From aad01f7a90d9a65f330f84f0ee5a3453725c00b2 Mon Sep 17 00:00:00 2001
From: Wolfgang Bumiller <w.bumiller@proxmox.com>
Date: Wed, 8 Mar 2023 13:26:50 +0100
Subject: [PATCH] rest-server: support unix sockets in create_daemon

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Reviewed-by: Lukas Wagner <l.wagner@proxmox.com>
---
 proxmox-rest-server/src/daemon.rs | 103 ++++++++++++++++++++++--------
 1 file changed, 76 insertions(+), 27 deletions(-)

diff --git a/proxmox-rest-server/src/daemon.rs b/proxmox-rest-server/src/daemon.rs
index 86d77dc0..fedbf545 100644
--- a/proxmox-rest-server/src/daemon.rs
+++ b/proxmox-rest-server/src/daemon.rs
@@ -2,12 +2,13 @@
 
 use std::ffi::CString;
 use std::future::Future;
-use std::io::{Read, Write};
+use std::io::{self, Read, Write};
 use std::os::raw::{c_char, c_int, c_uchar};
 use std::os::unix::ffi::OsStrExt;
 use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
 use std::panic::UnwindSafe;
 use std::path::PathBuf;
+use std::pin::Pin;
 
 use anyhow::{bail, format_err, Error};
 use futures::future::{self, Either};
@@ -22,7 +23,8 @@ type BoxedStoreFunc = Box<dyn FnMut() -> Result<String, Error> + UnwindSafe + Se
 
 // Helper trait to "store" something in the environment to be re-used after re-executing the
 // service on a reload.
-trait Reloadable: Sized {
+#[doc(hidden)] // not public api
+pub trait Reloadable: Sized {
     fn restore(var: &str) -> Result<Self, Error>;
     fn get_store_func(&self) -> Result<BoxedStoreFunc, Error>;
 }
@@ -222,33 +224,79 @@ impl Reloader {
     }
 }
 
+fn fd_store_func(fd: RawFd) -> Result<BoxedStoreFunc, Error> {
+    let mut fd_opt = Some(unsafe {
+        OwnedFd::from_raw_fd(nix::fcntl::fcntl(
+            fd,
+            nix::fcntl::FcntlArg::F_DUPFD_CLOEXEC(0),
+        )?)
+    });
+    Ok(Box::new(move || {
+        let fd = fd_opt.take().unwrap();
+        fd_change_cloexec(fd.as_raw_fd(), false)?;
+        Ok(fd.into_raw_fd().to_string())
+    }))
+}
+
+/// NOTE: This must only be used for *async* I/O objects!
+unsafe fn fd_restore_func<T>(var: &str) -> Result<T, Error>
+where
+    T: FromRawFd,
+{
+    let fd = var
+        .parse::<u32>()
+        .map_err(|e| format_err!("invalid file descriptor: {}", e))? as RawFd;
+    fd_change_cloexec(fd, true)?;
+    Ok(unsafe { T::from_raw_fd(fd) })
+}
+
 // For now all we need to do is store and reuse a tcp listening socket:
 impl Reloadable for tokio::net::TcpListener {
     // NOTE: The socket must not be closed when the store-function is called:
-    // FIXME: We could become "independent" of the TcpListener and its reference to the file
-    // descriptor by `dup()`ing it (and check if the listener still exists via kcmp()?)
     fn get_store_func(&self) -> Result<BoxedStoreFunc, Error> {
-        let mut fd_opt = Some(unsafe {
-            OwnedFd::from_raw_fd(nix::fcntl::fcntl(
-                self.as_raw_fd(),
-                nix::fcntl::FcntlArg::F_DUPFD_CLOEXEC(0),
-            )?)
-        });
-        Ok(Box::new(move || {
-            let fd = fd_opt.take().unwrap();
-            fd_change_cloexec(fd.as_raw_fd(), false)?;
-            Ok(fd.into_raw_fd().to_string())
-        }))
+        fd_store_func(self.as_raw_fd())
     }
 
     fn restore(var: &str) -> Result<Self, Error> {
-        let fd = var
-            .parse::<u32>()
-            .map_err(|e| format_err!("invalid file descriptor: {}", e))? as RawFd;
-        fd_change_cloexec(fd, true)?;
-        Ok(Self::from_std(unsafe {
-            std::net::TcpListener::from_raw_fd(fd)
-        })?)
+        Ok(Self::from_std(unsafe { fd_restore_func(var) }?)?)
+    }
+}
+
+// For now all we need to do is store and reuse a tcp listening socket:
+impl Reloadable for tokio::net::UnixListener {
+    // NOTE: The socket must not be closed when the store-function is called:
+    fn get_store_func(&self) -> Result<BoxedStoreFunc, Error> {
+        fd_store_func(self.as_raw_fd())
+    }
+
+    fn restore(var: &str) -> Result<Self, Error> {
+        Ok(Self::from_std(unsafe { fd_restore_func(var) }?)?)
+    }
+}
+
+pub trait Listenable: Reloadable {
+    type Address;
+    fn bind(addr: &Self::Address) -> Pin<Box<dyn Future<Output = io::Result<Self>> + Send + '_>>;
+}
+
+impl Listenable for tokio::net::TcpListener {
+    type Address = std::net::SocketAddr;
+
+    fn bind(addr: &Self::Address) -> Pin<Box<dyn Future<Output = io::Result<Self>> + Send + '_>> {
+        Box::pin(Self::bind(addr))
+    }
+}
+
+impl Listenable for tokio::net::UnixListener {
+    type Address = std::os::unix::net::SocketAddr;
+
+    fn bind(addr: &Self::Address) -> Pin<Box<dyn Future<Output = io::Result<Self>> + Send + '_>> {
+        Box::pin(async move {
+            let addr = addr.as_pathname().ok_or_else(|| {
+                io::Error::new(io::ErrorKind::Other, "missing path for unix socket")
+            })?;
+            Self::bind(addr)
+        })
     }
 }
 
@@ -259,20 +307,21 @@ impl Reloadable for tokio::net::TcpListener {
 /// socket.  The finished listening socket is then passed to the `create_service` function which
 /// can be used to setup the TLS and the HTTP daemon. The returned future has to call
 /// [systemd_notify] with [SystemdNotify::Ready] when the service is ready.
-pub async fn create_daemon<F, S>(
-    address: std::net::SocketAddr,
+pub async fn create_daemon<F, S, L>(
+    address: L::Address,
     create_service: F,
     pidfn: Option<&str>,
 ) -> Result<(), Error>
 where
-    F: FnOnce(tokio::net::TcpListener) -> Result<S, Error>,
+    L: Listenable,
+    F: FnOnce(L) -> Result<S, Error>,
     S: Future<Output = Result<(), Error>>,
 {
     let mut reloader = Reloader::new()?;
 
-    let listener: tokio::net::TcpListener = reloader
+    let listener: L = reloader
         .restore("PROXMOX_BACKUP_LISTEN_FD", move || async move {
-            Ok(tokio::net::TcpListener::bind(&address).await?)
+            Ok(L::bind(&address).await?)
         })
         .await?;