Precache the first and last parts of Google Drive MP3s to reduce the

number of requests when using accurate tagging.

ext/clementine-tagreader/googledrivestream.cpp

@@ -25,7 +25,11 @@
 
 #include <taglib/id3v2framefactory.h>
 #include <taglib/mpegfile.h>
-using TagLib::ByteVector;
+
+namespace {
+  static const int kTaglibPrefixCacheBytes = 64 * 1024;  // Should be enough.
+  static const int kTaglibSuffixCacheBytes = 2 * 1024;
+}
 
 GoogleDriveStream::GoogleDriveStream(
     const QUrl& url, const QString& filename, const long length,
@@ -37,7 +41,8 @@ GoogleDriveStream::GoogleDriveStream(
       auth_(auth),
       cursor_(0),
       network_(network),
-      cache_(length) {
+      cache_(length),
+      num_requests_(0) {
 }
 
 TagLib::FileName GoogleDriveStream::name() const {
@@ -68,6 +73,25 @@ TagLib::ByteVector GoogleDriveStream::GetCached(int start, int end) {
   return ret;
 }
 
+void GoogleDriveStream::Precache() {
+  // For reading the tags of an MP3, TagLib tends to request:
+  // 1. The first 1024 bytes
+  // 2. Somewhere between the first 2KB and first 60KB
+  // 3. The last KB or two.
+  // 4. Somewhere in the first 64KB again
+  //
+  // So, if we precache the first 64KB and the last 2KB we should be sorted :-)
+  // Ideally, we would use bytes=0-655364,-2048 but Google Drive does not seem
+  // to support multipart byte ranges yet so we have to make do with two
+  // requests.
+
+  seek(0, TagLib::IOStream::Beginning);
+  readBlock(kTaglibPrefixCacheBytes);
+  seek(kTaglibSuffixCacheBytes, TagLib::IOStream::End);
+  readBlock(kTaglibSuffixCacheBytes);
+  clear();
+}
+
 TagLib::ByteVector GoogleDriveStream::readBlock(ulong length) {
   const uint start = cursor_;
   const uint end = qMin(cursor_ + length - 1, length_ - 1);
@@ -89,6 +113,7 @@ TagLib::ByteVector GoogleDriveStream::readBlock(ulong length) {
       "Range", QString("bytes=%1-%2").arg(start).arg(end).toUtf8());
 
   QNetworkReply* reply = network_->get(request);
+  ++num_requests_;
 
   QEventLoop loop;
   QObject::connect(reply, SIGNAL(finished()), &loop, SLOT(quit()));
@@ -103,11 +128,11 @@ TagLib::ByteVector GoogleDriveStream::readBlock(ulong length) {
   return bytes;
 }
 
-void GoogleDriveStream::writeBlock(const ByteVector&) {
+void GoogleDriveStream::writeBlock(const TagLib::ByteVector&) {
   qLog(Debug) << Q_FUNC_INFO << "not implemented";
 }
 
-void GoogleDriveStream::insert(const ByteVector&, ulong, ulong) {
+void GoogleDriveStream::insert(const TagLib::ByteVector&, ulong, ulong) {
   qLog(Debug) << Q_FUNC_INFO << "not implemented";
 }
 

ext/clementine-tagreader/googledrivestream.h

@@ -47,6 +47,17 @@ class GoogleDriveStream : public TagLib::IOStream {
   virtual long length();
   virtual void truncate(long);
 
+  google::sparsetable<char>::size_type cached_bytes() const {
+    return cache_.num_nonempty();
+  }
+
+  int num_requests() const {
+    return num_requests_;
+  }
+
+  // Use educated guess to request the bytes that TagLib will probably want.
+  void Precache();
+
  private:
   bool CheckCache(int start, int end);
   void FillCache(int start, TagLib::ByteVector data);
@@ -63,6 +74,7 @@ class GoogleDriveStream : public TagLib::IOStream {
   QNetworkAccessManager* network_;
 
   google::sparsetable<char> cache_;
+  int num_requests_;
 };
 
 #endif // GOOGLEDRIVESTREAM_H

ext/clementine-tagreader/tagreaderworker.cpp

@@ -616,10 +616,11 @@ void TagReaderWorker::ReadGoogleDrive(const QUrl& download_url,
 
   GoogleDriveStream* stream = new GoogleDriveStream(
       download_url, title, size, access_token, network_);
+  stream->Precache();
   TagLib::MPEG::File tag(
       stream,  // Takes ownership.
       TagLib::ID3v2::FrameFactory::instance(),
-      TagLib::AudioProperties::Fast);
+      TagLib::AudioProperties::Accurate);
   if (tag.tag()) {
     song->set_title(tag.tag()->title().toCString(true));
     song->set_artist(tag.tag()->artist().toCString(true));
@@ -631,6 +632,10 @@ void TagReaderWorker::ReadGoogleDrive(const QUrl& download_url,
     if (tag.audioProperties()) {
       song->set_length_nanosec(tag.audioProperties()->length() * kNsecPerSec);
     }
+    qLog(Debug) << "Google Drive Tagging Stats for:"
+                << song->title().c_str();
+    qLog(Debug) << "Downloaded bytes:" << stream->cached_bytes()
+                << "Number of requests:" << stream->num_requests();
   }
 }
 #endif // HAVE_GOOGLE_DRIVE