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Communicating with a classic TCP socket

I'm writing my first application with NetMQ (ZeroMQ implementation for .NET).
I also need to listen to information sent from a client using a traditional TCP socket (a.k.a a non-0MQ socket).
I've seen references to the availability of this socket type in the official ZeroMQ documentation here, (look for ZMQ_STREAM), but there's very few details on how to use it (and that doesn't help much either, the .NET API is quite a bit different from the C++ API).
The offical NetMQ documentation also makes no mention of the Streaming socket type.
Finally I had a look over to the Test suite for NetMQ on Github, and found a partial answer to my question in the method RawSocket.
The following snippet works:
using (NetMQContext context = NetMQContext.Create())
{
using (var routerSocket = context.CreateRouterSocket())
{
routerSocket.Options.RouterRawSocket = true;
routerSocket.Bind("tcp://127.0.0.1:5599");
byte[] id = routerSocket.Receive();
byte[] message = routerSocket.Receive();
Console.WriteLine(Encoding.ASCII.GetString(id));
Console.WriteLine(Encoding.ASCII.GetString(message));
}
}
When using standard TCP/IP test-tools, the byte[] message is printed out nicely, e.g. like this:
Hello World!
but the byte[] id is printed out like this:
???♥
In other words, I have no clue what's up with the id part. Why is routerSocket.Receive called twice? What is contained within the id? Is this something ZeroMQ/NetMQ specific, or is something TCP/IP specific information being extracted here?

Thanks to #Mangist for pointing this out.
The answer is in the RouterSocket documentation:
An identity, sometimes called an address, is just a binary string
with no meaning except "this is a unique handle to the connection".
Then, when you send a message via a ROUTER socket, you first send an
identity frame.
When receiving messages a ZMQ_ROUTER socket shall prepend a message
part containing the identity of the originating peer to the message
before passing it to the application. Messages received are
fair-queued from among all connected peers. When sending messages a
ZMQ_ROUTER socket shall remove the first part of the message and use
it to determine the identity of the peer the message shall be routed
to.
Identities are a difficult concept to understand, but it's essential
if you want to become a ZeroMQ expert. The ROUTER socket invents a
random identity for each connection with which it works. If there are
three REQ sockets connected to a ROUTER socket, it will invent three
random identities, one for each REQ socket.
This image illustrates the core concept of the ID frames:

32feet.net: How to connect to a specific COM port via BluetoothClient

I am trying to build a windows application with C#/Visual Studio 2010 which would do the following functions (in sequence): For bluetooth operations, I am using 32feet.Net library functions.
Find the bluetooth devices and list them in the list/combo box for the user to select. (I want to allow user to select multiple devices and hence NOT going for SelectBluetoothDeviceDialog class option.). I can get the list of devices via BluetoothClient.DiscoverDevices(), however, it is not an async operation. If possible, I would like to go for the async operation. I read about the BluetoothComponent class with events DiscoverDevicesProgress and DiscoverDevicesComplete and method DiscoverDevicesAsync but could not get it working. If possible, kindly share a sample code for this.
User selects the devices from the list and clicks 'Pair' button. So far I can successfully pair the devices via BluetoothSecurity.PairRequest. No issues here.
User now selects one/multiple device(s) from the 'paired' list and clicks 'connect'. Here I tried to connect to the device using BeginConnect (for async operation) and Connected methods of the BluetoothClient class but getting following exception.
System.Net.Sockets.SocketsException: {"An invalid argument was
supplied 000319002CC6:0000110100001000800000805f9b34fb"}.
The number in the above exception is GUID number required for the Connected method which I passed using BluetoothService.SerialPort. This will fail as my device is expecting to be connected at COM7 port. I am not sure how can I connect/pair a device at the specific COM port? Is is even possible by 32feet.Net library functions? If so, kindly provide a code sample.
References Note:I have already read and tried to implement the code explained in the article below on StackOverflow. However, due to my requirements (allowing user to pair and connect to multiple devices at COM ports) I am unable to run the same code. However, it did help understanding the concept.
32feet.net howto discover nearby bluetooth devices async in c#
Request you to advise the best way to handle this situation. In case I should try using any other library/functions other than 32feet.Net , do let me know.
My ultimate goal is to BOTH read and write data from and to the connected device(s). So, as of now, I am just trying to get connected on a specific COM port via bluetooth.
Regards,
Rumit
===========================
EDIT: updated information for answer 1:
I have received a bluetooh device (a patch) which is supposed to be connected to TOSHIBA VIRTUAL BT COM port. I apologize if the TOSHIBA information was necessary to better answer the question. I am new to the communication with ports. So far I know that I need to use COM7. I have an application built in C++ which connects to the same patch on COM7 via bluetooh. However, I don't have the source code and I have been asked to implement the same utility in C#. From your reply, can I assume that the C++ application might be using Windows Sockets 2 by any chance?
Also, I could see an option to specify a port (integer value) value in BluetoothEndClient but that also did not work. So, I assume that the port was not COM and was some other type of port.
Regards,
Rumit

