feat(QMCv2): add decoder

(cherry picked from commit 29ac94d1fe52e666fda619f8716d2bc0b120a9ee)

src/decrypt/qmc.test.ts

@@ -0,0 +1,32 @@
+import fs from "fs";
+import {QmcDecoder} from "@/decrypt/qmc";
+import {BytesEqual} from "@/decrypt/utils";
+
+function loadTestDataDecoder(name: string): {
+  cipherText: Uint8Array,
+  clearText: Uint8Array
+} {
+  const cipherBody = fs.readFileSync(`./testdata/${name}_raw.bin`);
+  const cipherSuffix = fs.readFileSync(`./testdata/${name}_suffix.bin`);
+  const cipherText = new Uint8Array(cipherBody.length + cipherSuffix.length);
+  cipherText.set(cipherBody);
+  cipherText.set(cipherSuffix, cipherBody.length);
+  return {
+    cipherText,
+    clearText: fs.readFileSync(`testdata/${name}_target.bin`)
+  }
+}
+
+test("qmc: real file", async () => {
+  const cases = ["mflac0_rc4", "mflac_map", "mgg_map", "qmc0_static"]
+  for (const name of cases) {
+    const {clearText, cipherText} = loadTestDataDecoder(name)
+    const c = new QmcDecoder(cipherText)
+    const buf = c.decrypt()
+
+    expect(BytesEqual(buf, clearText)).toBeTruthy()
+  }
+})
+
+
+

src/decrypt/qmc.ts

@@ -1,4 +1,4 @@
-import {QmcStaticCipher} from "./qmc_cipher";
+import {QmcMapCipher, QmcRC4Cipher, QmcStaticCipher, StreamCipher} from "./qmc_cipher";
 import {
   AudioMimeType,
   GetArrayBuffer,
@@ -16,6 +16,7 @@ import {DecryptQMCv2} from "./qmcv2";
 import iconv from "iconv-lite";
 import {DecryptResult} from "@/decrypt/entity";
 import {queryAlbumCover} from "@/utils/api";
+import {QmcDecryptKey} from "@/decrypt/qmc_key";
 
 interface Handler {
   ext: string
@@ -137,3 +138,63 @@ async function getCoverImage(title: string, artist?: string, album?: string): Pr
   }
   return ""
 }
+
+export class QmcDecoder {
+  file: Uint8Array
+  size: number
+  decoded: boolean = false
+  audioSize?: number
+  cipher?: StreamCipher
+
+  constructor(file: Uint8Array) {
+    this.file = file
+    this.size = file.length
+    this.searchKey()
+  }
+
+  decrypt(): Uint8Array {
+    if (!this.cipher) {
+      throw new Error("no cipher found")
+    }
+    if (!this.audioSize || this.audioSize <= 0) {
+      throw new Error("invalid audio size")
+    }
+    const audioBuf = this.file.subarray(0, this.audioSize)
+
+    if (!this.decoded) {
+      this.cipher.decrypt(audioBuf, 0)
+      this.decoded = true
+    }
+
+    return audioBuf
+  }
+
+  private searchKey() {
+    const last4Byte = this.file.slice(this.size - 4);
+    const textEnc = new TextDecoder()
+    if (textEnc.decode(last4Byte) === 'QTag') {
+      const sizeBuf = this.file.slice(this.size - 8, this.size - 4)
+      const sizeView = new DataView(sizeBuf.buffer, sizeBuf.byteOffset)
+      const keySize = sizeView.getUint32(0, false)
+      this.audioSize = this.size - keySize - 8
+      const rawKey = this.file.subarray(this.audioSize, this.size - 8)
+      const keyEnd = rawKey.findIndex(v => v == ','.charCodeAt(0))
+      const keyDec = QmcDecryptKey(rawKey.subarray(0, keyEnd))
+      this.cipher = new QmcRC4Cipher(keyDec)
+    } else {
+      const sizeView = new DataView(last4Byte.buffer, last4Byte.byteOffset);
+      const keySize = sizeView.getUint32(0, true)
+      if (keySize < 0x300) {
+        this.audioSize = this.size - keySize - 4
+        const rawKey = this.file.subarray(this.audioSize, this.size - 4)
+        const keyDec = QmcDecryptKey(rawKey)
+        this.cipher = new QmcMapCipher(keyDec)
+      } else {
+        this.audioSize = this.size
+        this.cipher = new QmcStaticCipher()
+      }
+    }
+  }
+
+
+}

src/decrypt/qmc_key.test.ts

@@ -1,4 +1,4 @@
-import {DecryptKey, simpleMakeKey,} from "@/decrypt/qmc_key";
+import {QmcDecryptKey, simpleMakeKey,} from "@/decrypt/qmc_key";
 import fs from "fs";
 
 test("key dec: make simple key", () => {
@@ -23,7 +23,7 @@ test("key dec: real file", async () => {
   const cases = ["mflac_map", "mgg_map", "mflac0_rc4"]
   for (const name of cases) {
     const {clearText, cipherText} = loadTestDataKeyDecrypt(name)
-    const buf = DecryptKey(cipherText)
+    const buf = QmcDecryptKey(cipherText)
 
     expect(buf).toStrictEqual(clearText)
   }

src/decrypt/qmc_key.ts

@@ -83,8 +83,9 @@ function decryptTencentTea(inBuf: Uint8Array, key: Uint8Array): Uint8Array {
   return outBuf
 }
 
-export function DecryptKey(raw: Uint8Array): Uint8Array {
-  const rawDec = Buffer.from(raw.toString(), 'base64')
+export function QmcDecryptKey(raw: Uint8Array): Uint8Array {
+  const textDec = new TextDecoder()
+  const rawDec = Buffer.from(textDec.decode(raw), 'base64')
   let n = rawDec.length;
   if (n < 16) {
     throw Error("key length is too short")

src/decrypt/utils.ts

@@ -32,6 +32,13 @@ export function BytesHasPrefix(data: Uint8Array, prefix: number[]): boolean {
     })
 }
 
+export function BytesEqual(a: Uint8Array, b: Uint8Array,): boolean {
+    if (a.length != b.length) return false
+    return a.every((val, idx) => {
+        return val === b[idx];
+    })
+}
+
 
 export function SniffAudioExt(data: Uint8Array, fallback_ext: string = "mp3"): string {
     if (BytesHasPrefix(data, MP3_HEADER)) return "mp3"