Add with_backlog functionality to TcpListener and UnixListener

library/std/src/net/tcp.rs

@@ -707,10 +707,48 @@ impl fmt::Debug for TcpStream {
 }
 
 impl TcpListener {
+    /// Default listen backlog.
+    const DEFAULT_BACKLOG: usize = 128;
+
     /// Creates a new `TcpListener` which will be bound to the specified
     /// address.
     ///
-    /// The returned listener is ready for accepting connections.
+    /// The given backlog specifies the maximum number of outstanding
+    /// connections that will be buffered in the OS waiting to be accepted by
+    /// [`TcpListener::accept`]. The backlog argument overrides the default
+    /// value of 128; that default is reasonable for most use cases.
+    ///
+    /// This function is otherwise [`TcpListener::bind`]: see that
+    /// documentation for full details of operation.
+    ///
+    /// # Examples
+    ///
+    /// Creates a TCP listener bound to `127.0.0.1:80` with a backlog of 1000:
+    ///
+    /// ```no_run
+    /// #![feature(bind_with_backlog)]
+    /// use std::net::TcpListener;
+    ///
+    /// let listener = TcpListener::bind_with_backlog("127.0.0.1:80", 1000).unwrap();
+    /// ```
+    ///
+    /// # Errors
+    ///
+    /// The specified backlog may be larger than supported by the underlying
+    /// system. In this case an [`io::Error`] with
+    /// [`io::ErrorKind::InvalidData`] will be returned.
+    #[unstable(feature = "bind_with_backlog", issue = "94406")]
+    pub fn bind_with_backlog<A: ToSocketAddrs>(addr: A, backlog: usize) -> io::Result<TcpListener> {
+        super::each_addr(addr, move |a| net_imp::TcpListener::bind_with_backlog(a, backlog))
+            .map(TcpListener)
+    }
+
+    /// Creates a new `TcpListener` which will be bound to the specified
+    /// address. The returned listener is ready for accepting
+    /// connections.
+    ///
+    /// The listener will have a backlog of 128.  See the documentation for
+    /// [`TcpListener::bind_with_backlog`] for further information.
     ///
     /// Binding with a port number of 0 will request that the OS assigns a port
     /// to this listener. The port allocated can be queried via the
@@ -748,7 +786,7 @@ impl TcpListener {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<TcpListener> {
-        super::each_addr(addr, net_imp::TcpListener::bind).map(TcpListener)
+        Self::bind_with_backlog(addr, TcpListener::DEFAULT_BACKLOG)
     }
 
     /// Returns the local socket address of this listener.

library/std/src/net/tcp/tests.rs

@@ -48,7 +48,7 @@ fn connect_error() {
 #[test]
 fn listen_localhost() {
     let socket_addr = next_test_ip4();
-    let listener = t!(TcpListener::bind(&socket_addr));
+    let listener = t!(TcpListener::bind_with_backlog(&socket_addr, 1));
 
     let _t = thread::spawn(move || {
         let mut stream = t!(TcpStream::connect(&("localhost", socket_addr.port())));
@@ -64,7 +64,7 @@ fn listen_localhost() {
 #[test]
 fn connect_loopback() {
     each_ip(&mut |addr| {
-        let acceptor = t!(TcpListener::bind(&addr));
+        let acceptor = t!(TcpListener::bind_with_backlog(&addr, 1));
 
         let _t = thread::spawn(move || {
             let host = match addr {
@@ -85,7 +85,7 @@ fn connect_loopback() {
 #[test]
 fn smoke_test() {
     each_ip(&mut |addr| {
-        let acceptor = t!(TcpListener::bind(&addr));
+        let acceptor = t!(TcpListener::bind_with_backlog(&addr, 1));
 
         let (tx, rx) = channel();
         let _t = thread::spawn(move || {
@@ -172,11 +172,33 @@ fn multiple_connect_serial() {
     })
 }
 