Just briefly just now. You seem to be mostly on the right lines.
1) That error is presumably the one with name 'InvalidArgument' and code 10022 (check SocketException.SocketErrorCode).
So for the MSFT Bluetooth stack it has meaning (See http://32feet.codeplex.com/wikipage?title=Errors):
"Plug and Play, driver-stack event, or other error caused failure."
So that means that something is going wrong at the hardware level with the connection, either with the dongle itself or the pair of devices are mis-communicating. It's not a Parani module you are connecting to, is it?
Pair with it manually in the Bluetooth UI, then see if the connection works then.
2) Do you really want a COM port?
I very much prefer working with Sockets and System.IO.Streams. COM ports are hard to set-up, very hard to maintain, and hard to use. Only if you have a third-party program that only uses COM ports should you need to use them.
BluetoothClient doesn't create a COM port, it uses Sockets and returns a Stream to read and write to.

I have found a solution to successfully connect to a bluetooth device using WCL library as described below.
Step1: Make the wclClient's Transpport property to ctSerial.
client.Transport = wclClientTransport.ctSerial; //This makes the wclClient to listen to the COM ports.
Step2: Specify the COM port number by setting client.SerialParams.Port property. For Example,
client.SerialParams.Port = 5; // For COM5
Regards,
Rumit

Using WinSocks in C to send data to a c# application on same machine, "target host refusing connectiong(c# part)

I am trying to get data from my interface, written in c, to another application, in c#.
Now, I'm not sure if WinSocks is pure c, but I'm using visual studio and the rest of my interface is 100% pure C.
Here is my "client" written in c#
http://pastebin.com/X9SNcVqn
here is my "server" written in c - loops waiting for a connection, this builds AND RUNS without issues
NOTE: DEFAULT_PORT is 18042, used the same port for client and server side.
I've downloaded wireshark and used the command "tcp.port eq "
http://pastebin.com/FHZyre2V
I also tried going through my windows firewall and NORTON to allow this connection, I couldn't figure out what to do. Most of the tuts I saw where outdated and tabs and options are changed in WINDOWS 7
I chose a port that wasn't being used, I tried using wireshark to see the connections, no luck BUT I scanned the port I used with nmap, before AND after I ran the "server", so it must of atleast have been created

In your C# code you are mixing TcpClient and Socket objects. You don't need both, only the TcpClient. (The Socket code is using the wrong port as well). Once the TcpClient object is connected, call the GetStream method to get a NetworkStream object that you can read and write to to send and receive data to the server process.
See the example code in the documentation, here: http://msdn.microsoft.com/en-us/library/system.net.sockets.tcpclient.aspx

Your client code contains:
IPEndPoint endPoint = new IPEndPoint(IPAddress.Parse("192.168.1.4"), 18041);
I would not necessarily expect the IP address bound to a network card to necessarily work for localhost-to-localhost connections. I'd recommend changing your client to use 127.0.0.1 or another suitable loopback address.

First,check if the IP adress is correct and if the corresponding port is listeing.
netstat -an | find "port number"
and I think, in the server side code
local.sin_port = (unsigned short)DEFAULT_PORT;
Should be:
local.sin_port = htons((unsigned short)DEFAULT_PORT);

Send Raw IP packet in C#, everything above the ethernet layer

I don't want to modify the ethernet portions of the frame, but I need to modify the IP packet and the data portion of the frame.
I try sending a raw frame and it still puts in the IP information. I basically need to send a frame without defining the endpoint except in the bits I'm sending.
Here's what I got:
Socket s = new Socket(AddressFamily.Unspecified, SocketType.Raw, ProtocolType.Raw);
EndPoint ep = new IPEndPoint(IPAddress.Parse("205.188.100.58"),80);
s.SendTo(GetBytes(""),ep); //im sending nothing, so i expect the frame to just have ethernet stuff
s.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.HeaderIncluded, false);
My question:
Using SendTo adds the IP portion of the frame, I don't want that as I want to spoof the source IP. Using "Send" will crash because it says I need to specify an endpoint. Any suggestions on what to do? I just want to send a packet and define the IP section and data section myself.
Note: No I'm not making a DOS attack, I need this for a legitimate use!
I know how to define the IP portion, its just a matter of actually sending the data without a generated IP portion.

Your question is very well answered here: How send raw ethernet packet with C#?
Using Pcap.Net sort of a library, you can easily modify individual data packets in any way you want (as it uses the underlaying WinPcap implementation which is very powerful).
You can also completely skip the IP layer and send to MAC addresses as in: http://www.codeproject.com/KB/IP/sendrawpacket.aspx where I used a similar approach to communicate with a micro-controller (Atmel ATmega) over Ethernet which provides almost realtime communications.

"Using Pcap.Net sort of a library, you can easily modify individual data packets in any way you want (as it uses the underlaying WinPcap implementation which is very powerful)."
Wrong! WinPcap cant do filtering/packet dropping/ create packet. By other words, its just lets you monitor the packet in an async fashion...
Raw packet /Promiscuous mode/ Driver filter / packet routing is another talk.

