path: root/src/pty.c

/* pty spawn. Hand-rolled rather than forkpty() so we need no libutil and
 * behave identically under musl.
 *
 * Windows has no fork and no pty; src/pty_win.c implements the same three
 * functions on ConPTY instead. */
#ifndef _WIN32
#define _GNU_SOURCE
#include "slosh.h"

#include <errno.h>
#include <sys/stat.h>

#include "terminfo.h"
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/wait.h>
#include <time.h>
#include <termios.h>
#include <unistd.h>

/* What a pane's TERM should be. xterm-ghostty is the truth -- the terminal
 * core is ghostty's -- but the truth is useless to a program whose curses
 * cannot find the entry: the entry ships with ghostty, and a machine that
 * has never seen ghostty has ncurses' database and nothing else. There,
 * nano exits on the spot ("Error opening terminal"), which reads as `C-a e`
 * flashing a pane; and a shell that cannot look up kbs guesses at what
 * backspace sends. So the entry is looked up the way curses would --
 * $TERMINFO, ~/.terminfo, $TERMINFO_DIRS, then the system directories, in
 * the letter layout (x/) and Darwin's hashed one (78/) -- and when it is
 * not there, TERM says xterm-256color: in every ncurses database since
 * forever, and close enough to what we speak that everything works. The
 * lookup happens where it matters: panes run on the server's machine.
 *
 * Computed once, in the parent, before the first fork. */
/* Write the embedded xterm-ghostty terminfo entry into ~/.terminfo, which
 * is the first place curses looks: no root, no package, no conflict with a
 * ghostty the machine may install later. Written under every name the
 * entry answers to, in the letter layout and Darwin's hashed one, because
 * the lookup is by filename. Quiet: pty_term() below calls this on its own
 * when the entry is nowhere to be found, and `--install-terminfo` is the
 * same write with a friendly report around it. */
int pty_terminfo_install(void) {
  const char *home = getenv("HOME");
  if (!home || !*home) return -1;
  static const char *const spots[][2] = {
      {"x", "xterm-ghostty"},
      {"78", "xterm-ghostty"},
      {"g", "ghostty"},
      {"67", "ghostty"},
  };
  char path[1024];
  snprintf(path, sizeof path, "%s/.terminfo", home);
  if (mkdir(path, 0755) != 0 && errno != EEXIST) return -1;
  for (size_t i = 0; i < sizeof spots / sizeof *spots; i++) {
    snprintf(path, sizeof path, "%s/.terminfo/%s", home, spots[i][0]);
    if (mkdir(path, 0755) != 0 && errno != EEXIST) return -1;
    snprintf(path, sizeof path, "%s/.terminfo/%s/%s", home, spots[i][0],
             spots[i][1]);
    FILE *f = fopen(path, "wb");
    if (!f || fwrite(TERMINFO_GHOSTTY, 1, sizeof TERMINFO_GHOSTTY, f) !=
                  sizeof TERMINFO_GHOSTTY) {
      if (f) fclose(f);
      return -1;
    }
    fclose(f);
  }
  return 0;
}

static bool term_add(char *dirs, size_t cap, size_t *n, const char *d) {
  if (!d || !*d) return false;
  int w = snprintf(dirs + *n, cap - *n, "%s%s", *n ? ":" : "", d);
  if (w > 0) *n = *n + (size_t)w < cap ? *n + (size_t)w : cap - 1;
  return true;
}

static const char *pty_term(void) {
  static const char *cached = NULL;
  if (cached) return cached;
  cached = "xterm-256color";

  char dirs[2048] = "";
  size_t n = 0;
  term_add(dirs, sizeof dirs, &n, getenv("TERMINFO"));
  const char *home = getenv("HOME");
  char user_ti[1024];
  if (home) {
    snprintf(user_ti, sizeof user_ti, "%s/.terminfo", home);
    term_add(dirs, sizeof dirs, &n, user_ti);
  }
  term_add(dirs, sizeof dirs, &n, getenv("TERMINFO_DIRS"));
  term_add(dirs, sizeof dirs, &n,
           "/etc/terminfo:/lib/terminfo:/usr/share/terminfo:"
           "/usr/local/share/terminfo");

  char *save = NULL;
  for (char *d = strtok_r(dirs, ":", &save); d;
       d = strtok_r(NULL, ":", &save)) {
    char path[1200];
    snprintf(path, sizeof path, "%s/x/xterm-ghostty", d);
    if (access(path, R_OK) == 0) {
      cached = "xterm-ghostty";
      break;
    }
    snprintf(path, sizeof path, "%s/78/xterm-ghostty", d);
    if (access(path, R_OK) == 0) {
      cached = "xterm-ghostty";
      break;
    }
  }

  /* Nowhere at all: put our own copy in ~/.terminfo and use it. The write
   * happens only when the entry is missing everywhere -- an entry that
   * exists is somebody's, possibly newer than ours, and stays theirs. On a
   * $HOME that cannot be written the fallback stands, and everything still
   * works at xterm-256color. */
  if (strcmp(cached, "xterm-256color") == 0 && pty_terminfo_install() == 0)
    cached = "xterm-ghostty";
  return cached;
}

int pty_spawn(pty_t *p, const char *const argv[], uint16_t cols, uint16_t rows,
              const char *cwd, uint16_t cell_w, uint16_t cell_h,
              uint32_t pane_id) {
  int master = posix_openpt(O_RDWR | O_NOCTTY);
  if (master < 0) return -1;
  if (grantpt(master) < 0 || unlockpt(master) < 0) {
    close(master);
    return -1;
  }

  char slave_name[128];
  if (ptsname_r(master, slave_name, sizeof slave_name) != 0) {
    close(master);
    return -1;
  }

