I'm currently working on transitioning a small console application to a TCP server / client application. The client will connect to the server via any Telnet client, and the server will replicate the standard console interface for each Telnet connection.
I started looking into doing this using the techniques I've learned from Beej's guide to network programming -- accepting the connection and then using fork() to separate it into its own process.
However, I would prefer to maintain my use of streaming IO (the original console application uses cin / cout, using similar functions for the networking logic would make the conversion process much simpler).
I've discovered the TCPStream class, hiding within sockets.h (http://www.gnutelephony.org/doxy/bayonne2/a00215.html)
It appears this class will allow me to use the server with streaming IO. However, I can't find a single example of using this class, nor can I find an explanation as to how to use fork() with it.
Any ideas? Thanks in advance for any help.
I think you are confusing the trees for the forest. One socket class is such a small part of what you need to do overall that it is not worth focusing on that.
If your objective is just to get your project working then just use an existing framework rather than trying to pull individual classes out of a large project. POCO has a TCPServer class that will do 90% of the work for you. QT, ACE and others have similar classes. There is not a huge amount of documentation on POCO but they do cover TCPServer pretty well and you can learn a lot from reading the source code if that is really where your interest lies.
Related
For my scientific collaboration, I wrote a C++ server/client (terminal server for linux, and cross-platform GUI client using Qt) that is mainly meant to transfer data from multiple clients around the world to store it on one server for analysis (pretty much like LIGO and Virgo that caught gravitational waves). For the communication low-level protocol I used boost::asio::ssl.
The "odd" part: In my programs, I created my own half-duplex messaging protocol between the server and the client from scratch. The messaging was in string form containing the version of the protocol, endianness of the computer, length of the message, type of the message (login/file/error/etc...), an MD5 hash for verification of the completeness of the transferred data. I got highly criticized on Stackoverflow chat when I said I did this. The part that got specially criticized is: Writing my own messaging protocol.
Now I created this, and I know there should be better protocols that are already written that I shouldn't rewrite it from scratch. However, I wanted to learn how to do this myself, and I did, and the program works, and my collaboration is satisfied, and the sky is blue with birds singing.
My question: If I am to rewrite this program again, what kind of libraries should I use? I'm looking for a protocol, using which I can send messages/data and get the server to respond with messages/data, including username/password to authenticate the user before any communication is transferred? How would you have done it?
PS: Please consider this question coming from a beginner in writing network and internet wide programs. And please don't hesitate to ask for more details.
Background
For my project, I'm attempting to control an AUV using an Arduino mega with an ethernet shield that receives instruction from a laptop (running Windows). The server side (laptop) will be written in C++.
Since there'll only be a one to one network using TCP/IP, I am trying to avoid the use of routers in order to simplify the hardware. I found out that you could do a direct connection between two devices (with auto-MDIX).
Therefore...
I have briefly looked into Boost:asio but I think it's probably an overkill (because I won't need to consider multiple clients etc) crossover for what I'm trying to achieve here. Am I right?
Any advice would be appreciated! Thanks.
TL;DR:
Looking for a C++ networking library (that works on Windows) that allows a clean, simple code to do a one-to-one TCP/IP connection.
The simplest way is to set-up your arduino as a web server. See this example sektch for the details.
On your Windows box use a web client library.
This way you can test the arduino even without your client software using your browser.
I am implementing a messaging system using C++ and Qt. After much thought, I have determined that multicasting or a multicast-style technique will work best to solve my problem. However, I have learned about UDP's unreliability and believe it to be unacceptable.
My requirements are as follows:
Messages are to be sent in a binary serialized form.
From any given node on the network, I must be able to send messages to the other nodes.
Message delivery must be insured.
I have heard of OpenPGM and NORM as alternatives for UDP. If anyone has experience with either of these, could you please share?
I am also open to the possibility of implementing "reliable" multicast by myself, in the application layer, but I would prefer not to if there is a library that already implements this.
I am using C++ and Qt, therefore .NET or Java-based solutions are not acceptable unless they are open-source and I may port them to C++.
Thank you very much.
EDIT 20120816T1853 MDT: An additional question: would either PGM or NORM have to be implemented at the hardware/IP level? Or can they be overlayed on top of existing protocols?
We have implemented our own reliable multicast protocol over UDP called RSP, since we needed something cross-platform and at the time couldn't find a good solution between Linux and Windows. The Windows PGM implementation disconnects slow clients which leave the send window, whereas our implementation throttles the sender similar to TCP. Afaik OpenPGM can be configured to do the same.
The open source NORM at http://cs.itd.nrl.navy.mil/work/norm can be built as a library and has C++ API with Python and Java language bindings. If you ping the developer (me) via the mailing list, I can help get you started.
There is a large RFC division of reliable multicast protocols, and many implementations out there. It's a long time since I looked at this but there are TRAM, LRMP, ...
Im looking for code that connects to another computer via remote desktop connection and checks if the connection was successful or not.
I packet logged and found out there was a galaxy worth of packets so i was wondering if there was some easy code out there.
There really isn't anything easy about RDP, that protocol stack is huge and builds on the ITU OSI protocols, which includes a fair amount of ASN.1/BER.
Your best bet is the code that's in FreeRDP.
A bit of terminology: you want a "RDP client library for C++".
As others have mentioned, look into the "FreeRDP" and "rdesktop" projects.
