Help me track the status of a specific port: "LISTENING", "CLOSE_WAIT", "ESTABLISHED".
I have an analog solution with the netstat command:
local command = 'netstat -anp tcp | find ":1926 " '
local h = io.popen(command,"rb")
local result = h:read("*a")
h:close()
print(result)
if result:find("ESTABLISHED") then
print("Ok")
end
But I need to do the same with the Lua socket library.
Is it possible?
Like #Peter said, netstat uses the proc file system to gather network information, particularly port bindings. LuaSockets has it's own library to retrieve connection information. For example,
Listening
you can use master:listen(backlog) which specifies the socket is willing to receive connections, transforming the object into a server object. Server objects support the accept, getsockname, setoption, settimeout, and close methods. The parameter backlog specifies the number of client connections that can be queued waiting for service. If the queue is full and another client attempts connection, the connection is refused. In case of success, the method returns 1. In case of error, the method returns nil followed by an error message.
The following methods will return a string with the local IP address and a number with the port. In case of error, the method returns nil.
master:getsockname()
client:getsockname()
server:getsockname()
There also exists this method:
client:getpeername() That will return a string with the IP address of the peer, followed by the port number that peer is using for the connection. In case of error, the method returns nil.
For "CLOSE_WAIT", "ESTABLISHED", or other connection information you want to retrieve, please read the Official Documentation. It has everything you need with concise explanations of methods.
You can't query the status of a socket owned by another process using the sockets API, which is what LuaSocket uses under the covers.
In order to access information about another process, you need to query the OS instead. Assuming you are on Linux, this usually means looking at the proc filesystem.
I'm not hugely familiar with Lua, but a quick Google gives me this project: https://github.com/Wiladams/lj2procfs. I think this is probably what you need, assuming they have written a decoder for the relevant /proc/net files you need.
As for which file? If it's just the status, I think you want the tcp file as covered in http://www.onlamp.com/pub/a/linux/2000/11/16/LinuxAdmin.html
Related
I am interested in learning Vapor, so I decided to work on a website that displays government issued weather alerts. Alert distribution is done via a TCP/IP data stream (streaming1.naad-adna.pelmorex.com port 8080).
What I have in mind is to use IBM's BlueSocket (https://github.com/IBM-Swift/BlueSocket) to create a socket, though after this point, I gave it a bit of thought but was unable to come to a conclusion on what the next steps would be.
Alerts are streamed over the data stream, so I am aware the socket would need to be opened and listened on but wasn't able to get to much past that.
A few things with the data stream are that the start and end of an alert is detected using the start and end tags of the XML document (alert and /alert). There are no special or proprietary headers added to the data, it's only raw XML. I know some alerts also include an XML declaration so I assume the encoding should be taken into account if the declaration is available.
I was then thinking of using XMLParser to parse the XML and use the data I am interested in from the alert.
So really, the main thing I am struggling with is, when the socket is open, what would be the method to listen to it, determine the start and end of the alert and then pass that XML alert for processing.
I would appreciate any input, I am also not restricted to BlueSocket so if there is a better option for what I am trying to achieve, I would be more than open to it.
So really, the main thing I am struggling with is, when the socket is
open, what would be the method to listen to it, determine the start
and end of the alert and then pass that XML alert for processing.
The method that you should use is read(into data: inout Data). It stores any available data that the server has sent into data. There are a few reasons for this method to fail, such as the connection disconnecting.
Here's an example of how to use it:
import Foundation
import Socket
let s = try Socket.create()
try s.connect(to: "streaming1.naad-adna.pelmorex.com", port: 8080)
while true {
if try Socket.wait(for: [s], timeout: 0, waitForever: true) != nil {
var alert = Data()
try s.read(into: &alert)
if let message = String(data: alert, encoding: .ascii) {
print(message)
}
}
}
s.close()
First create the socket. The default is what we want, a IPv4 TCP Stream.
Second connect() to the server using the hostname and port. Without this step, the socket isn't connected and cannot receive or send any data.
wait() until hostname has sent us some data. It returns a list of sockets that have data available to read.
read() the data, decode it and print it. By default this call will block if there is no data available on the socket.
close() the socket. This is good practice.
You might also like to consider thinking about:
non blocking sockets
error handling
streaming (a single call to read() might not give a complete alert).
I hope this answers your question.
I'm using netty 4.x, and I finally find it calls
public boolean isActive() {
SocketChannel ch = javaChannel();
return ch.isOpen() && ch.isConnected();
}
can I use it to check whether the connection between client and server is readable/writeable?
If the answer is yes, then I believe isActive use sth. like heartbeat to check the status of the client. but when I grab the tcp packets I can't find any packets work as heartbeat through wireshark filter tcp.port==12093(it's my server port).
any suggestion is helps.
Channel.isActive() works by looking up the querying the underlying socket to see if it is connected.
So if we want to know how it works we should dig a little deeper, if you are using netty with tcp connections, you are almost sure you are using the java nio sockets.
From io.netty.channel.socket.nio.NioSocketChannel:
#Override
public boolean isActive() {
SocketChannel ch = javaChannel();
return ch.isOpen() && ch.isConnected();
}
Both of the above methods aren't that interesting, and are simply boolean flags set to the correct value by native code.
However, since isActive() just returns those boolean flags, you cannot be sure that the connection is still working at the moment you call the function, the best way would be to change your protocol to include some kind of ping message, for example IRC has a ping command, or FTP has the NOOB command.
When sending a ping message, you must make sure that it leaves enough headroom for partial network dropout, for example if your computer is connected through WIFI, there will be some packet loss. However, the native tcp layer in the operating system should handle these packet loss combined with resending for you, but it may mean that after you send a ping message, it may take up to a full minute before isActive() will return false.
