95 lines
3.1 KiB
TypeScript
95 lines
3.1 KiB
TypeScript
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import QMCCryptoModule from '@jixun/qmc2-crypto';
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// EOF Magic detection.
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const DETECTION_SIZE = 40;
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// Process in 2m buffer size
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const DECRYPTION_BUF_SIZE = 2 * 1024 * 1024;
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/**
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* 解密一个 QMC2 加密的文件。
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*
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* 如果检测并解密成功，返回解密后的 Uint8Array 数组，按顺序拼接即可得到完整文件。
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* 若失败，返回 `null`。
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* @param {ArrayBuffer} mggBlob 读入的文件 Blob
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* @param {string} name 文件名
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* @return {Promise<Uint8Array[]|null>}
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*/
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export async function decryptMGG(mggBlob: ArrayBuffer) {
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// 初始化模组
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const QMCCrypto = await QMCCryptoModule();
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// 申请内存块，并文件末端数据到 WASM 的内存堆
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const detectionBuf = new Uint8Array(mggBlob.slice(-DETECTION_SIZE));
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const pDetectionBuf = QMCCrypto._malloc(detectionBuf.length);
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QMCCrypto.writeArrayToMemory(detectionBuf, pDetectionBuf);
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// 检测结果内存块
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const pDetectionResult = QMCCrypto._malloc(QMCCrypto.sizeof_qmc_detection());
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// 进行检测
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const detectOK = QMCCrypto.detectKeyEndPosition(
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pDetectionResult,
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pDetectionBuf,
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detectionBuf.length
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);
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// 提取结构体内容：
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// (pos: i32; len: i32; error: char[??])
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const position = QMCCrypto.getValue(pDetectionResult, "i32");
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const len = QMCCrypto.getValue(pDetectionResult + 4, "i32");
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const detectionError = QMCCrypto.UTF8ToString(pDetectionResult + 8);
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// 释放内存
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QMCCrypto._free(pDetectionBuf);
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QMCCrypto._free(pDetectionResult);
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if (detectOK) {
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// 计算解密后文件的大小。
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// 之前得到的 position 为相对当前检测数据起点的偏移。
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const decryptedSize = mggBlob.byteLength - DETECTION_SIZE + position;
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// $prog.max = decryptedSize;
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// 提取嵌入到文件的 EKey
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const ekey = new Uint8Array(
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mggBlob.slice(decryptedSize, decryptedSize + len)
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);
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// 解码 UTF-8 数据到 string
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const decoder = new TextDecoder();
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const ekey_b64 = decoder.decode(ekey);
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// 初始化加密与缓冲区
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const hCrypto = QMCCrypto.createInstWidthEKey(ekey_b64);
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const buf = QMCCrypto._malloc(DECRYPTION_BUF_SIZE);
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const decryptedParts = [];
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let offset = 0;
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let bytesToDecrypt = decryptedSize;
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while (bytesToDecrypt > 0) {
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const blockSize = Math.min(bytesToDecrypt, DECRYPTION_BUF_SIZE);
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// 解密一些片段
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const blockData = new Uint8Array(
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mggBlob.slice(offset, offset + blockSize)
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);
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QMCCrypto.writeArrayToMemory(blockData, buf);
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QMCCrypto.decryptStream(hCrypto, buf, offset, blockSize);
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decryptedParts.push(QMCCrypto.HEAPU8.slice(buf, buf + blockSize));
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offset += blockSize;
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bytesToDecrypt -= blockSize;
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// $prog.value = offset;
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// 避免网页卡死，让 event loop 处理一下其它事件。
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// Worker 应该不需要等待也可以？
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// await new Promise((resolve) => setTimeout(resolve));
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}
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QMCCrypto._free(buf);
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hCrypto.delete();
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return decryptedParts;
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} else {
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throw new Error("ERROR: could not decrypt\n " + detectionError);
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}
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}
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