common/proto/structmask/structmask.proto

// Copyright 2021 The LUCI Authors.
//
// Licensed 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.

syntax = "proto3";

package structmask;

option go_package = "go.chromium.org/luci/common/proto/structmask";

// StructMask selects a subset of a google.protobuf.Struct.
//
// Usually used as a repeated field, to allow specifying a union of different
// subsets.
message StructMask {
  // A field path inside the struct to select.
  //
  // Each item can be:
  //   * `some_value` - a concrete dict key to follow (unless it is a number or
  //     includes `*`, use quotes in this case).
  //   * `"some_value"` - same, but quoted. Useful for selecting `*` or numbers
  //     literally. See https://pkg.go.dev/strconv#Unquote for syntax.
  //   * `<number>` (e.g. `0`) - a zero-based list index to follow.
  //     **Not implemented**.
  //   *  `*` - follow all dict keys and all list elements. Applies **only** to
  //     dicts and lists. Trying to recurse into a number or a string results
  //     in an empty match.
  //
  // When examining a value the following exceptional conditions result in
  // an empty match, which is represented by `null` for list elements or
  // omissions of the field for dicts:
  //   * Trying to follow a dict key while examining a list.
  //   * Trying to follow a key which is not present in the dict.
  //   * Trying to use `*` mask with values that aren't dicts or lists.
  //
  // When using `*`, the result is always a subset of the input. In particular
  // this is important when filtering lists: if a list of size N is selected by
  // the mask, then the filtered result will also always be a list of size N,
  // with elements filtered further according to the rest of the mask (perhaps
  // resulting in `null` elements on type mismatches, as explained above).
  repeated string path = 1;
}