If you want to add automatic ping messages to your protocol, it may be wise to look into the IdleStateHandler and the WriteTimeoutHandler.
If I open up a port on our server to listen out for incoming messages (ie - strings of text), how can i send those messages? are their any example codes out there that are useful?
I have downloaded a few sample projects but none seem to do i want.
what code is used to specify the ip address and port number?
Here you wil find exactly what you need.
It is a wrapper class called AsyncSocket; to connect you just send it the string with the ip and an int with the port.
It will do all the work on ints own.
To send info you just turn your string into NSData if I remember correctly.
It has a very easy to follow sample so you should be up and running in about 20 min.
Look up any tutorial text on networking.
For instance, there are a bunch of echo server implmentations at rosettacode.
I need an app that sends an UDP packet to some network server and receives the response. The server replies to the same port number where request came from, so I first need to bind() my socket to any UDP port number.
Hardcoding the UDP port number is a bad idea, as it might be used by any other application running on the same PC.
Is there a way to bind an UDP socket to any port available? IMO it should be an effective way to quickly obtain a free port #, which is used by e.g. accept() function.
If no, then what's the best strategy to try binding and check for WSAEADDRINUSE/EADDRINUSE status: try the ports sequentially starting from from 1025, or 1025+rand(), or some other?
Another option is to specify port 0 to bind(). That will allow you to bind to a specific IP address (in case you have multiple installed) while still binding to a random port. If you need to know which port was picked, you can use getsockname() after the binding has been performed.
Call sendto without calling bind first, the socket will be bound automatically (to a free port).
I must be missing something, why don't you use the udp socket to send back data?
Start with sendto and then use recvfrom function to read incoming data also you get as a bonus the address from which the data was sent, right there for you to send a response back.
I am writing a UDP test client/server and i want to get it through firewall. Supposedly all i need to do is have both sides send to the correct IP and server. Getting an IP is not a problem but how do i have the client pick a random free port and report it to the user? I eventually would want it to connect to a matchmaker server but right now i need a simple working prototype and i would like to cout the port number so my friend/tester can send me the # via IM so we can test.
How do i get the port number?
sorry for the long desc. I notice people tell me not to do what i am asking when i dont give a desc :(
To use the highly technical term, this is actually a pretty icky problem or even a pair of icky problems. Depending on the configuration of the firewall, it will usually allow responses from another endpoint on the IP endpoint as the request came from. So... if you friend receives the UDP datagram using something like the recvfrom() system call, the address parameter will receive the IP endpoint information to respond to. So the other end should be able to respond with a sendto() using the same addressing information. Something like:
/* initiator */
struct sockaddr_in hisaddr;
memset(&hisaddr, 0, sizeof(hisaddr));
hisaddr.sin_addr.s_addr = htonl(target_ip);
hisaddr.sin_port = htons(target_port);
sendto(sd, msg_ptr, msg_sz, 0, (struct sockaddr*)&hisaddr, sizeof(hisaddr));
/* receiver */
struct sockaddr_in peeraddr;
socklen_t peer_sz = sizeof(peeraddr);
recvfrom(sd, buf_ptr, buf_sz, 0, (struct sockaddr*)&peeraddr, &peer_sz);
/* build response */
sendto(sd, msg_ptr, msg_sz, 0, (struct sockaddr*)&peeraddr, peer_sz);
The peeraddr on the other side will be your external address or, more correctly, the IP address of your firewall and the port number that it chose to use. The port number that you specify in your code may be completely different than the port that your friend would have to send data to. Ultimately, it might not matter what port you choose to use since the firewall might be sending and receiving on an entirely different port - this is what Network Address Translation is all about. I would recommend reading RFC3235 for some tips on how to overcome that hurdle.
The best approach IMHO is to:
Let the OS choose a port by either calling bind() with a zero port number or skipping the bind altogether
Having the client receive the address information from the socket layer (e.g., the fifth and sixth arguments to recvfrom())
The client sends response to the endpoint retrieved in the previous step
Tweak the firewall configurations until the previous steps work
Of course, all of the magic is in the last step. If you can disable NAT or ensure that the firewall is never going to switch ports, then nailing down a port number and bind-ing to it will work as well. You might want to take a look at %WINDIR%\system32\drivers\etc\services (or /etc/services depending on your OS inclination) to get an idea of what port numbers are reserved or generally in use.
bind() the socket before you send your data. Specify port 0 to bind(), and the OS will pick an unused port for you. You can then use getsockname() to find out what port wsa chosen.
Generally speaking - you - as the developer - choose the port. You can set your application to read the port from a config file or user input - but no magic firewall is going to tell you what port to use...
If I'm understanding your question correctly, I'm not sure there's a way to do what you want programatically (and even if there is, I don't think it's the right approach). I think you need to find a port that isn't in use on the server machine (and perhaps a different or the same port on the client machine, if communication is bi-directional) AND that port must be able to pass through your firewall. I assume since you say "getting an IP is not a problem", you've already configured your firewall to forward some or all ports to a specific computer inside the firewall? If so, the port you seek is one of the ones you forwarded. You can just pick an arbitrary one, as long as no other service is running on that port. Ports below 1024 are reserved, so you probably want to pick a higher number than that. You can use a simple portscanning tool such as nmap to see which services are running on your computer on which ports and pick a different one. Note that nmap can be fooled by firewalls and various bind rules when sockets are created.
I think you're better off picking a fixed port rather than relying on the random port number chosen by the O/S.
If you use a random port you'd have to change your firewall settings each and every time you run the program.
If you're using WINSOCK check this link:
http://msdn.microsoft.com/en-us/library/aa280717(VS.60).aspx
Basically you have 2 choices set the port to 0 and let the system assign you one or chose a random one try to open the socket if it doesn't work try another (be sure to steer clear of reserved ports)