1 files changed, 103 insertions, 0 deletions
diff --git a/src/sys.rs b/src/sys.rs
new file mode 100644
index 0000000..9cf6a44
--- /dev/null
+++ b/src/sys.rs
@@ -0,0 +1,103 @@
+use std::os::unix::io::{FromRawFd as _, IntoRawFd as _};
+
+pub fn create_pt() -> nix::Result<(std::fs::File, std::path::PathBuf)> {
+    let pt = nix::pty::posix_openpt(
+        nix::fcntl::OFlag::O_RDWR | nix::fcntl::OFlag::O_NOCTTY,
+    )?;
+    nix::pty::grantpt(&pt)?;
+    nix::pty::unlockpt(&pt)?;
+
+    let ptsname = nix::pty::ptsname_r(&pt)?.into();
+
+    let pt_fd = pt.into_raw_fd();
+
+    // Safety: posix_openpt (or the previous functions operating on the
+    // result) would have returned an Err (causing us to return early) if the
+    // file descriptor was invalid. additionally, into_raw_fd gives up
+    // ownership over the file descriptor, allowing the newly created File
+    // object to take full ownership.
+    let pt = unsafe { std::fs::File::from_raw_fd(pt_fd) };
+
+    Ok((pt, ptsname))
+}
+
+pub fn set_term_size(
+    fh: &impl std::os::unix::io::AsRawFd,
+    size: crate::Size,
+) -> nix::Result<()> {
+    let size = size.into();
+    let fd = fh.as_raw_fd();
+
+    // Safety: std::fs::File is required to contain a valid file descriptor
+    // and size is guaranteed to be initialized because it's a normal rust
+    // value, and nix::pty::Winsize is a repr(C) struct with the same layout
+    // as `struct winsize` from sys/ioctl.h.
+    unsafe {
+        set_term_size_unsafe(fd, std::ptr::NonNull::from(&size).as_ptr())
+    }
+    .map(|_| ())
+}
+
+pub fn setup_subprocess(
+    pt: &impl std::os::unix::io::AsRawFd,
+    pts: impl std::os::unix::io::IntoRawFd,
+) -> nix::Result<(
+    std::process::Stdio,
+    std::process::Stdio,
+    std::process::Stdio,
+    impl FnMut() -> std::io::Result<()>,
+)> {
+    let pt_fd = pt.as_raw_fd();
+    let pts_fd = pts.into_raw_fd();
+
+    let stdin = nix::unistd::dup(pts_fd)?;
+    let stdout = nix::unistd::dup(pts_fd)?;
+    let stderr = nix::unistd::dup(pts_fd)?;
+
+    // Safety: these file descriptors were all just returned from dup, so they
+    // must be valid
+    Ok((
+        unsafe { std::process::Stdio::from_raw_fd(stdin) },
+        unsafe { std::process::Stdio::from_raw_fd(stdout) },
+        unsafe { std::process::Stdio::from_raw_fd(stderr) },
+        move || {
+            nix::unistd::setsid()?;
+            set_controlling_terminal(pts_fd)?;
+
+            // in the parent, destructors will handle closing these file
+            // descriptors (other than pt, used by the parent to
+            // communicate with the child) when the function ends, but in
+            // the child, we end by calling exec(), which doesn't call
+            // destructors.
+
+            nix::unistd::close(pt_fd)?;
+            nix::unistd::close(pts_fd)?;
+            // at this point, stdin/stdout/stderr have already been
+            // reopened as fds 0/1/2 in the child, so we can (and should)
+            // close the originals
+            nix::unistd::close(stdin)?;
+            nix::unistd::close(stdout)?;
+            nix::unistd::close(stderr)?;
+
+            Ok(())
+        },
+    ))
+}
+
+fn set_controlling_terminal(fd: std::os::unix::io::RawFd) -> nix::Result<()> {
+    // Safety: std::fs::File is required to contain a valid file descriptor
+    unsafe { set_controlling_terminal_unsafe(fd, std::ptr::null()) }
+        .map(|_| ())
+}
+
+nix::ioctl_write_ptr_bad!(
+    set_term_size_unsafe,
+    libc::TIOCSWINSZ,
+    nix::pty::Winsize
+);
+
+nix::ioctl_write_ptr_bad!(
+    set_controlling_terminal_unsafe,
+    libc::TIOCSCTTY,
+    libc::c_int
+);