Empty WCOM fields in id3v2 tags

[Mike Dawson]

Hi All,

 

We've ran across quite a few tracks with empty WCOM frames in id3v2 tags. 

            - Contents of WCOM:

                        * frameID=WCOM

                        * frameSize = 0                                      

                        * d->dataLengthIndicator = false

 

Taglib rejects the frame as invalid in id3v2framefactory.cpp and id3v2tag.cpp and invalidates the complete tag.

According to //id3.org/id3v2.3.0 the frame is actually illegal, so taglibs reaction is technically correct.



3.3. ID3v2 frame overview

    A tag must contain at least one frame. A frame must be at least 1 byte big, excluding the

    header.

 

However, many other parsers skip the bad frame and continue parsing the tag, for instance

Winamp, Mp3tag, iTunes. Would a better method be to check for a valid field following the empty field,

and then continue parsing?

 

Although the same issue exists for the code in taglib.git at master, for illustration of the problem and not a suggested fix, 

the following two patches to version 1.7 allow the id3v2 tags with empty WCOM fields to be parsed:

 ===========================

diff --git a/taglib-1.7/taglib/mpeg/id3v2/id3v2framefactory.cpp b/taglib-1.7/taglib/mpeg/id3v2/id3v2framefactory.cpp

index c531aaa..4fab414 100755

--- a/taglib-1.7/taglib/mpeg/id3v2/id3v2framefactory.cpp

+++ b/taglib-1.7/taglib/mpeg/id3v2/id3v2framefactory.cpp

@@ -105,9 +105,12 @@ Frame *FrameFactory::createFrame(const ByteVector &origData, Header *tagHeader)

 

   // A quick sanity check -- make sure that the frameID is 4 uppercase Latin1

   // characters.  Also make sure that there is data in the frame.

-

-  if(!frameID.size() == (version < 3 ? 3 : 4) ||

+//MED 

+/*  if(!frameID.size() == (version < 3 ? 3 : 4) ||

      header->frameSize() <= uint(header->dataLengthIndicator() ? 4 : 0) ||

+ */

+  if(frameID.size() != (version < 3 ? 3 : 4) ||                      /*1.8 fix*/

+     (header->dataLengthIndicator() &&  (header->frameSize() <= uint(4)) ) || /*Empty URL fix*/

      header->frameSize() > data.size())

   {

     delete header;



=======================

diff --git a/taglib-1.7/taglib/mpeg/id3v2/id3v2tag.cpp b/taglib-1.7/taglib/mpeg/id3v2/id3v2tag.cpp
index 7e8012b..3fb5148 100755
--- a/taglib-1.7/taglib/mpeg/id3v2/id3v2tag.cpp
+++ b/taglib-1.7/taglib/mpeg/id3v2/id3v2tag.cpp
@@ -446,12 +446,14 @@ void ID3v2::Tag::parse(const ByteVector &origData)
       return;
 
     // Checks to make sure that frame parsed correctly.
-
-    if(frame->size() <= 0) {
+//MED - empty URL fix
+//Add check somehow for frame.d.header.d.dataLengthIndicator()
+// if(frame->size() <=0 && frame.d.header.d.dataLengthIndicator()
+/*    if(frame->size() <= 0) {
       delete frame;
       return;
     }
-
+*/
     frameDataPosition += frame->size() + Frame::headerSize(d->header.majorVersion());
     addFrame(frame);
   }


Thanks for any help.


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