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//
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//
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syntax = "proto3";

package grpc.lb.v1;

message Duration {
  // Signed seconds of the span of time. Must be from -315,576,000,000
  // to +315,576,000,000 inclusive.
  int64 seconds = 1;

  // Signed fractions of a second at nanosecond resolution of the span
  // of time. Durations less than one second are represented with a 0
  // `seconds` field and a positive or negative `nanos` field. For durations
  // of one second or more, a non-zero value for the `nanos` field must be
  // of the same sign as the `seconds` field. Must be from -999,999,999
  // to +999,999,999 inclusive.
  int32 nanos = 2;
}

message Timestamp {

  // Represents seconds of UTC time since Unix epoch
  // 1970-01-01T00:00:00Z. Must be from 0001-01-01T00:00:00Z to
  // 9999-12-31T23:59:59Z inclusive.
  int64 seconds = 1;

  // Non-negative fractions of a second at nanosecond resolution. Negative
  // second values with fractions must still have non-negative nanos values
  // that count forward in time. Must be from 0 to 999,999,999
  // inclusive.
  int32 nanos = 2;
}

service LoadBalancer {
  // Bidirectional rpc to get a list of servers.
  rpc BalanceLoad(stream LoadBalanceRequest)
      returns (stream LoadBalanceResponse);
}

message LoadBalanceRequest {
  oneof load_balance_request_type {
    // This message should be sent on the first request to the load balancer.
    InitialLoadBalanceRequest initial_request = 1;

    // The client stats should be periodically reported to the load balancer
    // based on the duration defined in the InitialLoadBalanceResponse.
    ClientStats client_stats = 2;
  }
}

message InitialLoadBalanceRequest {
  // Name of load balanced service (IE, balancer.service.com)
  // length should be less than 256 bytes.
  string name = 1;
}

// Contains client level statistics that are useful to load balancing. Each
// count except the timestamp should be reset to zero after reporting the stats.
message ClientStats {
  // The timestamp of generating the report.
  Timestamp timestamp = 1;

  // The total number of RPCs that started.
  int64 num_calls_started = 2;

  // The total number of RPCs that finished.
  int64 num_calls_finished = 3;

  // The total number of RPCs that were dropped by the client because of rate
  // limiting.
  int64 num_calls_finished_with_drop_for_rate_limiting = 4;

  // The total number of RPCs that were dropped by the client because of load
  // balancing.
  int64 num_calls_finished_with_drop_for_load_balancing = 5;

  // The total number of RPCs that failed to reach a server except dropped RPCs.
  int64 num_calls_finished_with_client_failed_to_send = 6;

  // The total number of RPCs that finished and are known to have been received
  // by a server.
  int64 num_calls_finished_known_received = 7;
}

message LoadBalanceResponse {
  oneof load_balance_response_type {
    // This message should be sent on the first response to the client.
    InitialLoadBalanceResponse initial_response = 1;

    // Contains the list of servers selected by the load balancer. The client
    // should send requests to these servers in the specified order.
    ServerList server_list = 2;
  }
}

message InitialLoadBalanceResponse {
  // This is an application layer redirect that indicates the client should use
  // the specified server for load balancing. When this field is non-empty in
  // the response, the client should open a separate connection to the
  // load_balancer_delegate and call the BalanceLoad method. Its length should
  // be less than 64 bytes.
  string load_balancer_delegate = 1;

  // This interval defines how often the client should send the client stats
  // to the load balancer. Stats should only be reported when the duration is
  // positive.
  Duration client_stats_report_interval = 2;
}

message ServerList {
  // Contains a list of servers selected by the load balancer. The list will
  // be updated when server resolutions change or as needed to balance load
  // across more servers. The client should consume the server list in order
  // unless instructed otherwise via the client_config.
  repeated Server servers = 1;

  // Indicates the amount of time that the client should consider this server
  // list as valid. It may be considered stale after waiting this interval of
  // time after receiving the list. If the interval is not positive, the
  // client can assume the list is valid until the next list is received.
  Duration expiration_interval = 3;
}

// Contains server information. When none of the [drop_for_*] fields are true,
// use the other fields. When drop_for_rate_limiting is true, ignore all other
// fields. Use drop_for_load_balancing only when it is true and
// drop_for_rate_limiting is false.
message Server {
  // A resolved address for the server, serialized in network-byte-order. It may
  // either be an IPv4 or IPv6 address.
  bytes ip_address = 1;

  // A resolved port number for the server.
  int32 port = 2;

  // An opaque but printable token given to the frontend for each pick. All
  // frontend requests for that pick must include the token in its initial
  // metadata. The token is used by the backend to verify the request and to
  // allow the backend to report load to the gRPC LB system.
  //
  // Its length is variable but less than 50 bytes.
  string load_balance_token = 3;

  // Indicates whether this particular request should be dropped by the client
  // for rate limiting.
  bool drop_for_rate_limiting = 4;

  // Indicates whether this particular request should be dropped by the client
  // for load balancing.
  bool drop_for_load_balancing = 5;
}
