Add wasm32-wasip2 target support (#639)

Rework of #532, addressing review feedback:

- Reuses sys/unix.rs instead of creating sys/wasi.rs (per code review feedback)
- MaybeUninitSlice stays unconditional since libc::iovec is available on WASI,
  eliminating 11+ scattered cfg gates
- Internal cfg changes concentrated in the sys module

Opt-in cfg patterns use `all(target_os = "wasi", not(target_env = "p1"))`
to match how the libc crate gates WASI p2 socket support. Opt-out
patterns use bare `target_os = "wasi"` for features unavailable on any
WASI version.

WASI tests run in CI with wasmtime (27/27 pass). Tests for unsupported
socket options are gated out with references to the relevant WASI spec
issues (SO_BROADCAST, SO_LINGER, IPV6_V6ONLY).

```bash
export CARGO_TARGET_WASM32_WASIP2_RUNNER="wasmtime --wasi inherit-network"
cargo test --target wasm32-wasip2 --lib --tests
```

Closes #268

Based-on: #532
Co-authored-by: Nicola Krumschmidt <git@nkcom.de>

Author: ricochet

.github/workflows/main.yml

@@ -105,6 +105,7 @@ jobs:
           - x86_64-unknown-netbsd
           - x86_64-unknown-openbsd
           - x86_64-unknown-redox
+          - wasm32-wasip2
     steps:
     - uses: actions/checkout@v4
     - uses: dtolnay/rust-toolchain@nightly

Cargo.toml

@@ -49,7 +49,7 @@ targets = [
 [package.metadata.playground]
 features = ["all"]
 
-[target."cfg(unix)".dependencies]
+[target.'cfg(any(unix, target_os = "wasi"))'.dependencies]
 libc = "0.2.172"
 
 [target.'cfg(windows)'.dependencies.windows-sys]

src/lib.rs

@@ -61,11 +61,11 @@
 #![doc(test(attr(deny(warnings))))]
 
 use std::fmt;
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 use std::io::IoSlice;
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 use std::marker::PhantomData;
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 use std::mem;
 use std::mem::MaybeUninit;
 use std::net::SocketAddr;
@@ -109,7 +109,7 @@ macro_rules! from {
     ($from: ty, $for: ty) => {
         impl From<$from> for $for {
             fn from(socket: $from) -> $for {
-                #[cfg(unix)]
+                #[cfg(any(unix, all(target_os = "wasi", not(target_env = "p1"))))]
                 unsafe {
                     <$for>::from_raw_fd(socket.into_raw_fd())
                 }
@@ -176,11 +176,14 @@ mod sockaddr;
 mod socket;
 mod sockref;
 
-#[cfg_attr(unix, path = "sys/unix.rs")]
+#[cfg_attr(
+    any(unix, all(target_os = "wasi", not(target_env = "p1"))),
+    path = "sys/unix.rs"
+)]
 #[cfg_attr(windows, path = "sys/windows.rs")]
 mod sys;
 
-#[cfg(not(any(windows, unix)))]
+#[cfg(not(any(windows, unix, all(target_os = "wasi", not(target_env = "p1")))))]
 compile_error!("Socket2 doesn't support the compile target");
 
 use sys::c_int;
@@ -192,6 +195,7 @@ pub use sockaddr::{sa_family_t, socklen_t, SockAddr, SockAddrStorage};
     target_os = "netbsd",
     target_os = "redox",
     target_os = "solaris",
+    target_os = "wasi",
 )))]
 pub use socket::InterfaceIndexOrAddress;
 pub use socket::Socket;
@@ -221,6 +225,7 @@ impl Domain {
     pub const IPV6: Domain = Domain(sys::AF_INET6);
 
     /// Domain for Unix socket communication, corresponding to `AF_UNIX`.
+    #[cfg(not(target_os = "wasi"))]
     pub const UNIX: Domain = Domain(sys::AF_UNIX);
 
     /// Returns the correct domain for `address`.
@@ -274,11 +279,14 @@ impl Type {
     pub const DCCP: Type = Type(sys::SOCK_DCCP);
 
     /// Type corresponding to `SOCK_SEQPACKET`.
-    #[cfg(all(feature = "all", not(target_os = "espidf")))]
+    #[cfg(all(feature = "all", not(any(target_os = "espidf", target_os = "wasi"))))]
     pub const SEQPACKET: Type = Type(sys::SOCK_SEQPACKET);
 
