sdk/fidl/fuchsia.audio.mixer/graph.fidl

// Copyright 2022 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.audio.mixer;

using fuchsia.audio;
using fuchsia.audio.effects;
using fuchsia.media2;
using zx;

alias NodeId = uint64;
alias ThreadId = uint64;
alias GainControlId = uint64;

/// By convention, the zero ID is never used.
const INVALID_ID uint64 = 0;

/// Maximum length of a `name` string.
const MAX_NAME_LENGTH uint32 = 256;

/// Maximum number of GainControls that can be attached to each graph edge.
const MAX_GAIN_CONTROLS_PER_EDGE uint32 = 32;

/// A factory for creating [`Graph`] protocols.
@discoverable
closed protocol GraphCreator {
    /// Creates a new graph that lives until the channel is closed.
    strict Create(resource table {
        /// Required.
        1: graph server_end:Graph;

        /// Name of this graph, used for diagnostics only.
        /// If specified, ideally this should be globally unique and have a
        /// printable CamelCase format, but uniqueness is not required.
        ///
        /// Optional. Empty if not specified.
        2: name string:MAX_NAME_LENGTH;

        /// Deadline profile for the FIDL thread.
        ///
        /// This is to ensure time-sensitive requests are handled properly. For
        /// example, packets sent on a [`fuchsia.audio.StreamSink`] channel must
        /// be read immediately, otherwise the caller may miss their deadline.
        ///
        /// Optional. If not specified, the FIDL thread runs at a normal priority.
        3: fidl_thread_deadline_profile zx.Handle:PROFILE;

        /// If specified, the graph will use synthetic clocks that are created
        /// and controlled over the given channel. This can be used to run the
        /// graph faster than real time, which is useful in integration tests.
        ///
        /// If specified, then ALL clocks used by this graph MUST be created by
        /// this realm OR by [`Graph.CreateGraphControlledReferenceClock`],
        /// which will use this realm internally.
        ///
        /// Optional. If not specified, the graph uses real clocks.
        4: synthetic_clock_realm server_end:SyntheticClockRealm;
    }) -> (table {}) error CreateGraphError;
};

