// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
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syntax = "proto3";

package google.protobuf;

option csharp_namespace = "Google.Protobuf.WellKnownTypes";
option java_package = "com.google.protobuf";
option java_outer_classname = "FieldMaskProto";
option java_multiple_files = true;
option objc_class_prefix = "GPB";
option java_generate_equals_and_hash = true;

// `FieldMask` represents a set of symbolic field paths, for example:
//
//     paths: "f.a"
//     paths: "f.b.d"
//
// Here `f` represents a field in some root message, `a` and `b`
// fields in the message found in `f`, and `d` a field found in the
// message in `f.b`.
//
// Field masks are used to specify a subset of fields that should be
// returned by a get operation or modified by an update operation.
// Field masks also have a custom JSON encoding (see below).
//
// # Field Masks in Projections
//
// When used in the context of a projection, a response message or
// sub-message is filtered by the API to only contain those fields as
// specified in the mask. For example, if the mask in the previous
// example is applied to a response message as follows:
//
//     f {
//       a : 22
//       b {
//         d : 1
//         x : 2
//       }
//       y : 13
//     }
//     z: 8
//
// The result will not contain specific values for fields x,y and z
// (their value will be set to the default, and omitted in proto text
// output):
//
//
//     f {
//       a : 22
//       b {
//         d : 1
//       }
//     }
//
// A repeated field is not allowed except at the last position of a
// field mask.
//
// If a FieldMask object is not present in a get operation, the
// operation applies to all fields (as if a FieldMask of all fields
// had been specified).
//
// Note that a field mask does not necessarily apply to the
// top-level response message. In case of a REST get operation, the
// field mask applies directly to the response, but in case of a REST
// list operation, the mask instead applies to each individual message
// in the returned resource list. In case of a REST custom method,
// other definitions may be used. Where the mask applies will be
// clearly documented together with its declaration in the API.  In
// any case, the effect on the returned resource/resources is required
// behavior for APIs.
//
// # Field Masks in Update Operations
//
// A field mask in update operations specifies which fields of the
// targeted resource are going to be updated. The API is required
// to only change the values of the fields as specified in the mask
// and leave the others untouched. If a resource is passed in to
// describe the updated values, the API ignores the values of all
// fields not covered by the mask.
//
// If a repeated field is specified for an update operation, the existing
// repeated values in the target resource will be overwritten by the new values.
// Note that a repeated field is only allowed in the last position of a field
// mask.
//
// If a sub-message is specified in the last position of the field mask for an
// update operation, then the existing sub-message in the target resource is
// overwritten. Given the target message:
//
//     f {
//       b {
//         d : 1
//         x : 2
//       }
//       c : 1
//     }
//
// And an update message:
//
//     f {
//       b {
//         d : 10
//       }
//     }
//
// then if the field mask is:
//
//  paths: "f.b"
//
// then the result will be:
//
//     f {
//       b {
//         d : 10
//       }
//       c : 1
//     }
//
// However, if the update mask was:
//
//  paths: "f.b.d"
//
// then the result would be:
//
//     f {
//       b {
//         d : 10
//         x : 2
//       }
//       c : 1
//     }
//
// In order to reset a field's value to the default, the field must
// be in the mask and set to the default value in the provided resource.
// Hence, in order to reset all fields of a resource, provide a default
// instance of the resource and set all fields in the mask, or do
// not provide a mask as described below.
//
// If a field mask is not present on update, the operation applies to
// all fields (as if a field mask of all fields has been specified).
// Note that in the presence of schema evolution, this may mean that
// fields the client does not know and has therefore not filled into
// the request will be reset to their default. If this is unwanted
// behavior, a specific service may require a client to always specify
// a field mask, producing an error if not.
//
// As with get operations, the location of the resource which
// describes the updated values in the request message depends on the
// operation kind. In any case, the effect of the field mask is
// required to be honored by the API.
//
// ## Considerations for HTTP REST
//
// The HTTP kind of an update operation which uses a field mask must
// be set to PATCH instead of PUT in order to satisfy HTTP semantics
// (PUT must only be used for full updates).
//
// # JSON Encoding of Field Masks
//
// In JSON, a field mask is encoded as a single string where paths are
// separated by a comma. Fields name in each path are converted
// to/from lower-camel naming conventions.
//
// As an example, consider the following message declarations:
//
//     message Profile {
//       User user = 1;
//       Photo photo = 2;
//     }
//     message User {
//       string display_name = 1;
//       string address = 2;
//     }
//
// In proto a field mask for `Profile` may look as such:
//
//     mask {
//       paths: "user.display_name"
//       paths: "photo"
//     }
//
// In JSON, the same mask is represented as below:
//
//     {
//       mask: "user.displayName,photo"
//     }
//
// # Field Masks and Oneof Fields
//
// Field masks treat fields in oneofs just as regular fields. Consider the
// following message:
//
//     message SampleMessage {
//       oneof test_oneof {
//         string name = 4;
//         SubMessage sub_message = 9;
//       }
//     }
//
// The field mask can be:
//
//     mask {
//       paths: "name"
//     }
//
// Or:
//
//     mask {
//       paths: "sub_message"
//     }
//
// Note that oneof type names ("test_oneof" in this case) cannot be used in
// paths.
message FieldMask {
  // The set of field mask paths.
  repeated string paths = 1;
}