I am looking to write a program that will connect to many computers from a single computer. Sort of like "Command Center" where you can monitor all the remote system remotely on a single PC.
My plan is to have multiple Client Sockets on a form. They will connect to individual PCs remotely. So, they can request information from them to display on the Window. Remote PCs will be hosts. Is this possible?
Direct answer to your question: Yes, you can do that.
Long answer: Yes, you can do that but are you sure your design is correct? Are you sure you want to create parallel connections, one to each client? Probably you don't! If yes, then you probably want to run them in separate threads.
If you want to send some commands from time to time (and you are not doing some kind of constant video monitoring) why don't you just use one connection and 'switch' between clients?
I can't tell you more about the design because from your question is not clear about what you want to build (what exactly you are 'monitoring').
VERY IMPORTANT!
Two important notices to take into account before designing your app (both relevants only if the remote computers are not in the LAN (you connect to them via Internet)):
If the remote computers are running as servers, you will have lots of problems to explain your customers (if they are connected (and they probably are) to Internet via a router) how to setup the router and the software firewall. For example, if a remote computer is listening for commands from you, on port 1234 (for example) the firewall in the router will block BY DEFAULT any connection attempt from a 'foreign' computer (from you) to that port.
If your remote computers are running as clients, how they will know master's IP (your IP). Do you have a static IP?
What you actually need is one ServerSocket on the module running on your machine.
To which all your remote PC's will connect through their individual ClientSocket.
You can make your design other way round by putting ClientSocket on the module running on your machine and ServerSocket on the module running on remote machine.
But you will end up creating one ClientSocket to each ServerSocket, what if you have the number of remote servers increase.
Now if you still want to have multiple ClientSockets on your machine then as Altar said you could need a multi threaded application where each thread is responsible for one ClientSocket.
I would recommend Internet Direct (Indy) as they work well in threads, and you can specify a connect time-out per connection, so that your monitoring app will be able to get a 'negative' test result faster than with the default OS connect time-out.
Instead of placing them on the form, I would wrap each client in a class which runs an internal monitoring thread. More work initially but easier to keep independent from each other.
Related
I am presently working on a client-server solution to transfer files to another machine via a socket network connection. Since I intend to do some evaluation on the receiving end as well I am assuming that I will need to have some kind of client or server programme running there, too.
I am fairly new to the whole client-server thing and therefore have the following elementary question:
My present understanding is that client and server will be two independent programmes running on two different machines. How would one typically ensure that the communication partner (i.e., the server when sending from a client and the client when sending from a server) is actually up and running on the remote machine that I want to transfer a file to?
So far, I have been looking into the following options:
In the sending programme include an ssh access to the remote
machine and start an instance of the receiving programme on the
remote machine.
Have the receiving programme run as a demon process on the remote
machine. This would mean that the receiving programme should always
be running on the remote machine. However, how would I know whether
the process has crashed or has been shut down for some reason and
how would one recover from that without option 1) above?
So, my main question is: Are there any additional options that might be worth considering?
Thanks for your view on this!
Depending on how your client server messages are setup, a ping (I don't mean the ICMP ping, but the basic idea) message, where the server can respond with "I am alive" would help. This way at least you know the server end is running.
It is not uncommon in production environments using these that monitoring systems are put in place. Other options worth considering - xinet.d scripts - stuff that gets started on incoming connections.
There probably new ways to achieve the automatic start/restart or start on connection of this with systemd/systemctl but I am not familiar enough with them to give you the specifics.
A somewhat crude, but effective means may be a cron job that periodically runs a script to enforce keeping the service up.
I have two applications (.exe) that are running on the same machine (Windows XP x86) and I know are communicating with eachother (I dont know how, I didn't write them). I would like to find a way to sniff the communication between the applications. Is there a way to do this?
I've done some messing with ProMon and i can probably figure it out from there but I'm wondering if there is something a little more specific to this purpose. ProMon can be a bit intimidating.
First, you could watch your two applications with a system call tracer like StraceNT (or see this question). With some luck, you should be able to figure out whether the processes communicate through a local socket, a TCP connection (via localhost undoubtedly), a pipe, a named file, or shared memory.
You can also run netstat while the applications are running to see if they are opening any network ports.
Once you know what you're looking for, you can choose a more specific monitoring tool. If it's network communication (even over a loopback interface), you could try capturing the data with something like WinDump. If the communication is via shared memory, you could attach a debugger to one of the two processes and inspect the shared memory periodically.
How can I detect if a machine is connected/available in the present network.
It has several uses of course, but my main concern here is that my application uses resources located in specific machines and if they are not available it will not even attempt the connection and will use local resources.
you can try making a ping to the machine. check this article Making a PING with Delphi and the WMI.
ICMP echo request (PING) will tell you if the machine is up and reachable on the network. It will not tell you if the service you want to connect to is available on the machine (up and running).
Best bet would probably be to just attempt the connection and fall back to local resources if the connection fails.
Just try to use the resource and if you get an error use the local resource instead. The strategy you are trying to implement suffers from several problems including timing windows between the test and the use, during which the resource may become unavailable, and also doesn't actually test the resource for availability, only some lower-order thing like a TCP port or the ICMP echo part of the stack. In general the best way to detect whether a resource is available is just to try to use it, and recover from the failures. You have to write code to handle those failures anyway, why do it all twice?
A different strategy than trying to connect: let the server tell the clients if the services are still available, by sending UDP Broadcast or some kind of heartbeat signal over middleware (pipes?), which the clients listens to - a publish/subscribe communication model.
I want to create a client server application to test socket created and threads are running between client and server.
I want to check this for internet application.
But being on local machine. I cannot check.
You could run a virtual machine on your real machine and a bridge-mode network connection between the two. Then run the server on one and the client on the other.
However, you will not get a good picture of how well it responds under heavily loaded network conditions. For that you truly need a private network with a phantom load generator.
VirtualBox, VirtualPC, and vmware can do this. You might get better/more responses on superuser.com.
How can I disconnect any process from the Internet? PID process and IP (local / remote) are known.
It sounds like you want to control which applications can access the network/Internet.
If you just want to pick and choose which applications can have network access or which protocols you want to be used, I recommend any free or commercial firewall product.
If you need more control, such as disconnecting existing connections for a given process/protocol, I don't know of a simple API call. It would mean more effort, but you could use a local proxy server written in Delphi. If applications use this proxy to get to the outside world, you can add the ability to disconnect specific connections.
You could kill the process itself, or disconnect the network card from the network (the later would effect all processes on the machine though). AFIK most current software firewalls do not allow apply rule changes to existing connections, just when new connections are requested.