/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * Protocol Buffers describing the Runner API, which is the runner-independent,
 * SDK-independent definition of the Beam model.
 */

syntax = "proto3";

package org.apache.beam.model.pipeline.v1;

option go_package = "pipeline_v1";
option java_package = "org.apache.beam.model.pipeline.v1";
option java_outer_classname = "RunnerApi";

import "endpoints.proto";
import "google/protobuf/any.proto";
import "google/protobuf/descriptor.proto";
import "google/protobuf/timestamp.proto";

message BeamConstants {
  enum Constants {
    // All timestamps in milliseconds since Jan 1, 1970.

    // All timestamps of elements or window boundaries must be within
    // the interval [MIN_TIMESTAMP_MILLIS, MAX_TIMESTAMP_MILLIS].
    // The smallest representable timestamp of an element or a window boundary.
    MIN_TIMESTAMP_MILLIS = 0 [(beam_constant) = "-9223372036854775"];
    // The largest representable timestamp of an element or a window boundary.
    MAX_TIMESTAMP_MILLIS = 1 [(beam_constant) =  "9223372036854775"];

    // The maximum timestamp for the global window.
    // Triggers use max timestamp to set timers' timestamp. Timers fire when
    // the watermark passes their timestamps. So, the timestamp needs to be
    // smaller than the MAX_TIMESTAMP_MILLIS.
    // One standard day is subtracted from MAX_TIMESTAMP_MILLIS to make sure
    // the max timestamp is smaller than MAX_TIMESTAMP_MILLIS even after rounding up
    // to seconds or minutes.
    GLOBAL_WINDOW_MAX_TIMESTAMP_MILLIS = 2 [(beam_constant) = "9223371950454775"];
  }
}

// A set of mappings from id to message. This is included as an optional field
// on any proto message that may contain references needing resolution.
message Components {
  // (Required) A map from pipeline-scoped id to PTransform.
  map<string, PTransform> transforms = 1;

  // (Required) A map from pipeline-scoped id to PCollection.
  map<string, PCollection> pcollections = 2;

  // (Required) A map from pipeline-scoped id to WindowingStrategy.
  map<string, WindowingStrategy> windowing_strategies = 3;

  // (Required) A map from pipeline-scoped id to Coder.
  map<string, Coder> coders = 4;

  // (Required) A map from pipeline-scoped id to Environment.
  map<string, Environment> environments = 5;
}

// A Pipeline is a hierarchical graph of PTransforms, linked
// by PCollections. A typical graph may look like:
//
//   Impulse -> PCollection -> ParDo -> PCollection -> GroupByKey -> ...
//                                   \> PCollection -> ParDo      -> ...
//                                                  \> ParDo      -> ...
//   Impulse -> PCollection -> ParDo -> PCollection -> ...
//
// This is represented by a number of by-reference maps to transforms,
// PCollections, SDK environments, coders, etc., for
// supporting compact reuse and arbitrary graph structure.
message Pipeline {

  // (Required) The coders, UDFs, graph nodes, etc, that make up
  // this pipeline.
  Components components = 1;

  // (Required) The ids of all PTransforms that are not contained within another
  // PTransform. These must be in shallow topological order, so that traversing
  // them recursively in this order yields a recursively topological traversal.
  repeated string root_transform_ids = 2;

  // (Optional) Static display data for the pipeline. If there is none,
  // it may be omitted.
  repeated DisplayData display_data = 3;

  // (Optional) A set of requirements that the runner MUST understand and be
  // able to faithfully provide in order to execute this pipeline. These
  // may indicate that a runner must inspect new fields on a component or
  // provide additional guarantees when processing specific transforms.
  // A runner should reject any pipelines with unknown requirements.
  repeated string requirements = 4;
}

// Transforms are the operations in your pipeline, and provide a generic
// processing framework. You provide processing logic in the form of a function
// object (colloquially referred to as “user code”), and your user code is
// applied to each element of an input PCollection (or more than one
// PCollection). Depending on the pipeline runner and back-end that you choose,
// many different workers across a cluster may execute instances of your user
// code in parallel. The user code running on each worker generates the output
// elements that are ultimately added to the final output PCollection that the
// transform produces.
//
// The Beam SDKs contain a number of different transforms that you can apply to
// your pipeline’s PCollections. These include general-purpose core transforms,
// such as ParDo or Combine. There are also pre-written composite transforms
// included in the SDKs, which combine one or more of the core transforms in a
// useful processing pattern, such as counting or combining elements in a
// collection. You can also define your own more complex composite transforms to
// fit your pipeline’s exact use case.
message PTransform {

  // (Required) A unique name for the application node.
  //
  // Ideally, this should be stable over multiple evolutions of a pipeline
  // for the purposes of logging and associating pipeline state with a node,
  // etc.
  //
  // If it is not stable, then the runner decides what will happen. But, most
  // importantly, it must always be here and be unique, even if it is
  // autogenerated.
  string unique_name = 5;

  // (Optional) A URN and payload that, together, fully defined the semantics
  // of this transform.
  //
  // If absent, this must be an "anonymous" composite transform.
  //
  // For primitive transform in the Runner API, this is required, and the
  // payloads are well-defined messages. When the URN indicates ParDo it
  // is a ParDoPayload, and so on. For some special composite transforms,
  // the payload is also officially defined. See StandardPTransforms for
  // details.
  FunctionSpec spec = 1;

  // (Optional) A list of the ids of transforms that it contains.
  //
  // Primitive transforms are not allowed to specify this.
  repeated string subtransforms = 2;

  // (Required) A map from local names of inputs (unique only with this map, and
  // likely embedded in the transform payload and serialized user code) to
  // PCollection ids.
  //
  // The payload for this transform may clarify the relationship of these
  // inputs. For example:
  //
  //  - for a Flatten transform they are merged
  //  - for a ParDo transform, some may be side inputs
  //
  // All inputs are recorded here so that the topological ordering of
  // the graph is consistent whether or not the payload is understood.
  map<string, string> inputs = 3;

  // (Required) A map from local names of outputs (unique only within this map,
  // and likely embedded in the transform payload and serialized user code)
  // to PCollection ids.
  //
  // The URN or payload for this transform node may clarify the type and
  // relationship of these outputs. For example:
  //
  //  - for a ParDo transform, these are tags on PCollections, which will be
  //    embedded in the DoFn.
  map<string, string> outputs = 4;

  // (Optional) Static display data for this PTransform application. If
  // there is none, it may be omitted.
  repeated DisplayData display_data = 6;

  // Environment where the current PTransform should be executed in.
  //
  // Transforms that are required to be implemented by a runner must omit this.
  // All other transforms are required to specify this.
  string environment_id = 7;
}

message StandardPTransforms {
  // Primitive transforms may not specify composite sub-transforms.
  enum Primitives {
    // ParDo is a Beam transform for generic parallel processing. The ParDo
    // processing paradigm is similar to the “Map” phase of a
    // Map/Shuffle/Reduce-style algorithm: a ParDo transform considers each
    // element in the input PCollection, performs some processing function
    // (your user code) on that element, and emits zero, one, or multiple
    // elements to an output PCollection.
    //
    // See https://beam.apache.org/documentation/programming-guide/#pardo
    // for additional details.
    //
    // Payload: ParDoPayload
    PAR_DO = 0 [(beam_urn) = "beam:transform:pardo:v1"];

