I'm reading through my textbook and I see this:
The first constructor:
public Datagrampacket (byte ibuf [], int ilength)
constructs a DatagramPacket for receiving packets of length ilength.
Is this just an odd wording, or do DatagramPacket's actually receive data along with sending it? I always thought DatagramPackets were just classes containing information you would send between DatagramSockets
DatagramPacket does not send or receive data. Instead, it is used by by DataSocket in two ways.
It is used by DatagramSocket.receive(DatagramPacket packet) which populates packet with some received data,
or it is used by DatagramSocket.send(DatagramPacket packet) to send the data contained in packet.
Hope this helps.
Check the Javadoc. DatagramPackets are used for both sending and receiving. See DatagramSocket.receive().
Related
I'm using:
socket = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.IP);
to get information from a network NIC on a specific IP.
I stripped the IP header and the protocol header (whether that is TCP, UDP or ICMP).
Now getting to the actual message, I already supposed this is not possible, but I'm new to network programming.
Is there a universal way to decode messages that are coming in from the byteArray?
Most people do this:
string temp = Encoding.ASCII.GetString(packetData);
I guess assuming that the original encoding is in ASCII.
Is there a way to walk through the byte[] array of the message part and decrypt it systematically to its original value?
Or do you need to have the foreknowledge of the original encoding type and offsets?
thanks!
I've been working in a socket tcp connection to a game server. The big problem here is that the game server send the data without any separators - since it sends the packet lenght inside the data -, making impossible to use socket:receive("*a") or "*l". The data received from the server does not have a static size and are sent in HEX format. I'm using this solution:
while true do
local rect, r, st = socket.select({_S.sockets.main, _S.sockets.bulle}, nil, 0.2)
for i, con in ipairs(rect) do
resp, err, part = con:receive(1)
if resp ~= nil then
dataRecv = dataRecv..resp
end
end
end
As you can see, I can only get all the data from the socket by reading one byte and appending it to a string, not a good way since I have two sockets to read. Is there a better way to receive data from this socket?
I don't think there is any other option; usually in a situation like this the client reads a packet of specific length to figure out how much it needs to read from the rest of the stream. Some protocols combine new line and the length; for example HTTP uses line separators for headers, with one of the headers specifying the length of the content that follows the headers.
Still, you don't need to read the stream one-by-one character as you can switch to non-blocking read and request any number of characters. If there is not enough to read, you'll get partially read content plus "timeout" signaled, which you can handle in your logic; from the documentation:
In case of error, the method returns nil followed by an error message
which can be the string 'closed' in case the connection was closed
before the transmission was completed or the string 'timeout' in case
there was a timeout during the operation. Also, after the error
message, the function returns the partial result of the transmission.
as I can see in XMLSocket the data can be readed fully until the end, on the other hand the Socket class read data by parts, so long string will be concatinated by parts, I wonder if is possible to use the Socket class and still read the full data until the end package
private function readResponse():void {
var str:String = readUTFBytes(bytesAvailable);
response += str;
trace2(response);
}
private function socketDataHandler(event:ProgressEvent):void {
trace2("socketDataHandler: " + event);
readResponse();
}
so as I've saw in the docs the only data handler is the ProgressEvent, but how to handle the data to get the full string, not by parts?, I don't want to use the XMLSocket, is there a way?
XMLSocket reads data in internal buffer, and when terminating null byte is received it parses all of the XML received since the previous zero byte or, if that is the first message received, since the connection was established.
You need to wrap Socket object, read messages to internal buffer and fire event when you need.
I am writing the callout driver for Hyper-V 2012 where I need to filter the packets sent from virtual machines.
I added filter at FWPM_LAYER_EGRESS_VSWITCH_TRANSPORT_V4 layer in WFP. Callout function receive packet buffer which I am typecasting it to NET_BUFFER_LIST. I am doing following to get the data pointer
pNetBuffer = NET_BUFFER_LIST_FIRST_NB((NET_BUFFER_LIST*)pClassifyData->pPacket);
pContiguousData = NdisGetDataBuffer(pNetBuffer, NET_BUFFER_DATA_LENGTH(pNetBuffer), 0, 1, 0);
I have simple client-server application to test the packet data. Client is on VM and server is another machine. As I observed, data sent from client to server is truncated and some garbage value is added at the end. There is no issue for sending message from server to client. If I dont add this layer filter client-server works without any issue.
Callback function receives the metadata which incldues ipHeaderSize and transportHeaderSize. Both these values are zero. Are these correct values or should those be non-zero??
Can somebody help me to extract the data from packet in callout function and forward it safely to further layers?
Thank You.
These are the TCP packets. I looked into size and offset information. It seems the problem is consistent across packets.
I checked below values in (NET_BUFFER_LIST*)pClassifyData->pPacket.
NET_BUFFER_LIST->NetBUfferListHeader->NetBUfferListData->FirstNetBuffer->NetBuffe rHeader->NetBufferData->CurrentMdl->MappedSystemVa
First 24 bytes are only sent correctly and remaining are garbage.
For example total size of the packet is 0x36 + 0x18 = 0x4E I don't know what is there in first 0x36 bytes which is constant for all the packets. Is it a TCP/IP header? Second part 0x18 is the actual data which i sent.
I even tried with API NdisQueryMdl() to retrieve from MDL list.
So on the receiver side I get only 24 bytes correct and remaining is the garbage. How to read the full buffer from NET_BUFFER_LIST?
I need to get the whole message(response), but socket.ReceiveBytes(); returns just part of the message. I tried to loop it but it fails on timeout when no bytes to receive.
List<byte> lb = new List<byte>();
byte[] receivedMsg = socket.ReceiveBytes();
while (receivedMsg.Length > 0)
{
lb.AddRange(receivedMsg);
receivedMsg = socket.ReceiveBytes();
}
So, how I can check if there are byte to read? How I can read the whole message?
Since its a Chilkat implementation, you should probably contact the developer. But I found this that could help: http://www.cknotes.com/?p=302
Ultimately, you need to know how much to read from the socket to constitute a whole message. For example, if the overlying protocol is a portmapper, then you know that you are expecting messsages in the format that the RFC specifies (http://tools.ietf.org/html/rfc1833.)
If you are rolling your own protocol over a socket connection, then use the method in the Chilkat blog post about putting the size of the total message in the first 4 bytes.