Add a rustix::pty module. (#673)

Add a `rustix::pty` module, providing functions that wrap
`posix_openpt`, `grantpt`, `unlockpt`, `ptsname`, and so on.

Author: sunfishcode

Cargo.toml

@@ -166,6 +166,9 @@ param = ["fs"]
 # Enable this to enable `rustix::io::proc_self_*` (on Linux) and `ttyname`.
 procfs = ["once_cell", "itoa", "fs"]
 
+# Enable `rustix::pty::*`.
+pty = ["itoa", "fs"]
+
 # Enable `rustix::termios::*`.
 termios = []
 
@@ -188,6 +191,7 @@ all-apis = [
     "param",
     "process",
     "procfs",
+    "pty",
     "rand",
     "runtime",
     "termios",

README.md

@@ -63,6 +63,7 @@ by default. The rest of the API is conditional with cargo feature flags:
 | `net`      | [`rustix::net`] and [`rustix::path`]—Network-related operations.
 | `param`    | [`rustix::param`]—Process parameters.
 | `process`  | [`rustix::process`]—Process-associated operations.
+| `pty`      | [`rustix::pty`]—Pseduoterminal operations.
 | `rand`     | [`rustix::rand`]—Random-related operations.
 | `termios`  | [`rustix::termios`]—Terminal I/O stream operations.
 | `thread`   | [`rustix::thread`]—Thread-associated operations.
@@ -76,6 +77,7 @@ by default. The rest of the API is conditional with cargo feature flags:
 [`rustix::net`]: https://docs.rs/rustix/*/rustix/net/index.html
 [`rustix::param`]: https://docs.rs/rustix/*/rustix/param/index.html
 [`rustix::process`]: https://docs.rs/rustix/*/rustix/process/index.html
+[`rustix::pty`]: https://docs.rs/rustix/*/rustix/pty/index.html
 [`rustix::rand`]: https://docs.rs/rustix/*/rustix/rand/index.html
 [`rustix::termios`]: https://docs.rs/rustix/*/rustix/termios/index.html
 [`rustix::thread`]: https://docs.rs/rustix/*/rustix/thread/index.html

src/backend/libc/mod.rs

@@ -72,6 +72,10 @@ pub(crate) mod param;
 #[cfg(not(windows))]
 pub(crate) mod process;
 #[cfg(not(windows))]
+#[cfg(not(target_os = "wasi"))]
+#[cfg(feature = "pty")]
+pub(crate) mod pty;
+#[cfg(not(windows))]
 #[cfg(feature = "rand")]
 pub(crate) mod rand;
 #[cfg(not(windows))]

src/backend/libc/process/syscalls.rs

@@ -1,11 +1,9 @@
 //! libc syscalls supporting `rustix::process`.
 
 use super::super::c;
-#[cfg(not(any(target_os = "wasi", target_os = "fuchsia")))]
-use super::super::conv::borrowed_fd;
-use super::super::conv::{c_str, ret, ret_c_int, ret_discarded_char_ptr};
 #[cfg(not(target_os = "wasi"))]
-use super::super::conv::{ret_infallible, ret_pid_t, ret_usize};
+use super::super::conv::{borrowed_fd, ret_infallible, ret_pid_t, ret_usize};
+use super::super::conv::{c_str, ret, ret_c_int, ret_discarded_char_ptr};
 #[cfg(any(target_os = "android", target_os = "linux"))]
 use super::super::conv::{syscall_ret, syscall_ret_u32};
 #[cfg(any(
@@ -15,7 +13,7 @@ use super::super::conv::{syscall_ret, syscall_ret_u32};
     target_os = "linux",
 ))]
 use super::types::RawCpuSet;
-#[cfg(not(any(target_os = "wasi", target_os = "fuchsia")))]
+#[cfg(not(target_os = "wasi"))]
 use crate::fd::BorrowedFd;
 #[cfg(target_os = "linux")]
 use crate::fd::{AsRawFd, OwnedFd};
@@ -648,3 +646,9 @@ pub(crate) fn sethostname(name: &[u8]) -> io::Result<()> {
         ))
     }
 }
+
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
+#[inline]
+pub(crate) fn ioctl_tiocsctty(fd: BorrowedFd<'_>) -> io::Result<()> {
+    unsafe { ret(c::ioctl(borrowed_fd(fd), c::TIOCSCTTY as _, &0_u32)) }
+}

src/backend/libc/pty/mod.rs

@@ -0,0 +1 @@
+pub(crate) mod syscalls;