+#[test]
+fn multiple_connect_serial_with_backlog() {
+    each_ip(&mut |addr| {
+        let max = 10;
+        let acceptor = t!(TcpListener::bind_with_backlog(&addr, max));
+
+        let _t = thread::spawn(move || {
+            for _ in 0..max {
+                let mut stream = t!(TcpStream::connect(&addr));
+                t!(stream.write(&[99]));
+            }
+        });
+
+        for stream in acceptor.incoming().take(max) {
+            let mut stream = t!(stream);
+            let mut buf = [0];
+            t!(stream.read(&mut buf));
+            assert_eq!(buf[0], 99);
+        }
+    })
+}
+
 #[test]
 fn multiple_connect_interleaved_greedy_schedule() {
     const MAX: usize = 10;
     each_ip(&mut |addr| {
-        let acceptor = t!(TcpListener::bind(&addr));
+        let acceptor = t!(TcpListener::bind_with_backlog(&addr, MAX));
 
         let _t = thread::spawn(move || {
             let acceptor = acceptor;
@@ -213,7 +235,7 @@ fn multiple_connect_interleaved_greedy_schedule() {
 fn multiple_connect_interleaved_lazy_schedule() {
     const MAX: usize = 10;
     each_ip(&mut |addr| {
-        let acceptor = t!(TcpListener::bind(&addr));
+        let acceptor = t!(TcpListener::bind_with_backlog(&addr, MAX));
 
         let _t = thread::spawn(move || {
             for stream in acceptor.incoming().take(MAX) {

library/std/src/os/unix/net/listener.rs

@@ -5,6 +5,7 @@ use crate::sys::cvt;
 use crate::sys::net::Socket;
 use crate::sys_common::{AsInner, FromInner, IntoInner};
 use crate::{fmt, io, mem};
+use core::convert::TryInto;
 
 /// A structure representing a Unix domain socket server.
 ///
@@ -53,8 +54,14 @@ impl fmt::Debug for UnixListener {
 }
 
 impl UnixListener {
+    /// Default backlog for `bind` and `bind_addr`.
+    const DEFAULT_BACKLOG: usize = 128;
+
     /// Creates a new `UnixListener` bound to the specified socket.
     ///
+    /// The listener will have a backlog of 128. See the documentation for
+    /// [`UnixListener::bind_with_backlog`] for further information.
+    ///
     /// # Examples
     ///
     /// ```no_run
@@ -70,19 +77,61 @@ impl UnixListener {
     /// ```
     #[stable(feature = "unix_socket", since = "1.10.0")]
     pub fn bind<P: AsRef<Path>>(path: P) -> io::Result<UnixListener> {
+        UnixListener::bind_with_backlog(path, UnixListener::DEFAULT_BACKLOG)
+    }
+
+    /// Creates a new `UnixListener` bound to the specified socket.
+    ///
+    /// The given backlog specifies the maximum number of outstanding
+    /// connections that will be buffered in the OS waiting to be accepted
+    /// by [`UnixListener::accept`]. The backlog argument overrides the
+    /// default backlog of 128; that default is reasonable for most use
+    /// cases.
+    ///
+    /// This function is otherwise [`UnixListener::bind`]: see that
+    /// documentation for full details of operation.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// #![feature(bind_with_backlog)]
+    /// use std::os::unix::net::UnixListener;
+    ///
+    /// let listener = match UnixListener::bind_with_backlog("/path/to/the/socket", 1000) {
+    ///     Ok(sock) => sock,
+    ///     Err(e) => {
+    ///         println!("Couldn't connect: {:?}", e);
+    ///         return
+    ///     }
+    /// };
+    /// ```
+    ///
+    /// # Errors
+    ///
+    /// The specified backlog may be larger than supported by the underlying
+    /// system. In this case an [`io::Error`] with
+    /// [`io::ErrorKind::InvalidData`] will be returned.
+    #[unstable(feature = "bind_with_backlog", issue = "94406")]
+    pub fn bind_with_backlog<P: AsRef<Path>>(path: P, backlog: usize) -> io::Result<UnixListener> {
         unsafe {
+            let backlog = backlog
+                .try_into()
+                .map_err(|e| crate::io::Error::new(crate::io::ErrorKind::InvalidData, e))?;
             let inner = Socket::new_raw(libc::AF_UNIX, libc::SOCK_STREAM)?;
             let (addr, len) = sockaddr_un(path.as_ref())?;
 
             cvt(libc::bind(inner.as_inner().as_raw_fd(), &addr as *const _ as *const _, len as _))?;
-            cvt(libc::listen(inner.as_inner().as_raw_fd(), 128))?;
+            cvt(libc::listen(inner.as_inner().as_raw_fd(), backlog))?;
 