    // Flatten is a Beam transform for PCollection objects that store the same
    // data type. Flatten merges multiple PCollection objects into a single
    // logical PCollection.
    //
    // See https://beam.apache.org/documentation/programming-guide/#flatten
    // for additional details.
    //
    // Payload: None
    FLATTEN = 1 [(beam_urn) = "beam:transform:flatten:v1"];

    // GroupByKey is a Beam transform for processing collections of key/value
    // pairs. It’s a parallel reduction operation, analogous to the Shuffle
    // phase of a Map/Shuffle/Reduce-style algorithm. The input to GroupByKey is
    // a collection of key/value pairs that represents a multimap, where the
    // collection contains multiple pairs that have the same key, but different
    // values. Given such a collection, you use GroupByKey to collect all of the
    // values associated with each unique key.
    //
    // See https://beam.apache.org/documentation/programming-guide/#groupbykey
    // for additional details.
    //
    // Never defines an environment as the runner is required to implement this
    // transform.
    //
    // Payload: None
    GROUP_BY_KEY = 2 [(beam_urn) = "beam:transform:group_by_key:v1"];

    // A transform which produces a single empty byte array at the minimum
    // timestamp in the GlobalWindow.
    //
    // Never defines an environment as the runner is required to implement this
    // transform.
    //
    // Payload: None
    IMPULSE = 3 [(beam_urn) = "beam:transform:impulse:v1"];

    // Windowing subdivides a PCollection according to the timestamps of its
    // individual elements. Transforms that aggregate multiple elements, such as
    // GroupByKey and Combine, work implicitly on a per-window basis — they
    // process each PCollection as a succession of multiple, finite windows,
    // though the entire collection itself may be of unbounded size.
    //
    // See https://beam.apache.org/documentation/programming-guide/#windowing
    // for additional details.
    //
    // Payload: WindowIntoPayload
    ASSIGN_WINDOWS = 4 [(beam_urn) = "beam:transform:window_into:v1"];

    // A testing input that generates an unbounded {@link PCollection} of
    // elements, advancing the watermark and processing time as elements are
    // emitted. After all of the specified elements are emitted, ceases to
    // produce output.
    //
    // See https://beam.apache.org/blog/2016/10/20/test-stream.html
    // for additional details.
    //
    // Payload: TestStreamPayload
    TEST_STREAM = 5 [(beam_urn) = "beam:transform:teststream:v1"];

    // Represents mapping of main input window onto side input window.
    //
    // Side input window mapping function:
    // Input: KV<nonce, MainInputWindow>
    // Output: KV<nonce, SideInputWindow>
    //
    // For each main input window, the side input window is returned. The
    // nonce is used by a runner to associate each input with its output.
    // The nonce is represented as an opaque set of bytes.
    //
    // Payload: SideInput#window_mapping_fn FunctionSpec
    MAP_WINDOWS = 6 [(beam_urn) = "beam:transform:map_windows:v1"];

    // Used to merge windows during a GroupByKey.
    //
    // Window merging function:
    // Input: KV<nonce, iterable<OriginalWindow>>
    // Output: KV<nonce, KV<iterable<UnmergedOriginalWindow>, iterable<KV<MergedWindow, iterable<ConsumedOriginalWindow>>>>
    //
    // For each set of original windows, a list of all unmerged windows is
    // output alongside a map of merged window to set of consumed windows.
    // All original windows must be contained in either the unmerged original
    // window set or one of the consumed original window sets. Each original
    // window can only be part of one output set. The nonce is used by a runner
    // to associate each input with its output. The nonce is represented as an
    // opaque set of bytes.
    //
    // Payload: WindowingStrategy#window_fn FunctionSpec
    MERGE_WINDOWS = 7 [(beam_urn) = "beam:transform:merge_windows:v1"];
  }
  enum DeprecatedPrimitives {
    // Represents the operation to read a Bounded or Unbounded source.
    // Payload: ReadPayload.
    READ = 0 [(beam_urn) = "beam:transform:read:v1"];

    // Runners should move away from translating `CreatePCollectionView` and treat this as
    // part of the translation for a `ParDo` side input.
    CREATE_VIEW = 1 [(beam_urn) = "beam:transform:create_view:v1"];
  }
  enum Composites {
    // Represents the Combine.perKey() operation.
    // If this is produced by an SDK, it is assumed that the SDK understands
    // each of CombineComponents.
    // Payload: CombinePayload
    COMBINE_PER_KEY = 0 [(beam_urn) = "beam:transform:combine_per_key:v1"];

    // Represents the Combine.globally() operation.
    // If this is produced by an SDK, it is assumed that the SDK understands
    // each of CombineComponents.
    // Payload: CombinePayload
    COMBINE_GLOBALLY = 1 [(beam_urn) = "beam:transform:combine_globally:v1"];

    // Represents the Reshuffle operation.
    RESHUFFLE = 2 [(beam_urn) = "beam:transform:reshuffle:v1"];

    // Less well-known. Payload: WriteFilesPayload.
    WRITE_FILES = 3 [(beam_urn) = "beam:transform:write_files:v1"];
  }
  // Payload for all of these: CombinePayload
  enum CombineComponents {
    // Represents the Pre-Combine part of a lifted Combine Per Key, as described
    // in the following document:
    // https://s.apache.org/beam-runner-api-combine-model#heading=h.ta0g6ase8z07
    // Payload: CombinePayload
    COMBINE_PER_KEY_PRECOMBINE = 0 [(beam_urn) = "beam:transform:combine_per_key_precombine:v1"];

    // Represents the Merge Accumulators part of a lifted Combine Per Key, as
    // described in the following document:
    // https://s.apache.org/beam-runner-api-combine-model#heading=h.jco9rvatld5m
    // Payload: CombinePayload
    COMBINE_PER_KEY_MERGE_ACCUMULATORS = 1 [(beam_urn) = "beam:transform:combine_per_key_merge_accumulators:v1"];

    // Represents the Extract Outputs part of a lifted Combine Per Key, as
    // described in the following document:
    // https://s.apache.org/beam-runner-api-combine-model#heading=h.i9i6p8gtl6ku
    // Payload: CombinePayload
    COMBINE_PER_KEY_EXTRACT_OUTPUTS = 2 [(beam_urn) = "beam:transform:combine_per_key_extract_outputs:v1"];

    // Represents the Combine Grouped Values transform, as described in the
    // following document:
    // https://s.apache.org/beam-runner-api-combine-model#heading=h.aj86ew4v1wk
    // Payload: CombinePayload
    COMBINE_GROUPED_VALUES = 3 [(beam_urn) = "beam:transform:combine_grouped_values:v1"];

    // Represents the Convert To Accumulators transform, as described in the
    // following document:
    // https://s.apache.org/beam-runner-api-combine-model#heading=h.h5697l1scd9x
    // Payload: CombinePayload
    COMBINE_PER_KEY_CONVERT_TO_ACCUMULATORS = 4
        [(beam_urn) =
             "beam:transform:combine_per_key_convert_to_accumulators:v1"];
  }
  // Payload for all of these: ParDoPayload containing the user's SDF
  enum SplittableParDoComponents {
    // Pairs the input element with its initial restriction.
    // Input: element; output: KV(element, restriction).
    PAIR_WITH_RESTRICTION = 0 [(beam_urn) = "beam:transform:sdf_pair_with_restriction:v1"];

