private SortedDictionary <RadioTapType, RadioTapField> ReadRadioTapFields()
{
var bitmasks = this.Present;
var retval = new SortedDictionary <RadioTapType, RadioTapField>();
var bitIndex = 0;
// create a binary reader that points to the memory immediately after the bitmasks
var offset = this.header.Offset + RadioFields.PresentPosition + (bitmasks.Length) * Marshal.SizeOf(typeof(UInt32));
var br = new BinaryReader(new MemoryStream(this.header.Bytes, offset, this.Length - offset));
// now go through each of the bitmask fields looking at the least significant
// bit first to retrieve each field
foreach (var bmask in bitmasks)
{
var bmaskArray = new int[1];
bmaskArray[0] = (int)bmask;
var ba = new BitArray(bmaskArray);
var unhandledFieldFound = false;
// look at all of the bits, note we don't want to consider the
// highest bit since that indicates another bitfield that follows
for (var x = 0; x < 31; x++)
{
if (ba[x])
{
var field = RadioTapField.Parse(bitIndex, br);
if (field != null)
{
retval[field.FieldType] = field;
}
else
{
//We have found a field that we dont handle. As we dont know how big
//it is we can't handle any fields after it. We will just copy
//the rest of the data around as a lump
unhandledFieldFound = true;
break;
}
}
bitIndex++;
}
if (unhandledFieldFound)
{
break;
}
}
//this will read the rest of the bytes. We pass in max value because we dont know how
//much there is but this will ensure we get up to the end of the buffer
this.UnhandledFieldBytes = br.ReadBytes(UInt16.MaxValue);
return(retval);
}
/// <summary>
/// Add the specified field to the packet.
/// </summary>
/// <param name='field'>
/// Field to be added
/// </param>
public void Add(RadioTapField field)
{
RadioTapFields[field.FieldType] = field;
Length += field.Length;
var presenceBit = (int)field.FieldType;
var presenceField = (presenceBit / 32);
if (Present.Length <= presenceField)
{
var newPresentFields = new UInt32[presenceField];
Array.Copy(Present, newPresentFields, Present.Length);
//set bit 31 to true for every present field except the last one
for (int i = 0; i < newPresentFields.Length - 1; i++)
{
newPresentFields[i] |= 0x80000000;
}
Present = newPresentFields;
}
Present[presenceField] |= (UInt32)(1 << presenceBit);
}
