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tagparser
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Detect APE tags, emit according messages and update README 

It is likely not worth adding support for APE tags at this point.
However, it still makes sense to acknowledge the presence of them
despite not being actually supported to avoid possible confusion.

With this change, APE tags at the beginning of the file will be
dropped when applying changes as the container offset is updated
when skipping the tag. I suppose that makes sense considering
putting those tags at the beginning is not recommended anyways.
The diag messages and README have been updated accordingly.
This commit is contained in:
Martchus 2023-05-06 13:04:01 +02:00
parent 9e4d221bb1
commit 0a2b948f26
4 changed files with 51 additions and 2 deletions
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8
README.md
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@ -7,11 +7,19 @@ The tag library can read and write the following tag formats:
* iTunes-style MP4/M4A tags (MP4-DASH is supported)
* ID3v1 and ID3v2 tags
* conversion between ID3v1 and different versions of ID3v2 is possible
* mainly for use in MP3 files but can be added to any kind of file
* Vorbis, Opus and FLAC comments in Ogg streams
* cover art via "METADATA_BLOCK_PICTURE" is supported
* Vorbis comments and "METADATA_BLOCK_PICTURE" in raw FLAC streams
* Matroska/WebM tags and attachments
Further remarks:
* Unsupported file contents (such as unsupported tag formats) are *generally* preserved as-is.
* Note that APE tags are *not* supported. APE tags in the beginning of a file are strongly
unrecommended and thus discarded when applying changes. APE tags at the end of the file
are preserved as-is when applying changes.
## File layout options
### Tag position
The library allows you to choose whether tags should be placed at the beginning or at

39
mediafileinfo.cpp
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@ -254,6 +254,23 @@ startParsingSignature:
static_cast<OggContainer *>(m_container.get())->setChecksumValidationEnabled(isForcingFullParse());
break;
case ContainerFormat::Unknown:
case ContainerFormat::ApeTag:
// skip APE tag if the specified size makes sense at all
if (m_containerFormat == ContainerFormat::ApeTag) {
if (const auto apeEnd = m_containerOffset + 32 + LE::toUInt32(buff + 12); apeEnd <= static_cast<std::streamoff>(size())) {
// take record of APE tag
diag.emplace_back(DiagLevel::Critical,
argsToString("Found an APE tag at the beginning of the file at offset ", m_containerOffset,
". This tag format is not supported and the tag will therefore be ignored. It will NOT be preserved when saving as "
"placing an APE tag at the beginning of a file is strongly unrecommended."),
context);
// continue reading signature
m_containerOffset = apeEnd;
goto startParsingSignature;
}
m_containerFormat = ContainerFormat::Unknown;
}
// check for magic numbers at odd offsets
// -> check for tar (magic number at offset 0x101)
if (size() > 0x107) {
@ -378,12 +395,14 @@ void MediaFileInfo::parseTags(Diagnostics &diag, AbortableProgressFeedback &prog
static const string context("parsing tag");
// check for ID3v1 tag
if (size() >= 128) {
auto effectiveSize = static_cast<std::streamoff>(size());
if (effectiveSize >= 128) {
m_id3v1Tag = make_unique<Id3v1Tag>();
try {
stream().seekg(-128, ios_base::end);
stream().seekg(effectiveSize - 128, std::ios_base::beg);
m_id3v1Tag->parse(stream(), diag);
m_fileStructureFlags += MediaFileStructureFlags::ActualExistingId3v1Tag;
effectiveSize -= 128;
} catch (const NoDataFoundException &) {
m_id3v1Tag.reset();
} catch (const OperationAbortedException &) {
@ -395,6 +414,22 @@ void MediaFileInfo::parseTags(Diagnostics &diag, AbortableProgressFeedback &prog
}
}
// check for APE tag at the end of the file (APE tags a the beginning are already covered when parsing the container format)
if (constexpr auto apeHeaderSize = 32; effectiveSize >= apeHeaderSize) {
const auto footerOffset = effectiveSize - apeHeaderSize;
char buffer[apeHeaderSize];
stream().seekg(footerOffset, std::ios_base::beg);
stream().read(buffer, sizeof(buffer));
if (BE::toUInt64(buffer) == 0x4150455441474558ul /* APETAGEX */) {
// take record of APE tag
const auto tagSize = static_cast<std::streamoff>(LE::toUInt32(buffer + 12));
diag.emplace_back(DiagLevel::Warning,
argsToString("Found an APE tag at the end of the file at offset ", (footerOffset - tagSize),
". This tag format is not supported and the tag will therefore be ignored. It will be preserved when saving as-is."),
context);
}
}
// check for ID3v2 tags: the offsets of the ID3v2 tags have already been parsed when parsing the container format
m_id3v2Tags.clear();
for (const auto offset : m_actualId3v2TagOffsets) {

5
signature.cpp
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@ -13,6 +13,7 @@ namespace TagParser {
* \brief Holds 64-bit signatures.
*/
enum Sig64 : std::uint64_t {
ApeTag = 0x4150455441474558ul, // APETAGEX
Ar = 0x213C617263683E0A,
Asf1 = 0x3026B2758E66CF11ul,
Asf2 = 0xA6D900AA0062CE6Cul,
@ -126,6 +127,8 @@ ContainerFormat parseSignature(std::string_view buffer)
}
// return corresponding container format
switch (sig) { // check 64-bit signatures
case ApeTag:
return ContainerFormat::ApeTag;
case Ar:
return ContainerFormat::Ar;
case Asf1:
@ -490,6 +493,8 @@ std::string_view containerFormatName(ContainerFormat containerFormat)
return "Zstandard compressed file";
case ContainerFormat::Id2v2Tag:
return "ID3v2 tag";
case ContainerFormat::ApeTag:
return "APE tag";
default:
return "unknown";
}

1
signature.h
View File

@ -67,6 +67,7 @@ enum class ContainerFormat : unsigned int {
Zip, /**< ZIP archive */
Aiff, /**< Audio Interchange File Format */
Zstd, /**< Zstandard-compressed data */
ApeTag, /**< APE tag */
};
TAG_PARSER_EXPORT ContainerFormat parseSignature(const char *buffer, std::size_t bufferSize);