    // Splits the restriction of each element/restriction pair and returns the
    // resulting splits, with a corresponding floating point size estimation
    // for each.
    //
    // A reasonable value for size is the number of bytes expected to be
    // produced by this (element, restriction) pair.
    //
    // Input: KV(element, restriction)
    // Output: KV(KV(element, restriction), size))
    SPLIT_AND_SIZE_RESTRICTIONS = 1 [(beam_urn) = "beam:transform:sdf_split_and_size_restrictions:v1"];

    // Applies the DoFn to every element and restriction.
    //
    // All primary and residuals returned from checkpointing or splitting must
    // have the same type as the input to this transform.
    //
    // Input: KV(KV(element, restriction), size); output: DoFn's output.
    PROCESS_SIZED_ELEMENTS_AND_RESTRICTIONS = 2 [(beam_urn) = "beam:transform:sdf_process_sized_element_and_restrictions:v1"];
  }
}

message StandardSideInputTypes {
  enum Enum {
    // Represents a view over a PCollection<V>.
    //
    // StateGetRequests performed on this side input must use
    // StateKey.IterableSideInput.
    ITERABLE = 0 [(beam_urn) = "beam:side_input:iterable:v1"];

    // Represents a view over a PCollection<KV<K, V>>.
    //
    // StateGetRequests performed on this side input must use
    // StateKey.IterableSideInput or StateKey.MultimapSideInput.
    MULTIMAP = 1 [(beam_urn) = "beam:side_input:multimap:v1"];
  }
}

// A PCollection!
message PCollection {

  // (Required) A unique name for the PCollection.
  //
  // Ideally, this should be stable over multiple evolutions of a pipeline
  // for the purposes of logging and associating pipeline state with a node,
  // etc.
  //
  // If it is not stable, then the runner decides what will happen. But, most
  // importantly, it must always be here, even if it is autogenerated.
  string unique_name = 1;

  // (Required) The id of the Coder for this PCollection.
  string coder_id = 2;

  // (Required) Whether this PCollection is bounded or unbounded
  IsBounded.Enum is_bounded = 3;

  // (Required) The id of the windowing strategy for this PCollection.
  string windowing_strategy_id = 4;

  // (Optional) Static display data for the PCollection. If there is none,
  // it may be omitted.
  repeated DisplayData display_data = 5;
}

// The payload for the primitive ParDo transform.
message ParDoPayload {

  // (Required) The FunctionSpec of the DoFn.
  FunctionSpec do_fn = 1;

  // (Optional) A mapping of local input names to side inputs, describing
  // the expected access pattern.
  map<string, SideInput> side_inputs = 3;

  // (Optional) A mapping of local state names to state specifications.
  // If this is set, the stateful processing requirement should also
  // be placed in the pipeline requirements.
  map<string, StateSpec> state_specs = 4;

  // (Optional) A mapping of local timer family names to timer family
  // specifications. If this is set, the stateful processing requirement should
  // also be placed in the pipeline requirements.
  map<string, TimerFamilySpec> timer_family_specs = 9;

  // (Optional) Only set when this ParDo contains a splittable DoFn.
  // If this is set, the corresponding standard requirement should also
  // be placed in the pipeline requirements.
  string restriction_coder_id = 7;

  // (Optional) Only set when this ParDo can request bundle finalization.
  // If this is set, the corresponding standard requirement should also
  // be placed in the pipeline requirements.
  bool requests_finalization = 8;

  // Whether this stage requires time sorted input.
  // If this is set, the corresponding standard requirement should also
  // be placed in the pipeline requirements.
  bool requires_time_sorted_input = 10;

  // Whether this stage requires stable input.
  // If this is set, the corresponding standard requirement should also
  // be placed in the pipeline requirements.
  bool requires_stable_input = 11;

  reserved 6;
}

message StateSpec {
  oneof spec {
    ReadModifyWriteStateSpec read_modify_write_spec = 1;
    BagStateSpec bag_spec = 2;
    CombiningStateSpec combining_spec = 3;
    MapStateSpec map_spec = 4;
    SetStateSpec set_spec = 5;
  }
}

message ReadModifyWriteStateSpec {
  string coder_id = 1;
}

message BagStateSpec {
  string element_coder_id = 1;
}

message CombiningStateSpec {
  string accumulator_coder_id = 1;
  FunctionSpec combine_fn = 2;
}

message MapStateSpec {
  string key_coder_id = 1;
  string value_coder_id = 2;
}

message SetStateSpec {
  string element_coder_id = 1;
}

message TimerFamilySpec {
  TimeDomain.Enum time_domain = 1;
  string timer_family_coder_id = 2;
}

message IsBounded {
  enum Enum {
    UNSPECIFIED = 0;
    UNBOUNDED = 1;
    BOUNDED = 2;
  }
}

// The payload for the primitive Read transform.
message ReadPayload {

  // (Required) The FunctionSpec of the source for this Read.
  FunctionSpec source = 1;

  // (Required) Whether the source is bounded or unbounded
  IsBounded.Enum is_bounded = 2;

  // TODO: full audit of fields required by runners as opposed to SDK harness
}

// The payload for the WindowInto transform.
message WindowIntoPayload {

  // (Required) The FunctionSpec of the WindowFn.
  FunctionSpec window_fn = 1;
}

// The payload for the special-but-not-primitive Combine transform.
message CombinePayload {

  // (Required) The FunctionSpec of the CombineFn.
  FunctionSpec combine_fn = 1;

  // (Required) A reference to the Coder to use for accumulators of the CombineFn
  string accumulator_coder_id = 2;
}

// The payload for the test-only primitive TestStream
message TestStreamPayload {

  // (Required) the coder for elements in the TestStream events
  string coder_id = 1;

  // (Optional) If specified, the TestStream will replay these events.
  repeated Event events = 2;

  // (Optional) If specified, points to a TestStreamService to be
  // used to retrieve events.
  ApiServiceDescriptor endpoint = 3;

  message Event {
    oneof event {
      AdvanceWatermark watermark_event = 1;
      AdvanceProcessingTime processing_time_event = 2;
      AddElements element_event = 3;
    }

    // Advances the watermark to the specified timestamp.
    message AdvanceWatermark {
      // (Required) The watermark to advance to.
      int64 new_watermark = 1;

      // (Optional) The output watermark tag for a PCollection. If unspecified
      // or with an empty string, this will default to the Main PCollection
      // Output
      string tag = 2;
    }

    // Advances the processing time clock by the specified amount.
    message AdvanceProcessingTime {
      // (Required) The duration to advance by.
      int64 advance_duration = 1;
    }

    // Adds elements to the stream to be emitted.
    message AddElements {
      // (Required) The elements to add to the TestStream.
      repeated TimestampedElement elements = 1;

      // (Optional) The output PCollection tag to add these elements to. If
      // unspecified or with an empty string, this will default to the Main
      // PCollection Output.
      string tag = 3;
    }
  }

  // A single element inside of the TestStream.
  message TimestampedElement {
    // (Required) The element encoded. Currently the TestStream only supports
    // encoding primitives.
    bytes encoded_element = 1;

