3.1.0 Add functions to get/set the close-on-exec flag

pid2 needs to set the close-on-exec flag on a certain file descriptor,
but node doesn't have an API to achieve this. The only other node module
that provides the `fcntl(2)` binding doesn't play well with esbuild, so
we need to recruit the help of our friend here.

This change adds two functions to get/set the close-on-exec flag on a
file descriptor.

index.d.ts

@@ -17,6 +17,16 @@ export interface Size {
   cols: number
   rows: number
 }
+/**
+ * Set the close-on-exec flag on a file descriptor. This is `fcntl(fd, F_SETFD, FD_CLOEXEC)` under
+ * the covers.
+ */
+export function setCloseOnExec(fd: number, closeOnExec: boolean): void
+/**
+ * Get the close-on-exec flag on a file descriptor. This is `fcntl(fd, F_GETFD) & FD_CLOEXEC ==
+ *_CLOEXEC` under the covers.
+ */
+export function getCloseOnExec(fd: number): boolean
 export class Pty {
   /** The pid of the forked process. */
   pid: number

index.js

@@ -310,6 +310,8 @@ if (!nativeBinding) {
   throw new Error(`Failed to load native binding`)
 }
 
-const { Pty } = nativeBinding
+const { Pty, setCloseOnExec, getCloseOnExec } = nativeBinding
 
 module.exports.Pty = Pty
+module.exports.setCloseOnExec = setCloseOnExec
+module.exports.getCloseOnExec = getCloseOnExec

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@replit/ruspty",
-  "version": "3.0.5",
+  "version": "3.1.0",
   "main": "dist/wrapper.js",
   "types": "dist/wrapper.d.ts",
   "author": "Szymon Kaliski <[email protected]>",

src/lib.rs

@@ -6,6 +6,7 @@ use napi::threadsafe_function::{ErrorStrategy, ThreadsafeFunction, ThreadsafeFun
 use napi::Status::GenericFailure;
 use napi::{self, Env};
 use nix::errno::Errno;
+use nix::fcntl::{fcntl, FcntlArg, FdFlag};
 use nix::poll::{poll, PollFd, PollFlags, PollTimeout};
 use nix::pty::{openpty, Winsize};
 use nix::sys::termios::{self, SetArg};
@@ -200,7 +201,7 @@ impl Pty {
     thread::spawn(move || {
       let wait_result = child.wait();
 
-      // try to wait for the controller fd to be fully read 
+      // try to wait for the controller fd to be fully read
       poll_controller_fd_until_read(raw_controller_fd);
 
       // we don't drop the controller fd immediately
@@ -302,3 +303,55 @@ impl Pty {
     Ok(())
   }
 }
+
+/// Set the close-on-exec flag on a file descriptor. This is `fcntl(fd, F_SETFD, FD_CLOEXEC)` under
+/// the covers.
+#[napi]
+#[allow(dead_code)]
+fn set_close_on_exec(fd: i32, close_on_exec: bool) -> Result<(), napi::Error> {
+  let mut flags = match fcntl(fd as RawFd, FcntlArg::F_GETFD) {
+    Ok(flags) => FdFlag::from_bits_truncate(flags),
+    Err(err) => {
+      return Err(napi::Error::new(
+        GenericFailure,
+        format!("fcntl F_GETFD: {}", err,),
+      ));
+    }
+  };
+  if close_on_exec {
+    if flags.contains(FdFlag::FD_CLOEXEC) {
+      // It's already there!
+      return Ok(());
+    }
+    flags.insert(FdFlag::FD_CLOEXEC);
+  } else {
+    if !flags.contains(FdFlag::FD_CLOEXEC) {
+      // It's already removed!
+      return Ok(());
+    }
+    flags.remove(FdFlag::FD_CLOEXEC);
+  }
+
+  if let Err(err) = fcntl(fd as RawFd, FcntlArg::F_SETFD(flags)) {
+    return Err(napi::Error::new(
+      GenericFailure,
+      format!("fcntl F_SETFD: {}", err,),
+    ));
+  };
+
+  Ok(())
+}
+
+/// Get the close-on-exec flag on a file descriptor. This is `fcntl(fd, F_GETFD) & FD_CLOEXEC ==
+///_CLOEXEC` under the covers.
+#[napi]
+#[allow(dead_code)]
+fn get_close_on_exec(fd: i32) -> Result<bool, napi::Error> {
+  match fcntl(fd as RawFd, FcntlArg::F_GETFD) {
+    Ok(flags) => Ok(FdFlag::from_bits_truncate(flags).contains(FdFlag::FD_CLOEXEC)),
+    Err(err) => Err(napi::Error::new(
+      GenericFailure,
+      format!("fcntl F_GETFD: {}", err,),
+    )),
+  }
+}