/// A mixer Graph.
///
/// ## Directed Acyclic Graphs (DAGs)
///
/// Each graph includes a set of nodes connected into one or more DAGs. Audio
/// data flows from Producer nodes to Consumer nodes, and in between, may flow
/// through processing nodes, including Mixers, Splitters, and Custom nodes.
///
/// Each node has zero or more incoming and outgoing edges. Each edge represents
/// a single stream of audio data. Incoming edges are called "source streams"
/// and outgoing edges are called "destination streams".
///
/// Audio is strongly typed: each node declares the audio format(s) it can
/// ingest from source streams and the audio format(s) it can produce to
/// destination streams. It is illegal to connect nodes with incompatible
/// formats.
///
/// ## Execution Model
///
/// Execution is driven by Consumers. Each Consumer wakes every N ms (N is
/// configurable per Consumer) and pulls N ms of audio from its sources, which
/// pull audio from their sources, and so on, up to the connected Producers. As
/// audio is pulled down the graph, it is processed and mixed into a single
/// stream that is written into the Consumer.
///
/// Each Consumer is attached to a Thread, which gives the Consumer a place to
/// do its work. Threads usually need deadline profiles to meet real-time
/// constraints. The client is responsible for creating Thread objects,
/// assigning Consumers to Threads, and attaching appropriate deadline profiles
/// when needed.
///
/// When the DAG includes nodes with multiple outgoing edges, such as Splitters,
/// we can end up in a situation where two Consumers A and B share the same
/// dependencies (via the Splitter's source). If A and B run on different
/// threads, it's unclear which Thread should process those shared dependencies,
/// making it unclear how much deadline capacity is required by each thread. To
/// avoid this problem, we partition the DAG so that each Consumer is the root
/// of an inverted tree. At nodes with multiple outgoing edges, such as
/// Splitters, we partition the node into a hidden Consumer node (which drives
/// the sources) and hidden Producer nodes (which drive the destinations). When
/// the client creates a Splitter, they must assign a Thread to the Splitter's
/// hidden Consumer. This ensures that each node is processed on a unique
/// thread, making it simpler to analyze the needed capacity for each Thread.
///
/// ## Method Semantics
///
/// Methods will be executed sequentially in the order they are called. Method
/// calls can be pipelined, but if more than an implementation-defined number of
/// requests are in flight at one time, the server reserves the right to assume
/// a DoS attack and close the connection.
///
/// Most methods use a minimal set of arguments plus an "options" table to allow
/// for extensibility.
///
/// ## IDs and names
///
/// Every object is identified by a numeric `id`. Within each object type
/// (Nodes, Threads, and GainControls) IDs are guaranteed to be unique. Old IDs
/// for deleted objects will never be reused for new objects.
///
/// Every object has an optional string `name`. If specified, ideally this name
/// should be unique within the [`Graph`] and have a printable CamelCase format,
/// but uniqueness is not required. Names are used for developer-visible
/// diagnostics only -- they do not need to be unique. Duplicate names can at
/// worst lead to potentially-confusing diagnostics. IDs, not names, should be
/// used when unique identification is required.
///
/// ## Clocks
///
/// Each audio stream is associated with a *reference clock*. Different streams
/// can use different clocks. Any two clocks can differ in both value (the
/// current time) and the rate, where the rate may [change over
/// time](https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_update) as
/// long as the clock remains [continuous and
/// monotonic](https://fuchsia.dev/fuchsia-src/reference/kernel_objects/clock).
/// This reflects many real situations. For example, a speaker may have an
/// internal clock separate from the CPU's physical clock. Or, a stream may
/// originate from some other computer on the network whose clock is not
/// precisely synchronized to our local clock.
///
/// Every node must specify the reference clock used by the node's destination
/// streams, except for Consumers, which must specify a clock for the Consumer's
/// source stream. To connect two streams that use different clocks, we must
/// translate one stream onto the other stream's clock. This is done at Mixer
/// nodes, which use sample rate conversion (SRC) to translate source streams
/// onto the Mixer's destination reference clock.
///
/// Reference clocks can change rate over time. These rate changes are typically
/// controlled by the client. If the client doesn't need precise control over
/// reference clocks, a cheaper option is to use Graph-controlled clocks (see
/// [`Graph.CreateGraphControlledReferenceClock`]), which can avoid a
/// potentially-expensive SRC in many cases. For example, if a Producer flows to
/// a Consumer, where the Producer uses a Graph-controlled clock and the
/// Consumer uses a client-controlled clock, the `Graph` will adjust the
/// Producer clock's rate to synchronize the Producer and Consumer clocks,
/// eliminating the need for SRC.
closed protocol Graph {
    /// Creates a Producer node with the given options.
    ///
    /// Producer nodes generate audio which can be consumed by other nodes. For
    /// example, a Producer node might encapsulate audio coming from an
    /// application or from a microphone. Producer nodes cannot have any
    /// incoming edges and may have at most one outgoing edge.
    strict CreateProducer(resource table {
        /// Name of this node, used for diagnostics only. See "IDs and names" in the
        /// comments for [`Graph`].
        ///
        /// Optional. Empty if not specified.
        1: name string:MAX_NAME_LENGTH;

        /// Direction of audio data produced by this node.
        ///
        /// Required.
        2: direction PipelineDirection;

        /// Data source for this producer.
        ///
        /// Required.
        3: data_source ProducerDataSource;

        /// If the `direction` is INPUT, this must be specified. This reports
        /// the maximum delay between when a frame is captured at an input
        /// microphone and when that frame is available at this producer.
        ///
        /// If `direction` is OUTPUT, this must be empty.
        4: external_delay_watcher ExternalDelayWatcher;
    }) -> (table {
        /// ID of the newly-created node. Guaranteed to be unique.
        1: id NodeId;
    }) error CreateNodeError;

    /// Creates a Consumer node with the given options.
    ///
    /// Consumer nodes write audio to a sink. For example, a Consumer node might
    /// encapsulate audio being written to a speaker or to an application (which
    /// may be capturing audio from a microphone). Consumer nodes can have at
    /// most one incoming edge.
    ///
    /// Audio pipelines are driven by Consumers. Each Consumer is attached to a
    /// Thread, which gives the Consumer a place to do work. A Consumer wakes
    /// every `N` ms (`N` is configurable), pulls `N` ms of audio from its
    /// incoming edge, then writes that audio to the Consumer's sink.
    ///
    /// For more details, see "Execution Model" under the description for
    /// [`Graph`].
    strict CreateConsumer(resource table {
        /// Name of this node, used for diagnostics only. See "IDs and names" in the
        /// comments for [`Graph`].
        ///
        /// Optional. Empty if not specified.
        1: name string:MAX_NAME_LENGTH;

