path: root/chrome/browser/sync/protocol/sync.proto

// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// Sync protocol for communication between sync client and server.

// Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
// any fields in this file.

syntax = "proto2";

option optimize_for = LITE_RUNTIME;
option retain_unknown_fields = true;

package sync_pb;

import "encryption.proto";
import "client_debug_info.proto";

// Used for inspecting how long we spent performing operations in different
// backends. All times must be in millis.
message ProfilingData {
  optional int64 meta_data_write_time = 1;
  optional int64 file_data_write_time = 2;
  optional int64 user_lookup_time = 3;
  optional int64 meta_data_read_time = 4;
  optional int64 file_data_read_time = 5;
  optional int64 total_request_time = 6;
}

message EntitySpecifics {
  // If a datatype is encrypted, this field will contain the encrypted
  // original EntitySpecifics. The extension for the datatype will continue
  // to exist, but contain only the default values.
  // Note that currently passwords employ their own legacy encryption scheme and
  // do not use this field.
  optional EncryptedData encrypted = 1;

  // To add new datatype-specific fields to the protocol, extend
  // EntitySpecifics.  First, pick a non-colliding tag number by
  // picking a revision number of one of your past commits
  // to src.chromium.org.  Then, in a different protocol buffer
  // definition that includes this, do the following:
  //
  //   extend EntitySpecifics {
  //     MyDatatypeSpecifics my_datatype = 32222;
  //   }
  //
  // where:
  //   - 32222 is the non-colliding tag number you picked earlier.
  //   - MyDatatypeSpecifics is the type (probably a message type defined
  //     in your new .proto file) that you want to associate with each
  //     object of the new datatype.
  //   - my_datatype is the field identifier you'll use to access the
  //     datatype specifics from the code.
  //
  // Server implementations are obligated to preserve the contents of
  // EntitySpecifics when it contains unrecognized extensions.  In this
  // way, it is possible to add new datatype fields without having
  // to update the server.
  extensions 30000 to max;
}

message SyncEntity {
  // This item's identifier.  In a commit of a new item, this will be a
  // client-generated ID.  If the commit succeeds, the server will generate
  // a globally unique ID and return it to the committing client in the
  // CommitResponse.EntryResponse.  In the context of a GetUpdatesResponse,
  // |id_string| is always the server generated ID.  The original
  // client-generated ID is preserved in the |originator_client_id| field.
  // Present in both GetUpdatesResponse and CommitMessage.
  optional string id_string = 1;

  // An id referencing this item's parent in the hierarchy.  In a
  // CommitMessage, it is accepted for this to be a client-generated temporary
  // ID if there was a new created item with that ID appearing earlier
  // in the message.  In all other situations, it is a server ID.
  // Present in both GetUpdatesResponse and CommitMessage.
  optional string parent_id_string = 2;

  // old_parent_id is only set in commits and indicates the old server
  // parent(s) to remove. When omitted, the old parent is the same as
  // the new.
  // Present only in CommitMessage.
  optional string old_parent_id = 3;

  // The version of this item -- a monotonically increasing value that is
  // maintained by for each item.  If zero in a CommitMessage, the server
  // will interpret this entity as a newly-created item and generate a
  // new server ID and an initial version number.  If nonzero in a
  // CommitMessage, this item is treated as an update to an existing item, and
  // the server will use |id_string| to locate the item.  Then, if the item's
  // current version on the server does not match |version|, the commit will
  // fail for that item.  The server will not update it, and will return
  // a result code of CONFLICT.  In a GetUpdatesResponse, |version| is
  // always positive and indentifies the revision of the item data being sent
  // to the client.
  // Present in both GetUpdatesResponse and CommitMessage.
  required int64 version = 4;

  // Last modification time (in java time milliseconds)
  // Present in both GetUpdatesResponse and CommitMessage.
  optional int64 mtime = 5;

  // Creation time.
  // Present in both GetUpdatesResponse and CommitMessage.
  optional int64 ctime = 6;

  // The name of this item.
  // Historical note:
  //   Since November 2010, this value is no different from non_unique_name.
  //   Before then, server implementations would maintain a unique-within-parent
  //   value separate from its base, "non-unique" value.  Clients had not
  //   depended on the uniqueness of the property since November 2009; it was
  //   removed from Chromium by http://codereview.chromium.org/371029 .
  // Present in both GetUpdatesResponse and CommitMessage.
  required string name = 7;

