public static UdpFrame ParseFrame(IPFrame ip, bool checksum = true)
{
if (ip == null)
{
return(null);
}
UdpFrame frame = null;
BufferSegment payload = ip.Payload;
payload.UnsafeAddrOfPinnedArrayElement((p) =>
{
udp_hdr *udphdr = (udp_hdr *)p;
if (udphdr == null)
{
return;
}
if (payload.Length != CheckSum.ntohs(udphdr->len)) // 错误的数据报
{
return;
}
int offset = sizeof(udp_hdr);
int len = payload.Length - offset;
if (len <= 0)
{
return;
}
if (checksum && udphdr->chksum != 0)
{
uint pseudo_checksum = CheckSum.inet_chksum_pseudo((byte *)p.ToPointer(),
(uint)ProtocolType.Udp,
(uint)payload.Length,
ip.SourceAddressV4,
ip.DestinationAddressV4);
if (pseudo_checksum != 0)
{
return;
}
}
BufferSegment message = new BufferSegment(payload.Buffer, payload.Offset + offset, len);
frame = new UdpFrame(
new IPEndPoint(ip.Source, CheckSum.ntohs(udphdr->src)),
new IPEndPoint(ip.Destination, CheckSum.ntohs(udphdr->dest)), message)
{
Ttl = ip.Ttl,
SourceMacAddress = ip.SourceMacAddress,
DestinationMacAddress = ip.DestinationMacAddress
};
});
return(frame);
}
public static IPFrame ToIPFrame(UdpFrame frame)
{
if (frame == null)
{
throw new ArgumentNullException(nameof(frame));
}
if (frame.AddressFamily != AddressFamily.InterNetwork)
{
throw new ArgumentNullException("UDP frames of this address family type are not supported.");
}
if (frame.Payload.Length <= 0)
{
return(null);
}
int offset = sizeof(udp_hdr);
int payload_len = frame.Payload.Length;
byte[] message = new byte[offset + payload_len];
fixed(byte *pinned = message)
{
udp_hdr *udphdr = (udp_hdr *)pinned;
udphdr->dest = CheckSum.htons((ushort)frame.Destination.Port);
udphdr->src = CheckSum.htons((ushort)frame.Source.Port);
udphdr->len = CheckSum.htons((ushort)message.Length);
using (MemoryStream ms = new MemoryStream(message, offset, payload_len))
{
ms.Write(frame.Payload.Buffer, frame.Payload.Offset, payload_len);
}
ushort pseudo_checksum = CheckSum.inet_chksum_pseudo(pinned,
(uint)ProtocolType.Udp,
(uint)message.Length,
IPFrame.GetAddressV4(frame.Source.Address),
IPFrame.GetAddressV4(frame.Destination.Address));
if (pseudo_checksum == 0)
{
pseudo_checksum = 0xffff;
}
udphdr->chksum = pseudo_checksum;
}
return(new IPFrame(ProtocolType.Udp, frame.Source.Address, frame.Destination.Address, new BufferSegment(message))
{
Ttl = frame.Ttl,
SourceMacAddress = frame.SourceMacAddress,
DestinationMacAddress = frame.DestinationMacAddress,
});
}
