[depends] patch taglib: Efficient lookup for an ID3v2 tag in MPEG files with garbage.

2 files changed, 74 insertions, 1 deletions

diff --git a/tools/depends/target/taglib/ID3v2Lookup.patch b/tools/depends/target/taglib/ID3v2Lookup.patch
new file mode 100644
index 0000000000..b31cf6a089
--- /dev/null
+++ b/tools/depends/target/taglib/ID3v2Lookup.patch
@@ -0,0 +1,72 @@
+From d2e0e5522308ce4c905c205c7bf5972ea71cd6e5 Mon Sep 17 00:00:00 2001
+From: Tsuda Kageyu <tsuda.kageyu@gmail.com>
+Date: Fri, 20 Jan 2017 21:14:38 +0900
+Subject: [PATCH] Efficient lookup for an ID3v2 tag in MPEG files with garbage.
+
+This looks for an ID3v2 tag until reaching the first valid MPEG frame in O(n) time.
+---
+ taglib/mpeg/mpegfile.cpp | 45 +++++++++++++++++++++++++++++----------------
+ 1 file changed, 29 insertions(+), 16 deletions(-)
+
+diff --git a/taglib/mpeg/mpegfile.cpp b/taglib/mpeg/mpegfile.cpp
+index af7253f..c634eeb 100644
+--- a/taglib/mpeg/mpegfile.cpp
++++ b/taglib/mpeg/mpegfile.cpp
+@@ -488,28 +488,41 @@ long MPEG::File::findID3v2()
+   const ByteVector headerID = ID3v2::Header::fileIdentifier();
+ 
+   seek(0);
++  if(readBlock(headerID.size()) == headerID)
++    return 0;
+ 
+-  const ByteVector data = readBlock(headerID.size());
+-  if(data.size() < headerID.size())
++  Header firstHeader(this, 0, true);
++  if(firstHeader.isValid())
+     return -1;
+ 
+-  if(data == headerID)
+-    return 0;
++  // Look for an ID3v2 tag until reaching the first valid MPEG frame.
+ 
+-  if(firstSyncByte(data[0]) && secondSynchByte(data[1]))
+-    return -1;
++  char frameSyncBytes[2] = {};
++  char tagHeaderBytes[4] = {};
++  long position = 0;
+ 
+-  // Look for the entire file, if neither an MEPG frame or ID3v2 tag was found
+-  // at the beginning of the file.
+-  // We don't care about the inefficiency of the code, since this is a seldom case.
++  while(true) {
++    seek(position);
++    const ByteVector buffer = readBlock(bufferSize());
++    if(buffer.isEmpty())
++      return -1;
+ 
+-  const long tagOffset = find(headerID);
+-  if(tagOffset < 0)
+-    return -1;
++    for(unsigned int i = 0; i < buffer.size(); ++i) {
++      frameSyncBytes[0] = frameSyncBytes[1];
++      frameSyncBytes[1] = buffer[i];
++      if(firstSyncByte(frameSyncBytes[0]) && secondSynchByte(frameSyncBytes[1])) {
++        Header header(this, position + i - 1, true);
++        if(header.isValid())
++          return -1;
++      }
+ 
+-  const long frameOffset = firstFrameOffset();
+-  if(frameOffset < tagOffset)
+-    return -1;
++      tagHeaderBytes[0] = tagHeaderBytes[1];
++      tagHeaderBytes[1] = tagHeaderBytes[2];
++      tagHeaderBytes[2] = buffer[i];
++      if(headerID == tagHeaderBytes)
++        return position + i - 2;
++    }
+ 
+-  return tagOffset;
++    position += bufferSize();
++  }
+ }
diff --git a/tools/depends/target/taglib/Makefile b/tools/depends/target/taglib/Makefile
index bc619c045b..069de1a65c 100644
--- a/tools/depends/target/taglib/Makefile
+++ b/tools/depends/target/taglib/Makefile
@@ -1,5 +1,5 @@
 include ../../Makefile.include
-DEPS= ../../Makefile.include Makefile
+DEPS= ../../Makefile.include Makefile ID3v2Lookup.patch
 
 LIBNAME=taglib
 VERSION=1.11
@@ -16,6 +16,7 @@ $(PLATFORM): $(TARBALLS_LOCATION)/$(ARCHIVE) $(DEPS)
 	rm -rf $(PLATFORM); mkdir -p $(PLATFORM)
 	cd $(PLATFORM); $(ARCHIVE_TOOL) $(ARCHIVE_TOOL_FLAGS) $(TARBALLS_LOCATION)/$(ARCHIVE)
 	cd $(PLATFORM); rm -rf build; mkdir -p build
+	cd $(PLATFORM); patch -p1 -i ../ID3v2Lookup.patch
 	cd $(PLATFORM)/build; $(CMAKE) -DCMAKE_LIBRARY_PATH=$(TOOLCHAIN)/lib/$(HOST) -DBUILD_SHARED_LIBS=OFF ..
 
 $(LIBDYLIB): $(PLATFORM)