        /// Direction of audio data consumed by this node.
        ///
        /// Required.
        2: direction PipelineDirection;

        /// Data sink for this consumer.
        ///
        /// Required.
        3: data_sink ConsumerDataSink;

        /// The consumer's source edge must have the given sample type. If not
        /// specified, this defaults to the same sample type as `data_sink`.
        ///
        /// No matter what, the source edge source must have the same frame
        /// rate and channelization as `data_sink`. Put differently, consumers
        /// can perform sample type conversion, but they cannot perform rate
        /// conversion or rechannelization.
        4: source_sample_type fuchsia.audio.SampleType;

        /// The Consumer's mix job should execute on this thread.
        ///
        /// Required.
        5: thread ThreadId;

        /// If `direction` is OUTPUT, this must be specified. This reports the
        /// delay between when a frame is written by this consumer and when that
        /// frame is rendered at its final destination (such as a speaker).
        ///
        /// If `direction` is INPUT, this must be empty.
        6: external_delay_watcher ExternalDelayWatcher;
    }) -> (table {
        /// ID of the newly-created node. Guaranteed to be unique.
        1: id NodeId;
    }) error CreateNodeError;

    /// Creates a Mixer node with the given options.
    ///
    /// Mixer nodes combine multiple PCM source streams into a single PCM
    /// destination stream. Mixers apply format conversion and sample rate
    /// conversion to the source streams to produce a destination stream with a
    /// fixed format.
    strict CreateMixer(resource table {
        /// Name of this node, used for diagnostics only. See "IDs and names" in the
        /// comments for [`Graph`].
        ///
        /// Optional. Empty if not specified.
        1: name string:MAX_NAME_LENGTH;

        /// Direction of audio data produced by this node.
        ///
        /// Required.
        2: direction PipelineDirection;

        /// Format of the Mixer's destination stream.
        ///
        /// Required.
        3: dest_format fuchsia.audio.Format;

        /// Clock for this node's destination stream.
        ///
        /// Required.
        4: dest_reference_clock ReferenceClock;

        /// Size of the internal mix buffer. This defines the maximum number of
        /// frames that can be mixed at one time.
        ///
        /// Optional. If not specified, a default size is used.
        5: dest_buffer_frame_count uint64;
    }) -> (table {
        /// ID of the newly-created node. Guaranteed to be unique.
        1: id NodeId;
    }) error CreateNodeError;

    /// Creates a Splitter node with the given options.
    ///
    /// Splitter nodes copy a single source stream into multiple destination
    /// streams. Each Splitter node has a hidden Consumer node which is
    /// responsible for pulling data from the Splitter's source and writing that
    /// data to an intermediate buffer. Destination streams read directly from
    /// this buffer. For more details on this behavior, see "Execution Model"
    /// under the description for [`Graph`].
    ///
    /// Each Splitter is assigned to a thread which drives the hidden Consumer's
    /// work to fill the intermediate buffer. Destination streams can be
    /// assigned to any thread. If a destination stream is assigned to the same
    /// thread as the Splitter, that stream can copy the Splitter's source
    /// stream without any additional latency. If a destination stream is
    /// assigned to a different thread T, then extra buffering is required to
    /// avoid data races -- that extra buffering adds additional latency of
    /// `T.period`.
    ///
    /// Current limitation: The Splitter does not fill its intermediate buffer
    /// unless it has at least one destination stream that is started and that
    /// is assigned to the same thread as the Splitter. This limitation may be
    /// lifted at a future time.
    strict CreateSplitter(resource table {
        /// Name of this node, used for diagnostics only. See "IDs and names" in the
        /// comments for [`Graph`].
        ///
        /// Optional. Empty if not specified.
        1: name string:MAX_NAME_LENGTH;

        /// Direction of audio data produced by this node.
        ///
        /// Required.
        2: direction PipelineDirection;

        /// Format of the Splitter's source and destination streams.
        ///
        /// Required.
        3: format fuchsia.audio.Format;

        /// The thread which drives this Splitter's hidden consumer.
        ///
        /// Required.
        4: thread ThreadId;

