I'm trying to read data from the server with SSH protocol. For this, I'm using the j2ssh library. My server connects with the other server in ssh without any problem. The problem is when I try to read any data from the shell command line. Whatever "command" I send to program "read = in.read(buffer)" never get any data, I tried with "ls" with "cat filename.txt" and other commands.
Only one command works fine and is "tail -f filename.txt". With this command, I can see the buffer is not empty, this contain the text of file, but the tail command does not close and while listening, sends the program in loop.
Can Anyone help me to know why I can't get any data from othere command?
This is my code:
private String exec(String cmd) throws SSHHandlerException {
String result = null;
session = ssh.openSessionChannel();
if(session.startShell())
{
session.getOutputStream().write((cmd+"\n").getBytes());
session.getOutputStream().close();
result = read(session,log);
}
session.close();
ssh.disconnect();
return result;
}
private static String read(SessionChannelClient session, ProcessLogger log) throws Exception{
byte buffer[] = new byte[255];
int read;
StringBuffer out=new StringBuffer();
InputStream in = session.getInputStream();
while((read = in.read(buffer)) > 0) {
out.append(new String(buffer, 0, read));
}
return out.toString();
}
If your goal is to transfer files, you should be using an SFTP client instead. SFTP is exactly what you're looking for: a file transfer protocol on top of SSH. It's much, much more efficient than using some command on the host and redirecting the stream.
J2SSH has an SftpClient implementation that can be constructed with an SshClient. Just use one of the get methods. Javadocs are here.
Edit after learning that you're not trying to transfer files:
You need to request a pseudo-terminal before you start the shell. From the docs:
The remote process may require a pseudo terminal. Call this method before executing a command or starting a shell.
Also, because it appears that you're using a Linux environment, I would recommend using terminal type "xterm" rather than their example of "vt100".
The reason that tail was working and not the other commands was because you were calling tail interactively. The interactive command creates its own pseudo-terminal of sorts. If, instead, you call tail -n 16 filename.txt then you will get the same results as with the other commands because it won't be interactive.
Related
I am using jna module to connect two processes that both perform FFMPEG commands. Send SDTOUT of FFMPEG command on the server side to NampedPipe and receive STDIN from that NampedPipe for other FFMPEG command on the Client side.
this is how I capture STDOUT and send into the pipe in server Side:
InputStream out = inputProcess.getInputStream();
byte[] buffer = new byte[maxBufferSize];
while (inputProcess.isAlive()) {
int no = out.available();
if (no > 0 && no > maxBufferSize) {
int n = out.read(buffer, 0,maxBufferSize);
IntByReference lpNumberOfBytesWritten = new IntByReference(maxBufferSize);
Kernel32.INSTANCE.WriteFile(pipe, buffer, buffer.length, lpNumberOfBytesWritten, null);
}
}
And this is how I capture STDIN and feed it to the Client Side:
OutputStream in = outputProcess.getOutputStream();
while (pipeOpenValue >= 1 && outputProcess.isAlive() && ServerIdState) {
// read from pipe
resp = Kernel32.INSTANCE.ReadFile(handle, readBuffer,readBuffer.length, lpNumberOfBytesRead, null);
// Write to StdIn inputProcess
if (outputProcess != null) {
in.write(readBuffer);
in.flush();
}
// check pipe status
Kernel32.INSTANCE.GetNamedPipeHandleState(handle, null,PipeOpenStatus, null, null, null, 2048);
pipeOpenValue = PipeOpenStatus.getValue();
WinDef.ULONGByReference ServerId = new WinDef.ULONGByReference();
ServerIdState = Kernel32.INSTANCE.GetNamedPipeServerProcessId(handle, ServerId);
}
But I faced two problems:
High CPU usage due to iterating two loops in Server and Client. (find by profiling resources by VisualVM)
Slower operation than just connecting two FFMPEG command with regular | in command prompt. Speed depends on buffer size but large buffer size blocks operation and small buffer size reduce speed further.
Questions:
Is there any way not to send and receive in chunks of bytes? Just stream STDOUT to the Namedpipe and capture it in Client. (Eliminate two Loops)
If I cant use NampedPipe, is there any other way to Connect two FFMPEG process that runs in different java modules but in the same machine?
Thanks
Seems like you're constantly polling process states stdin on server side without waiting for any events or sleeping the thread.
Probably you want to take a look here:
Concurrent read/write of named pipe in Java (on windows)
Cheers!
