From 43e517cea6704f0d8424a88b13a1d40550c7e9ca Mon Sep 17 00:00:00 2001
From: Jesse Luehrs <doy@tozt.net>
Date: Thu, 30 Dec 2021 16:15:14 -0500
Subject: add spawn_pg

---
 src/blocking/command.rs | 24 ++++++++++++++++++++++++
 src/command.rs          | 24 ++++++++++++++++++++++++
 src/sys.rs              | 26 ++++++++++++++++++++++++++
 3 files changed, 74 insertions(+)

diff --git a/src/blocking/command.rs b/src/blocking/command.rs
index ed36443..2cbfb97 100644
--- a/src/blocking/command.rs
+++ b/src/blocking/command.rs
@@ -128,6 +128,30 @@ impl Command {
         Ok(self.inner.spawn()?)
     }
 
+    pub fn spawn_pg(
+        &mut self,
+        pg: Option<u32>,
+    ) -> crate::Result<std::process::Child> {
+        let mut set_process_group = crate::sys::set_process_group_child(pg);
+        // Safety: setpgid() is an async-signal-safe function and ioctl() is a
+        // raw syscall (which is inherently async-signal-safe).
+        if let Some(mut custom) = self.pre_exec.take() {
+            unsafe {
+                self.inner.pre_exec(move || {
+                    set_process_group()?;
+                    custom()?;
+                    Ok(())
+                })
+            };
+        } else {
+            unsafe { self.inner.pre_exec(set_process_group) };
+        }
+
+        let child = self.inner.spawn()?;
+        crate::sys::set_process_group_parent(child.id(), pg)?;
+        Ok(child)
+    }
+
     pub fn uid(&mut self, id: u32) -> &mut Self {
         self.inner.uid(id);
         self
diff --git a/src/command.rs b/src/command.rs
index cd1c8a3..c6dac9d 100644
--- a/src/command.rs
+++ b/src/command.rs
@@ -128,6 +128,30 @@ impl Command {
         Ok(self.inner.spawn()?)
     }
 
+    pub fn spawn_pg(
+        &mut self,
+        pg: Option<u32>,
+    ) -> crate::Result<async_process::Child> {
+        let mut set_process_group = crate::sys::set_process_group_child(pg);
+        // Safety: setpgid() is an async-signal-safe function and ioctl() is a
+        // raw syscall (which is inherently async-signal-safe).
+        if let Some(mut custom) = self.pre_exec.take() {
+            unsafe {
+                self.inner.pre_exec(move || {
+                    set_process_group()?;
+                    custom()?;
+                    Ok(())
+                })
+            };
+        } else {
+            unsafe { self.inner.pre_exec(set_process_group) };
+        }
+
+        let child = self.inner.spawn()?;
+        crate::sys::set_process_group_parent(child.id(), pg)?;
+        Ok(child)
+    }
+
     pub fn uid(&mut self, id: u32) -> &mut Self {
         self.inner.uid(id);
         self
diff --git a/src/sys.rs b/src/sys.rs
index 0d897bc..36d87c1 100644
--- a/src/sys.rs
+++ b/src/sys.rs
@@ -76,6 +76,32 @@ pub fn session_leader(
     }
 }
 
+pub fn set_process_group_child(
+    pg: Option<u32>,
+) -> impl FnMut() -> std::io::Result<()> {
+    move || {
+        nix::unistd::setpgid(
+            nix::unistd::Pid::from_raw(0),
+            pg.map_or(nix::unistd::Pid::from_raw(0), |pid| {
+                nix::unistd::Pid::from_raw(pid.try_into().unwrap())
+            }),
+        )?;
+        Ok(())
+    }
+}
+
+pub fn set_process_group_parent(
+    pid: u32,
+    pg: Option<u32>,
+) -> nix::Result<()> {
+    nix::unistd::setpgid(
+        nix::unistd::Pid::from_raw(pid.try_into().unwrap()),
+        pg.map_or(nix::unistd::Pid::from_raw(0), |pid| {
+            nix::unistd::Pid::from_raw(pid.try_into().unwrap())
+        }),
+    )
+}
+
 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()) }
-- 
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