// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

library fuchsia.net.tun;

using zx;
using fuchsia.hardware.network;
using fuchsia.net;

/// Maximum number of multicast filters that a device will hold in `MacState`.
// NOTE: this number mirrors the number in the low level banjo definition in
// [`fuchsia.hardware.network.mac/MAX_MAC_FILTER`] which was chosen, in turn, based on common maximum
// number of multicast groups supported in established OSes.
const uint32 MAX_MULTICAST_FILTERS = 64;

/// Maximum number of pending [`fuchsia.net.tun/Device.WriteFrame`] or
/// [`fuchsia.net.tun/Device.ReadFrame`] that are allowed.
// NOTE: This number is chosen arbitrarily to maintain a determined upper bound on memory
// consumption for a `Device` instance.
const uint32 MAX_PENDING_OPERATIONS = 32;

/// Signals set in the `eventpair` returned by [`fuchsia.net.tun/Device.GetSignals`].
bits Signals : uint32 {
    /// Indicates that write buffers are available to be used through
    /// [`fuchsia.net.tun/Device.WriteFrame`].
    WRITABLE = 0x01000000; // ZX_USER_SIGNAL_0
    /// Indicates that read buffers are available to be used through
    /// [`fuchsia.net.tun/Device.ReadFrame`].
    READABLE = 0x02000000; // ZX_USER_SIGNAL_1
};

/// Maximum supported MTU.
// NOTE: Selected as the smallest power of 2 that will fit conventional jumbo frame sizes of 9KB.
// Source: https://en.wikipedia.org/wiki/Jumbo_frame. The value is chosen arbitrarily low (while
// abiding by the conventional jumbo frame sizes) to encourage sensible memory usage for clients of
// the NetworkDevice interface, as receive buffers must be at least MTU-sized for valid operation.
const uint32 MAX_MTU = 16384;

/// Common configuration used to create a `Device` or `DevicePair`.
table BaseConfig {
    /// Device MTU (maximum transmit unit).
    ///
    /// If a value greater than `MAX_MTU` is provided, creating a device will fail.
    /// Defaults to `MAX_MTU`.
    1: uint32 mtu;
    /// Supported Rx frame types for device. Required.
    ///
    /// Must be non-empty, otherwise creating the device will fail.
    2: vector<fuchsia.hardware.network.FrameType>:fuchsia.hardware.network.MAX_FRAME_TYPES rx_types;
    /// Supported Tx frame types on device. Required.
    ///
    /// Must be non-empty, otherwise creating the device will fail.
    3: vector<fuchsia.hardware.network.FrameTypeSupport>:fuchsia.hardware.network.MAX_FRAME_TYPES tx_types;
    /// Report frame metadata on receiving frames. Defaults to `false`.
    4: bool report_metadata;
    /// Minimum requested TX buffer length, in bytes. Defaults to zero.
    5: uint32 min_tx_buffer_length;
};

/// Configuration used to create a [`fuchsia.net.tun/Device`].
table DeviceConfig {
    /// Common configuration. Required.
    1: BaseConfig base;
    /// Start device with link online. Defaults to `false`.
    2: bool online;
    /// If `true`, [`fuchsia.net.tun/Device.WriteFrame`] and [`fuchsia.net.tun/Device.ReadFrame`]
    /// will block returning until the corresponding buffers are available to complete the call.
    /// Defaults to `false`.
    3: bool blocking;
    /// MAC address to report. If provided, device will support the
    /// [`fuchsia.hardware.network/MacAddressing`] protocol through `ConnectProtocols`.
    4: fuchsia.net.MacAddress mac;
};