        /// Clock for this node's source and destination streams.
        ///
        /// Required.
        5: reference_clock ReferenceClock;
    }) -> (table {
        /// ID of the newly-created node. Guaranteed to be unique.
        1: id NodeId;
    }) error CreateNodeError;

    /// Creates a Custom node with the given options.
    ///
    /// Custom nodes apply custom effects to one or more source streams,
    /// producing one or more destination streams. The effects are implemented
    /// out-of-process via a call to a FIDL interface.
    ///
    /// Custom nodes are composite nodes that encapsulate a fixed number of
    /// sources and destinations. We assign an ID to each of these source and
    /// destination slots -- see [`CustomNodeProperties`]. This allows creating
    /// edges that target a specific slot. For example, a node that implements
    /// AEC will have loopback and microphone source slots and the caller will
    /// need to connect each source slot to an appropriate source. The caller
    /// can do this by calling `CreateEdge` using a specific [`NodeId`] from
    /// [`CustomNodeProperties.source_ids`]. These internal IDs cannot be
    /// deleted, except by deleting the entire Custom node.
    ///
    /// The returned `id` describes the composite node. Passing `id` to
    /// [`DeleteNode`] will delete the composite node as well as any internal
    /// source and destination nodes. The returned `id` cannot be used in
    /// [`CreateEdge`]. Edges must target a specific source or destination slot
    /// as described above.
    strict CreateCustom(resource table {
        /// Name of this node, used for diagnostics only. See "IDs and names" in the
        /// comments for [`Graph`].
        ///
        /// Optional. Empty if not specified.
        1: name string:MAX_NAME_LENGTH;

        /// Direction of audio data produced by this node.
        ///
        /// Required.
        2: direction PipelineDirection;

        /// Description of the out-of-process effects processor.
        /// This includes a description of the node's source and destination
        /// streams.
        ///
        /// Required.
        3: config fuchsia.audio.effects.ProcessorConfiguration;

        /// Clock for this node's source and destination streams.
        ///
        /// Required.
        4: reference_clock ReferenceClock;
    }) -> (resource table {
        /// ID of the newly-created node. Guaranteed to be unique.
        1: id NodeId;

        /// Additional properties of the newly-created node.
        2: node_properties CustomNodeProperties;
    }) error CreateNodeError;

    /// Deletes the given node.
    ///
    /// The node must exist. `DeleteNode(x)` will delete all incoming and
    /// outgoing edges of node `x` before deleting the node itself. Once the node
    /// has been deleted it cannot be mentioned by any future method calls.
    strict DeleteNode(table {
        /// ID of the node to delete.
        1: id NodeId;
    }) -> (table {}) error DeleteNodeError;

    /// Creates an edge from the source node to the destination node.
    ///
    /// Both nodes must exist. The source's format must be supported by the
    /// destination node. Mixer nodes support arbitrary source formats. Other
    /// nodes support only specific (fixed) source formats.
    ///
    /// Both ends must use the same reference clock, unless the destination is a
    /// Mixer, in which case the source can use any clock.
    ///
    /// If the source's direction is `INPUT`, the dest's direction cannot be
    /// `OUTPUT`. See [`PipelineDirection`] for additional discussion.
    strict CreateEdge(resource table {
        /// ID of the destination node.
        /// Required.
        1: dest_id NodeId;

        /// ID of the source node.
        /// Required.
        2: source_id NodeId;

        /// This selects the sampler to use when performing sample rate conversion
        /// on the source. Valid only when the dest node is a Mixer.
        ///
        /// Optional. If not specified, a default sampler is selected.
        3: mixer_sampler Sampler;

        /// Gains to apply to this edge. Since gain is applied by Mixer nodes,
        /// either the source or dest node must be a Mixer.
        ///
        /// Optional. If empty, no gain is applied.
        4: gain_controls vector<GainControlId>:MAX_GAIN_CONTROLS_PER_EDGE;
    }) -> (table {}) error CreateEdgeError;

    /// Deletes the edge connecting the source node to the destination node.
    ///
    /// The edge must exist.
    strict DeleteEdge(table {
        /// ID of the destination node.
        1: dest_id NodeId;

        /// ID of the source node.
        2: source_id NodeId;
    }) -> (table {}) error DeleteEdgeError;