             Ok(UnixListener(inner))
         }
     }
 
     /// Creates a new `UnixListener` bound to the specified [`socket address`].
     ///
+    /// The listener will have a backlog of 128. See the documentation for
+    /// [`UnixListener::bind_addr_with_backlog`] for further information.
+    ///
     /// [`socket address`]: crate::os::unix::net::SocketAddr
     ///
     /// # Examples
@@ -107,14 +156,59 @@ impl UnixListener {
     /// ```
     #[unstable(feature = "unix_socket_abstract", issue = "85410")]
     pub fn bind_addr(socket_addr: &SocketAddr) -> io::Result<UnixListener> {
+        UnixListener::bind_addr_with_backlog(socket_addr, UnixListener::DEFAULT_BACKLOG)
+    }
+
+    /// Creates a new `UnixListener` bound to the specified [`socket address`].
+    ///
+    /// The given backlog specifies the maximum number of outstanding
+    /// connections that will be buffered in the OS waiting to be accepted
+    /// by [`UnixListener::accept`]. The backlog argument overrides the
+    /// default of 128; that default is reasonable for most use cases.
+    ///
+    /// This function is otherwise [`UnixListener::bind_addr`]: see that
+    /// documentation for full details of operation.
+    ///
+    /// [`socket address`]: crate::os::unix::net::SocketAddr
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// #![feature(unix_socket_abstract)]
+    /// #![feature(bind_with_backlog)]
+    /// use std::os::unix::net::{UnixListener};
+    ///
+    /// fn main() -> std::io::Result<()> {
+    ///     let listener1 = UnixListener::bind("path/to/socket")?;
+    ///     let addr = listener1.local_addr()?;
+    ///
+    ///     let listener2 = match UnixListener::bind_addr_with_backlog(&addr, 1000) {
+    ///         Ok(sock) => sock,
+    ///         Err(err) => {
+    ///             println!("Couldn't bind: {:?}", err);
+    ///             return Err(err);
+    ///         }
+    ///     };
+    ///     Ok(())
+    /// }
+    /// ```
+    //#[unstable(feature = "unix_socket_abstract", issue = "85410")]
+    #[unstable(feature = "bind_with_backlog", issue = "94406")]
+    pub fn bind_addr_with_backlog(
+        socket_addr: &SocketAddr,
+        backlog: usize,
+    ) -> io::Result<UnixListener> {
         unsafe {
+            let backlog = backlog
+                .try_into()
+                .map_err(|e| crate::io::Error::new(crate::io::ErrorKind::InvalidData, e))?;
             let inner = Socket::new_raw(libc::AF_UNIX, libc::SOCK_STREAM)?;
             cvt(libc::bind(
                 inner.as_raw_fd(),
                 &socket_addr.addr as *const _ as *const _,
                 socket_addr.len as _,
             ))?;
-            cvt(libc::listen(inner.as_raw_fd(), 128))?;
+            cvt(libc::listen(inner.as_raw_fd(), backlog))?;
             Ok(UnixListener(inner))
         }
     }

library/std/src/os/unix/net/tests.rs

@@ -41,7 +41,7 @@ fn basic() {
     let msg1 = b"hello";
     let msg2 = b"world!";
 
-    let listener = or_panic!(UnixListener::bind(&socket_path));
+    let listener = or_panic!(UnixListener::bind_with_backlog(&socket_path, 1));
     let thread = thread::spawn(move || {
         let mut stream = or_panic!(listener.accept()).0;
         let mut buf = [0; 5];
@@ -111,7 +111,7 @@ fn try_clone() {
     let msg1 = b"hello";
     let msg2 = b"world";
 