    // (Required) The event timestamp of this element.
    int64 timestamp = 2;
  }
}

service TestStreamService {
  // A TestStream will request for events using this RPC.
  rpc Events(EventsRequest) returns (stream TestStreamPayload.Event) {}
}

message EventsRequest {
  // The set of PCollections to read from. These are the PTransform outputs
  // local names. These are a subset of the TestStream's outputs. This allows
  // Interactive Beam to cache many PCollections from a pipeline then replay a
  // subset of them.
  repeated string output_ids = 1;
}

// The payload for the special-but-not-primitive WriteFiles transform.
message WriteFilesPayload {

  // (Required) The FunctionSpec of the FileBasedSink.
  FunctionSpec sink = 1;

  // (Required) The format function.
  FunctionSpec format_function = 2;

  bool windowed_writes = 3;

  bool runner_determined_sharding = 4;

  map<string, SideInput> side_inputs = 5;
}

// A coder, the binary format for serialization and deserialization of data in
// a pipeline.
message Coder {

  // (Required) A specification for the coder, as a URN plus parameters. This
  // may be a cross-language agreed-upon format, or it may be a "custom coder"
  // that can only be used by a particular SDK. It does not include component
  // coders, as it is beneficial for these to be comprehensible to a runner
  // regardless of whether the binary format is agreed-upon.
  FunctionSpec spec = 1;

  // (Optional) If this coder is parametric, such as ListCoder(VarIntCoder),
  // this is a list of the components. In order for encodings to be identical,
  // the FunctionSpec and all components must be identical, recursively.
  repeated string component_coder_ids = 2;
}

message StandardCoders {
  enum Enum {
    // Components: None
    BYTES = 0 [(beam_urn) = "beam:coder:bytes:v1"];

    // Components: None
    STRING_UTF8 = 10 [(beam_urn) = "beam:coder:string_utf8:v1"];

    // Components: The key and value coder, in that order.
    KV = 1 [(beam_urn) = "beam:coder:kv:v1"];

    // Components: None
    BOOL = 12 [(beam_urn) = "beam:coder:bool:v1"];

    // Variable length Encodes a 64-bit integer.
    // Components: None
    VARINT = 2 [(beam_urn) = "beam:coder:varint:v1"];

    // Encodes the floating point value as a big-endian 64-bit integer
    // according to the IEEE 754 double format bit layout.
    // Components: None
    DOUBLE = 11 [(beam_urn) = "beam:coder:double:v1"];

    // Encodes an iterable of elements.
    //
    // The encoding for an iterable [e1...eN] of known length N is
    //
    //    fixed32(N)
    //    encode(e1) encode(e2) encode(e3) ... encode(eN)
    //
    // If the length is unknown, it is batched up into groups of size b1..bM
    // and encoded as
    //
    //     fixed32(-1)
    //     varInt64(b1) encode(e1) encode(e2) ... encode(e_b1)
    //     varInt64(b2) encode(e_(b1+1)) encode(e_(b1+2)) ... encode(e_(b1+b2))
    //     ...
    //     varInt64(bM) encode(e_(N-bM+1)) encode(e_(N-bM+2)) ... encode(eN)
    //     varInt64(0)
    //
    // Components: Coder for a single element.
    ITERABLE = 3 [(beam_urn) = "beam:coder:iterable:v1"];

    // Encodes a timer containing a user key, a dynamic timer tag, a clear bit,
    // a fire timestamp, a hold timestamp, the windows and the paneinfo.
    // The encoding is represented as:
    //   user key - user defined key, uses the component coder.
    //   dynamic timer tag - a string which identifies a timer.
    //   windows - uses component coders.
    //   clear bit - a boolean set for clearing the timer.
    //   fire timestamp - a big endian 8 byte integer representing millis-since-epoch.
    //     The encoded representation is shifted so that the byte representation of
    //     negative values are lexicographically ordered before the byte representation
    //     of positive values. This is typically done by subtracting -9223372036854775808
    //     from the value and encoding it as a signed big endian integer. Example values:
    //
    //     -9223372036854775808: 00 00 00 00 00 00 00 00
    //                     -255: 7F FF FF FF FF FF FF 01
    //                       -1: 7F FF FF FF FF FF FF FF
    //                        0: 80 00 00 00 00 00 00 00
    //                        1: 80 00 00 00 00 00 00 01
    //                      256: 80 00 00 00 00 00 01 00
    //      9223372036854775807: FF FF FF FF FF FF FF FF
    //   hold timestamp - similar to the fire timestamp.
    //   paneinfo - similar to the paneinfo of the windowed_value.
    // Components: Coder for the key and windows.
    TIMER = 4 [(beam_urn) = "beam:coder:timer:v1"];

    /*
     * The following coders are typically not specified manually by the user,
     * but are used at runtime and must be supported by every SDK.
     */
    // Components: None
    INTERVAL_WINDOW = 5 [(beam_urn) = "beam:coder:interval_window:v1"];

    // Components: The coder to attach a length prefix to
    LENGTH_PREFIX = 6 [(beam_urn) = "beam:coder:length_prefix:v1"];

    // Components: None
    GLOBAL_WINDOW = 7 [(beam_urn) = "beam:coder:global_window:v1"];

    // Encodes an element, the windows it is in, the timestamp of the element,
    // and the pane of the element. The encoding is represented as:
    // timestamp windows pane element
    //   timestamp - A big endian 8 byte integer representing millis-since-epoch.
    //     The encoded representation is shifted so that the byte representation
    //     of negative values are lexicographically ordered before the byte
    //     representation of positive values. This is typically done by
    //     subtracting -9223372036854775808 from the value and encoding it as a
    //     signed big endian integer. Example values:
    //
    //     -9223372036854775808: 00 00 00 00 00 00 00 00
    //                     -255: 7F FF FF FF FF FF FF 01
    //                       -1: 7F FF FF FF FF FF FF FF
    //                        0: 80 00 00 00 00 00 00 00
    //                        1: 80 00 00 00 00 00 00 01
    //                      256: 80 00 00 00 00 00 01 00
    //      9223372036854775807: FF FF FF FF FF FF FF FF
    //
    //   windows - The windows are encoded using the beam:coder:iterable:v1
    //     format, where the windows are encoded using the supplied window
    //     coder.
    //
    //   pane - The first byte of the pane info determines which type of
    //     encoding is used, as well as the is_first, is_last, and timing
    //     fields. If this byte is bits [0 1 2 3 4 5 6 7], then:
    //     * bits [0 1 2 3] determine the encoding as follows:
    //         0000 - The entire pane info is encoded as a single byte.
    //                The is_first, is_last, and timing fields are encoded
    //                as below, and the index and non-speculative index are
    //                both zero (and hence are not encoded here).
    //         0001 - The pane info is encoded as this byte plus a single
    //                VarInt encoed integer representing the pane index. The
    //                non-speculative index can be derived as follows:
    //                  -1 if the pane is early, otherwise equal to index.
    //         0010 - The pane info is encoded as this byte plus two VarInt
    //                encoded integers representing the pane index and
    //                non-speculative index respectively.
    //     * bits [4 5] encode the timing as follows:
    //         00 - early
    //         01 - on time
    //         10 - late
    //         11 - unknown
    //     * bit 6 is 1 if this is the first pane, 0 otherwise.
    //     * bit 7 is 1 if this is the last pane, 0 otherwise.
    //
    //   element - The element incoded using the supplied element coder.
    //
    // Components: The element coder and the window coder, in that order.
    WINDOWED_VALUE = 8 [(beam_urn) = "beam:coder:windowed_value:v1"];

