private static Task <DbfHeader> BuildDbfHeaderData(IRandomAccessStream stream, Encoding encoding, CancellationTokenSource cancellationTokenSource)
{
var token = cancellationTokenSource.Token;
var task = Task.Factory.StartNew(async() =>
{
if (cancellationTokenSource.IsCancellationRequested)
{
return(null);
}
if (stream.Size < 32)
{
throw new NotSupportedException(InvalidFormat);
}
using (var dataStream = stream.CloneStream())
{
byte[] header = new byte[32];
await dataStream.ReadAsync(header.AsBuffer(), 32u, InputStreamOptions.Partial);
byte fileType = header[0];
if (!AllowedTypes.Contains(fileType))
{
throw new NotSupportedException(InvalidFormat);
}
DbfHeader dbfHeader = new DbfHeader();
dbfHeader.RecordsCount = BitConverter.ToInt32(header, 4);
dbfHeader.RecordsOffset = BitConverter.ToInt16(header, 8);
dbfHeader.RecordLength = BitConverter.ToInt16(header, 10);
if (encoding == null)
{
byte languageDriver = header[29];
encoding = DbfEncoding.GetEncoding(languageDriver);
}
dbfHeader.Encoding = encoding;
// header is 32 bytes + n field descriptors * 32 bytes + carriage return byte (0x0D)
int fieldDescriptorCount = (dbfHeader.RecordsOffset - 32 - 1) / 32;
byte[] fieldDescriptor;
DbfFieldInfo dbfField;
for (int i = 0; i < fieldDescriptorCount; i++)
{
if (cancellationTokenSource.IsCancellationRequested)
{
return(null);
}
fieldDescriptor = new byte[32];
await dataStream.ReadAsync(fieldDescriptor.AsBuffer(), 32u, InputStreamOptions.Partial);
dbfField = new DbfFieldInfo();
dbfField.Name = encoding.GetString(fieldDescriptor, 0, 11).Replace("\0", string.Empty);
dbfField.NativeDbfType = (char)fieldDescriptor[11];
dbfField.Length = fieldDescriptor[16];
dbfField.DecimalCount = fieldDescriptor[17];
dbfHeader.Fields.Add(dbfField);
}
return(dbfHeader);
}
},
token).Unwrap();
return(task);
}
private static object TransformDbfValue(DbfFieldInfo field, string fieldValue, IAttributeValueConverter valueConverter)
{
switch (field.NativeDbfType)
{
// Currency
case 'Y':
// Numeric
case 'N':
// Float
case 'F':
// Double
case 'B':
// NOTE: numeric overflow is physically stored as asterisks in the DBF file.
fieldValue = fieldValue.TrimStart(' ', '*');
break;
// Integer
case 'I':
// TODO: Handle integer overflow
// NOTE: Integer fields cannot handle overflow as asterisks in DBF file because they are stored in binary format.
// Overflow in integer field is represented by the lowest integer value -2**32.
fieldValue = fieldValue.TrimStart(' ');
break;
// Date
case 'D':
if (string.IsNullOrEmpty(fieldValue.TrimEnd(' ')))
{
fieldValue = DateTime.MinValue.ToString(CultureInfo.InvariantCulture);
}
else
{
fieldValue = fieldValue.Substring(0, 4) + "-" + fieldValue.Substring(4, 2) + "-" + fieldValue.Substring(6, 2);
}
break;
// DateTime
case 'T':
fieldValue = fieldValue.Substring(0, 4)
+ "-"
+ fieldValue.Substring(4, 2)
+ "-"
+ fieldValue.Substring(6, 2)
+ " "
+ fieldValue.Substring(8, 2)
+ ":"
+ fieldValue.Substring(10, 2)
+ ":"
+ fieldValue.Substring(12, 2);
break;
case 'L':
if (fieldValue.ToUpper() == "T" || fieldValue.ToUpper() == "Y")
{
fieldValue = bool.TrueString;
}
else
{
fieldValue = bool.FalseString;
}
break;
default:
fieldValue = fieldValue.TrimEnd(' ');
break;
}
object result = null;
if (!string.IsNullOrEmpty(fieldValue))
{
result = Convert.ChangeType(fieldValue, field.MappedType, CultureInfo.InvariantCulture);
}
// NOTE: Optionally allow the user to customize the field value / field value type.
if (valueConverter != null)
{
result = valueConverter.Convert(result, field.Name, field.MappedType);
}
return(result);
}
