rename cli/ -> cursetree/

cursetree/_pty.c

@@ -0,0 +1,177 @@
+/* WARNING: The mkpty(), forkmkpty(), & bindpty() functions are based on
+ * WARNING: the glibc openpty(), forkpty(), & login_tty() functions respectively.
+ * WARNING:
+ * WARNING: The GNU C Library's COPYING & COPYING.LIB licenses are available at
+ * WARNING: LICENSES/GLIBC-COPYING & LICENSES/GLIBC-COPYING.LIB in this repo.
+ * WARNING:
+ * WARNING: login_tty() maintains the original University of California license
+ * WARNING: available at LICENSES/UC-LICENSE in this repo.
+ */
+
+/* _XOPEN_SOURCE unlocks <stdlib.h> pty/ptmx/pts declarations. */
+#define _XOPEN_SOURCE 600
+/* _GNU_SOURCE unlocks the ptsname_r declaration*/
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdlib.h>
+#include <asm/termbits.h>  /* TIOC* constants */
+#include <sys/ioctl.h>
+
+#include "_pty.h"
+
+/* Allocate PTY master and slave file descriptors.
+ * errno will have been set if newpty() fails.
+ *
+ * NOTE: This function is my alternative to GLibC's
+ * NOTE: openpty() function. It exists as a learning resource.
+ * REF: https://sourceware.org/git/glibc.git -> ./login/openpty.c
+ */
+int mkpty(int *fdmx, int *fds) {
+  int _fdmx = -1, _fds = -1;
+  char sname[TTYNAME_MAX];  
+
+  // Configure PTY master (file descriptor)
+  _fdmx = posix_openpt(O_RDWR | O_NOCTTY);
+  if (_fdmx == -1)
+    return EXIT_FAILURE;
+
+  if (grantpt(_fdmx))
+    goto fail;
+  if (unlockpt(_fdmx))
+    goto fail;
+
+#ifdef TIOCGPTPEER
+  /* Try to allocate slave fd solely based on PTMX fd first. */
+  _fds = ioctl(_fdmx, TIOCGPTPEER, O_RDWR | O_NOCTTY);
+#endif
+  if (_fds == -1) {
+    /* Fallback to path-based slave fd allocation
+     * (if the kernel doesn't support TIOCGPTPEER, ie Linux <4.13) */
+    if(ptsname_r(_fdmx, sname, sizeof(sname)))
+      goto fail;
+
+    _fds = open(sname, O_RDWR | O_NOCTTY);
+    if (_fds == -1)
+      goto fail;
+  }
+
+  /* Propagate file descriptors via parameters */
+  *fdmx = _fdmx;
+  *fds = _fds;
+  return EXIT_SUCCESS;
+
+fail:
+  if (_fdmx == -1) {
+    close(_fdmx);
+    if (_fds == -1)
+      close(_fds);
+  }
+  return EXIT_FAILURE;
+}
+
+/* Set fdty as the controlling terminal for the calling process.
+ * Returns 0 on success, and 1 on failure.
+ * NOTE: This function is my alternative to GLibC's
+ * NOTE: login_tty() function. It exists as a learning resource.
+ * REF: https://sourceware.org/git/glibc.git -> ./login/login_tty.c
+ */
+static inline int setctty(const int fdty) {  
+  /* We assume any kernel compiling this defines TIOCSCTTY,
+   * otherwise this implementation won't exactly work... */
+  return (ioctl(fdty, TIOCSCTTY, 0) != -1);
+}
+
+/* Bind fdty (terminal fd) to stdin/stdout/stderr for the calling process. 
+ * This functions blocks until the EBUSY (see `man dup2`) race condition lifts.
+ * NOTE: This function is my alternative to GLibC's
+ * NOTE: login_tty() function. It exists as a learning resource.
+ * WARNING: This function maintains the original University of California
+ * WARNING: LICENSE (1990-1993) as per glibc.git:/login/login_tty.c
+ * WARNING: available at LICENSES/UC-LICENSE in this repo.
+ * REF: https://sourceware.org/git/glibc.git -> ./login/login_tty.c
+ */
+void bindpty(const int fdty) {
+  /* Adjust stdin/stdout/stderr to refer to fd*/
+  BIND(fdty, STDIN_FILENO);
+  BIND(fdty, STDOUT_FILENO);
+  BIND(fdty, STDERR_FILENO);
+  if (fdty > 2)
+    close(fdty);
+}
+
+/* Allocate a PTY and fork, giving ptmx (master) to the parent
+ * and binding the child's stdin/stdout/stderr to pts (slave).
+ * Return value is indentical to fork(2).
+ * NOTE: This function is my alternative to GLibC's
+ * NOTE: forkpty() function. It exists as a learning resource.
+ * REF: https://sourceware.org/git/glibc.git -> ./login/forkpty.c
+ */
+pid_t forkmkpty(int *fdmx) {
+  int _fdmx, fds;
+  pid_t pid;
+  if (mkpty(&_fdmx, &fds))
+    return EXIT_FAILURE;
+
+  switch (pid = fork()) {
+  case -1:
+    close(_fdmx);
+    close(fds);
+    return -1;    
+  case 0:
+    /* Child Process */
+    close(_fdmx);
+    setctty(fds);
+    bindpty(fds);
+    break;
+    
+  default:
+    /* Parent Process */
+    close(fds);
+    // propagate ptmx (master) fd
+    *fdmx = _fdmx;
+    break;
+  }
+
+  /* Both Processes */
+  return pid;
+}
+
+/* Set pseudoterminal slave's window size.
+ * Returns 0 on success, and fails with -1 if the kernel doesn't
+ * implement this, or 1 for general errors (errno will be set).
+ * NOTE: Typically this is part of a glibc openpty() call.
+ */
+int setptsxy(const unsigned short rows, const unsigned short cols, const int fds) {
+#ifndef TIOCSWINSZ
+  /* Fail if kernel doesn't support TIOCSWINSZ. */
+  return -1;
+#else
+  struct winsize win = {
+    .ws_row = rows,
+    .ws_col = cols,
+  };
+  
+  if (ioctl(fds, TIOCSWINSZ, &win) == -1)
+    return EXIT_FAILURE;
+  return EXIT_SUCCESS;
+#endif /* TIOCSWINSZ */
+}
+
+/* Get pseudoterminal slave's window size.
+ * Returns 0 on success, and fails with -1 if the kernel doesn't
+ * implement this, or 1 for general errors (errno will be set).
+ */
+int getptsxy(unsigned short *rows, unsigned short *cols, const int fds) {
+#ifndef TIOCGWINSZ
+  /* Fail if kernel doesn't support TIOCGWINSZ. */
+  return -1;
+#else
+  struct winsize win = (struct winsize){ 0 };
+  if (ioctl(fds, TIOCGWINSZ, &win) == -1)
+    return EXIT_FAILURE;
+  *rows = win.ws_row;
+  *cols = win.ws_col;
+  return EXIT_SUCCESS;
+#endif /* TIOCGWINSZ */
+}
+