From 8341dcf3e6697e785f0ad1f17f7cf47fef94fe5d Mon Sep 17 00:00:00 2001
From: Peter Pentchev <roam@ringlet.net>
Date: Sun, 27 Oct 2024 22:43:56 +0200
Subject: [PATCH] Do not invoke accept() on an already-established connection

Listener::new() already records the fact that this listener is actually
a connection that has already been established via socket activation.
Let Listener::accept() honor that flag.

Fixes #73.
---
 varlink/src/server.rs | 51 +++++++++++++++++++++++++++++++++----------
 1 file changed, 39 insertions(+), 12 deletions(-)

diff --git a/varlink/src/server.rs b/varlink/src/server.rs
index d6c648f..346737f 100644
--- a/varlink/src/server.rs
+++ b/varlink/src/server.rs
@@ -151,6 +151,13 @@ impl Listener {
         }
     }
 
+    pub const fn is_already_accepted(&self) -> bool {
+        match *self {
+            Self::TCP(_, value) => value,
+            Self::UNIX(_, value) => value,
+        }
+    }
+
     #[cfg(windows)]
     pub fn accept(&self, timeout: u64) -> Result<Box<dyn Stream>> {
         use winapi::um::winsock2::WSAEINTR as EINTR;
@@ -194,13 +201,21 @@ impl Listener {
         }
 
         match self {
-            &Listener::TCP(Some(ref l), _) => {
-                let (s, _addr) = l.accept().map_err(map_context!())?;
-                Ok(Box::new(s))
+            &Listener::TCP(Some(ref l), accepted) => {
+                if accepted {
+                    unsafe { Ok(Box::new(TcpStream::from_raw_fd(l.as_raw_fd()))) }
+                } else {
+                    let (s, _addr) = l.accept().map_err(map_context!())?;
+                    Ok(Box::new(s))
+                }
             }
-            Listener::UNIX(Some(ref l), _) => {
-                let (s, _addr) = l.accept().map_err(map_context!())?;
-                Ok(Box::new(s))
+            Listener::UNIX(Some(ref l), accepted) => {
+                if *accepted {
+                    unsafe { Ok(Box::new(UnixStream::from_raw_fd(l.as_raw_fd()))) }
+                } else {
+                    let (s, _addr) = l.accept().map_err(map_context!())?;
+                    Ok(Box::new(s))
+                }
             }
             _ => Err(context!(ErrorKind::ConnectionClosed)),
         }
@@ -250,13 +265,21 @@ impl Listener {
             }
         }
         match self {
-            &Listener::TCP(Some(ref l), _) => {
-                let (s, _addr) = l.accept().map_err(map_context!())?;
-                Ok(Box::new(s))
+            &Listener::TCP(Some(ref l), accepted) => {
+                if accepted {
+                    unsafe { Ok(Box::new(TcpStream::from_raw_fd(l.as_raw_fd()))) }
+                } else {
+                    let (s, _addr) = l.accept().map_err(map_context!())?;
+                    Ok(Box::new(s))
+                }
             }
-            Listener::UNIX(Some(ref l), _) => {
-                let (s, _addr) = l.accept().map_err(map_context!())?;
-                Ok(Box::new(s))
+            Listener::UNIX(Some(ref l), accepted) => {
+                if *accepted {
+                    unsafe { Ok(Box::new(UnixStream::from_raw_fd(l.as_raw_fd()))) }
+                } else {
+                    let (s, _addr) = l.accept().map_err(map_context!())?;
+                    Ok(Box::new(s))
+                }
             }
             _ => Err(context!(ErrorKind::ConnectionClosed)),
         }
@@ -607,5 +630,9 @@ pub fn listen<S: ?Sized + AsRef<str>, H: crate::ConnectionHandler + Send + Sync
                 }
             }
         });
+
+        if listener.is_already_accepted() {
+            return Ok(());
+        }
     }
 }