/*
Package event provides a service for subscribing to state change events.
*/
syntax = "proto3";

package subscribe;

import "proto/pbservice/node.proto";

// StateChangeSubscription service allows consumers to subscribe to topics of
// state change events. Events are streamed as they happen.
// buf:lint:ignore SERVICE_SUFFIX
service StateChangeSubscription {
  // Subscribe to a topic to receive events when there are changes to the topic.
  //
  // If SubscribeRequest.Index is 0 the event stream will start with one or
  // more snapshot events, followed by an EndOfSnapshot event. Subsequent
  // events will be a live stream of events as they happen.
  //
  // If SubscribeRequest.Index is > 0 it is assumed the client already has a
  // snapshot, and is trying to resume a stream that was disconnected. The
  // client will either receive a NewSnapshotToFollow event, indicating the
  // client view is stale and it must reset its view and prepare for a new
  // snapshot. Or, if no NewSnapshotToFollow event is received, the client
  // view is still fresh, and all events will be the live stream.
  //
  // Subscribe may return a gRPC status error with codes.ABORTED to indicate
  // the client view is now stale due to a change on the server. The client
  // must reset its view and issue a new Subscribe call to restart the stream.
  // This error is used when the server can no longer correctly maintain the
  // stream, for example because the ACL permissions for the token changed, or
  // because the server state was restored from a snapshot.
  // buf:lint:ignore RPC_RESPONSE_STANDARD_NAME
  rpc Subscribe(SubscribeRequest) returns (stream Event) {}
}

// Topic enumerates the supported event topics.
enum Topic {
  Unknown = 0;
  // ServiceHealth topic contains events for any changes to service health.
  ServiceHealth = 1;
  // ServiceHealthConnect topic contains events for any changes to service
  // health for connect-enabled services.
  ServiceHealthConnect = 2;
}

// SubscribeRequest used to subscribe to a topic.
message SubscribeRequest {
  // Topic identifies the set of events the subscriber is interested in.
  Topic Topic = 1;

  // Key is a topic-specific identifier that restricts the scope of the
  // subscription to only events pertaining to that identifier. For example,
  // to receive events for a single service, the service's name is specified
  // as the key.
  string Key = 2;

  // Token is the ACL token to authenticate the request. The token must have
  // sufficient privileges to read the requested information otherwise events
  // will be filtered, possibly resulting in an empty snapshot and no further
  // updates sent.
  string Token = 3;

  // Index is the raft index the subscriber has already observed up to. This
  // is zero on an initial streaming call, but then can be provided by a
  // client on subsequent re-connections such that the full snapshot doesn't
  // need to be resent if the client is up to date.
  uint64 Index = 4;

  // Datacenter specifies the Consul datacenter the request is targeted at.
  // If it's not the local DC the server will forward the request to
  // the remote DC and proxy the results back  to the subscriber. An empty
  // string defaults to the local datacenter.
  string Datacenter = 5;

  // Namespace which contains the resources. If Namespace is not specified the
  // default namespace will be used.
  //
  // Namespace is an enterprise-only feature.
  string Namespace = 6;

  // Partition which contains the resources. If Partition is not specified the
  // default partition will be used.
  //
  // Partition is an enterprise-only feature.
  string Partition = 7;

  // PeerName is the name of the peer that the requested service was imported from.
  string PeerName = 8;
}

// Event describes a streaming update on a subscription. Events are used both to
// describe the current "snapshot" of the result as well as ongoing mutations to
// that snapshot.
message Event {
  // Index is the raft index at which the mutation took place. At the top
  // level of a subscription there will always be at most one Event per index.
  // If multiple events are published to the same topic in a single raft
  // transaction then the batch of events will be encoded inside a single
  // top-level event to ensure they are delivered atomically to clients.
  uint64 Index = 1;

  // Payload is the actual event content.
  oneof Payload {
    // EndOfSnapshot indicates the event stream for the initial snapshot has
    // ended. Subsequent Events delivered will be mutations to that result.
    bool EndOfSnapshot = 2;

    // NewSnapshotToFollow indicates that the client view is stale. The client
    // must reset its view before handing any more events. Subsequent events
    // in the stream will be for a new snapshot until an EndOfSnapshot event
    // is received.
    bool NewSnapshotToFollow = 3;

    // EventBatch is a set of events. This is typically used as the payload
    // type where multiple events are emitted in a single topic and raft
    // index (e.g. transactional updates). In this case the Topic and Index
    // values of all events will match and the whole set should be delivered
    // and consumed atomically.
    EventBatch EventBatch = 4;

    // ServiceHealth is used for ServiceHealth and ServiceHealthConnect
    // topics.
    ServiceHealthUpdate ServiceHealth = 10;
  }
}

message EventBatch {
  repeated Event Events = 1;
}

enum CatalogOp {
  Register = 0;
  Deregister = 1;
}

message ServiceHealthUpdate {
  CatalogOp Op = 1;
  service.CheckServiceNode CheckServiceNode = 2;
}