I have done a fair amount of research these last few weeks trying to create a connection diagnostic tool, I don't so much want to just check to see if the connection is available but to diagnose if there is jitter, packet loss, etc..
So far it seems that Java doesn't support a true ICMP request and that there are a few workarounds out there but none of which achieve what I'm trying to do.
Does anyone know if this sort of tool can be built or should I start looking into other options?
It seems that InetAdress is using ICMP when its possible:
https://docs.oracle.com/javase/7/docs/api/java/net/InetAddress.html
take a look at public boolean isReachable(int timeout)
Test whether that address is reachable. Best effort is made by the
implementation to try to reach the host, but firewalls and server
configuration may block requests resulting in a unreachable status
while some specific ports may be accessible. A typical implementation
will use ICMP ECHO REQUESTs if the privilege can be obtained,
otherwise it will try to establish a TCP connection on port 7 (Echo)
of the destination host.
You can find a simple use example here:
How to test if a remote system is reachable
or here How to ping an IP address
I believe ICMP4J does exactly what you need: Internet Control Message Protocol for Java
You can use 'Exec' to run ping at the command line (assuming your OS supports this), or JNI to interface to a native application to do the pinging.
Creating your own implementation of the ICMP protocol would not be trivial.
If you do use Exec be aware of it's limitations which are not always obvious in initial testing:
http://www.javaworld.com/article/2071275/core-java/when-runtime-exec---won-t.html
Related
I am using MySQL workbench on windows, which I want to connect to a Node-Red running on the IBM cloud. Since I don't run them on the same server the host 127.0.0.1 and port 3306 does not seem to work. What permissions should I give?
I'm going to make a LOT of assumptions here, because there really isn't enough information in your question.
First assumption, by "running on IBM" you mean that Node-RED is running on the IBM Cloud hosting service.
The short answer is you can not do what you want.
The longer version is that you probably could actually make this work but doing it is a REALLY bad idea.
Second assumption, you are doing this from home (even if you are doing it from a office location the same problems are likely to apply). This means you are connected to a local LAN using RFC 1918 address range (e.g. 192.168.0.x), this means you are behind a router that is performing NAT (Network Address Translation). This means you are going to need to set up portforwarding on the router so that when traffic arrives at the router it will send it on to your Windows machine. How you do this will depend on your router.
Next problem, your broadband probably doesn't have a static IP address which means it will change every time your connection drops. There are work arounds for this using things like Dynamic DNS. But that's too complicated to get into here.
Assuming you get all of that sorted out you still have the problem that you have now exposed your mysql database to the internet, so you need to make sure you have enabled all the right security measures to prevent people logging in and at best seeing all your data.
There are 2 much better solutions to this
Run Node-RED on the same machine or at least on the same local network as the database.
Use one of IBM Clouds hosted database solutions, these are a lot easier to connect to a IBM Cloud instance of Node-RED.
If you do not want to open ports to your network I recommend using a free MYSQL remote server
A simple website is https://remotemysql.com
Just take the screenshot of the credentials of your database after registration.
Keep in mind if your database is empty it will get deleted after some time.
WebRTC comes essentially in 3 flavors depending on the network situation:
No NAT - session is peer to peer
NAT - session uses STUN but is eventually peer to peer for the media
NAT+Firewall: in which case session is not peer to peer and media goes through a TURN server.
Is there a way/tool to figure out for an existing live session if it is using a TURN server or if it's peer to peer?
I am using chrome. If a tool exists for other browsers I am happy to know about it as well.
Thx
this pull request for the webrtc samples makes the constraints/getStats sample show the ip address. Instead of the local and remote ip around here you want the candidateType property.
If either of them is "relay" you are using a turn server. If both are "host" this is a direct connection without NAT. For all other cases NAT is used.
Note that this sample is currently a bit of a mess since the getStats API changed a bit.
How does a Server know to close a Web Socket connection in HTML5 on below scenarios and other cases.
Browser closed abruptly
Browser Refresh(A new Socket connection creation or still it will use existing Connection)
System abrupt power off
In case the client quits without being able to notify the server, the basic characteristics of the TCP implementation define the behavior.
As long as your application (and host system itself) do not attempt to send any data over this broken connection, the host will not realize that something is wrong. Hence, the connection could stay 'open' for a long while and allocate resources, from the server's point of view.
