netSendOnePosix

fn netSendOnePosix(
    t: *Threaded,
    socket_handle: net.Socket.Handle,
    message: *net.OutgoingMessage,
    flags: u32,
) (net.Socket.SendError || error{WouldBlock})!void {
    _ = t;
    var addr: PosixAddress = undefined;
    var iovec: posix.iovec_const = .{ .base = @constCast(message.data_ptr), .len = message.data_len };
    const msg: posix.msghdr_const = .{
        .name = &addr.any,
        .namelen = addressToPosix(message.address, &addr),
        .iov = (&iovec)[0..1],
        .iovlen = 1,
        // OS returns EINVAL if this pointer is invalid even if controllen is zero.
        .control = if (message.control.len == 0) null else @constCast(message.control.ptr),
        .controllen = @intCast(message.control.len),
        .flags = 0,
    };
    var syscall: if (is_windows) AlertableSyscall else Syscall = try .start();
    while (true) {
        const rc = posix.system.sendmsg(socket_handle, &msg, flags);
        switch (posix.errno(rc)) {
            .SUCCESS => {
                syscall.finish();
                message.data_len = @intCast(rc);
                return;
            },
            .INTR => {
                try syscall.checkCancel();
                continue;
            },
            .ACCES => return syscall.fail(error.AccessDenied),
            .AGAIN => return syscall.fail(error.WouldBlock),
            .ALREADY => return syscall.fail(error.FastOpenAlreadyInProgress),
            .CONNRESET => return syscall.fail(error.ConnectionResetByPeer),
            .MSGSIZE => return syscall.fail(error.MessageOversize),
            .NOBUFS => return syscall.fail(error.SystemResources),
            .NOMEM => return syscall.fail(error.SystemResources),
            .PIPE => return syscall.fail(error.SocketUnconnected),
            .AFNOSUPPORT => return syscall.fail(error.AddressFamilyUnsupported),
            .HOSTUNREACH => return syscall.fail(error.HostUnreachable),
            .NETUNREACH => return syscall.fail(error.NetworkUnreachable),
            .NOTCONN => return syscall.fail(error.SocketUnconnected),
            .TIMEDOUT => return syscall.fail(error.ConnectionTimedOut),
            .NETDOWN => return syscall.fail(error.NetworkDown),
            .BADF => |err| return syscall.errnoBug(err), // File descriptor used after closed.
            .DESTADDRREQ => |err| return syscall.errnoBug(err),
            .FAULT => |err| return syscall.errnoBug(err),
            .INVAL => |err| return syscall.errnoBug(err),
            .ISCONN => |err| return syscall.errnoBug(err),
            .NOTSOCK => |err| return syscall.errnoBug(err),
            .OPNOTSUPP => |err| return syscall.errnoBug(err),
            else => |err| return syscall.unexpectedErrno(err),
        }
    }
}