     /// Type corresponding to `SOCK_RAW`.
-    #[cfg(all(feature = "all", not(any(target_os = "redox", target_os = "espidf"))))]
+    #[cfg(all(
+        feature = "all",
+        not(any(target_os = "redox", target_os = "espidf", target_os = "wasi"))
+    ))]
     pub const RAW: Type = Type(sys::SOCK_RAW);
 }
 
@@ -306,9 +314,11 @@ pub struct Protocol(c_int);
 
 impl Protocol {
     /// Protocol corresponding to `ICMPv4`.
+    #[cfg(not(target_os = "wasi"))]
     pub const ICMPV4: Protocol = Protocol(sys::IPPROTO_ICMP);
 
     /// Protocol corresponding to `ICMPv6`.
+    #[cfg(not(target_os = "wasi"))]
     pub const ICMPV6: Protocol = Protocol(sys::IPPROTO_ICMPV6);
 
     /// Protocol corresponding to `TCP`.
@@ -361,11 +371,11 @@ impl From<Protocol> for c_int {
 /// Flags for incoming messages.
 ///
 /// Flags provide additional information about incoming messages.
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 #[derive(Copy, Clone, Eq, PartialEq)]
 pub struct RecvFlags(c_int);
 
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 impl RecvFlags {
     /// Check if the message contains a truncated datagram.
     ///
@@ -518,6 +528,7 @@ impl TcpKeepalive {
         target_os = "watchos",
         target_os = "windows",
         target_os = "cygwin",
+        all(target_os = "wasi", not(target_env = "p1")),
     ))]
     pub const fn with_interval(self, interval: Duration) -> Self {
         Self {
@@ -547,6 +558,7 @@ impl TcpKeepalive {
             target_os = "watchos",
             target_os = "cygwin",
             target_os = "windows",
+            all(target_os = "wasi", not(target_env = "p1")),
         )
     ))]
     pub const fn with_retries(self, retries: u32) -> Self {
@@ -561,15 +573,15 @@ impl TcpKeepalive {
 ///
 /// This wraps `msghdr` on Unix and `WSAMSG` on Windows. Also see [`MsgHdrMut`]
 /// for the variant used by `recvmsg(2)`.
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 #[repr(transparent)]
 pub struct MsgHdr<'addr, 'bufs, 'control> {
     inner: sys::msghdr,
     #[allow(clippy::type_complexity)]
     _lifetimes: PhantomData<(&'addr SockAddr, &'bufs IoSlice<'bufs>, &'control [u8])>,
 }
 
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 impl<'addr, 'bufs, 'control> MsgHdr<'addr, 'bufs, 'control> {
     /// Create a new `MsgHdr` with all empty/zero fields.
     #[allow(clippy::new_without_default)]
@@ -619,7 +631,7 @@ impl<'addr, 'bufs, 'control> MsgHdr<'addr, 'bufs, 'control> {
     }
 }
 
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 impl<'name, 'bufs, 'control> fmt::Debug for MsgHdr<'name, 'bufs, 'control> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         "MsgHdr".fmt(fmt)
@@ -630,7 +642,7 @@ impl<'name, 'bufs, 'control> fmt::Debug for MsgHdr<'name, 'bufs, 'control> {
 ///
 /// This wraps `msghdr` on Unix and `WSAMSG` on Windows. Also see [`MsgHdr`] for
 /// the variant used by `sendmsg(2)`.
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 #[repr(transparent)]
 pub struct MsgHdrMut<'addr, 'bufs, 'control> {
     inner: sys::msghdr,
@@ -642,7 +654,7 @@ pub struct MsgHdrMut<'addr, 'bufs, 'control> {
     )>,
 }
 
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 impl<'addr, 'bufs, 'control> MsgHdrMut<'addr, 'bufs, 'control> {
     /// Create a new `MsgHdrMut` with all empty/zero fields.
     #[allow(clippy::new_without_default)]
@@ -697,7 +709,7 @@ impl<'addr, 'bufs, 'control> MsgHdrMut<'addr, 'bufs, 'control> {
     }
 }
 
-#[cfg(not(target_os = "redox"))]
+#[cfg(not(any(target_os = "redox", target_os = "wasi")))]
 impl<'name, 'bufs, 'control> fmt::Debug for MsgHdrMut<'name, 'bufs, 'control> {
     fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
         "MsgHdrMut".fmt(fmt)

src/sockaddr.rs

@@ -1,13 +1,16 @@
 use std::hash::Hash;
 use std::mem::{self, size_of};
 use std::net::{SocketAddr, SocketAddrV4, SocketAddrV6};
+#[cfg(not(target_os = "wasi"))]
 use std::path::Path;
 use std::{fmt, io, ptr};
 
