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/*

* Handing a print document to the local API so it can be served from a real

* origin instead of a data: URL.

*

* The receipt printer loads its HTML as `data:text/html;...`, which has an

* opaque origin. The invoice markup links print.css and the shop's logo from

* the local API, and an opaque origin may not load either - so that window has

* always run with webSecurity disabled. It works, and it has been flagged as a

* finding every time anyone audits the repository, correctly.

*

* The fix is not to turn the flag on. It is to stop needing it: serve the

* document from `http://127.0.0.1:<port>/print/<token>` so the page, the

* stylesheet and the logo share one origin. Then web security can be on and

* nothing is cross-origin at all.

*

* Documents live in memory only. Writing a customer's invoice to a temporary

* file to print it would leave it on disk after the job, which is a worse

* trade than the one being fixed.

*

* Each token is single-use and short-lived. A print document is fetched once,

* immediately, by a window this process just opened - so anything else asking

* for it is not the print window, and there is nothing left to give.

*/

const crypto = require('crypto');

/* Long enough that guessing is not a strategy, on a loopback-only endpoint

that holds each document for seconds. */

const TOKEN_BYTES = 24;

/* If a window fails to open, or the print is cancelled before the page loads,

nothing collects the document. It must not sit in memory until the till is

next restarted. */

const TTL_MS = 60 * 1000;

const documents = new Map();

function sweep(now = Date.now()) {

for (const [token, entry] of documents) {

if (entry.expiresAt <= now) documents.delete(token);

}

}

/**

* Store a document and return the token that fetches it exactly once.

*

* @param {string} html a complete HTML document

* @returns {string} the token to put in the URL

*/

function put(html) {

if (typeof html !== 'string' || !html) {

throw new TypeError('a print document must be a non-empty string');

}

sweep();

const token = crypto.randomBytes(TOKEN_BYTES).toString('hex');

documents.set(token, { html, expiresAt: Date.now() + TTL_MS });

return token;

}

/**

* Fetch and forget.

*

* Single use: the second request for a token gets nothing, whoever makes it.

*

* @param {string} token

* @returns {string|null} the document, or null if it is unknown, spent or expired

*/

function take(token) {

sweep();

if (typeof token !== 'string') return null;

const entry = documents.get(token);

if (!entry) return null;

documents.delete(token);

return entry.html;

}

/** How many documents are waiting. For diagnostics and tests. */

function size() {

sweep();

return documents.size;

}

/** Drop everything. Used on shutdown so nothing outlives the process. */

function clear() {

documents.clear();

}

module.exports = { put, take, size, clear, TTL_MS };