalizes and validates a base64 string, returning canonical no-whitespace

* base64 only when the input has valid alphabet, padding, and length.

*/

export function canonicalizeBase64(base64: string): string | undefined {

let cleaned = "";

let padding = 0;

let sawPadding = false;

for (let i = 0; i < base64.length; i += 1) {

const code = base64.charCodeAt(i);

if (code <= 0x20) {

continue;

}

if (code === 0x3d) {

padding += 1;

if (padding > 2) {

return undefined;

}

sawPadding = true;

cleaned += "=";

continue;

}

if (sawPadding || !isBase64DataChar(code)) {

return undefined;

}

cleaned += base64[i];

}

if (!cleaned || cleaned.length % 4 !== 0) {

return undefined;

}

return cleaned;

}