    /// Creates a thread.
    ///
    /// Each `CreateThread` call creates a new thread in the mixer service. This
    /// new thread will be used to process audio for all Consumer nodes assigned
    /// to this thread.
    ///
    /// For more details, see "Execution Model" under the description for
    /// [`Graph`].
    strict CreateThread(resource table {
        /// Name of this thread, used for diagnostics only. See "IDs and names" in the
        /// comments for [`Graph`].
        ///
        /// Optional. Empty if not specified.
        1: name string:MAX_NAME_LENGTH;

        /// Deadline profile to apply to this thread.
        ///
        /// Optional. If not specified, the thread runs at a normal priority.
        2: deadline_profile zx.Handle:PROFILE;

        /// This thread will process audio in batches of size `period`.
        ///
        /// Required.
        3: period zx.Duration;

        /// This thread is expected to use up to this much CPU time per
        /// `period`. If `deadline_profile` is specified, then `cpu_per_period`
        /// should match the profile's "capacity".
        ///
        /// Required.
        4: cpu_per_period zx.Duration;
    }) -> (table {
        /// ID of the newly-created thread. Guaranteed to be unique.
        1: id ThreadId;
    }) error CreateThreadError;

    /// Deletes the given thread.
    ///
    /// The thread must exist. A thread cannot be deleted until all Consumer
    /// nodes assigned to that thread have been deleted.
    strict DeleteThread(table {
        /// ID of the thread to delete.
        /// Required.
        1: id ThreadId;
    }) -> (table {}) error DeleteThreadError;

    /// Creates a GainControl.
    ///
    /// A GainControl controls gain that should be applied to an audio stream.
    /// GainControls can be attached to edges going into and out of a Mixer node.
    /// Gain can be set to a specific value (e.g. in decibels) or it can be
    /// muted.
    ///
    /// By default, a GainControl applies no gain and is not muted.
    strict CreateGainControl(resource table {
        /// Name of this GainControl, used for diagnostics only. See "IDs and names"
        /// in the comments for [`Graph`].
        ///
        /// Optional. Empty if not specified.
        1: name string:MAX_NAME_LENGTH;

        /// Interface which controls this GainControl.
        ///
        /// Required.
        2: control server_end:fuchsia.audio.GainControl;

        /// Reference clock for this GainControl.
        ///
        /// Required.
        3: reference_clock ReferenceClock;
    }) -> (table {
        /// ID of the newly-created GainControl. Guaranteed to be unique.
        1: id GainControlId;
    }) error CreateGainControlError;

    /// Deletes the given GainControl.
    ///
    /// The GainControl must exist. A GainControl cannot be deleted until all
    /// associated edges have been deleted.
    strict DeleteGainControl(table {
        /// ID of the GainControl to delete.
        /// Required.
        1: id GainControlId;
    }) -> (table {}) error DeleteGainControlError;

    /// Creates a graph-controlled reference clock.
    ///
    /// The returned clock has `ZX_RIGHT_READ` and `ZX_RIGHT_DUPLICATE` but not
    /// `ZX_RIGHT_WRITE`. The clock may be duplicated and used wherever a
    /// reference clock is needed. The graph will rate change this clock until
    /// the `release_fence` is closed.
    ///
    /// For more details, see "Clocks" under the description for [`Graph`].
    ///
    /// * error Error from `zx_clock_create`
    strict CreateGraphControlledReferenceClock() -> (resource table {
        /// The new clock.
        1: reference_clock zx.Handle:CLOCK;

        /// The graph will control `reference_clock` until `release_fence` is
        /// closed, at which point the clock can still be used but it will no
        /// longer be rate-adjusted.
        2: release_fence zx.Handle:EVENTPAIR;
    }) error zx.Status;

    /// Starts a consumer or a producer at a specified time.
    ///
    /// When a call to this method succeeds, the response is typically sent when
    /// the operation actually occurs (that is, when it was scheduled to occur),
    /// but may complete sooner. When a call to this method fails, the response
    /// is sent when the failure is detected.
    ///
    /// If this method is called, and `when` specifies a time in the past, the
    /// stream timeline is started as soon as possible.
    ///
    /// If a `Start` or `Stop` request is received when a previous `Start` or
    /// `Stop` request is pending, the connection is closed. This request can be
    /// canceled using the `CancelStartOrStop` method.
    strict Start(table {
        /// ID of the consumer or producer node.
        ///
        /// Required.
        1: node_id NodeId;

        /// When to apply the start command.
        ///
        /// Required.
        2: when fuchsia.media2.RealTime;

