Experimental protobuf model for Jaeger using gogoprotobuf extensions

jaeger.proto

/* Jaeger test
   Cf. https://github.com/gogo/protobuf/blob/master/extensions.md
   Based on https://github.com/gogo/grpc-example
   
   The JSON is generated with the help of "github.com/cockroachdb/cockroach/pkg/util/protoutil"
   with `EmitDefaults: false` setting
   
        jsonpb := &protoutil.JSONPb{
                EmitDefaults: false,
                Indent:       "  ",
        }
   
   The lack of pointers in the generated structs is due to using this extension: `(gogoproto.nullable) = false`
*/

message TraceId {
  uint64 low = 1;
  uint64 high = 2;
}

// experiment with `oneof`
/* 
message KeyValue {
  string key = 1;
  oneof value {
    string vStr = 2;
    double  vDouble = 3;
    bool vBool = 4;
    int64 vLong = 5;
    bytes vBinary = 6;
  }
}
*/

message KeyValue {
  enum Type {
    STRING = 0;
    DOUBLE = 1;
    BOOL = 2;
    LONG = 3;
    BINARY = 4;
  };

  string key = 1;
  Type vType = 2;
  string vStr = 3;
  double  vDouble = 4;
  bool vBool = 5;
  int64 vLong = 6;
  bytes vBinary = 7;
}

message Log {
  google.protobuf.Timestamp timestamp = 1 [
    (gogoproto.stdtime) = true,
    (gogoproto.nullable) = false
  ];
  repeated KeyValue fields = 2 [
    (gogoproto.nullable) = false
  ];
}

message SpanRef {
  enum Type {
    CHILD_OF = 0;
    FOLLOWS_FROM = 1;
  };
  Type type = 1;
  TraceId trace_id = 2 [
    (gogoproto.nullable) = false
  ];
  uint64 span_id = 3;
}

message Process {
  string service_name = 1;
  repeated KeyValue tags = 2 [
    (gogoproto.nullable) = false
  ];
}

message Span {
  TraceId trace_id = 1 [
    (gogoproto.nullable) = false
  ];
  uint64 span_id = 2;
  uint64 parent_span_id = 3;
  string operation_name = 4;
  repeated SpanRef references = 5 [
    (gogoproto.nullable) = false
  ];
  uint32 flags = 6;
  google.protobuf.Timestamp startTime = 7 [
    (gogoproto.stdtime) = true,
    (gogoproto.nullable) = false
  ];
  google.protobuf.Duration duration = 8 [
    (gogoproto.stdduration) = true,
    (gogoproto.nullable) = false
  ];
  repeated KeyValue tags = 9 [
    (gogoproto.nullable) = false
  ];
  repeated Log logs = 10 [
    (gogoproto.nullable) = false
  ];
  repeated string warnings = 11;
  Process process = 12;
}

message Trace {
  repeated Span spans = 1 [
    (gogoproto.nullable) = false
  ];
}