C++ – How to tunnel TCP over reliable UDP

cnetwork-programmingnetworkingsockets

Assume I have a reliable UDP library, and want to tunnel arbitrary TCP connections over it. This is my current approach to doing so, but I feel that it may not be very efficient. Any suggestions are very welcome.

Client establishes a reliable UDP connection to server.
Client runs a local SOCKS5 proxy, which receives data from any app that connects to it and forwards it through the reliable UDP connection. Each packet includes a 4-byte id unique to each SOCKS connection.
Server receives data. If the 4-byte id is new, it makes a new connection to its local TCP socket and sends the data, and spawns a new thread which receives any replies from the server and forwards them through the reliable UDP connection with the appropriate id. If the 4-byte id is old, it simply sends the data over the existing TCP connection.
Client receives data, sending it over the existing SOCKS connection to whatever app started it.

Right now, this seems to work for making simple HTML requests from a browser, but since the server isn't directly connected to the client, it is unable to tell when the client terminates a connection. Is there a better way to do this?

EDIT: No, this is not homework. And please don't bother replying if you aren't aware of the advantages of reliable UDP libraries, or for that matter, haven't heard of them before. Thanks.

Best Answer

there are a few ready to use options:

OpenVPN: tunnels either IP or ethernet Frames on top of UDP
Teredo: tunnels IPv6 on top of UDPv4, manages both NAT traversing and full compatibility with IPv6
UDT: non-standard, reliable, high-performance, multi-transport, TCP-like protocol on top of UDP. Optionally lets you manage NAT traversal and then takes it from there

Setting a bit

Use the bitwise OR operator (|) to set a bit.

number |= 1UL << n;

That will set the nth bit of number. n should be zero, if you want to set the 1st bit and so on upto n-1, if you want to set the nth bit.

Use 1ULL if number is wider than unsigned long; promotion of 1UL << n doesn't happen until after evaluating 1UL << n where it's undefined behaviour to shift by more than the width of a long. The same applies to all the rest of the examples.

Clearing a bit

Use the bitwise AND operator (&) to clear a bit.

number &= ~(1UL << n);

That will clear the nth bit of number. You must invert the bit string with the bitwise NOT operator (~), then AND it.

Toggling a bit

The XOR operator (^) can be used to toggle a bit.

number ^= 1UL << n;

That will toggle the nth bit of number.

Checking a bit

You didn't ask for this, but I might as well add it.

To check a bit, shift the number n to the right, then bitwise AND it:

bit = (number >> n) & 1U;

That will put the value of the nth bit of number into the variable bit.

Changing the nth bit to x

Setting the nth bit to either 1 or 0 can be achieved with the following on a 2's complement C++ implementation:

number ^= (-x ^ number) & (1UL << n);

Bit n will be set if x is 1, and cleared if x is 0. If x has some other value, you get garbage. x = !!x will booleanize it to 0 or 1.

To make this independent of 2's complement negation behaviour (where -1 has all bits set, unlike on a 1's complement or sign/magnitude C++ implementation), use unsigned negation.

number ^= (-(unsigned long)x ^ number) & (1UL << n);

unsigned long newbit = !!x;    // Also booleanize to force 0 or 1
number ^= (-newbit ^ number) & (1UL << n);

It's generally a good idea to use unsigned types for portable bit manipulation.

number = (number & ~(1UL << n)) | (x << n);

(number & ~(1UL << n)) will clear the nth bit and (x << n) will set the nth bit to x.

It's also generally a good idea to not to copy/paste code in general and so many people use preprocessor macros (like the community wiki answer further down) or some sort of encapsulation.

Windows – How to you find out which process is listening on a TCP or UDP port on Windows

New answer, powershell

TCP

Get-Process -Id (Get-NetTCPConnection -LocalPort YourPortNumberHere).OwningProcess

UDP

Get-Process -Id (Get-NetUDPEndpoint -LocalPort YourPortNumberHere).OwningProcess

Old answer, cmd

 C:\> netstat -a -b

(Add -n to stop it trying to resolve hostnames, which will make it a lot faster.)

Note Dane's recommendation for TCPView. It looks very useful!

-a Displays all connections and listening ports.

-b Displays the executable involved in creating each connection or listening port. In some cases well-known executables host multiple independent components, and in these cases the sequence of components involved in creating the connection or listening port is displayed. In this case the executable name is in [] at the bottom, on top is the component it called, and so forth until TCP/IP was reached. Note that this option can be time-consuming and will fail unless you have sufficient permissions.

-n Displays addresses and port numbers in numerical form.

-o Displays the owning process ID associated with each connection.