    // A windowed value coder with parameterized timestamp, windows and pane info.
    // Encodes an element with only the value of the windowed value.
    // Decodes the value and assigns the parameterized timestamp, windows and pane info to the
    // windowed value.
    // Components: The element coder and the window coder, in that order
    // The payload of this coder is an encoded windowed value using the
    // beam:coder:windowed_value:v1 coder parameterized by a beam:coder:bytes:v1
    // element coder and the window coder that this param_windowed_value coder uses.
    PARAM_WINDOWED_VALUE = 14 [(beam_urn) = "beam:coder:param_windowed_value:v1"];

    // Encodes an iterable of elements, some of which may be stored elsewhere.
    //
    // The encoding for a state-backed iterable is the same as that for
    // an iterable, but the final varInt64(0) terminating the set of batches
    // may instead be replaced by
    //
    //     varInt64(-1)
    //     varInt64(len(token))
    //     token
    //
    // where token is an opaque byte string that can be used to fetch the
    // remainder of the iterable (e.g. over the state API).
    //
    // Components: Coder for a single element.
    // Experimental.
    STATE_BACKED_ITERABLE = 9 [(beam_urn) = "beam:coder:state_backed_iterable:v1"];

    // Additional Standard Coders
    // --------------------------
    // The following coders are not required to be implemented for an SDK or
    // runner to support the Beam model, but enable users to take advantage of
    // schema-aware transforms.

    // Encodes a "row", an element with a known schema, defined by an
    // instance of Schema from schema.proto.
    //
    // A row is encoded as the concatenation of:
    //   - The number of attributes in the schema, encoded with
    //     beam:coder:varint:v1. This makes it possible to detect certain
    //     allowed schema changes (appending or removing columns) in
    //     long-running streaming pipelines.
    //   - A byte array representing a packed bitset indicating null fields (a
    //     1 indicating a null) encoded with beam:coder:bytes:v1. The unused
    //     bits in the last byte must be set to 0. If there are no nulls an
    //     empty byte array is encoded.
    //     The two-byte bitset (not including the lenghth-prefix) for the row
    //     [NULL, 0, 0, 0, NULL, 0, 0, NULL, 0, NULL] would be
    //     [0b10010001, 0b00000010]
    //   - An encoding for each non-null field, concatenated together.
    //
    // Schema types are mapped to coders as follows:
    //   AtomicType:
    //     BYTE:      not yet a standard coder (BEAM-7996)
    //     INT16:     not yet a standard coder (BEAM-7996)
    //     INT32:     beam:coder:varint:v1
    //     INT64:     beam:coder:varint:v1
    //     FLOAT:     not yet a standard coder (BEAM-7996)
    //     DOUBLE:    beam:coder:double:v1
    //     STRING:    beam:coder:string_utf8:v1
    //     BOOLEAN:   beam:coder:bool:v1
    //     BYTES:     beam:coder:bytes:v1
    //   ArrayType:   beam:coder:iterable:v1 (always has a known length)
    //   MapType:     not yet a standard coder (BEAM-7996)
    //   RowType:     beam:coder:row:v1
    //   LogicalType: Uses the coder for its representation.
    //
    // The payload for RowCoder is an instance of Schema.
    // Components: None
    // Experimental.
    ROW = 13 [(beam_urn) = "beam:coder:row:v1"];
  }
}

// A windowing strategy describes the window function, triggering, allowed
// lateness, and accumulation mode for a PCollection.
//
// TODO: consider inlining field on PCollection
message WindowingStrategy {

  // (Required) The FunctionSpec of the UDF that assigns windows,
  // merges windows, and shifts timestamps before they are
  // combined according to the OutputTime.
  FunctionSpec window_fn = 1;

  // (Required) Whether or not the window fn is merging.
  //
  // This knowledge is required for many optimizations.
  MergeStatus.Enum merge_status = 2;

  // (Required) The coder for the windows of this PCollection.
  string window_coder_id = 3;

  // (Required) The trigger to use when grouping this PCollection.
  Trigger trigger = 4;

  // (Required) The accumulation mode indicates whether new panes are a full
  // replacement for prior panes or whether they are deltas to be combined
  // with other panes (the combine should correspond to whatever the upstream
  // grouping transform is).
  AccumulationMode.Enum accumulation_mode = 5;

  // (Required) The OutputTime specifies, for a grouping transform, how to
  // compute the aggregate timestamp. The window_fn will first possibly shift
  // it later, then the OutputTime takes the max, min, or ignores it and takes
  // the end of window.
  //
  // This is actually only for input to grouping transforms, but since they
  // may be introduced in runner-specific ways, it is carried along with the
  // windowing strategy.
  OutputTime.Enum output_time = 6;

  // (Required) Indicate when output should be omitted upon window expiration.
  ClosingBehavior.Enum closing_behavior = 7;

  // (Required) The duration, in milliseconds, beyond the end of a window at
  // which the window becomes droppable.
  int64 allowed_lateness = 8;

  // (Required) Indicate whether empty on-time panes should be omitted.
  OnTimeBehavior.Enum OnTimeBehavior = 9;

  // (Required) Whether or not the window fn assigns inputs to exactly one window
  //
  // This knowledge is required for some optimizations
  bool assigns_to_one_window = 10;

  // (Optional) Environment where the current window_fn should be applied in.
  // Runner that executes the pipeline may choose to override this if needed.
  // If not specified, environment will be decided by the runner.
  string environment_id = 11;
}

// Whether or not a PCollection's WindowFn is non-merging, merging, or
// merging-but-already-merged, in which case a subsequent GroupByKey is almost
// always going to do something the user does not want
message MergeStatus {
  enum Enum {
    UNSPECIFIED = 0;

    // The WindowFn does not require merging.
    // Examples: global window, FixedWindows, SlidingWindows
    NON_MERGING = 1;

    // The WindowFn is merging and the PCollection has not had merging
    // performed.
    // Example: Sessions prior to a GroupByKey
    NEEDS_MERGE = 2;

    // The WindowFn is merging and the PCollection has had merging occur
    // already.
    // Example: Sessions after a GroupByKey
    ALREADY_MERGED = 3;
  }
}

// Whether or not subsequent outputs of aggregations should be entire
// replacement values or just the aggregation of inputs received since
// the prior output.
message AccumulationMode {
  enum Enum {
    UNSPECIFIED = 0;

    // The aggregation is discarded when it is output
    DISCARDING = 1;

    // The aggregation is accumulated across outputs
    ACCUMULATING = 2;

    // The aggregation emits retractions when it is output
    RETRACTING = 3;
  }
}

// Controls whether or not an aggregating transform should output data
// when a window expires.
message ClosingBehavior {
  enum Enum {
    UNSPECIFIED = 0;

    // Emit output when a window expires, whether or not there has been
    // any new data since the last output.
    EMIT_ALWAYS = 1;

    // Only emit output when new data has arrives since the last output
    EMIT_IF_NONEMPTY = 2;
  }
}

// Controls whether or not an aggregating transform should output data
// when an on-time pane is empty.
message OnTimeBehavior {
  enum Enum {
    UNSPECIFIED = 0;

    // Always fire the on-time pane. Even if there is no new data since
    // the previous firing, an element will be produced.
    FIRE_ALWAYS = 1;

