refactor: improve flow of decryption (#2)

src/decrypt-worker/crypto/CryptoBase.ts

@@ -1,7 +1,12 @@
 export interface CryptoBase {
   cryptoName: string;
   checkByDecryptHeader: boolean;
-  decryptTargetAudio: boolean;
+
+  /**
+   * If set, this new extension will be used instead.
+   * Useful for non-audio format, e.g. qrc to lrc/xml.
+   */
+  overrideExtension?: string;
 
   checkBySignature?: (buffer: ArrayBuffer) => Promise<boolean>;
   decrypt(buffer: ArrayBuffer, blob: Blob): Promise<Blob | ArrayBuffer>;

src/decrypt-worker/crypto/CryptoFactory.ts

@@ -6,14 +6,14 @@ import { XiamiCrypto } from './xiami/xiami';
 
 export const allCryptoFactories: CryptoFactory[] = [
   // Xiami (*.xm)
-  () => new XiamiCrypto(),
+  XiamiCrypto.make,
 
   // QMCv2 (*.mflac)
-  () => new QMC2Crypto(),
+  QMC2Crypto.make,
 
   // Crypto that does not implement "checkBySignature" or need to decrypt the entire file and then check audio type,
   //   should be moved to the bottom of the list for performance reasons.
 
   // QMCv1 (*.qmcflac)
-  () => new QMC1Crypto(),
+  QMC1Crypto.make,
 ];

src/decrypt-worker/crypto/qmc/qmc_v1.ts

@@ -3,11 +3,14 @@ import type { CryptoBase } from '../CryptoBase';
 import key from './qmc_v1.key.ts';
 
 export class QMC1Crypto implements CryptoBase {
-  cryptoName = 'QMCv1';
+  cryptoName = 'QMC/v1';
   checkByDecryptHeader = true;
-  decryptTargetAudio = true;
 
-  async decrypt(_buffer: ArrayBuffer, blob: Blob): Promise<Blob> {
-    return transformBlob(blob, (p) => p.make.QMCv1(key));
+  async decrypt(buffer: ArrayBuffer): Promise<Blob> {
+    return transformBlob(buffer, (p) => p.make.QMCv1(key));
+  }
+
+  public static make() {
+    return new QMC1Crypto();
   }
 }

src/decrypt-worker/crypto/qmc/qmc_v2.ts

@@ -3,11 +3,14 @@ import type { CryptoBase } from '../CryptoBase';
 import { SEED, ENC_V2_KEY_1, ENC_V2_KEY_2 } from './qmc_v2.key.ts';
 
 export class QMC2Crypto implements CryptoBase {
-  cryptoName = 'QMCv2';
+  cryptoName = 'QMC/v2';
   checkByDecryptHeader = false;
-  decryptTargetAudio = true;
 
-  async decrypt(_buffer: ArrayBuffer, blob: Blob): Promise<Blob> {
-    return transformBlob(blob, (p) => p.make.QMCv2(p.make.QMCv2FooterParser(SEED, ENC_V2_KEY_1, ENC_V2_KEY_2)));
+  async decrypt(buffer: ArrayBuffer): Promise<Blob> {
+    return transformBlob(buffer, (p) => p.make.QMCv2(p.make.QMCv2FooterParser(SEED, ENC_V2_KEY_1, ENC_V2_KEY_2)));
+  }
+
+  public static make() {
+    return new QMC2Crypto();
   }
 }

src/decrypt-worker/crypto/xiami/xiami.ts

@@ -26,7 +26,6 @@ const u8Sub = (a: number, b: number) => {
 export class XiamiCrypto implements CryptoBase {
   cryptoName = 'Xiami';
   checkByDecryptHeader = false;
-  decryptTargetAudio = true;
 
   async checkBySignature(buffer: ArrayBuffer): Promise<boolean> {
     const header = new DataView(buffer);
@@ -45,4 +44,8 @@ export class XiamiCrypto implements CryptoBase {
     }
     return decrypted;
   }
+
+  public static make() {
+    return new XiamiCrypto();
+  }
 }

src/decrypt-worker/util/transformBlob.ts

@@ -1,7 +1,8 @@
 import { Transformer, Parakeet, TransformResult, fetchParakeet } from '@jixun/libparakeet';
+import { toArrayBuffer } from './buffer';
 
 export async function transformBlob(
-  blob: Blob,
+  blob: Blob | ArrayBuffer,
   transformerFactory: (p: Parakeet) => Transformer | Promise<Transformer>,
   parakeet?: Parakeet
 ) {
@@ -12,7 +13,7 @@ export async function transformBlob(
     const transformer = await transformerFactory(mod);
     cleanup.push(() => transformer.delete());
 
-    const reader = mod.make.Reader(await blob.arrayBuffer());
+    const reader = mod.make.Reader(await toArrayBuffer(blob));
     cleanup.push(() => reader.delete());
 
     const sink = mod.make.WriterSink();
@@ -21,7 +22,7 @@ export async function transformBlob(
 
     const result = transformer.Transform(writer, reader);
     if (result !== TransformResult.OK) {
-      throw new Error(`transform failed with error: ${TransformResult[result]} (${result})`);
+      throw new Error(`transformer<${transformer.Name}> failed with error: ${TransformResult[result]} (${result})`);
     }
 
     return sink.collectBlob();

src/decrypt-worker/worker/handler/decrypt.ts

@@ -46,17 +46,24 @@ class DecryptCommandHandler {
       return null;
     }
 
-    const decrypted = await this.log('decrypt', async () => crypto.decrypt(this.buffer, this.blob));
+    const decrypted = await this.log(`decrypt (${crypto.cryptoName})`, () => crypto.decrypt(this.buffer, this.blob));
 
     // Check if we had a successful decryption
-    const audioExt = await this.log(`detect-audio-ext`, async () => {
-      const header = await toArrayBuffer(decrypted.slice(0, TEST_FILE_HEADER_LEN));
-      return this.parakeet.detectAudioExtension(header);
-    });
+    const audioExt = crypto.overrideExtension ?? (await this.detectAudioExtension(decrypted));
+    if (crypto.checkByDecryptHeader && audioExt === 'bin') {
+      return null;
+    }
 
     return { decrypted: URL.createObjectURL(toBlob(decrypted)), ext: audioExt };
   }
 
+  async detectAudioExtension(data: Blob | ArrayBuffer): Promise<string> {
+    return this.log(`detect-audio-ext`, async () => {
+      const header = await toArrayBuffer(data.slice(0, TEST_FILE_HEADER_LEN));
+      return this.parakeet.detectAudioExtension(header);
+    });
+  }
+
   async acceptByDecryptFileHeader(crypto: CryptoBase): Promise<boolean> {
     // File too small, ignore.
     if (this.buffer.byteLength <= TEST_FILE_HEADER_LEN) {