 #[cfg(windows)]
 use windows_sys::Win32::Networking::WinSock::SOCKADDR_IN6_0;
 
-use crate::sys::{c_int, sockaddr_in, sockaddr_in6, sockaddr_storage, AF_INET, AF_INET6, AF_UNIX};
+#[cfg(not(target_os = "wasi"))]
+use crate::sys::AF_UNIX;
+use crate::sys::{c_int, sockaddr_in, sockaddr_in6, sockaddr_storage, AF_INET, AF_INET6};
 use crate::Domain;
 
 /// The integer type used with `getsockname` on this platform.
@@ -212,6 +215,7 @@ impl SockAddr {
     /// Constructs a `SockAddr` with the family `AF_UNIX` and the provided path.
     ///
     /// Returns an error if the path is longer than `SUN_LEN`.
+    #[cfg(not(target_os = "wasi"))]
     pub fn unix<P>(path: P) -> io::Result<SockAddr>
     where
         P: AsRef<Path>,
@@ -269,6 +273,7 @@ impl SockAddr {
 
     /// Returns true if this address is of a unix socket (for local interprocess communication),
     /// i.e. it is from the `AF_UNIX` family, false otherwise.
+    #[cfg(not(target_os = "wasi"))]
     pub fn is_unix(&self) -> bool {
         self.storage.ss_family == AF_UNIX as sa_family_t
     }
@@ -293,7 +298,7 @@ impl SockAddr {
                 ip,
                 port,
                 addr.sin6_flowinfo,
-                #[cfg(unix)]
+                #[cfg(any(unix, all(target_os = "wasi", not(target_env = "p1"))))]
                 addr.sin6_scope_id,
                 #[cfg(windows)]
                 unsafe {
@@ -350,7 +355,10 @@ impl From<SocketAddrV4> for SockAddr {
             storage.sin_family = AF_INET as sa_family_t;
             storage.sin_port = addr.port().to_be();
             storage.sin_addr = crate::sys::to_in_addr(addr.ip());
-            storage.sin_zero = Default::default();
+            #[cfg(not(target_os = "wasi"))]
+            {
+                storage.sin_zero = Default::default();
+            }
             mem::size_of::<sockaddr_in>() as socklen_t
         };
         #[cfg(any(
@@ -385,7 +393,7 @@ impl From<SocketAddrV6> for SockAddr {
             storage.sin6_port = addr.port().to_be();
             storage.sin6_addr = crate::sys::to_in6_addr(addr.ip());
             storage.sin6_flowinfo = addr.flowinfo();
-            #[cfg(unix)]
+            #[cfg(any(unix, all(target_os = "wasi", not(target_env = "p1"))))]
             {
                 storage.sin6_scope_id = addr.scope_id();
             }
@@ -469,6 +477,7 @@ mod tests {
         let addr = SockAddr::from(std);
         assert!(addr.is_ipv4());
         assert!(!addr.is_ipv6());
+        #[cfg(not(target_os = "wasi"))]
         assert!(!addr.is_unix());
         assert_eq!(addr.family(), AF_INET as sa_family_t);
         assert_eq!(addr.domain(), Domain::IPV4);
@@ -483,7 +492,7 @@ mod tests {
         assert_eq!(addr.as_socket(), Some(SocketAddr::V4(std)));
         assert_eq!(addr.as_socket_ipv4(), Some(std));
         assert!(addr.as_socket_ipv6().is_none());
-        #[cfg(unix)]
+        #[cfg(all(unix, not(target_os = "wasi")))]
         {
             assert!(addr.as_pathname().is_none());
             assert!(addr.as_abstract_namespace().is_none());
@@ -497,6 +506,7 @@ mod tests {
         let addr = SockAddr::from(std);
         assert!(addr.is_ipv6());
         assert!(!addr.is_ipv4());
+        #[cfg(not(target_os = "wasi"))]
         assert!(!addr.is_unix());
         assert_eq!(addr.family(), AF_INET6 as sa_family_t);
         assert_eq!(addr.domain(), Domain::IPV6);
@@ -511,7 +521,7 @@ mod tests {
         assert_eq!(addr.as_socket(), Some(SocketAddr::V6(std)));
         assert!(addr.as_socket_ipv4().is_none());
         assert_eq!(addr.as_socket_ipv6(), Some(std));
-        #[cfg(unix)]
+        #[cfg(all(unix, not(target_os = "wasi")))]
         {
             assert!(addr.as_pathname().is_none());
             assert!(addr.as_abstract_namespace().is_none());