config: allow attaching file descriptors to commands

Cargo.toml

@@ -14,7 +14,7 @@ panic = "abort"
 panic = "abort"
 
 [dependencies]
-uapi = "0.2.10"
+uapi = "0.2.12"
 thiserror = "1.0.56"
 ahash = "0.8.7"
 log = { version = "0.4.20", features = ["std"] }

jay-config/Cargo.toml

@@ -10,6 +10,6 @@ bincode = "1.3.3"
 serde = { version = "1.0.196", features = ["derive"] }
 log = "0.4.14"
 futures-util = {  version = "0.3.30", features = ["io"] }
-uapi = "0.2.10"
+uapi = "0.2.12"
 thiserror = "1.0.57"
 backtrace = "0.3.69"

jay-config/src/_private/client.rs

@@ -28,6 +28,7 @@ use {
         future::Future,
         mem,
         ops::Deref,
+        os::fd::IntoRawFd,
         panic::{catch_unwind, AssertUnwindSafe},
         pin::Pin,
         ptr,
@@ -264,11 +265,26 @@ impl Client {
             .iter()
             .map(|(a, b)| (a.to_string(), b.to_string()))
             .collect();
-        self.send(&ClientMessage::Run {
-            prog: &command.prog,
-            args: command.args.clone(),
-            env,
-        });
+        let fds: Vec<_> = command
+            .fds
+            .borrow_mut()
+            .drain()
+            .map(|(a, b)| (a, b.into_raw_fd()))
+            .collect();
+        if fds.is_empty() {
+            self.send(&ClientMessage::Run {
+                prog: &command.prog,
+                args: command.args.clone(),
+                env,
+            });
+        } else {
+            self.send(&ClientMessage::Run2 {
+                prog: &command.prog,
+                args: command.args.clone(),
+                env,
+                fds,
+            });
+        }
     }
 
     pub fn grab(&self, kb: InputDevice, grab: bool) {

jay-config/src/_private/ipc.rs

@@ -375,6 +375,12 @@ pub enum ClientMessage<'a> {
         pollable: PollableId,
         writable: bool,
     },
+    Run2 {
+        prog: &'a str,
+        args: Vec<String>,
+        env: Vec<(String, String)>,
+        fds: Vec<(i32, i32)>,
+    },
 }
 
 #[derive(Serialize, Deserialize, Debug)]

jay-config/src/exec.rs

@@ -1,6 +1,6 @@
 //! Tools for spawning programs.
 
-use std::collections::HashMap;
+use std::{cell::RefCell, collections::HashMap, os::fd::OwnedFd};
 
 /// Sets an environment variable.
 ///
@@ -14,6 +14,7 @@ pub struct Command {
     pub(crate) prog: String,
     pub(crate) args: Vec<String>,
     pub(crate) env: HashMap<String, String>,
+    pub(crate) fds: RefCell<HashMap<i32, OwnedFd>>,
 }
 
 impl Command {
@@ -28,6 +29,7 @@ impl Command {
             prog: prog.to_string(),
             args: vec![],
             env: Default::default(),
+            fds: Default::default(),
         }
     }
 
@@ -43,7 +45,39 @@ impl Command {
         self
     }
 
+    /// Sets a file descriptor of the process.
+    ///
+    /// By default, the process starts with exactly stdin, stdout, and stderr open and all
+    /// pointing to `/dev/null`.
+    pub fn fd<F: Into<OwnedFd>>(&mut self, idx: i32, fd: F) -> &mut Self {
+        self.fds.borrow_mut().insert(idx, fd.into());
+        self
+    }
+
+    /// Sets the stdin of the process.
+    ///
+    /// This is equivalent to `fd(0, fd)`.
+    pub fn stdin<F: Into<OwnedFd>>(&mut self, fd: F) -> &mut Self {
+        self.fd(0, fd)
+    }
+
+    /// Sets the stdout of the process.
+    ///
+    /// This is equivalent to `fd(1, fd)`.
+    pub fn stdout<F: Into<OwnedFd>>(&mut self, fd: F) -> &mut Self {
+        self.fd(1, fd)
+    }
+
+    /// Sets the stderr of the process.
+    ///
+    /// This is equivalent to `fd(2, fd)`.
+    pub fn stderr<F: Into<OwnedFd>>(&mut self, fd: F) -> &mut Self {
+        self.fd(2, fd)
+    }
+
     /// Executes the command.
+    ///
+    /// This consumes all attached file descriptors.
     pub fn spawn(&self) {
         get!().spawn(self);
     }

src/config/handler.rs

@@ -51,7 +51,7 @@ use {
     log::Level,
     std::{cell::Cell, ops::Deref, rc::Rc, time::Duration},
     thiserror::Error,
-    uapi::{c, fcntl_dupfd_cloexec},
+    uapi::{c, fcntl_dupfd_cloexec, OwnedFd},
 };
 
 pub(super) struct ConfigProxyHandler {
@@ -999,12 +999,17 @@ impl ConfigProxyHandler {
         prog: &str,
         args: Vec<String>,
         env: Vec<(String, String)>,
+        fds: Vec<(i32, i32)>,
     ) -> Result<(), CphError> {
+        let fds: Vec<_> = fds
+            .into_iter()
+            .map(|(a, b)| (a, Rc::new(OwnedFd::new(b))))
+            .collect();
         let forker = match self.state.forker.get() {
             Some(f) => f,
             _ => return Err(CphError::NoForker),
         };
-        forker.spawn(prog.to_string(), args, env);
+        forker.spawn(prog.to_string(), args, env, fds);
         Ok(())
     }
 
@@ -1305,7 +1310,7 @@ impl ConfigProxyHandler {
             ClientMessage::GetSeats => self.handle_get_seats(),
             ClientMessage::RemoveSeat { .. } => {}
             ClientMessage::Run { prog, args, env } => {
-                self.handle_run(prog, args, env).wrn("run")?
+                self.handle_run(prog, args, env, vec![]).wrn("run")?
             }
             ClientMessage::GrabKb { kb, grab } => self.handle_grab(kb, grab).wrn("grab")?,
             ClientMessage::SetColor { colorable, color } => {
@@ -1505,6 +1510,12 @@ impl ConfigProxyHandler {
             ClientMessage::AddInterest { pollable, writable } => self
                 .handle_add_interest(pollable, writable)
                 .wrn("add_interest")?,
+            ClientMessage::Run2 {
+                prog,
+                args,
+                env,
+                fds,
+            } => self.handle_run(prog, args, env, fds).wrn("run")?,
         }
         Ok(())
     }

src/forker.rs

@@ -170,8 +170,14 @@ impl ForkerProxy {
         self.pidfd(pidfd_id).await
     }
 
-    pub fn spawn(&self, prog: String, args: Vec<String>, env: Vec<(String, String)>) {
-        self.spawn_(prog, args, env, vec![], None)
+    pub fn spawn(
+        &self,
+        prog: String,
+        args: Vec<String>,
+        env: Vec<(String, String)>,
+        fds: Vec<(i32, Rc<OwnedFd>)>,
+    ) {
+        self.spawn_(prog, args, env, fds, None)
     }
 
     fn spawn_(