gh-85984: Add POSIX pseudo-terminal functions. (GH-102413)

Signed-off-by: Soumendra Ganguly <soumendraganguly@gmail.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
Co-authored-by: Petr Viktorin <encukou@gmail.com>

Doc/conf.py

@@ -97,19 +97,24 @@
     ('c:func', 'free'),
     ('c:func', 'gettimeofday'),
     ('c:func', 'gmtime'),
+    ('c:func', 'grantpt'),
     ('c:func', 'localeconv'),
     ('c:func', 'localtime'),
     ('c:func', 'main'),
     ('c:func', 'malloc'),
     ('c:func', 'mktime'),
+    ('c:func', 'posix_openpt'),
     ('c:func', 'printf'),
+    ('c:func', 'ptsname'),
+    ('c:func', 'ptsname_r'),
     ('c:func', 'realloc'),
     ('c:func', 'snprintf'),
     ('c:func', 'sprintf'),
     ('c:func', 'stat'),
     ('c:func', 'strftime'),
     ('c:func', 'system'),
     ('c:func', 'time'),
+    ('c:func', 'unlockpt'),
     ('c:func', 'vsnprintf'),
     # Standard C types
     ('c:type', 'FILE'),

Doc/library/os.rst

@@ -1122,6 +1122,20 @@ as internal buffering of data.
    .. versionchanged:: 3.12
       Added support for pipes on Windows.
 
+
+.. function:: grantpt(fd, /)
+
+   Grant access to the slave pseudo-terminal device associated with the
+   master pseudo-terminal device to which the file descriptor *fd* refers.
+   The file descriptor *fd* is not closed upon failure.
+
+   Calls the C standard library function :c:func:`grantpt`.
+
+   .. availability:: Unix, not Emscripten, not WASI.
+
+   .. versionadded:: 3.13
+
+
 .. function:: isatty(fd, /)
 
    Return ``True`` if the file descriptor *fd* is open and connected to a
@@ -1429,6 +1443,23 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    .. versionadded:: 3.3
 
 
+.. function:: posix_openpt(oflag, /)
+
+   Open and return a file descriptor for a master pseudo-terminal device.
+
+   Calls the C standard library function :c:func:`posix_openpt`. The *oflag*
+   argument is used to set file status flags and file access modes as
+   specified in the manual page of :c:func:`posix_openpt` of your system.
+
+   The returned file descriptor is :ref:`non-inheritable <fd_inheritance>`.
+   If the value :data:`O_CLOEXEC` is available on the system, it is added to
+   *oflag*.
+
+   .. availability:: Unix, not Emscripten, not WASI.
+
+   .. versionadded:: 3.13
+
+
 .. function:: preadv(fd, buffers, offset, flags=0, /)
 
    Read from a file descriptor *fd* at a position of *offset* into mutable
@@ -1486,6 +1517,21 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    .. versionadded:: 3.7
 
 
+.. function:: ptsname(fd, /)
+
+   Return the name of the slave pseudo-terminal device associated with the
+   master pseudo-terminal device to which the file descriptor *fd* refers.
+   The file descriptor *fd* is not closed upon failure.
+
+   Calls the reentrant C standard library function :c:func:`ptsname_r` if
+   it is available; otherwise, the C standard library function
+   :c:func:`ptsname`, which is not guaranteed to be thread-safe, is called.
+
+   .. availability:: Unix, not Emscripten, not WASI.
+
+   .. versionadded:: 3.13
+
+
 .. function:: pwrite(fd, str, offset, /)
 
    Write the bytestring in *str* to file descriptor *fd* at position of
@@ -1738,6 +1784,19 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    .. availability:: Unix.
 
 
+.. function:: unlockpt(fd, /)
+
+   Unlock the slave pseudo-terminal device associated with the master
+   pseudo-terminal device to which the file descriptor *fd* refers.
+   The file descriptor *fd* is not closed upon failure.
+
+   Calls the C standard library function :c:func:`unlockpt`.
+
+   .. availability:: Unix, not Emscripten, not WASI.
+
+   .. versionadded:: 3.13
+
+
 .. function:: write(fd, str, /)
 
    Write the bytestring in *str* to file descriptor *fd*.

