private bool TryReadValue(out ExifValue exifValue)
{
// 2 | 2 | 4 | 4
// tag | type | count | value offset
if (this.RemainingLength < 12)
{
exifValue = default;
return(false);
}
ExifTag tag = this.ToEnum(this.ReadUInt16(), ExifTag.Unknown);
uint type = this.ReadUInt16();
// Ensure that the data type is valid
if (type == 0 || type > 12)
{
exifValue = new ExifValue(tag, ExifDataType.Unknown, null, false);
return(true);
}
var dataType = (ExifDataType)type;
object value;
uint numberOfComponents = this.ReadUInt32();
// Issue #132: ExifDataType == Undefined is treated like a byte array.
// If numberOfComponents == 0 this value can only be handled as an inline value and must fallback to 4 (bytes)
if (dataType == ExifDataType.Undefined && numberOfComponents == 0)
{
numberOfComponents = 4;
}
uint size = numberOfComponents * ExifValue.GetSize(dataType);
this.TryReadSpan(4, out ReadOnlySpan <byte> offsetBuffer);
if (size > 4)
{
int oldIndex = this.position;
uint newIndex = this.ConvertToUInt32(offsetBuffer);
// Ensure that the new index does not overrun the data
if (newIndex > int.MaxValue)
{
this.invalidTags.Add(tag);
exifValue = default;
return(false);
}
this.position = (int)newIndex;
if (this.RemainingLength < size)
{
this.invalidTags.Add(tag);
this.position = oldIndex;
exifValue = default;
return(false);
}
this.TryReadSpan((int)size, out ReadOnlySpan <byte> dataBuffer);
value = this.ConvertValue(dataType, dataBuffer, numberOfComponents);
this.position = oldIndex;
}
else
{
value = this.ConvertValue(dataType, offsetBuffer, numberOfComponents);
}
exifValue = new ExifValue(tag, dataType, value, isArray: value != null && numberOfComponents != 1);
return(true);
}