I have a simple Java application, basically a server implemented using com.sun.net.HttpServer API, that reads a file and simply sends back the texts after some processing. The server part simply looks like this:
server = HttpServer.create(new InetSocketAddress(serverPort), 0);
logger.info("EventRetriever REST server listening to port: " + serverPort);
server.createContext("/getEvents", new MedatadaHandler());
server.setExecutor(null);
server.start();
// ...
#Override
public void handle(HttpExchange he) throws IOException {
//...
String response = requestEvents();
he.sendResponseHeaders(200, response.length());
OutputStream os = he.getResponseBody();
os.write(response.toString().getBytes());
os.close();
}
//...
public String requestEvents(){
//...
// this printing on the console looks fine though:
logger.info(jsonString);
return jsonString;
}
I run my jar file with java -jar myApp.jar on a command line or simply on my IDE. I'm witnessing some weird behaviors, sometimes just hanging, when it requires sending texts containing special characters, such as the music symbol ♪. When I call the IP:PORT/getEvent via a browser, the behavior is so weird:
If I run it on a Windows Powershell or Command Prompt, the symbol appears as ? on the console, and what I get from the browser is also shown as ?. But when I run the program on a linux server or my Eclipse IDE, it is shown correctly on the console (as ♪), but on the browser, I get the following error, although the status is 200 OK. I see on the console the java application keep looping printing the line every few seconds (as if it is trying to send the data, but can't maybe something is blocking it!). But I don't get any exception or errors on the app (I log all possible errors).
I'm very confused for this behavior. What's going on?!
First, why what I get is dependent on the environment I run my Java app?! If Windows Command Prompt/Powershell shows the character as ?, I expect it just showing it locally like that. Why should I see it also as ? on my browser?! Java app must be independent of the environment.
And second, what is going on with that error on the Linux/Eclipse envrionment when requesting a line that has this character?
The issue as could be predicted, was related to getBytes() and UTF-8 String representations. Did the following and it was all good then:
he.sendResponseHeaders(200, response.getBytes("UTF-8").length);
OutputStream os = he.getResponseBody();
os.write(response.getBytes("UTF-8"));
i need to send some messages from my java web application to some servers using Diameter protocol, in particular CCR-CCA scenario. I had a look at jdiameter opensource project, but my usecase does not require such complexity, since that i just need to send a single request and log the response (actually i don't even need the CER-CEA part).
So i thought i could just have used Seagull running under my webapp. I downloaded Seagull (for Windows), and what i'm trying to do is basically to run the .bat file coming from Seagull for the diameter environment from my java environment.
That's what i've done till now..
1) A simple test to invoke the client.. Here wrapper simply sets working dir and starts the process
public static void main(String[] args) {
List<String> cmd=new ArrayList<>();
cmd.add("cmd.exe");
cmd.add("/c");
cmd.add("my_start_client.bat");
JavaProcessBuilderWrapper wrapper = new JavaProcessBuilderWrapper();
Process p = wrapper.createProcess(RedirectErrorsTo.STDERR,
new HashMap<>(), new File("my_working_dir"), cmd);
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
StringBuilder output = new StringBuilder();
String line;
try {
while ((line = reader.readLine()) != null) {
output.append(line);
}
System.out.println(line);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
2) I modified the client's and server's .bat files coming from Seagull to use CCR-CCA protocol.
Running Java main with this configuration caused a
Fatal: Keyboard saved configuration failure error
on my logs.
3) So, as mentioned here i further modified my client's .bat file to run in background mode, adding -bg at the end. Now my client's bat look like this
#ECHO OFF
rem
"Diameter Start Script Sample"
"Local env"
SET RUN_DIR=C:\Program Files\Seagull
set PATH=%PATH%;%RUN_DIR%
set LD_LIBRARY_PATH=%RUN_DIR%
set RUN_DIR=%RUN_DIR%\diameter-env\run
cd %RUN_DIR%
cls
mode 81,25
echo "Seagull Diameter Client Sample Start"
seagull -conf ..\config\conf.client.xml -dico ..\config\base_ro_3gpp.xml -scen ..\scenario\ccr-cca.ro.client.xml -log ..\logs\ccr-cca.client.log -llevel ETM -bg
pause
Since i was facing some troubles, to keep things simple, i just tried to make it work at least via cmd (not using my java method), but i think background mode is messing around, because now when i start my server and then my client in bg mode, sometimes i get a
Fatal: Forking error
but the most of the times, the client send a single message and then on my console i see that my software is causing connection abort (error code -1), and from the log i see that the channel just get closed, and my client does not even receive an answer. (NB for now i left the configuration files untouched)
Has any of you faced this behaviour? Is something else closing the connection (firewall perhaps)? Do i have to provide other configurations to make this work?