  // The name of this item.  Same as |name|.
  // |non_unique_name| should take precedence over the |name| value if both
  // are supplied.  For efficiency, clients and servers should avoid setting
  // this redundant value.
  // Present in both GetUpdatesResponse and CommitMessage.
  optional string non_unique_name = 8;

  // A value from a monotonically increasing sequence that indicates when
  // this item was last updated on the server. This is now equivalent
  // to version. This is now deprecated in favor of version.
  // Present only in GetUpdatesResponse.
  optional int64 sync_timestamp = 9;

  // If present, this tag identifies this item as being a uniquely
  // instanced item.  The server ensures that there is never more
  // than one entity in a user's store with the same tag value.
  // This value is used to identify and find e.g. the "Google Chrome" settings
  // folder without relying on it existing at a particular path, or having
  // a particular name, in the data store.
  //
  // This variant of the tag is created by the server, so clients can't create
  // an item with a tag using this field.
  //
  // Use client_defined_unique_tag if you want to create one from the client.
  //
  // An item can't have both a client_defined_unique_tag and
  // a server_defined_unique_tag.
  //
  // Present only in GetUpdatesResponse.
  optional string server_defined_unique_tag = 10;

  // If this group is present, it implies that this SyncEntity corresponds to
  // a bookmark or a bookmark folder.
  //
  // This group is deprecated; clients should use the bookmark EntitySpecifics
  // protocol buffer extension instead.
  optional group BookmarkData = 11 {
    // We use a required field to differentiate between a bookmark and a
    // bookmark folder.
    // Present in both GetUpdatesMessage and CommitMessage.
    required bool bookmark_folder = 12;

    // For bookmark objects, contains the bookmark's URL.
    // Present in both GetUpdatesResponse and CommitMessage.
    optional string bookmark_url = 13;

    // For bookmark objects, contains the bookmark's favicon. The favicon is
    // represented as a 16X16 PNG image.
    // Present in both GetUpdatesResponse and CommitMessage.
    optional bytes bookmark_favicon = 14;
  }

  // Supplies a numeric position for this item, relative to other items with
  // the same parent.
  //
  // Present in both GetUpdatesResponse and CommitMessage.
  //
  // In a CommitMessage context, server implementations may choose whether
  // to compute a position based on this field or based on
  // |insert_after_item_id|.  Clients should set both values so that they
  // result in a consistent ordering regardless of which choice the server
  // makes.
  optional int64 position_in_parent = 15;


  // Contains the ID of the element (under the same parent) after which this
  // element resides. An empty string indicates that the element is the first
  // element in the parent.  This value is used during commits to specify
  // a relative position for a position change.  In the context of
  // a GetUpdatesMessage, |position_in_parent| is used instead to
  // communicate position.
  //
  // Present only in CommitMessage.
  //
  // This is being deprecated: clients should now explicitly set
  // an absolute |position_in_parent| value at commit time.  In the
  // interim, clients should supply both values and continue to honor
  // the |position_in_parent| value returned in the CommitResponse.
  optional string insert_after_item_id = 16;

  // Arbitrary key/value pairs associated with this item.
  // Present in both GetUpdatesResponse and CommitMessage.
  // Deprecated.
  // optional ExtendedAttributes extended_attributes = 17;

  // If true, indicates that this item has been (or should be) deleted.
  // Present in both GetUpdatesResponse and CommitMessage.
  optional bool deleted = 18 [default = false];

  // A GUID that identifies the the sync client who initially committed
  // this entity.  This value corresponds to |cache_guid| in CommitMessage.
  // This field, along with |originator_client_item_id|, can be used to
  // reunite the original with its official committed version in the case
  // where a client does not receive or process the commit response for
  // some reason.
  // Present only in GetUpdatesResponse.
  optional string originator_cache_guid = 19;

  // The local item id of this entry from the client that initially
  // committed this entity. Typically a negative integer.
  // Present only in GetUpdatesResponse.
  optional string originator_client_item_id = 20;

  // Extensible container for datatype-specific data.
  // This became available in version 23 of the protocol.
  optional EntitySpecifics specifics = 21;