    // Only fire the on-time pane if there is new data since the previous firing.
    FIRE_IF_NONEMPTY = 2;
  }
}

// When a number of windowed, timestamped inputs are aggregated, the timestamp
// for the resulting output.
message OutputTime {
  enum Enum {
    UNSPECIFIED = 0;

    // The output has the timestamp of the end of the window.
    END_OF_WINDOW = 1;

    // The output has the latest timestamp of the input elements since
    // the last output.
    LATEST_IN_PANE = 2;

    // The output has the earliest timestamp of the input elements since
    // the last output.
    EARLIEST_IN_PANE = 3;
  }
}

// The different time domains in the Beam model.
message TimeDomain {
  enum Enum {
    UNSPECIFIED = 0;

    // Event time is time from the perspective of the data
    EVENT_TIME = 1;

    // Processing time is time from the perspective of the
    // execution of your pipeline
    PROCESSING_TIME = 2;

    // Synchronized processing time is the minimum of the
    // processing time of all pending elements.
    //
    // The "processing time" of an element refers to
    // the local processing time at which it was emitted
    SYNCHRONIZED_PROCESSING_TIME = 3;
  }
}

// A small DSL for expressing when to emit new aggregations
// from a GroupByKey or CombinePerKey
//
// A trigger is described in terms of when it is _ready_ to permit output.
message Trigger {

  // Ready when all subtriggers are ready.
  message AfterAll {
    repeated Trigger subtriggers = 1;
  }

  // Ready when any subtrigger is ready.
  message AfterAny {
    repeated Trigger subtriggers = 1;
  }

  // Starting with the first subtrigger, ready when the _current_ subtrigger
  // is ready. After output, advances the current trigger by one.
  message AfterEach {
    repeated Trigger subtriggers = 1;
  }

  // Ready after the input watermark is past the end of the window.
  //
  // May have implicitly-repeated subtriggers for early and late firings.
  // When the end of the window is reached, the trigger transitions between
  // the subtriggers.
  message AfterEndOfWindow {

    // (Optional) A trigger governing output prior to the end of the window.
    Trigger early_firings = 1;

    // (Optional) A trigger governing output after the end of the window.
    Trigger late_firings = 2;
  }

  // After input arrives, ready when the specified delay has passed.
  message AfterProcessingTime {

    // (Required) The transforms to apply to an arriving element's timestamp,
    // in order
    repeated TimestampTransform timestamp_transforms = 1;
  }

  // Ready whenever upstream processing time has all caught up with
  // the arrival time of an input element
  message AfterSynchronizedProcessingTime {
  }

  // The default trigger. Equivalent to Repeat { AfterEndOfWindow } but
  // specially denoted to indicate the user did not alter the triggering.
  message Default {
  }

  // Ready whenever the requisite number of input elements have arrived
  message ElementCount {
    int32 element_count = 1;
  }

  // Never ready. There will only be an ON_TIME output and a final
  // output at window expiration.
  message Never {
  }

  // Always ready. This can also be expressed as ElementCount(1) but
  // is more explicit.
  message Always {
  }

  // Ready whenever either of its subtriggers are ready, but finishes output
  // when the finally subtrigger fires.
  message OrFinally {

    // (Required) Trigger governing main output; may fire repeatedly.
    Trigger main = 1;

    // (Required) Trigger governing termination of output.
    Trigger finally = 2;
  }

  // Ready whenever the subtrigger is ready; resets state when the subtrigger
  // completes.
  message Repeat {
    // (Require) Trigger that is run repeatedly.
    Trigger subtrigger = 1;
  }

  // The full disjoint union of possible triggers.
  oneof trigger {
    AfterAll after_all = 1;
    AfterAny after_any = 2;
    AfterEach after_each = 3;
    AfterEndOfWindow after_end_of_window = 4;
    AfterProcessingTime after_processing_time = 5;
    AfterSynchronizedProcessingTime after_synchronized_processing_time = 6;
    Always always = 12;
    Default default = 7;
    ElementCount element_count = 8;
    Never never = 9;
    OrFinally or_finally = 10;
    Repeat repeat = 11;
  }
}

// A specification for a transformation on a timestamp.
//
// Primarily used by AfterProcessingTime triggers to transform
// the arrival time of input to a target time for firing.
message TimestampTransform {
  oneof timestamp_transform {
    Delay delay = 1;
    AlignTo align_to = 2;
  }

  message Delay {
    // (Required) The delay, in milliseconds.
    int64 delay_millis = 1;
  }

  message AlignTo {
    // (Required) A duration to which delays should be quantized
    // in milliseconds.
    int64 period = 3;

    // (Required) An offset from 0 for the quantization specified by
    // alignment_size, in milliseconds
    int64 offset = 4;
  }
}

// A specification for how to "side input" a PCollection.
message SideInput {
  // (Required) URN of the access pattern required by the `view_fn` to present
  // the desired SDK-specific interface to a UDF.
  //
  // This access pattern defines the SDK harness <-> Runner Harness RPC
  // interface for accessing a side input.
  //
  // The only access pattern intended for Beam, because of its superior
  // performance possibilities, is "beam:sideinput:multimap" (or some such
  // URN)
  FunctionSpec access_pattern = 1;

  // (Required) The FunctionSpec of the UDF that adapts a particular
  // access_pattern to a user-facing view type.
  //
  // For example, View.asSingleton() may include a `view_fn` that adapts a
  // specially-designed multimap to a single value per window.
  FunctionSpec view_fn = 2;

  // (Required) The FunctionSpec of the UDF that maps a main input window
  // to a side input window.
  //
  // For example, when the main input is in fixed windows of one hour, this
  // can specify that the side input should be accessed according to the day
  // in which that hour falls.
  FunctionSpec window_mapping_fn = 3;
}

message StandardArtifacts {
  enum Types {
    // A URN for locally-accessible artifact files.
    // payload: ArtifactFilePayload
    FILE      = 0 [(beam_urn) = "beam:artifact:type:file:v1"];

    // A URN for artifacts described by URLs.
    // payload: ArtifactUrlPayload
    URL       = 1 [(beam_urn) = "beam:artifact:type:url:v1"];

    // A URN for artifacts embedded in ArtifactInformation proto.
    // payload: EmbeddedFilePayload.
    EMBEDDED  = 2 [(beam_urn) = "beam:artifact:type:embedded:v1"];

    // A URN for Python artifacts hosted on PYPI.
    // payload: PypiPayload
    PYPI      = 3 [(beam_urn) = "beam:artifact:type:pypi:v1"];

    // A URN for Java artifacts hosted on a Maven repository.
    // payload: MavenPayload
    MAVEN     = 4 [(beam_urn) = "beam:artifact:type:maven:v1"];

    // A URN for deferred artifacts.
    // payload: DeferredArtifactPayload
    DEFERRED = 5 [(beam_urn) = "beam:artifact:type:deferred:v1"];
  }
  enum Roles {
    // A URN for staging-to role.
    // payload: ArtifactStagingToRolePayload
    STAGING_TO  = 0 [(beam_urn) = "beam:artifact:role:staging_to:v1"];
  }
}

message ArtifactFilePayload {
  // a string for an artifact file path e.g. "/tmp/foo.jar"
  string path = 1;

