interface udp {
    use wasi:io/poll@0.2.0.{pollable};
    use network.{network, error-code, ip-socket-address, ip-address-family};

    /// A received datagram.
    record incoming-datagram {
        /// The payload.
        /// 
        /// Theoretical max size: ~64 KiB. In practice, typically less than 1500 bytes.
        data: list<u8>,

        /// The source address.
        ///
        /// This field is guaranteed to match the remote address the stream was initialized with, if any.
        ///
        /// Equivalent to the `src_addr` out parameter of `recvfrom`.
        remote-address: ip-socket-address,
    }

    /// A datagram to be sent out.
    record outgoing-datagram {
        /// The payload.
        data: list<u8>,

        /// The destination address.
        ///
        /// The requirements on this field depend on how the stream was initialized:
        /// - with a remote address: this field must be None or match the stream's remote address exactly.
        /// - without a remote address: this field is required.
        ///
        /// If this value is None, the send operation is equivalent to `send` in POSIX. Otherwise it is equivalent to `sendto`.
        remote-address: option<ip-socket-address>,
    }



    /// A UDP socket handle.
    resource udp-socket {
        /// Bind the socket to a specific network on the provided IP address and port.
        ///
        /// If the IP address is zero (`0.0.0.0` in IPv4, `::` in IPv6), it is left to the implementation to decide which
        /// network interface(s) to bind to.
        /// If the port is zero, the socket will be bound to a random free port.
        ///
        /// Unlike in POSIX, this function is async. This enables interactive WASI hosts to inject permission prompts.
        ///
        /// # Typical `start` errors
        /// - `invalid-argument`:          The `local-address` has the wrong address family. (EAFNOSUPPORT, EFAULT on Windows)
        /// - `invalid-state`:             The socket is already bound. (EINVAL)
        ///
        /// # Typical `finish` errors
        /// - `address-in-use`:            No ephemeral ports available. (EADDRINUSE, ENOBUFS on Windows)
        /// - `address-in-use`:            Address is already in use. (EADDRINUSE)
        /// - `address-not-bindable`:      `local-address` is not an address that the `network` can bind to. (EADDRNOTAVAIL)
        /// - `not-in-progress`:           A `bind` operation is not in progress.
        /// - `would-block`:               Can't finish the operation, it is still in progress. (EWOULDBLOCK, EAGAIN)
        ///
        /// # References
        /// - <https://pubs.opengroup.org/onlinepubs/9699919799/functions/bind.html>
        /// - <https://man7.org/linux/man-pages/man2/bind.2.html>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-bind>
        /// - <https://man.freebsd.org/cgi/man.cgi?query=bind&sektion=2&format=html>
        start-bind: func(network: borrow<network>, local-address: ip-socket-address) -> result<_, error-code>;
        finish-bind: func() -> result<_, error-code>;

        /// Set up inbound & outbound communication channels, optionally to a specific peer.
        ///
        /// This function only changes the local socket configuration and does not generate any network traffic.
        /// On success, the `remote-address` of the socket is updated. The `local-address` may be updated as well,
        /// based on the best network path to `remote-address`.
        ///
        /// When a `remote-address` is provided, the returned streams are limited to communicating with that specific peer:
        /// - `send` can only be used to send to this destination.
        /// - `receive` will only return datagrams sent from the provided `remote-address`.
        ///
        /// This method may be called multiple times on the same socket to change its association, but
        /// only the most recently returned pair of streams will be operational. Implementations may trap if
        /// the streams returned by a previous invocation haven't been dropped yet before calling `stream` again.
        /// 
        /// The POSIX equivalent in pseudo-code is:
        /// ```text
        /// if (was previously connected) {
        /// 	connect(s, AF_UNSPEC)
        /// }
        /// if (remote_address is Some) {
        /// 	connect(s, remote_address)
        /// }
        /// ```
        ///
        /// Unlike in POSIX, the socket must already be explicitly bound.
        /// 
        /// # Typical errors
        /// - `invalid-argument`:          The `remote-address` has the wrong address family. (EAFNOSUPPORT)
        /// - `invalid-argument`:          The IP address in `remote-address` is set to INADDR_ANY (`0.0.0.0` / `::`). (EDESTADDRREQ, EADDRNOTAVAIL)
        /// - `invalid-argument`:          The port in `remote-address` is set to 0. (EDESTADDRREQ, EADDRNOTAVAIL)
        /// - `invalid-state`:             The socket is not bound.
        /// - `address-in-use`:            Tried to perform an implicit bind, but there were no ephemeral ports available. (EADDRINUSE, EADDRNOTAVAIL on Linux, EAGAIN on BSD)
        /// - `remote-unreachable`:        The remote address is not reachable. (ECONNRESET, ENETRESET, EHOSTUNREACH, EHOSTDOWN, ENETUNREACH, ENETDOWN, ENONET)
        /// - `connection-refused`:        The connection was refused. (ECONNREFUSED)
        ///
        /// # References
        /// - <https://pubs.opengroup.org/onlinepubs/9699919799/functions/connect.html>
        /// - <https://man7.org/linux/man-pages/man2/connect.2.html>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-connect>
        /// - <https://man.freebsd.org/cgi/man.cgi?connect>
        %stream: func(remote-address: option<ip-socket-address>) -> result<tuple<incoming-datagram-stream, outgoing-datagram-stream>, error-code>;