Lib/test/test_os.py

@@ -4536,13 +4536,46 @@ def test_dup2(self):
         self.assertEqual(os.dup2(fd, fd3, inheritable=False), fd3)
         self.assertFalse(os.get_inheritable(fd3))
 
-    @unittest.skipUnless(hasattr(os, 'openpty'), "need os.openpty()")
+@unittest.skipUnless(hasattr(os, 'openpty'), "need os.openpty()")
+class PseudoterminalTests(unittest.TestCase):
+    def open_pty(self):
+        """Open a pty fd-pair, and schedule cleanup for it"""
+        main_fd, second_fd = os.openpty()
+        self.addCleanup(os.close, main_fd)
+        self.addCleanup(os.close, second_fd)
+        return main_fd, second_fd
+
     def test_openpty(self):
-        master_fd, slave_fd = os.openpty()
-        self.addCleanup(os.close, master_fd)
-        self.addCleanup(os.close, slave_fd)
-        self.assertEqual(os.get_inheritable(master_fd), False)
-        self.assertEqual(os.get_inheritable(slave_fd), False)
+        main_fd, second_fd = self.open_pty()
+        self.assertEqual(os.get_inheritable(main_fd), False)
+        self.assertEqual(os.get_inheritable(second_fd), False)
+
+    @unittest.skipUnless(hasattr(os, 'ptsname'), "need os.ptsname()")
+    @unittest.skipUnless(hasattr(os, 'O_RDWR'), "need os.O_RDWR")
+    @unittest.skipUnless(hasattr(os, 'O_NOCTTY'), "need os.O_NOCTTY")
+    def test_open_via_ptsname(self):
+        main_fd, second_fd = self.open_pty()
+        second_path = os.ptsname(main_fd)
+        reopened_second_fd = os.open(second_path, os.O_RDWR|os.O_NOCTTY)
+        self.addCleanup(os.close, reopened_second_fd)
+        os.write(reopened_second_fd, b'foo')
+        self.assertEqual(os.read(main_fd, 3), b'foo')
+
+    @unittest.skipUnless(hasattr(os, 'posix_openpt'), "need os.posix_openpt()")
+    @unittest.skipUnless(hasattr(os, 'grantpt'), "need os.grantpt()")
+    @unittest.skipUnless(hasattr(os, 'unlockpt'), "need os.unlockpt()")
+    @unittest.skipUnless(hasattr(os, 'ptsname'), "need os.ptsname()")
+    @unittest.skipUnless(hasattr(os, 'O_RDWR'), "need os.O_RDWR")
+    @unittest.skipUnless(hasattr(os, 'O_NOCTTY'), "need os.O_NOCTTY")
+    def test_posix_pty_functions(self):
+        mother_fd = os.posix_openpt(os.O_RDWR|os.O_NOCTTY)
+        self.addCleanup(os.close, mother_fd)
+        os.grantpt(mother_fd)
+        os.unlockpt(mother_fd)
+        son_path = os.ptsname(mother_fd)
+        son_fd = os.open(son_path, os.O_RDWR|os.O_NOCTTY)
+        self.addCleanup(os.close, son_fd)
+        self.assertEqual(os.ptsname(mother_fd), os.ttyname(son_fd))
 
     @unittest.skipUnless(hasattr(os, 'spawnl'), "need os.openpty()")
     def test_pipe_spawnl(self):

Misc/NEWS.d/next/Library/2023-03-15-03-21-18.gh-issue-85984.Xaq6ZN.rst

@@ -0,0 +1,2 @@
+Add POSIX pseudo-terminal functions :func:`os.posix_openpt`,
+:func:`os.grantpt`, :func:`os.unlockpt`, and :func:`os.ptsname`.