package main import ( "os" "os/exec" "os/signal" "syscall" "time" ptyDevice "github.com/elisescu/pty" "golang.org/x/crypto/ssh/terminal" ) type onWindowChangesCB func(int, int) // This defines a PTY Master whih will encapsulate the command we want to run, and provide simple // access to the command, to write and read IO, but also to control the window size. type ptyMaster struct { ptyFile *os.File command *exec.Cmd windowChangedCB onWindowChangesCB terminalInitState *terminal.State } func ptyMasterNew() *ptyMaster { return &ptyMaster{} } func (pty *ptyMaster) Start(command string, args []string, winChangedCB onWindowChangesCB) (err error) { pty.windowChangedCB = winChangedCB // Save the initial state of the terminal, before making it RAW. Note that this terminal is the // terminal under which the tty-share command has been started, and it's identified via the // stdin file descriptor (0 in this case) // We need to make this terminal RAW so that when the command (passed here as a string, a shell // usually), is receiving all the input, including the special characters: // so no SIGINT for Ctrl-C, but the RAW character data, so no line discipline. // Read more here: https://www.linusakesson.net/programming/tty/ pty.terminalInitState, err = terminal.MakeRaw(0) pty.command = exec.Command(command, args...) pty.ptyFile, err = ptyDevice.Start(pty.command) if err != nil { return } // Start listening for window changes go onWindowChanges(func(cols, rows int) { // TODO:policy: should the server decide here if we care about the size and set it // right here? pty.SetWinSize(rows, cols) // Notify the ptyMaster user of the window changes, to be sent to the remote side pty.windowChangedCB(cols, rows) }) // Set the initial window size cols, rows, err := terminal.GetSize(0) pty.SetWinSize(rows, cols) return } func (pty *ptyMaster) GetWinSize() (int, int, error) { cols, rows, err := terminal.GetSize(0) return cols, rows, err } func (pty *ptyMaster) Write(b []byte) (int, error) { return pty.ptyFile.Write(b) } func (pty *ptyMaster) Read(b []byte) (int, error) { return pty.ptyFile.Read(b) } func (pty *ptyMaster) SetWinSize(rows, cols int) { ptyDevice.Setsize(pty.ptyFile, rows, cols) } func (pty *ptyMaster) Refresh() { // We wanna force the app to re-draw itself, but there doesn't seem to be a way to do that // so we fake it by resizing the window quickly, making it smaller and then back big cols, rows, err := pty.GetWinSize() if err != nil { return } pty.SetWinSize(rows-1, cols) go func() { time.Sleep(time.Millisecond * 50) pty.SetWinSize(rows, cols) }() } func (pty *ptyMaster) Wait() (err error) { err = pty.command.Wait() // The terminal has to be restored from the RAW state, to its initial state terminal.Restore(0, pty.terminalInitState) return } func (pty *ptyMaster) Stop() (err error) { signal.Ignore(syscall.SIGWINCH) pty.command.Process.Signal(syscall.SIGTERM) // TODO: Find a proper wai to close the running command. Perhaps have a timeout after which, // if the command hasn't reacted to SIGTERM, then send a SIGKILL // (bash for example doesn't finish if only a SIGTERM has been sent) pty.command.Process.Signal(syscall.SIGKILL) return } func onWindowChanges(winChangedCb func(cols, rows int)) { winChangedSig := make(chan os.Signal, 1) signal.Notify(winChangedSig, syscall.SIGWINCH) // The interface for getting window changes from the pty slave to its process, is via signals. // In our case here, the tty-share command (built in this project) is the client, which should // get notified if the terminal window in which it runs has changed. To get that, it needs to // register for SIGWINCH signal, which is used by the kernel to tell process that the window // has changed its dimentions. // Read more here: https://www.linusakesson.net/programming/tty/ // Shortly, ioctl calls are used to communicate from the process to the pty slave device, // and signals are used for the communiation in the reverse direction: from the pty slave // device to the process. for { select { case <-winChangedSig: cols, rows, err := terminal.GetSize(0) if err == nil { winChangedCb(cols, rows) } else { log.Warnf("Can't get window size: %s", err.Error()) } } } }