        /// Get the current bound address.
        ///
        /// POSIX mentions:
        /// > If the socket has not been bound to a local name, the value
        /// > stored in the object pointed to by `address` is unspecified.
        ///
        /// WASI is stricter and requires `local-address` to return `invalid-state` when the socket hasn't been bound yet.
        /// 
        /// # Typical errors
        /// - `invalid-state`: The socket is not bound to any local address.
        ///
        /// # References
        /// - <https://pubs.opengroup.org/onlinepubs/9699919799/functions/getsockname.html>
        /// - <https://man7.org/linux/man-pages/man2/getsockname.2.html>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-getsockname>
        /// - <https://man.freebsd.org/cgi/man.cgi?getsockname>
        local-address: func() -> result<ip-socket-address, error-code>;

        /// Get the address the socket is currently streaming to.
        ///
        /// # Typical errors
        /// - `invalid-state`: The socket is not streaming to a specific remote address. (ENOTCONN)
        ///
        /// # References
        /// - <https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpeername.html>
        /// - <https://man7.org/linux/man-pages/man2/getpeername.2.html>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-getpeername>
        /// - <https://man.freebsd.org/cgi/man.cgi?query=getpeername&sektion=2&n=1>
        remote-address: func() -> result<ip-socket-address, error-code>;

        /// Whether this is a IPv4 or IPv6 socket.
        ///
        /// Equivalent to the SO_DOMAIN socket option.
        address-family: func() -> ip-address-family;

        /// Equivalent to the IP_TTL & IPV6_UNICAST_HOPS socket options.
        ///
        /// If the provided value is 0, an `invalid-argument` error is returned.
        ///
        /// # Typical errors
        /// - `invalid-argument`:     (set) The TTL value must be 1 or higher.
        unicast-hop-limit: func() -> result<u8, error-code>;
        set-unicast-hop-limit: func(value: u8) -> result<_, error-code>;

        /// The kernel buffer space reserved for sends/receives on this socket.
        ///
        /// If the provided value is 0, an `invalid-argument` error is returned.
        /// Any other value will never cause an error, but it might be silently clamped and/or rounded.
        /// I.e. after setting a value, reading the same setting back may return a different value.
        ///
        /// Equivalent to the SO_RCVBUF and SO_SNDBUF socket options.
        ///
        /// # Typical errors
        /// - `invalid-argument`:     (set) The provided value was 0.
        receive-buffer-size: func() -> result<u64, error-code>;
        set-receive-buffer-size: func(value: u64) -> result<_, error-code>;
        send-buffer-size: func() -> result<u64, error-code>;
        set-send-buffer-size: func(value: u64) -> result<_, error-code>;

        /// Create a `pollable` which will resolve once the socket is ready for I/O.
        ///
        /// Note: this function is here for WASI Preview2 only.
        /// It's planned to be removed when `future` is natively supported in Preview3.
        subscribe: func() -> pollable;
    }

