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import Tesseract from "./static/tesseract.esm.min.js";
let ocrWorker = null;
const WORKER_PATH = chrome.runtime.getURL("offscreen/ocr/static/worker.min.js");
const CORE_PATH = chrome.runtime.getURL("offscreen/ocr/static");
/**
* Creates (or reuses) a Tesseract.js worker and recognises text from
* the given image data URL. The worker is configured to only recognise
* uppercase alphanumerics (excluding `0`, `O`, `1`, `I`) suitable for
* CAPTCHA text.
*
* @param {string} dataURL - A `data:image/png;base64,…` string.
* @returns {{ text: string, confidence: number }}
*/
async function performOcrInOffscreen(dataURL) {
if (!ocrWorker) {
ocrWorker = await Tesseract.createWorker("eng", 1, {
workerPath: WORKER_PATH,
corePath: CORE_PATH,
workerBlobURL: false
});
await ocrWorker.setParameters({
// The only characters that appears
tessedit_char_whitelist: "ABCDEFGHJKLMNPQRSTUVWXYZ23456789"
});
}
const { data } = await ocrWorker.recognize(dataURL);
return data;
}
// Listen for messages from the Service Worker
/**
* Handles two message types from the background service worker:
* - `"OFFSCREEN_OCR_REQUEST"`: runs OCR on the supplied data URL.
* - `"OFFSCREEN_TERMINATE_OCR_WORKER"`: terminates the worker to free memory.
*/
chrome.runtime.onMessage.addListener((message, _sender, sendResponse) => {
if (message.type === "OFFSCREEN_OCR_REQUEST" && message.dataURL) {
performOcrInOffscreen(message.dataURL)
.then(function({ text, confidence }) {
sendResponse({ success: true, text, confidence });
})
.catch(function(error) {
sendResponse({ success: false, error: error.message });
});
return true;
}
if (message.type === "OFFSCREEN_TERMINATE_OCR_WORKER") {
if (ocrWorker) {
ocrWorker.terminate();
ocrWorker = null;
}
sendResponse({ success: true });
}
});
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