  // Indicate whether this is a folder or not. Available in version 23+.
  optional bool folder = 22 [default = false];

  // A client defined unique hash for this entity.
  // Similar to server_defined_unique_tag.
  //
  // When initially committing an entity, a client can request that the entity
  // is unique per that account. To do so, the client should specify a
  // client_defined_unique_tag. At most one entity per tag value may exist.
  // per account. The server will enforce uniqueness on this tag
  // and fail attempts to create duplicates of this tag.
  // Will be returned in any updates for this entity.
  //
  // The difference between server_defined_unique_tag and
  // client_defined_unique_tag is the creator of the entity. Server defined
  // tags are entities created by the server at account creation,
  // while client defined tags are entities created by the client at any time.
  //
  // During GetUpdates, a sync entity update will come back with ONE of:
  // a) Originator and cache id - If client committed the item as non "unique"
  // b) Server tag - If server committed the item as unique
  // c) Client tag - If client committed the item as unique
  //
  // May be present in CommitMessages for the initial creation of an entity.
  // If present in Commit updates for the entity, it will be ignored.
  //
  // Available in version 24+.
  //
  // May be returned in GetUpdatesMessage and sent up in CommitMessage.
  //
  optional string client_defined_unique_tag = 23;
};

// This message contains diagnostic information used to correlate
// commit-related traffic with extensions-related mutations to the
// data models in chromium.  It plays no functional role in
// processing this CommitMessage.
message ChromiumExtensionsActivity {
  // The human-readable ID identifying the extension responsible
  // for the traffic reported in this ChromiumExtensionsActivity.
  optional string extension_id = 1;

  // How many times the extension successfully invoked a write
  // operation through the bookmarks API since the last CommitMessage.
  optional uint32 bookmark_writes_since_last_commit = 2;
};

message CommitMessage {
  repeated SyncEntity entries = 1;

  // A GUID that identifies the committing sync client.  This value will be
  // returned as originator_cache_guid for any new items.
  optional string cache_guid = 2;

  repeated ChromiumExtensionsActivity extensions_activity = 3;
};

message GetUpdatesCallerInfo {
  enum GetUpdatesSource {
    UNKNOWN = 0;  // The source was not set by the caller.
    FIRST_UPDATE = 1;  // First request after browser restart.  Not to
                       // be confused with "NEW_CLIENT".
    LOCAL = 2;  // The source of the update was a local change.
    NOTIFICATION = 3;  // The source of the update was a p2p notification.
    PERIODIC = 4;  // The source of the update was periodic polling.
    SYNC_CYCLE_CONTINUATION = 5;  // The source of the update was a
                                  // continuation of a previous update.
    CLEAR_PRIVATE_DATA = 6;       // Source is a call to remove all private data
    NEWLY_SUPPORTED_DATATYPE = 7;   // The client is in configuration mode
                                    // because it's syncing all datatypes, and
                                    // support for a new datatype was recently
                                    // released via a software auto-update.
    MIGRATION = 8;         // The client is in configuration mode because a
                           // MIGRATION_DONE error previously returned by the
                           // server necessitated resynchronization.
    NEW_CLIENT = 9;        // The client is in configuration mode because the
                           // user enabled sync for the first time.  Not to be
                           // confused with FIRST_UPDATE.
    RECONFIGURATION = 10;  // The client is in configuration mode because the
                           // user opted to sync a different set of datatypes.
  }

  required GetUpdatesSource source = 1;

  // True only if notifications were enabled for this GetUpdateMessage.
  optional bool notifications_enabled = 2;
};

message DataTypeProgressMarker {
  // An integer identifying the data type whose progress is tracked by this
  // marker.  The legitimate values of this field correspond to the protobuf
  // field numbers of all EntitySpecifics extensions supported by the server.
  // These values are externally declared in per-datatype .proto files.
  optional int32 data_type_id = 1;