Connection between 2 computers via dial up modem without internet in c#

Hi Is there any way to connecting to computers via Dial Modem without internet?
Like windows Hyper terminal.
making connection sending files between computers.
Just Connection Between two Computers Directly and sending FIle.

Yes.
Assuming the modems are connected via a serial port (or emulate being connected via a serial port): you'll need one modem set up (learn your AT commands!) to listen for and answer incoming calls, and the other to dial the first.
You can then treat the pair as a rather long serial link.
However getting everything to work reliably is more of an art than a science, and something that is so rarely done today that much of it is forgotten. The last time I worked with modems in this way was more than fifteen years ago.

The way we used to do it back in the olden days was with a null-modem cable. We even used to do "networked" gaming that way, back in the day.
This is bascially an RS-232 cable with the receive and transmit pins crosswired. I still see some adapters around, so it shouldn't be too tough to get hold of one.
Much later some people created SLIP (Serial Line IP) to enable a serial line to act as a carrier for the entire TCP/IP stack. A bit later PPP was introduced as an improvement. I think SLIP is still available for most platforms, and PPP exists on every platform that can do dial-up internet.
So if the question basically boils down to wanting to network two computers via PPP without going through somebody else's dial-up server (like Earthlink), what you need is to install a PPP server on one of the two machines. They come with most Linux distros. For Windows you will have to go look. I'd help, but my corporate blocker is being overexuberant again.

Someone has written an XModem implementation in C# here: http://trackday.cc/b2evo/blog2.php/2007/08/02/net-xmodem It may help with what you're after.

One thing that's not clear from your question is whether you are attempting to directly connect two machines in the same physical location with a cable, or if you are attempting to dial in to one from the other over a PSTN.
If they are in the same place, eliminate the modem from the equation. This reduces complexity significantly.
If they are in separate locations (ie, dialing over an honest-to-God dial-up connection), there is some code here that might help you. The article talks about a Bluetooth or GPRS modem, but the core of it is about sending AT commands which can be used to talk to any AT-command set-compatible device. It might get you going in the right direction.
Update
See http://msdn2.microsoft.com/en-us/system.io.ports.serialport(VS.80).aspx
Since a modem should be attached to a COM port (COM1-COM12) even it is an internal modem, you should be able to use the .NET framework's SerialPort class to open the port, send AT commands, etc. Once you have an open connection, you could use the XModem library to transfer files, or straight serial for regular communications.
Do you need an IP stack, or are you happy with a straight serial protocol?

You can quite easily setup dial-up network connections within Windows that require the use of a modem (its under the option for setting up a VPN, but you can set it for just a dial up).
So I would assume that you can then map a network location to it for use by your C# code.
As already stated at least one of the modems must be on and listening for a connection.
* edit *
I believe that the following code will trigger a dial-up connection that has been placed within Network Connections
System.Diagnostics.ProcessStartInfo procStartInfo = new System.Diagnostics.ProcessStartInfo(#"c:\Local Area Connection 2 - Shortcut");
System.Diagnostics.Process proc = new System.Diagnostics.Process();
proc.StartInfo = procStartInfo;
proc.Start();
For link placed at c:\ drive and named "Local Area Connection 2 - Shortcut"
You could then ping the destination to see if its connected.
Ultimately though I think that your best solution may be to use RAS.
Have a look here at Codeplex: DotRAS
You can then use the following code:
RasDialer dialer = new RasDialer();
bool connected = false;
foreach (RasConnection connection in dialer.GetActiveConnections())
{
if (connection.EntryName == "MyFriendsPC")
{
connected = true;
break;
}
}
if (!connected) {
dialer.EntryName = "MyFriendsPC";
dialer.Dial();
// If you need to provide credentials, use the Dial(NetworkCredential) overload that's available.
}
This example assumes you already have an entry named MyFriendsPC in the default phone book. If you do not and need to create this connection programmatically, you can use the RasPhoneBook component for that.
RasPhoneBook pbk = new RasPhoneBook();
pbk.Open(); // This will open the phone book in the All Users profile.
RasEntry entry = new RasEntry("MyFriendsPC");
If you'd rather use the default settings for the connection you can use one of the static methods on the RasEntry class, or manually configured the connection here.
pbk.Entries.Add(entry);
Once the entry has been added to the collection, it will immediately be added into the phone book.

I recently wanted to connect a dial-up POS terminal to an analog modem. This is not difficult, but you need to introduce a 9-volt battery and a 200mA resistor in parallel for the modems to connect. https://www.youtube.com/watch?v=luarFqislIc describes the approach (skip to 11:30 to see the circuit). Without the battery and resistor to provide the loop current (about 18mA), the modems will not negotiate a connection (you'll hear the modem after entering ATA to answer, but you won't hear the final part of the modem negotiation). With the loop current, the modems will connect. The video even shows ZModem being used to transfer a file from one PC to the other.
One final item not mentioned in the video is with this circuit, there is no dial tone. To get around this, enable blind dialing (ATX1) on the calling modem. Also, since there are no rings with this approach, setting the receiving modem to auto-answer (ATS0=1) won't work. You have to enter ATA on the receiving modem to answer.