From c68fc6de5e2f0b9137d1838a3b01667c97ab0f44 Mon Sep 17 00:00:00 2001
From: Emile Clark-Boman <eclarkboman@gmail.com>
Date: Tue, 9 Sep 2025 15:43:54 +1000
Subject: [PATCH] add custom pty interface

---
 cli/main.c  |  24 ++++++++++
 cli/mkpty.c | 132 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 cli/mkpty.h |  14 ++++++
 3 files changed, 170 insertions(+)
 create mode 100644 cli/main.c
 create mode 100644 cli/mkpty.c
 create mode 100644 cli/mkpty.h

diff --git a/cli/main.c b/cli/main.c
new file mode 100644
index 0000000..86f4ffd
--- /dev/null
+++ b/cli/main.c
@@ -0,0 +1,24 @@
+#include "mkpty.h"
+#include "sys/types.h"
+
+
+// struct d_window {
+//   int ptmx; // fd
+// };
+
+// struct d_window new_window() {
+//   struct d_window w = {
+//     .ptmx = posix_openpt(O_RDWR | O_NOCTTY),
+//   };
+// }
+
+int main(int argc, char **argv) {
+  pid_t pid;
+  switch (pid = forkmkpty()) {
+  case -1:
+    break;
+  case 0:
+  default:
+    break;
+  }
+}
diff --git a/cli/mkpty.c b/cli/mkpty.c
new file mode 100644
index 0000000..4344a85
--- /dev/null
+++ b/cli/mkpty.c
@@ -0,0 +1,132 @@
+/* _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 <unistd.h>
+#include <asm/termbits.h>  /* TIOC* constants */
+#include <sys/ioctl.h>
+
+#ifdef PATH_MAX
+# define SNAME_MAX PATH_MAX
+#else
+# define SNAME_MAX 512
+#endif /* PATH_MAX */
+
+/* Allocate PTY master and slave file descriptors.
+ * errno will have been set if newpty() fails.
+ *
+ * NOTE: This function is my alternative to GLibC's
+ * openpty() function. It exists as a learning resource.
+ * REF: glibc.git:/login/openpty.c
+ */
+int mkpty(int *fdmx, int *fds) {
+  int _fdmx = -1, _fds = -1;
+  char sname[SNAME_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;
+}
+
+/*
+ */
+pid_t forkmkpty() {
+  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);
+    break;
+    
+  default:
+    /* Parent Process */
+    close(fds);
+    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))
+    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))
+    return EXIT_FAILURE;
+  *rows = win.ws_row;
+  *cols = win.ws_col;
+  return EXIT_SUCCESS;
+#endif /* TIOCGWINSZ */
+}
diff --git a/cli/mkpty.h b/cli/mkpty.h
new file mode 100644
index 0000000..ed0bce8
--- /dev/null
+++ b/cli/mkpty.h
@@ -0,0 +1,14 @@
+#ifndef DORNE_MKPTY_H
+#define DORNE_MKPTY_H
+
+#include <sys/types.h>
+
+/* Custom implementations of openpty() */
+int mkpty(int *fdmx, int *fds);
+/* Custom implementations of forkpty() */
+pid_t forkmkpty();
+
+int setptsxy(const unsigned short rows, const unsigned short cols, const int fds);
+int getptsxy(unsigned short *rows, unsigned short *cols, const int fds);
+
+#endif /* DORNE_MKPTY_H */