ID3v2: Render at most 255 child elements in a CTOC frame (#1479)

The entry count is a single byte, so a table of more than 255 children wrapped the count while still writing every child element ID, and readers took the surplus IDs as embedded frames. Render the first 255 with a matching count, as renderChplData does for Nero chapters.

taglib/mpeg/id3v2/frames/tableofcontentsframe.cpp

@@ -25,6 +25,7 @@
 
 #include "tableofcontentsframe.h"
 
+#include <algorithm>
 #include <utility>
 
 #include "tpropertymap.h"
@@ -293,8 +294,13 @@ ByteVector TableOfContentsFrame::renderFields() const
   if(d->isOrdered)
     flags += 1;
   data.append(flags);
-  data.append(static_cast<char>(entryCount()));
+  // The entry count is a single byte, so only the first 255 child elements are rendered.
+  const unsigned int count = std::min(entryCount(), 255U);
+  data.append(static_cast<char>(count));
+  unsigned int i = 0;
   for(const auto &element : std::as_const(d->childElements)) {
+    if(i++ >= count)
+      break;
     data.append(element);
     data.append('\0');
   }

tests/test_id3v2.cpp

@@ -137,6 +137,7 @@ class TestID3v2 : public CppUnit::TestFixture
   CPPUNIT_TEST(testRenderChapterFrame);
   CPPUNIT_TEST(testParseTableOfContentsFrame);
   CPPUNIT_TEST(testRenderTableOfContentsFrame);
+  CPPUNIT_TEST(testRenderTableOfContentsFrameWithManyChildren);
   CPPUNIT_TEST(testShrinkPadding);
   CPPUNIT_TEST(testEmptyFrame);
   CPPUNIT_TEST(testDuplicateTags);
@@ -1707,6 +1708,28 @@ public:
       f.render());
   }
 
+  void testRenderTableOfContentsFrameWithManyChildren()
+  {
+    const unsigned int counts[] = { 255, 256, 300 };
+    for(unsigned int count : counts) {
+      ID3v2::Header header;
+      ID3v2::TableOfContentsFrame f(&header, "CTOC");
+      f.setElementID("T");
+      for(unsigned int i = 0; i < count; ++i)
+        f.addChildElement(ByteVector("C") + ByteVector(String::number(i).toCString()));
+      auto eF = new ID3v2::TextIdentificationFrame("TIT2");
+      eF->setText("TC1");
+      f.addEmbeddedFrame(eF);
+
+      ID3v2::TableOfContentsFrame parsed(&header, f.render());
+      CPPUNIT_ASSERT_EQUAL(255U, parsed.entryCount());
+      CPPUNIT_ASSERT_EQUAL(ByteVector("C254"), parsed.childElements().back());
+      CPPUNIT_ASSERT_EQUAL(1U, parsed.embeddedFrameList().size());
+      CPPUNIT_ASSERT_EQUAL(ByteVector("TIT2"),
+                           parsed.embeddedFrameList().front()->frameID());
+    }
+  }
+
   void testShrinkPadding()
   {
     ScopedFileCopy copy("xing", ".mp3");