  // The hex-encoded sha256 checksum of the artifact.
  string sha256 = 2;
}

message ArtifactUrlPayload {
  // a string for an artifact URL e.g. "https://.../foo.jar" or "gs://tmp/foo.jar"
  string url = 1;
}

message EmbeddedFilePayload {
  // raw data bytes for an embedded artifact
  bytes data = 1;
}

message PyPIPayload {
  // Pypi compatible artifact id e.g. "apache-beam"
  string artifact_id = 1;

  // Pypi compatible version string.
  string version = 2;
}

message MavenPayload {
  // A string specifying Maven artifact.
  // The standard format is "groupId:artifactId:version[:packaging[:classifier]]"
  string artifact = 1;

  // (Optional) Repository URL. If not specified, Maven central is used by default.
  string repository_url = 2;
}

message DeferredArtifactPayload {
  // A unique string identifier assigned by the creator of this payload. The creator may use this key to confirm
  // whether they can parse the data.
  string key = 1;

  // Data for deferred artifacts. Interpretation of bytes is delegated to the creator of this payload.
  bytes data = 2;
}

message ArtifactStagingToRolePayload {
  // A generated staged name (relative path under staging directory).
  string staged_name = 1;
}

message ArtifactInformation {
  // A URN that describes the type of artifact
  string type_urn = 1;

  bytes type_payload = 2;

  // A URN that describes the role of artifact
  string role_urn = 3;

  bytes role_payload = 4;
}

// An environment for executing UDFs. By default, an SDK container URL, but
// can also be a process forked by a command, or an externally managed process.
message Environment {
  // (Required) The URN of the payload
  string urn = 2;

  // (Optional) The data specifying any parameters to the URN. If
  // the URN does not require any arguments, this may be omitted.
  bytes payload = 3;

  // (Optional) Static display data for the environment. If there is none,
  // it may be omitted.
  repeated DisplayData display_data = 4;

  // (Optional) A set of capabilities this environment supports. This is
  // typically a list of common URNs designating coders, transforms, etc. that
  // this environment understands (and a runner MAY use) despite not
  // appearing in the pipeline proto. This may also be used to indicate
  // support of optional protocols not tied to a concrete component.
  repeated string capabilities = 5;

  // (Optional) artifact dependency information used for executing UDFs in this environment.
  repeated ArtifactInformation dependencies = 6;

  reserved 1;
}

message StandardEnvironments {
  enum Environments {
    DOCKER = 0 [(beam_urn) = "beam:env:docker:v1"]; // A managed docker container to run user code.

    PROCESS = 1 [(beam_urn) = "beam:env:process:v1"]; // A managed native process to run user code.

    EXTERNAL = 2 [(beam_urn) = "beam:env:external:v1"]; // An external non managed process to run user code.
  }
}

// The payload of a Docker image
message DockerPayload {
  string container_image = 1;  // implicitly linux_amd64.
}

message ProcessPayload {
  string os = 1;  // "linux", "darwin", ..
  string arch = 2;  // "amd64", ..
  string command = 3; // process to execute
  map<string, string> env = 4; // Environment variables
}

message ExternalPayload {
  ApiServiceDescriptor endpoint = 1;
  map<string, string> params = 2;  // Arbitrary extra parameters to pass
}

// These URNs are used to indicate capabilities of environments that cannot
// simply be expressed as a component (such as a Coder or PTransform) that this
// environment understands.
message StandardProtocols {
  enum Enum {
    // Indicates suport for progress reporting via the legacy Metrics proto.
    LEGACY_PROGRESS_REPORTING = 0 [(beam_urn) = "beam:protocol:progress_reporting:v0"];

    // Indicates suport for progress reporting via the new MonitoringInfo proto.
    PROGRESS_REPORTING = 1 [(beam_urn) = "beam:protocol:progress_reporting:v1"];

    // Indicates suport for worker status protocol defined at
    // https://s.apache.org/beam-fn-api-harness-status.
    WORKER_STATUS = 2 [(beam_urn) = "beam:protocol:worker_status:v1"];

    // Indicates this SDK can take advantage of multiple cores when processing
    // concurrent process bundle requests. (Note that all SDKs must process
    // an unbounded number of concurrent process bundle requests; this capability
    // simply indicates this SDK can actually parallelize the work across multiple
    // cores.
    MULTI_CORE_BUNDLE_PROCESSING = 3 [(beam_urn) = "beam:protocol:multi_core_bundle_processing:v1"];
  }
}

// These URNs are used to indicate requirements of a pipeline that cannot
// simply be expressed as a component (such as a Coder or PTransform) that the
// runner must understand. In many cases, this indicates a particular field
// of a transform must be inspected and respected (which allows new fields
// to be added in a forwards-compatible way).
message StandardRequirements {
  enum Enum {
    // This requirement indicates the state_spec and time_spec fields of ParDo
    // transform payloads must be inspected.
    REQUIRES_STATEFUL_PROCESSING = 0 [(beam_urn) = "beam:requirement:pardo:stateful:v1"];

    // This requirement indicates the requests_finalization field of ParDo
    // transform payloads must be inspected.
    REQUIRES_BUNDLE_FINALIZATION = 1 [(beam_urn) = "beam:requirement:pardo:finalization:v1"];

    // This requirement indicates the requires_stable_input field of ParDo
    // transform payloads must be inspected.
    REQUIRES_STABLE_INPUT = 2 [(beam_urn) = "beam:requirement:pardo:stable_input:v1"];

    // This requirement indicates the requires_time_sorted_input field of ParDo
    // transform payloads must be inspected.
    REQUIRES_TIME_SORTED_INPUT = 3 [(beam_urn) = "beam:requirement:pardo:time_sorted_input:v1"];

    // This requirement indicates the restriction_coder_id field of ParDo
    // transform payloads must be inspected.
    REQUIRES_SPLITTABLE_DOFN = 4 [(beam_urn) = "beam:requirement:pardo:splittable_dofn:v1"];
  }
}

extend google.protobuf.EnumValueOptions {
  // An extension to be used for specifying the standard URN of various
  // pipeline entities, e.g. transforms, functions, coders etc.
  // Code should refer to the URNs of those entities by extracting
  // it from the (beam_urn) extension, rather than by hard-coding
  // the URN.
  //
  // The recommended pattern for declaring it is (exemplified by coders):
  //
  // message StandardCoders {
  //   enum Enum {
  //     BYTES = 0 [(beam_urn) = "beam:coder:bytes:v1"];
  //     ...
  //   }
  // }
  //
  // If there are multiple categories of entities of this type, use the
  // following pattern (exemplified by PTransforms):
  //
  // message StandardPTransforms {
  //   enum Primitives {
  //     ...
  //   }
  //   enum Composites {
  //     ...
  //   }
  // }
  string beam_urn = 185324356;
  // A value to store other constants
  string beam_constant = 185324357;
}

// A URN along with a parameter object whose schema is determined by the
// URN.
//
// This structure is reused in two distinct, but compatible, ways:
//
// 1. This can be a specification of the function over PCollections
//    that a PTransform computes.
// 2. This can be a specification of a user-defined function, possibly
//    SDK-specific. (external to this message must be adequate context
//    to indicate the environment in which the UDF can be understood).
//
// Though not explicit in this proto, there are two possibilities
// for the relationship of a runner to this specification that
// one should bear in mind:
//
// 1. The runner understands the URN. For example, it might be
//    a well-known URN like "beam:transform:Top" or
//    "beam:window_fn:FixedWindows" with
//    an agreed-upon payload (e.g. a number or duration,
//    respectively).
// 2. The runner does not understand the URN. It might be an
//    SDK specific URN such as "beam:dofn:javasdk:1.0"
//    that indicates to the SDK what the payload is,
//    such as a serialized Java DoFn from a particular
//    version of the Beam Java SDK. The payload will often
//    then be an opaque message such as bytes in a
//    language-specific serialization format.
message FunctionSpec {