        /// Stream time of the start frame.
        ///
        /// Required.
        3: stream_time fuchsia.media2.StreamTime;
    }) -> (table {
        /// The system time when the producer or consumer was actually started.
        ///
        /// Required.
        1: system_time zx.Time;

        /// The reference time when the producer or consumer was actually started.
        ///
        /// Required.
        2: reference_time zx.Time;

        /// The stream time at which the producer or consumer was actually started.
        ///
        /// Required.
        3: stream_time zx.Duration;

        /// The packet timestamp that corresponds to `stream_time`.
        ///
        /// Required.
        4: packet_timestamp int64;
    }) error StartError;

    /// Stops a consumer or a producer at a specified time.
    ///
    /// When a call to this method succeeds, the response is typically sent when
    /// the operation actually occurs (that is, when it was scheduled to occur),
    /// but may complete sooner. When a call to this method fails, the response
    /// is sent when the failure is detected.
    ///
    /// If this method is called when the stream timeline is stopped, the call
    /// fails immediately with an `ALREADY_STOPPED` error.
    ///
    /// Otherwise, if this method is called, and `when` specifies a time in the
    /// past, the stream timeline is stopped as soon as possible.
    ///
    /// If a `Start` or `Stop` request is received when a previous `Start` or
    /// `Stop` request is pending, the connection is closed. This request can be
    /// canceled using the `CancelStartOrStop` method.
    strict Stop(table {
        /// ID of the consumer or producer node.
        ///
        /// Required.
        1: node_id NodeId;

        /// When to apply the stop command.
        ///
        /// Required.
        2: when fuchsia.media2.RealOrStreamTime;
    }) -> (table {
        /// The system time when the producer or consumer was actually stopped.
        ///
        /// Required.
        1: system_time zx.Time;

        /// The reference time when the producer or consumer was actually stopped.
        ///
        /// Required.
        2: reference_time zx.Time;

        /// The stream time at which the producer or consumer was actually stopped.
        ///
        /// Required.
        3: stream_time zx.Duration;

        /// The packet timestamp that corresponds to `stream_time`.
        ///
        /// Required.
        4: packet_timestamp int64;
    }) error StopError;

    /// Cancels the previously-received `Start` or `Stop` request if it is still
    /// pending. Cancel requests race with the pending operations they are
    /// intended to cancel. The response to the request to be canceled indicates
    /// the outcome of the race. In typical usage, a `CancelStartOrStop` request
    /// should be followed in short order by a `Stop` or `Start` request so that
    /// the state of the service is known.
    strict CancelStartOrStop(table {
        /// ID of the consumer or producer node.
        ///
        /// Required.
        1: node_id NodeId;
    }) -> () error CancelStartOrStopError;

    /// Reports a producer's lead time. In output pipelines, a producer's lead
    /// time defines how early an audio frame must be received in order for that
    /// frame to be presented on time. If a client wishes to present an audio
    /// frame at time T, that frame must be delivered to this producer by time
    /// `T - LeadTime`.
    strict BindProducerLeadTimeWatcher(resource table {
        /// ID of a node that was created with CreateProducer. The producer must
        /// have `direction == OUTPUT`.
        1: id NodeId;

        /// Channel to serve updates.
        2: server_end server_end:fuchsia.audio.DelayWatcher;
    }) -> () error BindProducerLeadTimeWatcherError;
};

/// Type of errors returned by [`CreateGraph`].
type CreateGraphError = flexible enum {
    /// The provided `server_end:Graph` was invalid.
    INVALID_GRAPH_CHANNEL = 1;
};

/// Type of errors returned by CreateNode methods.
type CreateNodeError = flexible enum {
    /// A required field was not provided.
    MISSING_REQUIRED_FIELD = 1;

    /// A flexible field had an unsupported option. This can happen when a
    /// client built with API version X+1 talks to a server built with API
    /// version X.
    UNSUPPORTED_OPTION = 2;

    /// A parameter had an invalid value.
    INVALID_PARAMETER = 3;
};

/// Type of errors returned by [`DeleteNode`].
type DeleteNodeError = flexible enum {
    /// The given `id` is invalid.
    DOES_NOT_EXIST = 1;
};

/// Type of errors returned by [`CreateEdge`].
type CreateEdgeError = flexible enum {
    /// The given `dest_id` is invalid.
    INVALID_DEST_ID = 1;