  /* The slave is opened *here*, before the fork, and not by the child.
   *
   * Darwin attaches no line discipline to a pty master until its slave has
   * been opened: until then every TIOCSWINSZ on the master fails with ENOTTY
   * and the size is silently dropped. A pane is born 1x1 and told its real
   * size by the layout an instant later -- so with the child opening the
   * slave, that message raced the child's open() and usually lost, and
   * nothing ever sent it again. The pane's program spent its life believing
   * it had one row and one column, which is how `C-a e` produced an editor
   * drawing into a corner of the pane on macOS and nowhere else.
   *
   * Opening it in the parent closes the window entirely: the fork copies the
   * fd table, so the slave is open from the child's first instruction, and
   * every resize the parent sends afterwards lands. It is also what BSD
   * forkpty() does, for this reason.
   *
   * O_NOCTTY: we are not the process that wants this terminal. The child is,
   * and it says so with TIOCSCTTY after setsid(). */
  int slave = open(slave_name, O_RDWR | O_NOCTTY);
  if (slave < 0) {
    close(master);
    return -1;
  }

  /* The pixel fields matter: a program drawing images asks the tty how big a
   * cell is, and a winsize that says zero is a program that cannot size an
   * image. They are the *terminal's* pixels, so they are cols/rows times the
   * cell size the client reported.
   *
   * Set on the slave, which works on Linux and Darwin alike, and set before
   * the fork so it is ordered ahead of any resize the parent sends after it.
   * The child must not set it: by the time it ran, the size it was spawned
   * with could already be stale, and writing it back would undo the resize we
   * are here to deliver. */
  struct winsize ws = {.ws_col = cols,
                       .ws_row = rows,
                       .ws_xpixel = (unsigned short)(cols * cell_w),
                       .ws_ypixel = (unsigned short)(rows * cell_h)};
  ioctl(slave, TIOCSWINSZ, &ws);

  pty_term(); /* warm the cache in the parent; the child only reads it */

  pid_t pid = fork();
  if (pid < 0) {
    close(slave);
    close(master);
    return -1;
  }

  if (pid == 0) {
    /* child: new session, pty becomes the controlling terminal */
    setsid();
    ioctl(slave, TIOCSCTTY, 0);
    dup2(slave, STDIN_FILENO);
    dup2(slave, STDOUT_FILENO);
    dup2(slave, STDERR_FILENO);
    if (slave > STDERR_FILENO) close(slave);
    close(master);

    if (cwd) {
      if (chdir(cwd) != 0) { /* keep going in the old cwd */
      }
    }

    /* We are opinionated about the outer terminal (D11), and we present the
     * same contract inward. xterm-ghostty is what libghostty-vt implements. */
    setenv("TERM", pty_term(), 1);
    setenv("SLOSH", "1", 1);
    /* Which pane this is, so a program can act on its own pane instead of on
     * whichever one has focus. Set in the child, after the fork, because it is
     * per-pane: setting it in the parent would leak one pane's id into the
     * next spawn. Unset when there is no id, so a stale inherited value from
     * an outer session cannot be read as this one's. */
    if (pane_id) {
      char idbuf[16];
      snprintf(idbuf, sizeof idbuf, "%u", pane_id);
      setenv("SLOSH_PANE", idbuf, 1);
    } else {
      unsetenv("SLOSH_PANE");
    }
    unsetenv("ZELLIJ");

    signal(SIGPIPE, SIG_DFL);
    execvp(argv[0], (char *const *)argv);
    _exit(127);
  }

  /* parent: the child holds the slave now, and holding a second copy would
   * keep the master readable long after the program in the pane had gone. */
  close(slave);
  int flags = fcntl(master, F_GETFL, 0);
  fcntl(master, F_SETFL, flags | O_NONBLOCK);
  p->fd = master;
  p->pid = pid;
  return 0;
}

int pty_resize(pty_t *p, uint16_t cols, uint16_t rows, uint16_t cell_w,
               uint16_t cell_h) {
  struct winsize ws = {.ws_col = cols,
                       .ws_row = rows,
                       .ws_xpixel = (unsigned short)(cols * cell_w),
                       .ws_ypixel = (unsigned short)(rows * cell_h)};
  return ioctl(p->fd, TIOCSWINSZ, &ws);
}

void pty_close(pty_t *p) {
  if (p->fd >= 0) close(p->fd);
  p->fd = -1;
  if (p->pid > 0) {
    kill(p->pid, SIGHUP);
    /* Collect it, so a session that opens and closes panes all day does not
     * accumulate zombies. Bounded and short: almost everything is gone by the
     * first pass, and a program that outlives a SIGHUP is a bigger problem
     * than the process-table entry it leaves behind. */
    for (int i = 0; i < 5; i++) {
      if (waitpid(p->pid, NULL, WNOHANG) != 0) break;
      nanosleep(&(struct timespec){0, 200000}, NULL);
    }
  }
  p->pid = -1;
}

#endif /* !_WIN32 */