I am developing a C++ network application on Windows. I need to check if internet connection is there or not. I am using gethostbyname(), but it is giving incorrect information when the system is connected through a proxy. InternetCheckConnection() and InternetGetConnectedState() are also not giving reliable results under different conditions. Is there a reliable way to check for internet connectivity covering all the conditions such as proxy and VPN?
Update:
In our company network WinHttpGetProxyForUrl() is failing with the error ERROR_WINHTTP_AUTODETECTION_FAILED and WinHttpSendrequest() is failing with error ERROR_WINHTTP_NAME_NOT_RESOLVED.
In open network WinHttpSendrequest() is successful.
Plain old way !
Include:
#include <wininet.h>
#pragma comment(lib,"Wininet.lib")
In your Method:
char url[128];
strcat(url, "http://www.techtoolbox.com");
bool bConnect = InternetCheckConnection(url, FLAG_ICC_FORCE_CONNECTION, 0);
if (bConnect)
{
//internet connection exists !
}
else
{
//internet DOES NOT connection exists !
}
Hope it helps.
The best way to test the availability of any resource is to try to use it. You only care about the Internet if there is something out there you want to connect to. So, try to connect to it, in the normal course of your program, and handle the errors. Don't try to second-guess what might happen if you try. First, you're trying to predict the future. Second, you aren't necessarily exercising the same things that the actual connection would exercise. Third, your test may succeed and your subsequent use fail due to an intervening condition changing. Fourth, you have to handle the errors from the real use of the resource anyway: why write all that code twice?
A simple solution is to try to connect to a well-known host, if it succeeds then you have a connection.
In my opinion a way is to create a socket and try connecting a known host. These links will help:
For windows: http://msdn.microsoft.com/en-us/library/ms740673(VS.85).aspx and for unix http://www.tenouk.com/cnlinuxsockettutorials.html.
HTH
Anil
Related
I'm writing a transparent intercepting HTTPS capable proxy using boost::asio + openSSL. I have a default server context where I specify that the server is a TLSv1.2 server, when a client connects, I extract the host from the hello and use SSL_set_SSL_CTX to set the context (which either already exists or I've just created it after spoofing the upstream cert) and initiate the server (downstream) read/write volley as well as the upstream.
This was working before I started storing and sharing contexts. On each new incoming connection, I was creating a new client socket and context, loading ca-bundle as verify file, then creating a new server context, getting the spoofed certificate. It was functioning, but I started developing issues where EC_KEY objects were being double freed and such. I learned from another question of mine that I was going about this the wrong way and began refactoring to recycle and share CTX objects. To be specific, I'm using a single client CTX shared across the board that loads, at program startup, the CA-Bundle for verification.
However, since this refactor, I'm getting this on both the client and the server:
decryption failed or bad record mac
..mixed with a bajillion "short read"s. If I try to force everything TLSv1.2, I get
block cipher pad is wrong
Those errors are given to me after a read/write has failed and I call async_shutdown on either upstream or downstream sockets, which in the callback, error is set (so the shutdown failed).
I've scoured the interwebs finding jira posts from places like apache httpd and nginx where this error was fixed in different ways (resizing read buffers to be larger, openSSL patches, forcing SSLv3, so on and so forth).
I thought there might be an issue with multithreading (my io-service uses a thread pool) but I can see in the code that boost do_init sets locking mechanics for openSSL and all of my IO are wrapped into a single strand.
I'm at a total loss and am wondering if anyone can shed light on what might be happening. I realize I've posted no code, that's because I've got hundreds and hundreds of lines of it and don't want to turn people off with a huge code dump. I realize however this is a rather complicated program and thus a complicated issue so please ask and I'll provide whatever I can.
Edit
I guess I should mention for completeness that I'm getting these errors on both openssl 1.0.2 and 1.0.2a, Win 8.1 x64 and I'm intercepting and routing the http/https traffic through my proxy with with WinDivert.
Edit 2
Reduced entire program to 1 thread, same effect. Created new client CTX for each client connection, same issue. Tried disabling AES-NI, issue persists. Tried different computer, same effect. Recompiled openssl from source (was using precompiled binaries), issue persists. Tried setting additional OP_ workaround flags described in current docs related to downgrade detection, padding bugs, so on and so forth, issue persist. I think I'll just start randomly mashing the keyboard and compile button soon.
I was going to just delete this question, but I decided to answer it in light of the fact that nowhere on the net (that I could find) actually pointed to a correct solution to this problem. I've read every single report about this error that one could find and every single one of those reports, the people "solved" or "reduced" this error in a different way. Every single one of them, a different solution. This is what helped make this issue so difficult to reason out, because everyone everywhere has a different underlying causal explanation.