  // An opaque-to-the-client sequence of bytes that the server may interpret
  // as an indicator of the client's knowledge state.  If this is empty or
  // omitted by the client, it indicates that the client is initiating a
  // a first-time sync of this datatype.  Otherwise, clients must supply a
  // value previously returned by the server in an earlier GetUpdatesResponse.
  // These values are not comparable or generable on the client.
  //
  // The opaque semantics of this field are to afford server implementations
  // some flexibility in implementing progress tracking.  For instance,
  // a server implementation built on top of a distributed storage service --
  // or multiple heterogenous such services -- might need to supply a vector
  // of totally ordered monotonic update timestamps, rather than a single
  // monotonically increasing value.  Other optimizations may also be
  // possible if the server is allowed to embed arbitrary information in
  // the progress token.
  //
  // Server implementations should keep the size of these tokens relatively
  // small, on the order of tens of bytes, and they should remain small
  // regardless of the number of items synchronized.  (A possible bad server
  // implementation would be for progress_token to contain a list of all the
  // items ever sent to the client.  Servers shouldn't do this.)
  optional bytes token = 2;

  // Clients that previously downloaded updates synced using the timestamp based
  // progress tracking mechanism, but which wish to switch over to the opaque
  // token mechanism can set this field in a GetUpdatesMessage.  The server
  // will perform a get updates operation as normal from the indicated
  // timestamp, and return only an opaque progress token.
  optional int64 timestamp_token_for_migration = 3;

  // An opaque-to-the-client string of bytes, received through a notification,
  // that the server may interpret as a hint about the location of the latest
  // version of the data for this type.
  optional string notification_hint = 4;
}

message GetUpdatesMessage {
  // Indicates the client's current progress in downloading updates.  A
  // from_timestamp value of zero means that the client is requesting a first-
  // time sync.  After that point, clients should fill in this value with the
  // value returned in the last-seen GetUpdatesResponse.new_timestamp.
  //
  // from_timestamp has been deprecated; clients should use
  // |from_progress_marker| instead, which allows more flexibility.
  optional int64 from_timestamp = 1;

  // Indicates the reason for the GetUpdatesMessage.
  optional GetUpdatesCallerInfo caller_info = 2;

  // Indicates whether related folders should be fetched.
  optional bool fetch_folders = 3 [default = true];

  // The presence of an individual EntitySpecifics extension indicates that the
  // client requests sync object types associated with that extension.  This
  // determination depends only on the presence of the extension field, not its
  // contents -- thus clients should send empty extension messages.  For
  // backwards compatibility only bookmark objects will be sent to the client
  // should requested_types not be present.
  //
  // requested_types may contain multiple EntitySpecifics extensions -- in this
  // event, the server will return items of all the indicated types.
  //
  // requested_types has been deprecated; clients should use
  // |from_progress_marker| instead, which allows more flexibility.
  optional EntitySpecifics requested_types = 4;

  // Client-requested limit on the maximum number of updates to return at once.
  // The server may opt to return fewer updates than this amount, but it should
  // not return more.
  optional int32 batch_size = 5;

  // Per-datatype progress marker.  If present, the server will ignore
  // the values of requested_types and from_timestamp, using this instead.
  repeated DataTypeProgressMarker from_progress_marker = 6;

  // Indicates whether the response should be sent in chunks.  This may be
  // needed for devices with limited memory resources.  If true, the response
  // will include one or more ClientToServerResponses, with the frist one
  // containing GetUpdatesMetadataResponse, and the remaining ones, if any,
  // containing GetUpdatesStreamingResponse.  These ClientToServerResponses are
  // delimited by a length prefix, which is encoded as a varint.
  optional bool streaming = 7 [default = false];

  // Whether to request the syncable_bookmarks permanent item.
  optional bool include_syncable_bookmarks = 1000 [default = false];
};

message AuthenticateMessage {
  required string auth_token = 1;
};

// This message is sent to the server to clear data.  An asynchronous
// response is returned to the client indicating that the server has received
// the request and has begun to clear data.
message ClearUserDataMessage {
}

message ClearUserDataResponse {
}

message ClientToServerMessage {
  required string share = 1;
  optional int32 protocol_version = 2 [default = 30];
  enum Contents {
    COMMIT = 1;
    GET_UPDATES = 2;
    AUTHENTICATE = 3;
    CLEAR_DATA = 4;
  }

  required Contents message_contents = 3;
  optional CommitMessage commit = 4;
  optional GetUpdatesMessage get_updates = 5;
  optional AuthenticateMessage authenticate = 6;
  // