Set backlog size for listeners to match std lib

src/net/tcp/listener.rs

@@ -20,10 +20,7 @@ use crate::net::TcpStream;
 ))]
 use crate::sys::tcp::set_reuseaddr;
 #[cfg(not(all(target_os = "wasi", target_env = "p1")))]
-use crate::sys::{
-    tcp::{bind, listen, new_for_addr},
-    LISTEN_BACKLOG_SIZE,
-};
+use crate::sys::tcp::{bind, listen, new_for_addr};
 use crate::{event, sys, Interest, Registry, Token};
 
 /// A structure representing a socket server
@@ -85,7 +82,16 @@ impl TcpListener {
         set_reuseaddr(&listener.inner, true)?;
 
         bind(&listener.inner, addr)?;
-        listen(&listener.inner, LISTEN_BACKLOG_SIZE)?;
+        // Use the same backlog value as the standard libary.
+        // <https://github.com/rust-lang/rust/blob/0028f344ce9f64766259577c998a1959ca1f6a0b/library/std/src/sys/net/connection/socket/mod.rs#L559-L571>
+        let backlog = if cfg!(target_os = "horizon") {
+            20
+        } else if cfg!(target_os = "haiku") {
+            32
+        } else {
+            128
+        };
+        listen(&listener.inner, backlog)?;
         Ok(listener)
     }
 

src/sys/mod.rs

@@ -84,69 +84,3 @@ cfg_not_os_poll! {
         pub use self::unix::SourceFd;
     }
 }
-
-/// Define the `listen` backlog parameters. This helps avoid hardcoded
-/// unsynchronized values and allows better control of default values depending
-/// on the target.
-///
-/// Selecting a “valid” default value can be tricky due to:
-///
-/// - It often serves only as a hint and may be rounded, trimmed, or ignored by
-///   the OS.
-///
-/// - It is sometimes provided as a "magic" value, for example, -1. This
-///   value is undocumented and not standard, but it is often used to represent
-///   the largest possible backlog size. This happens due to signed/unsigned
-///   conversion and rounding to the upper bound performed by the OS.
-///
-/// - Default values vary depending on the OS and its version. Common defaults
-///   include: -1, 128, 1024, and 4096.
-///
-// The logic here is taken from the standard library for unix sockets. TCP
-// sockets in the standard library use much smaller sizes.
-// https://github.com/rust-lang/rust/blob/4f808ba6bf9f1c8dde30d009e73386d984491587/library/std/src/os/unix/net/listener.rs#L72
-//
-#[allow(dead_code)]
-#[cfg(any(
-    target_os = "windows",
-    target_os = "redox",
-    target_os = "espidf",
-    target_os = "horizon"
-))]
-pub(crate) const LISTEN_BACKLOG_SIZE: i32 = 128;
-
-/// This is a special case for some target(s) supported by `mio`.  This value
-/// is needed because `libc::SOMAXCON` (used as a fallback for unknown targets)
-/// is not implemented for them. Feel free to update this if the `libc` crate
-/// changes.
-#[allow(dead_code)]
-#[cfg(any(target_os = "hermit", target_os = "wasi"))]
-pub(crate) const LISTEN_BACKLOG_SIZE: i32 = 1024;
-
-#[allow(dead_code)]
-#[cfg(any(
-    // Silently capped to `/proc/sys/net/core/somaxconn`.
-    target_os = "linux",
-    // Silently capped to `kern.ipc.soacceptqueue`.
-    target_os = "freebsd",
-    // Silently capped to `kern.somaxconn sysctl`.
-    target_os = "openbsd",
-    // Silently capped to the default 128.
-    target_vendor = "apple",
-))]
-pub(crate) const LISTEN_BACKLOG_SIZE: i32 = -1;
-
-#[allow(dead_code)]
-#[cfg(not(any(
-    target_os = "windows",
-    target_os = "redox",
-    target_os = "espidf",
-    target_os = "horizon",
-    target_os = "linux",
-    target_os = "freebsd",
-    target_os = "openbsd",
-    target_os = "wasi",
-    target_os = "hermit",
-    target_vendor = "apple",
-)))]
-pub(crate) const LISTEN_BACKLOG_SIZE: i32 = libc::SOMAXCONN;

src/sys/unix/uds/listener.rs

@@ -8,7 +8,6 @@ use std::{io, mem};
 use crate::net::UnixStream;
 use crate::sys::unix::net::new_socket;
 use crate::sys::unix::uds::{path_offset, unix_addr};
-use crate::sys::LISTEN_BACKLOG_SIZE;
 
 pub(crate) fn bind_addr(address: &SocketAddr) -> io::Result<net::UnixListener> {
     let fd = new_socket(libc::AF_UNIX, libc::SOCK_STREAM)?;
@@ -17,7 +16,26 @@ pub(crate) fn bind_addr(address: &SocketAddr) -> io::Result<net::UnixListener> {
     let (unix_address, addrlen) = unix_addr(address);
     let sockaddr = &unix_address as *const libc::sockaddr_un as *const libc::sockaddr;
     syscall!(bind(fd, sockaddr, addrlen))?;
-    syscall!(listen(fd, LISTEN_BACKLOG_SIZE))?;
+    // Use the same backlog value as the standard libary.
+    // <https://github.com/rust-lang/rust/blob/0028f344ce9f64766259577c998a1959ca1f6a0b/library/std/src/os/unix/net/listener.rs#L75-L106>
+    let backlog = if cfg!(any(
+        target_os = "windows",
+        target_os = "redox",
+        target_os = "espidf",
+        target_os = "horizon"
+    )) {
+        128
+    } else if cfg!(any(
+        target_os = "linux",
+        target_os = "freebsd",
+        target_os = "openbsd",
+        target_vendor = "apple"
+    )) {
+        -1
+    } else {
+        libc::SOMAXCONN
+    };
+    syscall!(listen(fd, backlog))?;
 
     Ok(socket)
 }