    resource incoming-datagram-stream {
        /// Receive messages on the socket.
        ///
        /// This function attempts to receive up to `max-results` datagrams on the socket without blocking.
        /// The returned list may contain fewer elements than requested, but never more.
        ///
        /// This function returns successfully with an empty list when either:
        /// - `max-results` is 0, or:
        /// - `max-results` is greater than 0, but no results are immediately available.
        /// This function never returns `error(would-block)`.
        ///
        /// # Typical errors
        /// - `remote-unreachable`: The remote address is not reachable. (ECONNRESET, ENETRESET on Windows, EHOSTUNREACH, EHOSTDOWN, ENETUNREACH, ENETDOWN, ENONET)
        /// - `connection-refused`: The connection was refused. (ECONNREFUSED)
        ///
        /// # References
        /// - <https://pubs.opengroup.org/onlinepubs/9699919799/functions/recvfrom.html>
        /// - <https://pubs.opengroup.org/onlinepubs/9699919799/functions/recvmsg.html>
        /// - <https://man7.org/linux/man-pages/man2/recv.2.html>
        /// - <https://man7.org/linux/man-pages/man2/recvmmsg.2.html>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-recv>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-recvfrom>
        /// - <https://learn.microsoft.com/en-us/previous-versions/windows/desktop/legacy/ms741687(v=vs.85)>
        /// - <https://man.freebsd.org/cgi/man.cgi?query=recv&sektion=2>
        receive: func(max-results: u64) -> result<list<incoming-datagram>, error-code>;

        /// Create a `pollable` which will resolve once the stream is ready to receive again.
        ///
        /// Note: this function is here for WASI Preview2 only.
        /// It's planned to be removed when `future` is natively supported in Preview3.
        subscribe: func() -> pollable;
    }

    resource outgoing-datagram-stream {
        /// Check readiness for sending. This function never blocks.
        ///
        /// Returns the number of datagrams permitted for the next call to `send`,
        /// or an error. Calling `send` with more datagrams than this function has
        /// permitted will trap.
        ///
        /// When this function returns ok(0), the `subscribe` pollable will
        /// become ready when this function will report at least ok(1), or an
        /// error.
        /// 
        /// Never returns `would-block`.
        check-send: func() -> result<u64, error-code>;

        /// Send messages on the socket.
        ///
        /// This function attempts to send all provided `datagrams` on the socket without blocking and
        /// returns how many messages were actually sent (or queued for sending). This function never
        /// returns `error(would-block)`. If none of the datagrams were able to be sent, `ok(0)` is returned.
        ///
        /// This function semantically behaves the same as iterating the `datagrams` list and sequentially
        /// sending each individual datagram until either the end of the list has been reached or the first error occurred.
        /// If at least one datagram has been sent successfully, this function never returns an error.
        ///
        /// If the input list is empty, the function returns `ok(0)`.
        ///
        /// Each call to `send` must be permitted by a preceding `check-send`. Implementations must trap if
        /// either `check-send` was not called or `datagrams` contains more items than `check-send` permitted.
        ///
        /// # Typical errors
        /// - `invalid-argument`:        The `remote-address` has the wrong address family. (EAFNOSUPPORT)
        /// - `invalid-argument`:        The IP address in `remote-address` is set to INADDR_ANY (`0.0.0.0` / `::`). (EDESTADDRREQ, EADDRNOTAVAIL)
        /// - `invalid-argument`:        The port in `remote-address` is set to 0. (EDESTADDRREQ, EADDRNOTAVAIL)
        /// - `invalid-argument`:        The socket is in "connected" mode and `remote-address` is `some` value that does not match the address passed to `stream`. (EISCONN)
        /// - `invalid-argument`:        The socket is not "connected" and no value for `remote-address` was provided. (EDESTADDRREQ)
        /// - `remote-unreachable`:      The remote address is not reachable. (ECONNRESET, ENETRESET on Windows, EHOSTUNREACH, EHOSTDOWN, ENETUNREACH, ENETDOWN, ENONET)
        /// - `connection-refused`:      The connection was refused. (ECONNREFUSED)
        /// - `datagram-too-large`:      The datagram is too large. (EMSGSIZE)
        ///
        /// # References
        /// - <https://pubs.opengroup.org/onlinepubs/9699919799/functions/sendto.html>
        /// - <https://pubs.opengroup.org/onlinepubs/9699919799/functions/sendmsg.html>
        /// - <https://man7.org/linux/man-pages/man2/send.2.html>
        /// - <https://man7.org/linux/man-pages/man2/sendmmsg.2.html>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-send>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-sendto>
        /// - <https://learn.microsoft.com/en-us/windows/win32/api/winsock2/nf-winsock2-wsasendmsg>
        /// - <https://man.freebsd.org/cgi/man.cgi?query=send&sektion=2>
        send: func(datagrams: list<outgoing-datagram>) -> result<u64, error-code>;
        
        /// Create a `pollable` which will resolve once the stream is ready to send again.
        ///
        /// Note: this function is here for WASI Preview2 only.
        /// It's planned to be removed when `future` is natively supported in Preview3.
        subscribe: func() -> pollable;
    }
}