Once i can get this working, can i use my java web app (with a method similar to the one i already mentioned) to make diameter calls?
Thanks in advance, any help is really welcomed.
I have a utility where Jmeter sends a request and the utility sends back response to Jmeter. When load increases, the Utility shuts down with an "EXCEPTION_ACCESS_VIOLATION".
Since it is an error, I am not able to handle it in a catch block. I made a second utility to restart the first utility when the error occurs. Below is the code of the second, restart, utility. In this second utility's code, at the second while, my program sometimes hangs. How do I detect this and restart the process?
public static void main(String[] args)
{
String line = null;
String currPID = null;
try
{
while(true)
{
Process process = Runtime.getRuntime().exec("java -XX:+HeapDumpOnOutOfMemoryError -Xms250M -Xmx500M -XX:ErrorFile=NUL ws ");
BufferedReader input = new BufferedReader(new InputStreamReader(process.getInputStream()));
while ((line = input.readLine()) != null) //Program stucks at this Line
{
if(line.trim().length() != 0)
{
if(line.startsWith("PID"))
{
currPID = line.substring(line.indexOf("#")+1);
}
}
}
System.out.println("Ended");
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
I analysed process through jvisualvm where i found two java process is in running mode when i start second(restart) utility. I can see first utility is restarting regularly because its PID is changing frequently in jvisualvm and same happening in task manager. Everything is going on very well manner.
After sometime i found only one process is in Jvisualvm ie second(restart) utility.
It means first utility JVM is crashed just guessing not sure. Something unusual is happening here. Because if JVM is crashed so It should be restarted.
So i opened task manager and found first utility PID exists there but it is not changing as happening in starting. If i kill the process(first utility) explicitly from task manager.
Seconds utility again restarts first utility same thing happens again, After some time first utility disappeared from jvisualvm, exists in taskmanager and delete process from taskmanager. What needs to do?
Try using .ready() function.
try {
if (stdError.ready())
{
while((line= stdError.readLine()) != null){
logger.error(line);
}
}
}
Do the same for the stdout.
It worked like a charm for me.
Your problem with hanging appears to be at the call to readLine.
readLine is for reading lines. The method will not return until the call is sure the end of line has been reached. It expects either a newline character or the complete cease of communications.
Is your first utility not sending a new line char?
Does your first utility fail to close the stream?
Your while call will hang indefinitely if the answer to both questions is yes.
You might be better off consuming with a custom implementation of the Scanner class.
Try to use getErrorStream() it'll catches the error message, if you use getInputStream() it'll reads only the success message or feedback messages.
for ex: if you execute the following command & read the process message using getInputStream(),
Process process = Runtime.getRuntime().exec("net use u: \\sharedIP\sharedFolder");
BufferedReader input = new BufferedReader(new inputStreamReader(process.getInputStream()));
you can only get feedback messages like "network drive connected successfully" but not the error messages.
if you use getErrorStream() to read the process message it'll read the error messages like "the network drive was not found". when the process executed it'll give a message to either getInputStream() or getErrorStream(). so use both method to read the message from the process, if i'm correct this'll work. I'm just trying to give you an idea but i'm not sure.
I am looking for a way to access running java program from command line. The best woud be something that does the following:
Starting java app:
bash$java -jar MyBundle.jar App
Accessing app:
bash$test.sh param1 param2
So, test.sh calls App from MyBundle.jar somehow and passes values param1 & param2.
Important: I am looking for very fast approach. App hold database connection and it is very expensive to start App every time I need access do DB.
I need solution that will work in Ubuntu and Debian. If it will work on Mac - great.
Any help is appreciated!
I think you need to take a client-server approach. You app is the server, it runs as a background process and listens for connections on some port. And your client makes requests to the server and gets back the response.
A fast and simple way of implementing this in java would be to wrap your app in the Jetty servlet container. You could set it up to return JSON responses for example, which are easy to process.
It would be quite straightforward to open a TCP/IP socket and use netcat from the shell.
Java code
final ServerSocket serverSocket = new ServerSocket(9050);
while (true) {
final Socket socket = serverSocket.accept();
java.util.logging.Logger.getAnonymousLogger().info("Accepted");
final BufferedReader br = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
final String input = br.readLine();
final BufferedWriter bw = new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream()));
bw.write("You said [" + input + "]");
bw.flush();
socket.close();
}
Shell code
echo 'bla' | nc localhost 9050
You'd need to muck around with threads to keep the sockets open to serve multiple requests.