  // (Required) A URN that describes the accompanying payload.
  // For any URN that is not recognized (by whomever is inspecting
  // it) the parameter payload should be treated as opaque and
  // passed as-is.
  string urn = 1;

  // (Optional) The data specifying any parameters to the URN. If
  // the URN does not require any arguments, this may be omitted.
  bytes payload = 3;
}

// A set of well known URNs describing display data.
//
// All descriptions must contain how the value should be classified and how it
// is encoded. Note that some types are logical types which convey contextual
// information about the pipeline in addition to an encoding while others only
// specify the encoding itself.
message StandardDisplayData {
  enum DisplayData {
    // A string label and value. Has a payload containing an encoded
    // LabelledStringPayload.
    LABELLED_STRING = 0 [(beam_urn) = "beam:display_data:labelled_string:v1"];

    // Some samples that are being considered to become standard display data
    // types follow:

    // A path/location of a resource that this transform accesses. Encoded as
    // the well known google.protobuf.StringValue type.
    // INPUT_PATH = 1 [(beam_urn) = "beam:display_data:input_path:v1"];

    // A timestamp encoded as the well known protobuf type
    // google.protobuf.timestamp. Note that the value may be outside of the
    // RFC3339 limit imposed.
    // TIMESTAMP = 2 [(beam_urn) = "beam:display_data:timestamp:v1"];

    // A duration encoded as the well known protobuf type
    // google.protobuf.duration. Note that the value may be outside of the
    // RFC3339 limit imposed.
    // DURATION = 3 [(beam_urn) = "beam:display_data:duration:v1"];
  }
}

message LabelledStringPayload {
  // (Required) A human readable label for the value.
  string label = 1;

  // (Required) A value which will be displayed to the user. The urn describes
  // how the value can be interpreted and/or categorized.
  string value = 2;
}

// Static display data associated with a pipeline component. Display data is
// useful for pipeline runners IOs and diagnostic dashboards to display details
// about annotated components.
message DisplayData {
  // A key used to describe the type of display data. See StandardDisplayData
  // for the set of well known urns describing how the payload is meant to be
  // interpreted.
  string urn = 1;

  // (Optional) The data specifying any parameters to the URN. If
  // the URN does not require any arguments, this may be omitted.
  bytes payload = 2;
}


// The following transforms are not part of the RunnerApi specification,
// but may be useful for graph construction and manipulation.


// A disjoint union of all the things that may contain references
// that require Components to resolve.
message MessageWithComponents {

  // (Optional) The by-reference components of the root message,
  // enabling a standalone message.
  //
  // If this is absent, it is expected that there are no
  // references.
  Components components = 1;

  // (Required) The root message that may contain pointers
  // that should be resolved by looking inside components.
  oneof root {
    Coder coder = 2;
    CombinePayload combine_payload = 3;
    FunctionSpec function_spec = 4;
    ParDoPayload par_do_payload = 6;
    PTransform ptransform = 7;
    PCollection pcollection = 8;
    ReadPayload read_payload = 9;
    SideInput side_input = 11;
    WindowIntoPayload window_into_payload = 12;
    WindowingStrategy windowing_strategy = 13;
  }
}

// The payload for an executable stage. This will eventually be passed to an SDK in the form of a
// ProcessBundleDescriptor.
message ExecutableStagePayload {

  // (Required) Environment in which this stage executes.
  //
  // We use an environment rather than environment id
  // because ExecutableStages use environments directly. This may change in the future.
  Environment environment = 1;

  // The wire coder settings of this executable stage
  repeated WireCoderSetting wire_coder_settings = 9;

  // (Required) Input PCollection id. This must be present as a value in the inputs of any
  // PTransform the ExecutableStagePayload is the payload of.
  string input = 2;

  // The side inputs required for this executable stage. Each side input of each PTransform within
  // this ExecutableStagePayload must be represented within this field.
  repeated SideInputId side_inputs = 3;

  // PTransform ids contained within this executable stage. This must contain at least one
  // PTransform id.
  repeated string transforms = 4;

  // Output PCollection ids. This must be equal to the values of the outputs of any
  // PTransform the ExecutableStagePayload is the payload of.
  repeated string outputs = 5;

  // (Required) The components for the Executable Stage. This must contain all of the Transforms
  // in transforms, and the closure of all of the components they recognize.
  Components components = 6;

  // The user states required for this executable stage. Each user state of each PTransform within
  // this ExecutableStagePayload must be represented within this field.
  repeated UserStateId user_states = 7;

  // The timers required for this executable stage. Each timer of each PTransform within
  // this ExecutableStagePayload must be represented within this field.
  repeated TimerId timers = 8;

  // The timerfamilies required for this executable stage. Each timer familyof each PTransform within
  // this ExecutableStagePayload must be represented within this field.
  repeated TimerFamilyId timerFamilies = 10;

  // A reference to a side input. Side inputs are uniquely identified by PTransform id and
  // local name.
  message SideInputId {
    // (Required) The id of the PTransform that references this side input.
    string transform_id = 1;

    // (Required) The local name of this side input from the PTransform that references it.
    string local_name = 2;
  }

  // A reference to user state. User states are uniquely identified by PTransform id and
  // local name.
  message UserStateId {
    // (Required) The id of the PTransform that references this user state.
    string transform_id = 1;

    // (Required) The local name of this user state for the PTransform that references it.
    string local_name = 2;
  }

  // A reference to a timer. Timers are uniquely identified by PTransform id and
  // local name.
  message TimerId {
    // (Required) The id of the PTransform that references this timer.
    string transform_id = 1;

    // (Required) The local name of this timer for the PTransform that references it.
    string local_name = 2;
  }

  // A reference to a timer. Timers are uniquely identified by PTransform id and
  // local name.
  message TimerFamilyId {
    // (Required) The id of the PTransform that references this timer family.
    string transform_id = 1;

    // (Required) The local name of this timer family for the PTransform that references it.
    string local_name = 2;
  }
  // Settings that decide the coder type of wire coder.
  message WireCoderSetting {
    // (Required) The URN of the wire coder.
    // Note that only windowed value coder or parameterized windowed value coder are supported.
    string urn = 1;

    // (Optional) The data specifying any parameters to the URN. If
    // the URN is beam:coder:windowed_value:v1, this may be omitted. If the URN is
    // beam:coder:param_windowed_value:v1, the payload is an encoded windowed
    // value using the beam:coder:windowed_value:v1 coder parameterized by
    // a beam:coder:bytes:v1 element coder and the window coder that this
    // param_windowed_value coder uses.
    bytes payload = 2;

    // (Required) The target(PCollection or Timer) this setting applies to.
    oneof target {
      // The input or output PCollection id this setting applies to.
      string input_or_output_id = 3;
      // The timer id this setting applies to.
      TimerId timer = 4;
    }
  }
}