-    let listener = or_panic!(UnixListener::bind(&socket_path));
+    let listener = or_panic!(UnixListener::bind_with_backlog(&socket_path, 1));
     let thread = thread::spawn(move || {
         let mut stream = or_panic!(listener.accept()).0;
         or_panic!(stream.write_all(msg1));
@@ -135,7 +135,7 @@ fn iter() {
     let dir = tmpdir();
     let socket_path = dir.path().join("sock");
 
-    let listener = or_panic!(UnixListener::bind(&socket_path));
+    let listener = or_panic!(UnixListener::bind_with_backlog(&socket_path, 2));
     let thread = thread::spawn(move || {
         for stream in listener.incoming().take(2) {
             let mut stream = or_panic!(stream);
@@ -423,7 +423,7 @@ fn test_abstract_stream_connect() {
     let msg2 = b"world";
 
     let socket_addr = or_panic!(SocketAddr::from_abstract_namespace(b"namespace"));
-    let listener = or_panic!(UnixListener::bind_addr(&socket_addr));
+    let listener = or_panic!(UnixListener::bind_addr_with_backlog(&socket_addr, 1));
 
     let thread = thread::spawn(move || {
         let mut stream = or_panic!(listener.accept()).0;
@@ -451,7 +451,7 @@ fn test_abstract_stream_connect() {
 #[test]
 fn test_abstract_stream_iter() {
     let addr = or_panic!(SocketAddr::from_abstract_namespace(b"hidden"));
-    let listener = or_panic!(UnixListener::bind_addr(&addr));
+    let listener = or_panic!(UnixListener::bind_addr_with_backlog(&addr, 2));
 
     let thread = thread::spawn(move || {
         for stream in listener.incoming().take(2) {

library/std/src/sys/unix/l4re.rs

@@ -276,6 +276,10 @@ pub mod net {
             unimpl!();
         }
 
+        pub fn bind_with_backlog(_: io::Result<&SocketAddr>, _: usize) -> io::Result<TcpListener> {
+            unimpl!();
+        }
+
         pub fn socket(&self) -> &Socket {
             &self.inner
         }

library/std/src/sys/unsupported/net.rs

@@ -122,6 +122,10 @@ impl TcpListener {
         unsupported()
     }
 
+    pub fn bind_with_backlog(_: io::Result<&SocketAddr>, _: usize) -> io::Result<TcpListener> {
+        unsupported()
+    }
+
     pub fn socket_addr(&self) -> io::Result<SocketAddr> {
         self.0
     }

library/std/src/sys/wasi/net.rs

@@ -205,6 +205,10 @@ impl TcpListener {
         unsupported()
     }
 
+    pub fn bind_with_backlog(_: io::Result<&SocketAddr>, _: usize) -> io::Result<TcpListener> {
+        unsupported()
+    }
+
     pub fn socket_addr(&self) -> io::Result<SocketAddr> {
         unsupported()
     }

library/std/src/sys_common/net.rs

@@ -363,9 +363,17 @@ pub struct TcpListener {
 }
 
 impl TcpListener {
-    pub fn bind(addr: io::Result<&SocketAddr>) -> io::Result<TcpListener> {
+    pub fn bind_with_backlog(
+        addr: io::Result<&SocketAddr>,
+        backlog: usize,
+    ) -> io::Result<TcpListener> {
         let addr = addr?;
 
+        // Type-convert the backlog
+        let backlog = backlog
+            .try_into()
+            .map_err(|e| crate::io::Error::new(crate::io::ErrorKind::InvalidData, e))?;
+
         init();
 
         let sock = Socket::new(addr, c::SOCK_STREAM)?;
@@ -385,7 +393,7 @@ impl TcpListener {
         cvt(unsafe { c::bind(sock.as_raw(), addrp, len as _) })?;
 
         // Start listening
-        cvt(unsafe { c::listen(sock.as_raw(), 128) })?;
+        cvt(unsafe { c::listen(sock.as_raw(), backlog) })?;
         Ok(TcpListener { inner: sock })
     }