From 83aa01c6af938a067010fee87ac8b9cceae5c2ff Mon Sep 17 00:00:00 2001
From: Urs Fleisch <ufleisch@users.sourceforge.net>
Date: Mon, 8 Feb 2021 10:41:25 +0100
Subject: [PATCH] Ogg: Set granule position to -1 if no packets finish on page
 (#864)

---
 taglib/ogg/oggpage.cpp |  6 ++++++
 tests/test_ogg.cpp     | 28 ++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/taglib/ogg/oggpage.cpp b/taglib/ogg/oggpage.cpp
index 414d3d53..8cd15a5c 100644
--- a/taglib/ogg/oggpage.cpp
+++ b/taglib/ogg/oggpage.cpp
@@ -305,4 +305,10 @@ Ogg::Page::Page(const ByteVectorList &packets,
   }
   d->packets = packets;
   d->header.setPacketSizes(packetSizes);
+
+  // https://xiph.org/ogg/doc/framing.html, absolute granule position:
+  // A special value of '-1' (in two's complement) indicates that no packets
+  // finish on this page.
+  if(!lastPacketCompleted && packets.size() <= 1)
+    d->header.setAbsoluteGranularPosition(-1);
 }
diff --git a/tests/test_ogg.cpp b/tests/test_ogg.cpp
index 6564a247..0008429e 100644
--- a/tests/test_ogg.cpp
+++ b/tests/test_ogg.cpp
@@ -48,6 +48,7 @@ class TestOGG : public CppUnit::TestFixture
   CPPUNIT_TEST(testDictInterface2);
   CPPUNIT_TEST(testAudioProperties);
   CPPUNIT_TEST(testPageChecksum);
+  CPPUNIT_TEST(testPageGranulePosition);
   CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -222,6 +223,33 @@ public:
 
   }
 
+  void testPageGranulePosition()
+  {
+    ScopedFileCopy copy("empty", ".ogg");
+    {
+      Vorbis::File f(copy.fileName().c_str());
+      // Force the Vorbis comment packet to span more than one page and
+      // check if the granule position is -1 indicating that no packets
+      // finish on this page.
+      f.tag()->setComment(String(ByteVector(70000, 'A')));
+      f.save();
+
+      f.seek(0x3a);
+      CPPUNIT_ASSERT_EQUAL(ByteVector("OggS\0\0", 6), f.readBlock(6));
+      CPPUNIT_ASSERT_EQUAL(static_cast<long long>(-1), f.readBlock(8).toLongLong());
+    }
+    {
+      Vorbis::File f(copy.fileName().c_str());
+      // Use a small Vorbis comment package which ends on the seconds page and
+      // check if the granule position is zero.
+      f.tag()->setComment("A small comment");
+      f.save();
+
+      f.seek(0x3a);
+      CPPUNIT_ASSERT_EQUAL(ByteVector("OggS\0\0", 6), f.readBlock(6));
+      CPPUNIT_ASSERT_EQUAL(static_cast<long long>(0), f.readBlock(8).toLongLong());
+    }
+  }
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(TestOGG);