/// Configuration used to create a [`fuchsia.net.tun/DevicePair`].
table DevicePairConfig {
    /// Common configuration. Required.
    1: BaseConfig base;
    /// If `true`, transmit buffers on the left end will be dropped if no receive buffers are
    /// available on the right end to receive it. Otherwise, transmit buffers will wait until a
    /// receive buffer is available to copy them to. Defaults to `false`.
    2: bool fallible_transmit_left;
    /// Like `fallible_transmit_left` but allows writes to the right end to be fallible.
    3: bool fallible_transmit_right;
    /// MAC address to report on the left side of the pair. If provided, the left device will
    /// support the [`fuchsia.hardware.network/MacAddressing`] protocol through `ConnectProtocols`.
    4: fuchsia.net.MacAddress mac_left;
    /// Same as `mac_left`, but for the right side of the pair.
    5: fuchsia.net.MacAddress mac_right;
};

/// State associated with Mac Address filtering.
///
/// Devices never perform any MAC address filtering, but they implement the
/// [`fuchsia.hardware.network/MacAddressing`] interface and store the values to be retrieved
/// through the [`fuchsia.net.tun/InternalState`] structure.
table MacState {
    /// The currently configured MAC Address filtering mode.
    1: fuchsia.hardware.network.MacFilterMode mode;
    /// The full list of configured multicast address filtering.
    2: vector<fuchsia.net.MacAddress>:MAX_MULTICAST_FILTERS multicast_filters;
};

/// Internal device state.
table InternalState {
    /// Mac addressing state. Will only be provided if `mac` is provided in the `Config`
    /// structure upon creation of the device.
    1: MacState mac;
    /// `true` if there is a session currently opened and running with the `Device`'s network device
    /// endpoint.
    2: bool has_session;
};

/// Extra frame metadata.
///
/// This is an opaque holder for extra information that is associated with Network Device data
/// frames.
// NOTE(brunodalbo): NetworkDevice's `InfoType` definition is still in its infancy. This solution
// allows access to the raw bytes in the sidecar metadata. We expect that this will envolve into a
// more type-safe solution which will be more transparent.
struct FrameMetadata {
    /// Additional frame information type.
    fuchsia.hardware.network.InfoType info_type;
    /// Additional frame information value.
    bytes:4096 info;
    /// Frame flags. `RxFlags` for `WriteFrame` and `TxFlags` for `ReadFrame`.
    uint32 flags;
};

/// Collection of request protocols that tun devices can offer.
resource table Protocols {
    /// Connection request to the [`fuchsia.hardware.network/Device`] protocol.
    ///
    /// The request is always fulfilled.
    1: request<fuchsia.hardware.network.Device> network_device;
    /// Connection request to the [`fuchsia.hardware.network/MacAddressing`] protocol.
    ///
    /// The request will be immediately closed if the device was not created with a MAC address.
    2: request<fuchsia.hardware.network.MacAddressing> mac_addressing;
};

/// A frame written to or read from a [`fuchsia.net.tun/Device`].
///
/// Required fields must always be provided to [`fuchsia.net.tun/Device.WriteFrame`] and are always
/// present when returned by [`fuchsia.net.tun/Device.ReadFrame`].
table Frame {
    /// The type identifying this frame's payload. Required.
    1: fuchsia.hardware.network.FrameType frame_type;
    /// The frame's payload. Required. Must be non-empty.
    2: bytes:MAX_MTU data;
    /// Metadata associated with the frame.
    3: FrameMetadata meta;
};