    /// The destination does not support an additional source.
    DEST_NODE_HAS_TOO_MANY_INCOMING_EDGES = 2;

    /// The given `source_id` is invalid.
    INVALID_SOURCE_ID = 3;

    /// The source does not support an additional destination.
    SOURCE_NODE_HAS_TOO_MANY_OUTGOING_EDGES = 4;

    /// The source's format is not compatible with the dest.
    INCOMPATIBLE_FORMATS = 5;

    /// The source and dest are already connected.
    ALREADY_CONNECTED = 6;

    /// This edge would create a cycle.
    CYCLE = 7;

    /// The source node has PipelineDirection INPUT and the destination node has
    /// PipelineDirection OUTPUT.
    OUTPUT_PIPELINE_CANNOT_READ_FROM_INPUT_PIPELINE = 8;

    /// A flexible field had an unsupported option. This can happen when a
    /// client built with API version X+1 talks to a server built with API
    /// version X.
    UNSUPPORTED_OPTION = 9;

    /// A gain control in the given `gain_controls` is invalid.
    INVALID_GAIN_CONTROL = 10;
};

/// Type of errors returned by [`DeleteEdge`].
type DeleteEdgeError = flexible enum {
    /// The given `dest_id` is invalid.
    INVALID_DEST_ID = 1;

    /// The given `source_id` is invalid.
    INVALID_SOURCE_ID = 2;

    /// The edge does not exist.
    EDGE_NOT_FOUND = 3;
};

/// Type of errors returned by [`CreateThread`].
type CreateThreadError = flexible enum {
    /// A required field was not provided.
    MISSING_REQUIRED_FIELD = 1;

    /// A parameter had an invalid value.
    INVALID_PARAMETER = 2;
};

/// Type of errors returned by [`DeleteThread`].
type DeleteThreadError = flexible enum {
    /// The given `id` is invalid.
    INVALID_ID = 1;

    /// There are still Consumer nodes assigned to this thread. These Consumers
    /// must be deleted before the Thread can be deleted.
    STILL_IN_USE = 2;
};

/// Type of errors returned by [`CreateGainControl`].
type CreateGainControlError = flexible enum {
    /// A required field was not provided.
    MISSING_REQUIRED_FIELD = 1;

    /// A parameter had an invalid value.
    INVALID_PARAMETER = 2;
};

/// Type of errors returned by [`DeleteGainControl`].
type DeleteGainControlError = flexible enum {
    /// The given `id` is invalid.
    INVALID_ID = 1;

    /// There are still edges using this GainControl. These edges must be deleted
    /// before the GainControl can be deleted.
    STILL_IN_USE = 2;
};

/// Type of errors returned by [`Start`].
type StartError = flexible enum {
    /// A required field was not provided.
    MISSING_REQUIRED_FIELD = 1;

    /// A parameter had an invalid value.
    INVALID_PARAMETER = 2;

    /// A flexible field had an unsupported option. This can happen when a
    /// client built with API version X+1 talks to a server built with API
    /// version X.
    UNSUPPORTED_OPTION = 3;

    /// Request is canceled.
    CANCELED = 4;
};

/// Type of errors returned by [`Stop`].
type StopError = flexible enum {
    /// A required field was not provided.
    MISSING_REQUIRED_FIELD = 1;

    /// A parameter had an invalid value.
    INVALID_PARAMETER = 2;

    /// A flexible field had an unsupported option. This can happen when a
    /// client built with API version X+1 talks to a server built with API
    /// version X.
    UNSUPPORTED_OPTION = 3;

    /// Request is canceled.
    CANCELED = 4;

    /// The stream is already stopped.
    ALREADY_STOPPED = 5;
};

/// Type of errors returned by [`CancelStartOrStop`]
type CancelStartOrStopError = flexible enum {
    /// A required field was not provided.
    MISSING_REQUIRED_FIELD = 1;

    /// The given `node_id` does not refer to a producer or a consumer.
    INVALID_ID = 2;
};

/// Type of errors returned by [`BindProducerLeadTimeWatcher`].
type BindProducerLeadTimeWatcherError = flexible enum {
    /// A required field was not provided.
    MISSING_REQUIRED_FIELD = 1;

    /// The given `id` does not refer to a producer in an OUTPUT pipeline.
    INVALID_ID = 2;
};