/// <summary>Reads IPTC values and returns them in an <see cref="IptcDirectory"/>.</summary>
/// <remarks>
/// Note that IPTC data does not describe its own length, hence <paramref name="length"/> is required.
/// </remarks>
public IptcDirectory Extract([NotNull] SequentialReader reader, long length)
{
var directory = new IptcDirectory();
var offset = 0;
// for each tag
while (offset < length)
{
// identifies start of a tag
byte startByte;
try
{
startByte = reader.GetByte();
offset++;
}
catch (IOException)
{
directory.AddError("Unable to read starting byte of IPTC tag");
break;
}
if (startByte != IptcMarkerByte)
{
// NOTE have seen images where there was one extra byte at the end, giving
// offset==length at this point, which is not worth logging as an error.
if (offset != length)
directory.AddError($"Invalid IPTC tag marker at offset {offset - 1}. Expected '0x{IptcMarkerByte:X2}' but got '0x{startByte:X}'.");
break;
}
// we need at least five bytes left to read a tag
if (offset + 5 >= length)
{
directory.AddError("Too few bytes remain for a valid IPTC tag");
break;
}
int directoryType;
int tagType;
int tagByteCount;
try
{
directoryType = reader.GetByte();
tagType = reader.GetByte();
// TODO support Extended DataSet Tag (see 1.5(c), p14, IPTC-IIMV4.2.pdf)
tagByteCount = reader.GetUInt16();
offset += 4;
}
catch (IOException)
{
directory.AddError("IPTC data segment ended mid-way through tag descriptor");
break;
}
if (offset + tagByteCount > length)
{
directory.AddError("Data for tag extends beyond end of IPTC segment");
break;
}
try
{
ProcessTag(reader, directory, directoryType, tagType, tagByteCount);
}
catch (IOException)
{
directory.AddError("Error processing IPTC tag");
break;
}
offset += tagByteCount;
}
return directory;
}
/// <summary>Reads IPTC values and returns them in an <see cref="IptcDirectory"/>.</summary>
/// <remarks>
/// Note that IPTC data does not describe its own length, hence <paramref name="length"/> is required.
/// </remarks>
public IptcDirectory Extract(SequentialReader reader, long length)
{
var directory = new IptcDirectory();
var offset = 0;
// for each tag
while (offset < length)
{
// identifies start of a tag
byte startByte;
try
{
startByte = reader.GetByte();
offset++;
}
catch (IOException)
{
directory.AddError("Unable to read starting byte of IPTC tag");
break;
}
if (startByte != IptcMarkerByte)
{
// NOTE have seen images where there was one extra byte at the end, giving
// offset==length at this point, which is not worth logging as an error.
if (offset != length)
{
directory.AddError($"Invalid IPTC tag marker at offset {offset - 1}. Expected '0x{IptcMarkerByte:x2}' but got '0x{startByte:x}'.");
}
break;
}
// we need at least four bytes left to read a tag
if (offset + 4 > length)
{
directory.AddError("Too few bytes remain for a valid IPTC tag");
break;
}
int directoryType;
int tagType;
int tagByteCount;
try
{
directoryType = reader.GetByte();
tagType = reader.GetByte();
tagByteCount = reader.GetUInt16();
if (tagByteCount > 0x7FFF)
{
// Extended DataSet Tag (see 1.5(c), p14, IPTC-IIMV4.2.pdf)
tagByteCount = ((tagByteCount & 0x7FFF) << 16) | reader.GetUInt16();
offset += 2;
}
offset += 4;
}
catch (IOException)
{
directory.AddError("IPTC data segment ended mid-way through tag descriptor");
break;
}
if (offset + tagByteCount > length)
{
directory.AddError("Data for tag extends beyond end of IPTC segment");
break;
}
try
{
ProcessTag(reader, directory, directoryType, tagType, tagByteCount);
}
catch (IOException)
{
directory.AddError("Error processing IPTC tag");
break;
}
offset += tagByteCount;
}
return(directory);
}
public IptcDirectoryTests()
{
_directory = new IptcDirectory();
}