It's complicated, ready? This error will present itself if you cancel/abort a pending async SSL operation. Mind->boom(). It'll be even more confusing if you do what the docs say and use async_shutdown to do so, because even the call back to async_shutdown will fail (error code is set) and your error message will randomly be something stupid like "decryption failed or bad record mac" or "block cipher pad is wrong" or "SSLv3 alert!" so on and so forth. When seeing errors like this, ignore the errors and analyze the control flow of your IO ops, somewhere you're either prematurely ending them or getting them out of order.
In my case, the premature end was (sort of) intentional, since during this stupid heavy refactor I decided to change things outside the scope of the problem, like my HTTPHeader parser, which I bugged out and ended up cause it to fail nearly 100% and thus aborting the connections. :) The error strings were masking the real cause by telling me encryption failed for some reason or another. Dumb mistake I know, but I take comfort in being the first one (apparently) to recognize it. :)
Open a powershell and type this
(Invoke-WebRequest -Uri status.dev.azure.com).StatusDescription
https://devblogs.microsoft.com/devops/deprecating-weak-cryptographic-standards-tls-1-0-and-1-1-in-azure-devops-services/
I am running an ssh tunnel from an application using a QProcess:
QProcess* process = new QProcess();
process->start("ssh", QStringList()<<"-L"<<"27017:localhost:27017"<<"example.com");
So far it works great, the only problem being that there is no way for me to see when the port has actually been created.
When I run the command on a shell, it takes about 10 seconds to connect to the remote host after which the forwarded port is ready for usage. How do I detect it from my application?
EDIT:
As suggested by vahancho, I used the fact that post-connection there is some output on the terminal that can be used to detect that the connection has succeeded. However, there is a line which is run instantly after launch Pseudo-terminal will not be allocated because stdin is not a terminal, which probably would give a false alarm. The correct output is available in the second signal, emitted a bit later (which is a true indicator of the port having being opened). To get rid of the first message, I am now running ssh using ssh -t -t to force an stdin allocation.
So, the only question left is, can anyone help me without any concerns in this approach?
So, the only question left is, can anyone help me without any concerns in this approach?
This is not a stable and robust solution, unfortunately. It is similarly a broken concept to handling git outputs rather than using an actual library. The main problem is that these softwares do not have any guarantee for output compatibility, rightfully.
Just imagine that what happens if they have an unclear text, a typo, et all, unnoticed. They inherently need to fix the output respectively, and all the applications relying on the output would abruptly break.
This is also the reason behind working on dedicated libraries giving access to the functionality for reuse rather than working with the user facing output directly. In case of git, this means the libgit2 library, for instance.
Qt does not have an ssh mechanism in place by default like you can have such libraries in python, e.g. paramiko.
I would suggest to establish a way in your code by using libssh or libssh2 as you also noted yourself in the comment. I can understand the inconvenience that is not a truly Qt'ish way as of now, but at this point Qt cannot provide anything more robust without third-party.
That being said, it would be nice to see a similar add-on library in the Qt Project for the future, but this may not be happen any soon. If you write your software with proper design in mind, you will be able to switch to such a library withour major issues once someone stands up to maintain such an additional library to Qt or elsewhere.
I had the same problem, but in my case ssh do not output anything - so I couldn't just wait for output. I'm also using ssh to setupt tunnel, so I used QTcpSocket:
program = "ssh";
arguments << m_host << "-N" << "-L" << QString("3306:%1:3306").arg(m_host);
connect(tunnelProcess, &QProcess::started, this, &Database::waitForTunnel);
tunnelProcess->start(program, arguments);
waitForTunnel() slot:
QTcpSocket sock;
sock.connectToHost("127.0.0.1", 3306);
if(sock.waitForConnected(100000))
{
sock.disconnectFromHost();
openDatabaseConnection();
}
else
qDebug() << "timeout";
I hope this will help future people finding this question ;)
Well, three questions in less then 24 hours.But I suppose the lack of any helpful documentation (that i can find anyway) gives me no choice.
now i know all about the security stuff adobes got going, the policy file deal and sandbox limitations that have to be juggled around. ive done the suggested options changes, allowing network access in my AS3 project. I got my server ready to spit the policy file out instantly upon connection; but the problem is flash/AS3 whatever you wanna call it simply doesn't see my server (or the other way around)
AS3 delays for a few seconds, like the documentation say it will if its struggling to make a connection/find the policy file, but it never makes a connection period, tries for a while and then gives up and spits me a access error (because it didn't find the policy file it assumes its not allowed on the network so it get mad at me for trying... lil stubborn buggers)
Flash never gets what its looking for, and my server never detects any connections (failed or succeeded, nothing) I know my server is good because i've tested it with a test client i wrote in C++ and they talk just like best friends.
