cloudflare/quiche · error · io::Error

Unsupported

Unsupported

Error message

invalid address family

What it means

datagram-socket's socket abstraction only implements send paths for AF_INET/AF_INET6 sockets. This poll_send_to is a fallback stub (for unsupported address families, e.g. unix/other) that always returns io::ErrorKind::Unsupported, so any send attempted through it can never succeed.

Solutions

1. Ensure the socket is bound to an IPv4 or IPv6 address before using poll_send_to
2. Check how the socket was constructed (from_datagram / socket2 setup) and only use AF_INET/AF_INET6
3. If you need another family, add a real implementation for that cfg branch instead of relying on the stub

Example fix

// before
let addr: SocketAddr = "[::1]:443".parse()?; // fine; but a unix/other family addr hits the stub
socket.send_to(buf, addr).await?;
// after
if !matches!(addr, SocketAddr::V4(_) | SocketAddr::V6(_)) {
    return Err(io::Error::new(io::ErrorKind::Unsupported, "non-IP family"));
}
socket.send_to(buf, addr).await?;

fn is_ip_family(addr: std::net::SocketAddr) -> bool {
    matches!(addr, std::net::SocketAddr::V4(_) | std::net::SocketAddr::V6(_))
}
// call before send_to / poll_send_to
if !is_ip_family(target) { return Err(...); }

fn is_ip_family(addr: std::net::SocketAddr) -> bool {
    matches!(addr, std::net::SocketAddr::V4(_) | std::net::SocketAddr::V6(_))
}

When it happens

Trigger: Calling poll_send_to (via the AsyncSocket send path / poll_send machinery) on a datagram socket whose address family is not IPv4/IPv6, i.e. hitting the #[cfg] fallback implementation in datagram.rs:692.

Common situations: Passing a socket created from an address family other than IPv4/IPv6 into the datagram-socket send API; binding from a SocketAddr the crate does not support; misconfiguration on unusual platforms.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Error creating file for
• Error creating qlog file attempted path was
• send_to_gso() should not be called on non-linux platforms

AI-assisted analysis of cloudflare/quiche@9f96daa2c2 (2026-09-08). Data as JSON: /api/errors/955f4f88f02f26bc. Report an issue: GitHub.

Appendix: source

Thrown at datagram-socket/src/datagram.rs:692

    }

    fn into_fd(self) -> Option<OwnedFd> {
        Some(into_owned_fd(self.into_std().ok()?))
    }
}

#[cfg(unix)]
impl DatagramSocketSend for UnixDatagram {
    #[inline]
    fn poll_send(&self, cx: &mut Context, buf: &[u8]) -> Poll<io::Result<usize>> {
        UnixDatagram::poll_send(self, cx, buf)
    }

    #[inline]
    fn poll_send_to(
        &self, _: &mut Context, _: &[u8], _: SocketAddr,
    ) -> Poll<io::Result<usize>> {
        Poll::Ready(Err(io::Error::new(
            io::ErrorKind::Unsupported,
            "invalid address family",
        )))
    }

    #[cfg(target_os = "linux")]
    #[inline]
    fn poll_send_many(
        &self, cx: &mut Context, bufs: &[ReadBuf<'_>],
    ) -> Poll<io::Result<usize>> {
        crate::poll_sendmmsg!(self, cx, bufs)
    }
}

#[cfg(unix)]
impl DatagramSocketRecv for UnixDatagram {
    #[inline]
    fn poll_recv(

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