src/backend/libc/pty/syscalls.rs

@@ -0,0 +1,87 @@
+//! libc syscalls supporting `rustix::pty`.
+
+use super::super::c;
+use super::super::conv::{borrowed_fd, ret};
+use crate::fd::BorrowedFd;
+use crate::io;
+#[cfg(not(target_os = "android"))]
+use {super::super::conv::ret_owned_fd, crate::fd::OwnedFd, crate::pty::OpenptFlags};
+#[cfg(any(apple, linux_like, target_os = "freebsd", target_os = "fuchsia"))]
+use {
+    crate::ffi::{CStr, CString},
+    crate::path::SMALL_PATH_BUFFER_SIZE,
+    alloc::borrow::ToOwned,
+    alloc::vec::Vec,
+};
+
+#[cfg(not(any(target_os = "android", target_os = "linux")))]
+#[inline]
+pub(crate) fn openpt(flags: OpenptFlags) -> io::Result<OwnedFd> {
+    unsafe { ret_owned_fd(c::posix_openpt(flags.bits() as _)) }
+}
+
+#[cfg(any(apple, linux_like, target_os = "freebsd", target_os = "fuchsia"))]
+#[inline]
+pub(crate) fn ptsname(fd: BorrowedFd, mut buffer: Vec<u8>) -> io::Result<CString> {
+    // This code would benefit from having a better way to read into
+    // uninitialized memory, but that requires `unsafe`.
+    buffer.clear();
+    buffer.reserve(SMALL_PATH_BUFFER_SIZE);
+    buffer.resize(buffer.capacity(), 0_u8);
+
+    loop {
+        // On platforms with `ptsname_r`, use it.
+        #[cfg(any(target_os = "freebsd", linux_like, target_os = "fuchsia"))]
+        let r =
+            unsafe { libc::ptsname_r(borrowed_fd(fd), buffer.as_mut_ptr().cast(), buffer.len()) };
+
+        // MacOS 10.13.4 has `ptsname_r`; use it if we have it, otherwise fall
+        // back to calling the underlying ioctl directly.
+        #[cfg(apple)]
+        let r = unsafe {
+            weak! { fn ptsname_r(c::c_int, *mut c::c_char, c::size_t) -> c::c_int }
+
+            if let Some(libc_ptsname_r) = ptsname_r.get() {
+                libc_ptsname_r(borrowed_fd(fd), buffer.as_mut_ptr().cast(), buffer.len())
+            } else {
+                // The size declared in the `TIOCPTYGNAME` macro in sys/ttycom.h is 128.
+                let mut name: [u8; 128] = [0_u8; 128];
+                match libc::ioctl(borrowed_fd(fd), libc::TIOCPTYGNAME as u64, &mut name) {
+                    0 => {
+                        let len = CStr::from_ptr(name.as_ptr().cast()).to_bytes().len();
+                        std::ptr::copy_nonoverlapping(name.as_ptr(), buffer.as_mut_ptr(), len + 1);
+                        0
+                    }
+                    _ => libc_errno::errno().0,
+                }
+            }
+        };
+
+        if r == 0 {
+            return Ok(unsafe { CStr::from_ptr(buffer.as_ptr().cast()).to_owned() });
+        }
+        if r != libc::ERANGE {
+            return Err(io::Errno::from_raw_os_error(r));
+        }
+
+        buffer.reserve(1); // use `Vec` reallocation strategy to grow capacity exponentially
+        buffer.resize(buffer.capacity(), 0_u8);
+    }
+}
+
+#[inline]
+pub(crate) fn unlockpt(fd: BorrowedFd) -> io::Result<()> {
+    unsafe { ret(c::unlockpt(borrowed_fd(fd))) }
+}
+
+#[cfg(not(any(target_os = "android", target_os = "linux")))]
+#[inline]
+pub(crate) fn grantpt(fd: BorrowedFd) -> io::Result<()> {
+    unsafe { ret(c::grantpt(borrowed_fd(fd))) }
+}
+
+#[cfg(target_os = "linux")]
+#[inline]
+pub(crate) fn ioctl_tiocgptpeer(fd: BorrowedFd, flags: OpenptFlags) -> io::Result<OwnedFd> {
+    unsafe { ret_owned_fd(c::ioctl(borrowed_fd(fd), c::TIOCGPTPEER, flags.bits())) }
+}

src/backend/linux_raw/c.rs

@@ -32,4 +32,5 @@ pub(crate) use linux_raw_sys::general::{
     SO_SNDTIMEO_NEW, SO_SNDTIMEO_OLD, SO_TYPE, TCP_NODELAY,
 };
 pub(crate) use linux_raw_sys::general::{NFS_SUPER_MAGIC, PROC_SUPER_MAGIC, UTIME_NOW, UTIME_OMIT};
+pub(crate) use linux_raw_sys::general::{O_NOCTTY, O_RDWR};
 pub(crate) use linux_raw_sys::general::{XATTR_CREATE, XATTR_REPLACE};

src/backend/linux_raw/mod.rs

@@ -41,6 +41,8 @@ pub(crate) mod net;
 ))]
 pub(crate) mod param;
 pub(crate) mod process;
+#[cfg(feature = "pty")]
+pub(crate) mod pty;
 #[cfg(feature = "rand")]
 pub(crate) mod rand;
 #[cfg(feature = "runtime")]

src/backend/linux_raw/process/syscalls.rs

@@ -31,6 +31,7 @@ use linux_raw_sys::general::{
     __kernel_gid_t, __kernel_pid_t, __kernel_uid_t, membarrier_cmd, membarrier_cmd_flag, rlimit,
     rlimit64, PRIO_PGRP, PRIO_PROCESS, PRIO_USER, RLIM64_INFINITY, RLIM_INFINITY,
 };
+use linux_raw_sys::ioctl::TIOCSCTTY;
 #[cfg(not(target_os = "wasi"))]
 #[cfg(feature = "fs")]
 use {super::super::conv::ret_c_uint_infallible, crate::fs::Mode};
@@ -745,3 +746,15 @@ pub(crate) fn sethostname(name: &[u8]) -> io::Result<()> {
     let (ptr, len) = slice(name);
     unsafe { ret(syscall_readonly!(__NR_sethostname, ptr, len)) }
 }
+
+#[inline]
+pub(crate) fn ioctl_tiocsctty(fd: BorrowedFd<'_>) -> io::Result<()> {
+    unsafe {
+        ret(syscall_readonly!(
+            __NR_ioctl,
+            fd,
+            c_uint(TIOCSCTTY),
+            by_ref(&0_u32)
+        ))
+    }
+}

src/backend/linux_raw/pty/mod.rs

@@ -0,0 +1 @@
+pub(crate) mod syscalls;