So I'm pretty much and a loss for ideas now, I thought about re-creating the winsock classes in AS3, but i don't even know how the connect() function fro winsock actually works; i got the declaration, no definition for it that i can find.
I am not sure what you would really need from my source code, but there's over a thousand lines in the client alone already so posting it all isn't really an option. ill give here what i think is relevant at least.
function hwndEnterFrame(e:Event):void
{
//trace("Frame Entered");
if (firstframe)
{
trace("try to reconcile policy file...");
//Security.loadPolicyFile("192.168.1.2:843");
TSocket = new Socket("192.168.1.2",843);//must call flush() to send data***
firstframe = false;
}
The Security.loadpolicyfile doesnt seem to do anything as far ive noticed, i get the same msgs with or without it, the code seems to be looking for the policy file at the location specified in the socket declaration. Everything compiles fine, it just ain't doing what i want it do :P everyone else seems to be writing their servers in Perl or Python i haven't found much of an abundance of C++ material, although from what i understand TCP is a universal connection across any platform that supports it (can cross-language without any funny-business)
meh, that what i got for now, if you want other parts of the code (client or sever side, whatever you want) ill stick it up here quick-like.
EDIT:
I found a swf online that i downloaded, it connected fine to the example server that came with it (but that server was written in c sparp so its not much use to me) but it wont connect to my server. So a known good flash client WONT connect to my C++ server, but a C++ client WILL connect to my C++ server. So its clearly somthing on the server side, becuase it dosnt hear any connection whatsoever from the flash apps (mine or the expamle one)
Cheers;
-Tyler
I finally figured it out. I needed to AllowDomian(IPofserver). I thought I had already tried that but apparently not.
from my C++ source, I am starting an RPC service calling svc_run(). Everything looks just fine and I can see my service running if I type rpcinfo -p in my terminal.
Now I am working on a "cleanup" function which should stop this service and remove it from the rpcinfo -p list.
How can I do that? At the moment I am only able to stop it using sudo rpcinfo -d program version in my terminal. How can I do this from my source file?
Thanks.
After some time, I found out how to do this. Actually I faced some unexpected difficulties. The standard way to do this would be to use this:
svc_unregister(PROGID, VERSION)
but somehow, it did not work for me. After lots of trial and some online help (http://www.spinics.net/lists/linux-nfs/msg05619.html) I was able to delete the RPC service calling:
pmap_unset(PROGID, VERSION);
Hope this will help :)
Try to use void svc_exit(void) function. For more detailed description please refer to rpc_svc_calls chapter.
I tried this force stop of svc_run(), however did not find a solution, I however made the svc_run() stop from within the registered function and then it stopped - perhaps this could help you - please look at this : svc_exit Subroutine
The 'nicest' solution is to use both DevCpp's and Danilo's solution combined:
Among the RPC functions of your server, define one function which, when called by the client, executes svc_exit(). This will let your RPC server return from the svc_run() loop. Now you can either extend your RPC client application or create a separate client application to terminate your server.
In your RPC server's main program, right after the call to svc_run(), execute 'pmap_unset(PROGID, VERSION);'. This will let rpcbind unregister your RPC address.
Then do the usual cleanup of your application.
This combination allows your RPC server to run as a demon, i.e. without user interaction, while still offering a clean exit without having to cancel the process.
Does any one have a snippet of their code that, checks if the network is enabled on a machine and has an active IP Address.
I have a networking software that connects to other client machines, Although it works when the machine is connected but if i unplug the cable or disable the network, It throws a whole reem of exceptions.
It would be nice to just put a check on top :D
Thanks in Advance
Network is always in dynamic state, a simple check at beginning of the run is not enough for correct operation.
So unfortunately you have to check for any network operations succeess state.
As for not even starting program with network disconnected state... Consider if your program is automatically started after computer has crashed or power failure. Or if any other component has suffered something similar, or a glitch. These happen surprisingly often, and restarting program on n+1 computers just because some dweeb stumbled on network cable is quite annoying..
For checking a general availability of networking, you can always "ping -q -c 1 127.0.0.1" return value is 1 if localhost does not answer. This should be in startup script, quite unnecessary to code it in application.
You should probably just catch the exceptions: otherwise you'll have problems if the machine is connected to a network, but not one with the appropriate other machines on it.
I think you can get what you want with 'ifconfig' command in the terminal.