Package ghidra.pty

Interface Pty

All Superinterfaces:
AutoCloseable
All Known Implementing Classes:
ConPty, SshPty, UnixPty
public interface Pty extends AutoCloseable
A pseudo-terminal

A pseudo-terminal is essentially a two way pipe where one end acts as the parent, and the other acts as the child. The process opening the pseudo-terminal is given a handle to both ends. The child end is generally given to a subprocess, possibly designating the pty as the controlling tty of a new session. This scheme is how, for example, an SSH daemon starts a new login shell. The shell is given the child end, and the parent end is presented to the SSH client.

This is more powerful than controlling a process via standard in and standard out. 1) Some programs detect whether or not stdin/out/err refer to the controlling tty. For example, a program should avoid prompting for passwords unless stdin is the controlling tty. Using a pty can provide a controlling tty that is not necessarily controlled by a user. 2) Terminals have other properties and can, e.g., send signals to the foreground process group (job) by sending special characters. Normal characters are passed to the child, but special characters may be interpreted by the terminal's line discipline. A rather common case is to send Ctrl-C (character 003). Using stdin, the subprocess simply reads 003. With a properly-configured pty and session, the subprocess is interrupted (sent SIGINT) instead.

This class opens a pseudo-terminal and presents both ends as individual handles. The parent end simply provides an input and output stream. These are typical byte-oriented streams, except that the data passes through the pty, subject to interpretation by the OS kernel. On Linux, this means the pty will apply the configured line discipline. Consult the host OS documentation for special character sequences.

The child end also provides the input and output streams, but it is uncommon to use them from the same process. More likely, subprocess is launched in a new session, configuring the child as the controlling terminal. Thus, the child handle provides methods for obtaining the child pty file name and/or spawning a new session. Once spawned, the parent end is used to control the session.

Example: 

 Pty pty = factory.openpty();
 pty.getChild().session("bash");
 
 PrintWriter writer = new PrintWriter(pty.getParent().getOutputStream());
 writer.println("echo test");
 BufferedReader reader =
        new BufferedReader(new InputStreamReader(pty.getParent().getInputStream()));
 System.out.println(reader.readLine());
 System.out.println(reader.readLine());
 
 pty.close();

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    close()
    Closes both ends of the pty
    PtyChild
    getChild()
    Get a handle to the child side of the pty
    PtyParent
    getParent()
    Get a handle to the parent side of the pty

  • Method Details

    • getParent

      PtyParent getParent()
      Get a handle to the parent side of the pty
      Returns:
      the parent handle

    • getChild

      PtyChild getChild()
      Get a handle to the child side of the pty
      Returns:
      the child handle

    • close

      void close() throws IOException
      Closes both ends of the pty

      This only closes this process's handles to the pty. For the parent end, this should be the only process with a handle. The child end may be opened by any number of other processes. More than likely, however, those processes will terminate once the parent end is closed, since reads or writes on the child will produce EOF or an error.

      Specified by:
      close in interface AutoCloseable
      Throws:
      IOException - if an I/O error occurs