With FreeRDP, you're going to get a suite of libraries (each one doing it's thing). With rdesktop, you're going to get a client app (which you have to break the C code out of, and "build" your C++ api around).
If this is a new project, I'd pick FreeRDP over rdesktop, as they have libraries available with your C++ interface already in place.
Do you need to check if an RDP server is present, but not authenticate? In this case all you'd need are the first couple of packets used to negotiate protocol security. You can find the code in FreeRDP in libfreerdp-core/nego.c.
#Blanker1231 : You should have look on rdesktop code , its in c but can be very easily modified to be used in a C++ code , all you have to do is bridge their Struct Stream effectively .
moreover I have worked on a Rdp 7+ implementation ages ago in qt/c++ for a , so recently just for fun of it i used all of my experience and wrote a RDP parser and code generator and open sourced it on https://github.com/shashanksingh/Code-Generator-for-RDP
Right now it dead simple and i am still working on it more intelligent . Word of caution it doesn't generate everything . Examples includes demo.def which on compilation will generate all the class os ms-fscc used in ms-rdp
#Blanker1231 if you ever feel like , just fork the implementation and start pushing stuff in
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I have one computer that is running a c++ program to control a robot and another computer that is running a computer vision system (also written in c++). I would like for these two programs to be able to talk to one another. The communication would not have to be complex, I would just need the robot computer to be able to tell the vision computer when a trial begins and ends (when to start and stop a data collection sequence). Do any of you have advice on how to approach this problem? Rs232 communication between the computers? Some kind of networking solution? smoke signals? Any suggestions would be welcome.
thank you in advance
(edit) In case you think the statement above is vague:
I need to pass a binary (go/don't go) signal from one computer to another. Unfortunately I can't be more specific about what this will look like because (obviously) I don't know what is available. Both computers are on a network, and both computers are running windows. The goal is to syncronize data collected by the computer vision system with actions performed by the robot. The communication does need to be fast enough that it will not slow down either the robot or the computer-vision program. a "good" solution would be 1) easy to implement 2) fast. I do not know much about networking and I am looking for a place to start looking.
thank you again for your assistance
You might use a simple UDP protocol - the advantage being that if you understand the concepts of simple packet protocols on RS232 you'll find it easy to transfer that knowledge to sending the packets via UDP.
If you want a reliable (as in, other parts of the system will worry about errors and retries) stream of bytes between the two PCs, then TCP/IP is not much more complicated to use than UDP.
Both UDP and TCP are accessed through 'sockets'. I'm afraid you'll find that from C++ there is rather a lot of tedious boilerplate to getting that working, but there are lots and lots of examples around.
If they are network-connected you could just use sockets.
The best option will be to use network communication. The easiest way to approach this should be to look at the networking examples in Qt.
You basically will create a client and a server application. You decide what the client does when it sees a certain message from the server. That's all. Qt should take care of the rest of the stuff.
Other answers suggests TCP/IP, UDP, RS232, ... All those things are just options when you use QtNetwork module. I assume that since you ask your question, you don't know about the difference between those. So the safest bet will be to use the highest level (free) library, hence the suggestion to look into Qt.
Another option is to use Boost.Asio. I tend to prefer Qt solution since their API is nicer.
That sounds like a fairly good use for the network socket. If both your machines are on Windows you can even use named pipes.
For Windows, you will need to open the COM n port as a file to communicate over a serial port[1]. I don't have access to my code now, I can look it up when I get home.
RS232 is easy and I like it. However, it it is slow. You need to consider that in your design.
[1] For C++.
Most modern computers have Ethernet capability, so get yourself a cheap hub or switch and look at networking APIs. There's usually some fairly easy socket stuff. One advantage of this is that, if you want to increase communication ability later, such as having your vision software provide instructions and guidance to your robot, you've got the basics set up.
Alternately, set up your vision program so you can start and stop it by hitting random keys. When you're going to use it, put the keyboard in front of the robot computer's CD drive, and eject at the start and end of the robot run.
This may be overkill in your situation, but if I were in your shoes I would probably implement it using the HTTP protocol. The vision computer would run a HTTP server and the robot computer would communicate the state changes using POST requests. The Poco C++ Net library provides you with the facilities required to do this.
I would use a TCP/IP socket for communications. TCP guarantees that the data will make it. So, all you need to do is parse the data.
RS232 is an easy option to program for, however modern PCs don't tend to have RS232 ports. You may need to get USB-RS232 adapters or install a PCI card.
The other problem with RS232 is that you have an additional wire to worry about which can be a nusiance. Also RS232 cables can be limited in length (5-15m) unless you invest in some clunky RS232 repeaters or bluetooth connectors, etc.
On top of all that you're also adding one more item to your project that can go wrong and cost you time in deploying and debugging.
IMO, an elegant engineering solution would be to utilise the hardware that you have and use TCP/IP sockets to communicate.
The web is awash with examples on passing messages between servers and clients:
If you're using Linux:
http://www.linuxhowtos.org/C_C++/socket.htm
Using Windows:
http://www.adp-gmbh.ch/win/misc/sockets.html
I also might look at something like 0MQ to make the connection more robust. It will transmit and reassemble messages regardless of the transport, and handle buffering in the case of temporary loss of connectivity.
But the bottom line is that I would use TCP/IP, but depending on the nature of the robot you may want a slightly more robust connection system than TCP sockets. UDP is nice because it's connectionless-- if the robot temporarily travels out of range/sight/etc you wont have to rebuild the socket and context.