/// Provides control over the created device.
///
/// The lifetime of the device is tied to the channel over which this protocol is served; closing a
/// `Device` channel will trigger the destruction and deallocation of the underlying device, as well
/// as all associated endpoints.
protocol Device {
    /// Writes a frame to the device (data coming from network-end).
    /// Returns `ZX_ERR_BAD_STATE` if the device is offline.
    ///
    /// If the device was created with the [`fuchsia.net.tun/DeviceConfig.blocking`] option set to
    /// `true`, calls to `WriteFrame` will block until there is one buffer available to fulfill the
    /// request. Up to [`fuchsia.net.tun/MAX_PENDING_OPERATIONS`] calls to `WriteFrame` may be
    /// enqueued in such a way, after which `ZX_ERR_NO_RESOURCES` is returned.
    ///
    /// Alternatively, if `blocking` is set to `false` calls to `WriteFrame` will return
    /// `ZX_ERR_SHOULD_WAIT` if there are no buffers available to fulfill the request.
    WriteFrame(Frame frame) -> () error zx.status;
    /// Gets the next frame from the device (data coming from host-end).
    ///
    /// If the device was created with the [`fuchsia.net.tun/DeviceConfig.blocking`] option set to
    /// `true`, calls to `ReadFrame` will block until there is a frame available to be read. Up to
    /// [`fuchsia.net.tun/MAX_PENDING_OPERATIONS`] calls to `ReadFrame` may be enqueued in such a
    /// way, after which `ZX_ERR_NO_RESOURCES` is returned.
    ///
    /// Alternatively, if `blocking` is set to `false` calls to `ReadFrame` will return
    /// `ZX_ERR_SHOULD_WAIT` if there are no frames to be read.
    ReadFrame() -> (Frame frame) error zx.status;
    /// Retrieves an eventpair that is signalled with `SIGNAL_READABLE` and `SIGNAL_WRITABLE` when
    /// read and write buffers are available, respectively.
    GetSignals() -> (zx.handle:EVENTPAIR signals);
    /// Gets a snapshot of the device's internal state.
    GetState() -> (InternalState state);
    /// Observes changes to internal state.
    ///
    /// The first call will always return the current internal state, subsequent calls will block
    /// until the internal state differs from the last one returned from a `WatchState` call.
    ///
    /// `WatchState` does not provide full history of internal state changes. It is possible that
    /// intermediary internal state changes are missed in between `WatchState` calls.
    WatchState() -> (InternalState state);
    /// Sets the device's online status.
    ///
    /// The online status is visible through [`fuchsia.hardware.network/Device.GetStatus`]. Once
    /// `SetOnline` returns, the status reported through `GetStatus` is guaranteed to be the one
    /// passed to `SetOnline`, no guarantees can be made otherwise due to the asynchronous nature of
    /// multi-channel operations.
    SetOnline(bool online) -> ();
    /// Connects to the requested protocols for this `Device`.
    ConnectProtocols(Protocols protos);
};

/// A collection of connection requests to ends of a [`fuchsia.net.tun/DevicePair`].
///
/// Used to connect to a `DevicePair` through [`fuchsia.net.tun/DevicePair.ConnectProtocols`].
resource table DevicePairEnds {
    /// Connection request to protocols on the left end.
    1: Protocols left;
    /// Connection request to protocols on the right end.
    2: Protocols right;
};

/// Provides control over a pair of network devices.
///
/// A `DevicePair` is a simpler version of `Device` that "shorts" two network device interfaces,
/// named its "left" and "right" ends. The internal state of a `DevicePair` is not accessible, like
/// it is for `Device` and it provides a more streamlined (and considerably faster) pair of
/// [`fuchsia.hardware.network/Device`]s  (and optionally
/// [`fuchsia.hardware.network/MacAddressing`]s). The transmit side of the left end is connected to
/// the receive side of the right end, and vice-versa. A `DevicePair`'s online signal is handled
/// internally (online if any of the ends has an active data session), and if MAC addresses are
/// provided on creation, the only supported MAC filtering mode is `PROMISCUOUS`. The lifetime of
/// the underlying devices is tied to the `DevicePair` channel, closing a `DevicePair` channel will
/// trigger the destruction and deallocation of the underlying devices.
protocol DevicePair {
    /// Connects to the requested protocols of this `DevicePair`.
    ConnectProtocols(DevicePairEnds requests);
};

/// Control interface.
/// `Control` allows creating an arbitrary number of `Device`s and `DevicePair`s.
[Discoverable]
protocol Control {
    /// Creates a `Device` with given `config`.
    /// If `config` is not valid or the device could not be created, `device` is closed with an
    /// error epitaph.
    CreateDevice(DeviceConfig config, request<Device> device);
    /// Creates a `DevicePair` with given `config`.
    /// If `config` is not valid or the device could not be created, `device_pair` is closed
    /// with an error epitaph.
    CreatePair(DevicePairConfig config, request<DevicePair> device_pair);
};