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.
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How does ZeroC ICE compare to 0MQ? I know that 0MQ/Crossroads and DDS are very similar, but cant seem to figure out where ICE comes in.
I need to quickly implement a system that offloads real-time market-data from C++ to C#, as a first phase of my project. The next phase will be to implement an Event Based architecture with an underlying Pub/Sub design.
I am willing to use TCP.. but the the system is currently running on a single 24 core server.. so an IPC option would be nice. From what I understand ICE is only TCP, while DDS and 0mq have an IPC option.
Currently ,I am leaning towards using Protobuf with either ICE or Crossroads IO. Got turned off from the OpenSplice DDS website. Ive done lots research on the various options, was originally considering OpenMPI + boost:mpi, but there does not seem to be MPI for .NET.
My question is:
How does ICE compare to 0MQ? I cant wrap my head around this. Was unable to find anything online that compares the two.
thanks in advance.
........
More about my project:
Currently using CMAKE C++ on Windows, but the plan is to move to CentOS at some point. An additional desired feature is to store the tic data and all the messages in a "NoSql" database such as Hbase/Hadoop or HDF5. Do any of these middleware/messaging/pub-sub libraries have any database integration?
Some thoughts about ZeroC:
Very fast; Able to have multiple endpoints; Able to load balance on the endpoints; Able to reconnect to a different endpoint in case one of the node goes down. This is transparent to the end user; Has good tool chain (IceGrid, IceStorm, IceBox, etc); Distributed, high availability, multiple failover, etc
Apart from that, I have used it for hot swapping code modules (something similar to Erlang) by having the client create the proxy with multiple endpoints, and later on bring down each endpoint for a quick upgrade one by one. With the transparent retry to a different endpoint, I could have the system up and running the whole time i did an upgrade. Not sure if this is an advertised feature or an unadvertised side-effect :)
Overall, it is very easy to scale out your servers if need be using ZeroC Ice.
I know ZeroMQ provides a fantastic set of tools and messaging patterns and I would keep using it for my pet projects. However, The problem that i see is that it is very easy to go overboard and lose track of all your distributed components. This is a must have in a distributed environment. How will you know where your clients/server are when you need to upgrade? If one of components down the chain does not receive a message, how to identify where the issue is? the publisher? the client? or any one of the bridges (REP/REQ, XREP/XREQ, etc) in between?
Overall, ZeroC provides a much better toolset and ecosystem for enterprise solutions.
And it is open source :)
Jaybny,
ZMQ:
If you want real good performance and the only job for Phase 1 of your job is to move data from C++ to C#, then Zmq is the best option.
Having a pub/sub model for event driven architecture is also something that Zmq can help you with, with its in-built messaging pattern.
Zmq also supports your IPC requirements in this case. Eg: you can have one instance of your application that consumes 24 cores by multithreading and communicating via IPC.
ZeroC Ice:
Ice is a RPC framework very much like CORBA.
Eg.
Socket/ZMQ - You send message over the wire. Read it at the other end, parse the message, do some action, etc.
ZeroC Ice - Create a contract between client and server. Contract is nothing but a template of a class. Now the client calls a proxy method of that class, and the server implements/actions it and returns the value. Thus, int result = mathClass.Add(10,20) is what the client calls. The method, parameters, etc is marshalled and sent to the server, server implements the Add method, returns the result, and the client gets 30 as the result. Thus on the client side, the api is nothing but a proxy for a servant running on a remote host.
Conclusion:
ZeroC ICE has some nice enterprisy features which are really good. However, for your project requirements, ZMQ is the right tool.
Hope this helps.
For me.. the correct answer was Crossroads I/O . It does everything I need.. but still unable to pub/sub when using protobufs... im sure ZeroC ICE is great for distributed IPC, but 0MQ/Crossroads, gives you the added flexibility to use Inter-Thread-Communication.
Note: on windows, 0mq does not have IPC.
So, all in all, the crossroads fork of 0mq is the best. but you will have to roll your own windows/ipc (or use tcp::127..) , and publisher side topic filtering features for pub/sub.
nanomsg, from the guy who wrote crossroads and 0mq (i think).
http://nanomsg.org/
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
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.
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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.
I would like to create a chat application(desktop-app) in c++, so which protocol i would need to study and implement. UDP(?)
Please provide me some good thoughts and advices and links also.
UDP protocol is not the best choice for Internet chat program. UDP packets will be blocked by proxies. And UDP doesn't guarantee packets delivery. So probably TCP protocol will be a better choice.
Take a look on Boost.Asio Library. It already contains primitive implementation of chat program.
You don't give us much details here!
If your purpose is really to make a fully working and feature full chat application I suggest you look at XMPP which is an open instant-messenging protocol. Here is a list of some libraries implementing it.
If your purpose is to study network programming and you're more interested in UDP versus TCP for instance, then UDP is a bad choice for a chat application as it does not guarantee much about data integrity or ordering. Your messages might (and will!) be received in bad order or some might even be missing. TCP does that for kind of check for you.
In between (a very simple chat app) you can implement your very own protocol and use libraries others have suggested here like Boost.asio, ACE, POCO, or even wxWidgets and Qt, which will ease socket handling and also provide what you need to build a desktop app for the last 2.
Try using Boost.Asio. There are some examples of chat applications included in documentation.
You can use or look at an open-source networking library like ACE. A lot of goodies there.
You could use an existing library that handles instant messaging protocols, such as libpurple.
UDP is like a 'shoot and forget' kind of protocol. It's fast, but if you use it for communicating over the internet, there's no guarantee your messages will be recieved at all. Even if it's LAN, your packets can still be lost. It would be more convenient to use TCP which makes sure your packets arrive without errors and in the order you sent them.