Enable FileRef to detect file types by the actual content of a stream.

FileRef doesn't work with ByteVectorStream as reported at #796, since ByteVectorStream is not associated with a file name and FileRef detects file types based on file extensions.
This commit makes FileRef to work with ByteVectorStream by enabling it to detect file types based on the actual content of a stream.

taglib/ogg/flac/oggflacfile.cpp

@@ -27,6 +27,7 @@
 #include <tstring.h>
 #include <tdebug.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include <xiphcomment.h>
 #include "oggflacfile.h"
@@ -65,6 +66,18 @@ public:
   int commentPacket;
 };
 
+////////////////////////////////////////////////////////////////////////////////
+// static members
+////////////////////////////////////////////////////////////////////////////////
+
+bool Ogg::FLAC::File::isValidStream(IOStream *stream)
+{
+  // An Ogg FLAC file has IDs "OggS" and "fLaC" somewhere.
+
+  const ByteVector buffer = Utils::readHeader(stream, bufferSize(), false);
+  return (buffer.find("OggS") >= 0 && buffer.find("fLaC") >= 0);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // public members
 ////////////////////////////////////////////////////////////////////////////////

taglib/ogg/flac/oggflacfile.h

@@ -143,6 +143,14 @@ namespace TagLib {
        */
       bool hasXiphComment() const;
 
+      /*!
+       * Check if the given \a stream can be opened as an Ogg FLAC file.
+       *
+       * \note This method is designed to do a quick check.  The result may
+       * not necessarily be correct.
+       */
+      static bool isValidStream(IOStream *stream);
+
     private:
       File(const File &);
       File &operator=(const File &);

taglib/ogg/opus/opusfile.cpp

@@ -30,6 +30,7 @@
 #include <tstring.h>
 #include <tdebug.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include "opusfile.h"
 
@@ -53,6 +54,18 @@ public:
   Properties *properties;
 };
 
+////////////////////////////////////////////////////////////////////////////////
+// static members
+////////////////////////////////////////////////////////////////////////////////
+
+bool Ogg::Opus::File::isValidStream(IOStream *stream)
+{
+  // An Opus file has IDs "OggS" and "OpusHead" somewhere.
+
+  const ByteVector buffer = Utils::readHeader(stream, bufferSize(), false);
+  return (buffer.find("OggS") >= 0 && buffer.find("OpusHead") >= 0);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // public members
 ////////////////////////////////////////////////////////////////////////////////

taglib/ogg/opus/opusfile.h

@@ -113,6 +113,15 @@ namespace TagLib {
          */
         virtual bool save();
 
+        /*!
+         * Returns whether or not the given \a stream can be opened as an Opus
+         * file.
+         *
+         * \note This method is designed to do a quick check.  The result may
+         * not necessarily be correct.
+         */
+        static bool isValidStream(IOStream *stream);
+
       private:
         File(const File &);
         File &operator=(const File &);

taglib/ogg/speex/speexfile.cpp

@@ -30,6 +30,7 @@
 #include <tstring.h>
 #include <tdebug.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include "speexfile.h"
 
@@ -53,6 +54,18 @@ public:
   Properties *properties;
 };
 
+////////////////////////////////////////////////////////////////////////////////
+// static members
+////////////////////////////////////////////////////////////////////////////////
+
+bool Ogg::Speex::File::isValidStream(IOStream *stream)
+{
+  // A Speex file has IDs "OggS" and "Speex   " somewhere.
+
+  const ByteVector buffer = Utils::readHeader(stream, bufferSize(), false);
+  return (buffer.find("OggS") >= 0 && buffer.find("Speex   ") >= 0);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // public members
 ////////////////////////////////////////////////////////////////////////////////

taglib/ogg/speex/speexfile.h

@@ -113,6 +113,15 @@ namespace TagLib {
          */
         virtual bool save();
 
+        /*!
+         * Returns whether or not the given \a stream can be opened as a Speex
+         * file.
+         *
+         * \note This method is designed to do a quick check.  The result may
+         * not necessarily be correct.
+         */
+        static bool isValidStream(IOStream *stream);
+
       private:
         File(const File &);
         File &operator=(const File &);

taglib/ogg/vorbis/vorbisfile.cpp

@@ -28,10 +28,10 @@
 #include <tstring.h>
 #include <tdebug.h>
 #include <tpropertymap.h>
+#include <tagutils.h>
 
 #include "vorbisfile.h"
 
-
 using namespace TagLib;
 
 class Vorbis::File::FilePrivate
@@ -59,6 +59,18 @@ namespace TagLib {
   static const char vorbisCommentHeaderID[] = { 0x03, 'v', 'o', 'r', 'b', 'i', 's', 0 };
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// static members
+////////////////////////////////////////////////////////////////////////////////
+
+bool Vorbis::File::isValidStream(IOStream *stream)
+{
+  // An Ogg Vorbis file has IDs "OggS" and "\x01vorbis" somewhere.
+
+  const ByteVector buffer = Utils::readHeader(stream, bufferSize(), false);
+  return (buffer.find("OggS") >= 0 && buffer.find("\x01vorbis") >= 0);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // public members
 ////////////////////////////////////////////////////////////////////////////////

taglib/ogg/vorbis/vorbisfile.h

@@ -121,6 +121,14 @@ namespace TagLib {
        */
       virtual bool save();
 
+      /*!
+       * Check if the given \a stream can be opened as an Ogg Vorbis file.
+       *
+       * \note This method is designed to do a quick check.  The result may
+       * not necessarily be correct.
+       */
+      static bool isValidStream(IOStream *stream);
+
     private:
       File(const File &);
       File &operator=(const File &);