From: Tsuda Kageyu <tsuda.kageyu@gmail.com>
Date: Wed, 2 Nov 2016 06:44:50 +0000 (+0900)
Subject: Proper handling of MP4 atoms with zero length.
X-Git-Tag: v1.12-beta-1~122^2
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=f5ca097379b270d1f92368e283d30f8703161645;p=taglib

Proper handling of MP4 atoms with zero length.

If the size of an atom is 0, it designates the last atom which extends to the end of the file.
---

diff --git a/taglib/mp4/mp4atom.cpp b/taglib/mp4/mp4atom.cpp
index 5758173b..20709212 100644
--- a/taglib/mp4/mp4atom.cpp
+++ b/taglib/mp4/mp4atom.cpp
@@ -54,10 +54,15 @@ MP4::Atom::Atom(File *file)
 
   length = header.toUInt();
 
-  if(length == 1) {
+  if(length == 0) {
+    // The last atom which extends to the end of the file.
+    length = file->length() - offset;
+  }
+  else if(length == 1) {
+    // The atom has a 64-bit length.
     const long long longLength = file->readBlock(8).toLongLong();
     if(longLength <= LONG_MAX) {
-      // The atom has a 64-bit length, but it's actually a 31-bit value or long is 64-bit.
+      // The actual length fits in long. That's always the case if long is 64-bit.
       length = static_cast<long>(longLength);
     }
     else {
@@ -67,6 +72,7 @@ MP4::Atom::Atom(File *file)
       return;
     }
   }
+
   if(length < 8) {
     debug("MP4: Invalid atom size");
     length = 0;
diff --git a/tests/data/zero-length-mdat.m4a b/tests/data/zero-length-mdat.m4a
new file mode 100644
index 00000000..578d2ef7
Binary files /dev/null and b/tests/data/zero-length-mdat.m4a differ
diff --git a/tests/test_mp4.cpp b/tests/test_mp4.cpp
index dd36b21b..bc0ac01d 100644
--- a/tests/test_mp4.cpp
+++ b/tests/test_mp4.cpp
@@ -57,6 +57,7 @@ class TestMP4 : public CppUnit::TestFixture
   CPPUNIT_TEST(testProperties);
   CPPUNIT_TEST(testFuzzedFile);
   CPPUNIT_TEST(testRepeatedSave);
+  CPPUNIT_TEST(testWithZeroLengthAtom);
   CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -395,6 +396,15 @@ public:
     CPPUNIT_ASSERT_EQUAL(2862L, f.find("0123456789"));
     CPPUNIT_ASSERT_EQUAL(-1L, f.find("0123456789", 2863));
   }
+
+  void testWithZeroLengthAtom()
+  {
+    MP4::File f(TEST_FILE_PATH_C("zero-length-mdat.m4a"));
+    CPPUNIT_ASSERT(f.isValid());
+    CPPUNIT_ASSERT_EQUAL(1115, f.audioProperties()->lengthInMilliseconds());
+    CPPUNIT_ASSERT_EQUAL(22050, f.audioProperties()->sampleRate());
+  }
+
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(TestMP4);