However, in the moment data is attempted to be sent to the remote end, the remote end will not acknowledge the retrieval and TCP retransmission comes into play. It involves a certain number of repetitions and used timeouts. The exact parameters depend on the implementation (operating system in use). When the retransmission finally fails, the TCP connection is closed and resources are freed on the server side. So you can
rely on the fact that at some point your application might want to write to the missing remote end and while doing so trigger the detection of the dead connection or
detect missing remote ends yourself by using something like pings on the application level or
use something like pings on the operating system level, via TCP keepalive techniques.
The easiest part of your question is the browser refresh part. IE,FF and Chrome will close the opened connection and open a new one. I guess, that any other browser will do the same.
Point 1 and 3 i can only guess: If the client can still close the tcp connection cleanly, the server will immediately recognize that the connection has been closed. If you are using tomcat, the onClose method of the MessageInbound instance will be called.
If the client could not close the tcp connection cleanly, the server will wait for some kind of timeout. The server will definitely timeout fast when it tries to write something to the socket. You could implement a heartbeat mechanism to do this. Websockets seem to have the option of an automatic heartbeat but not all browsers and servers seem to support it.
If a user closes a browser tab with an opened web socket, the server will not know this one has been closed right away. However, as Jan-Philip says, if you attempt to write the operation will fail and using the error given you know the current state for the connection.
For example, when using the ws lib for nodejs, if you try to send data to a closed websocket an exception will be thrown, saying something like [Error: not opened]. Their you know the connection no longer exists and you can do any cleanup needed.
I have this project for my classes i'm currently workin' on. here it is:
WebPage client for Telnet not on standard ports, with ability to choose a port and connect
I have machines with telnet servers on them, just waiting for connection.
So my idea was to set up a nodeJS with express server on a dedicated machine. This would handle connections through telnet and host a page for clients, that would use socket.io to exchange information with server side.
But as i'm new to such technologies (telecommunications student) i wonder if it is possible. I spotted something like this - jsterm.com by Peter Nitsch, but i see there are some massive gaps in code and the demo does not really work so i don't know if it actually works. Did anyone try this?
My other problem is - when i send information to nodeJS server through websockets, which seems achievable for me, what do i do with this information? Do i just set up another websocket to pass the same data i got from client websocket directly to the telnet port?
Can sockets connect directly to specific port, without any websocket waiting on the other side?
If my idea is wrong, could anyone help me - maybe there exists some nice solution - i was thinking about Anyterm for example but i see that it requires an apache server and runs completely different technologies...
Just to be clear, WebSocket connections are not raw TCP socket connections. They have extra header information in each packet, browser to server data is masked using a running XOR, etc.
In order for the browser to communicate with a normal TCP server (e.g. a telnet server) you will need some sort of bridge service. It just so happens that such a thing already exists. websockify is a server that accepts WebSocket connections and bridges them to a raw TCP server.
In fact, the websockify project already includes a working telnet client as an example application. However, note that one limitation of websockify (for security reasons) is that the client cannot pick an arbitrary server address/port to connect to. The target address(es) must be predefined, either as a single target specified on the command line for websockify, or as multiple targets specified in a configuration file (and selected via a token in the WebSocket connect string).
There are multiple implementations of websockify in different languages (python, C, node, ruby, Clojure) however, only the python version currently supports multiple targets via a configuration file.
Disclaimer: I created websockify.
A process is connecting to a certain ip or domain, but I do not know what it is. The process can't connect to the server. How do I find and change it?
TCPView and netstat work best for connections already established, which isn't the original poster's position.
A better tool for this task is a packet sniffer, which can observe the connection attempt. I recommend Wireshark, which is available for all major platforms.
Details:
Install, then start Wireshark
Press Ctrl-K to start capturing
Select the network interface that you expect the program to use
Type "tcp[tcpflags] & (tcp-syn|tcp-ack) == tcp-syn" in the Capture Filter box (no quotes)
Start the capture, go make your program try to connect, and then stop the capture.
If you do the last step fast enough on a machine without a lot of other network activity, you will have only one captured packet. Otherwise, you'll have to dig through a list to find the one you want. This packet will show the TCP port the program is trying to use.
Type netstat at the cmd prompt to see what ports are being used by active processes. Aside from that, you can't change the port being used by the proc to connect (unless you built the app obviously)
TCPView is a nice little utility that will show you all the open connections and endpoints on the local machine.
If the program is connecting using a DNS name (e.g., example.com), you can use the hosts file (c:\windows\system32\drivers\etc\hosts) to make that name map to a different IP address.
If you mean redirect the connection programmatically, that is a lot more complicated. You're not writing malware, are you?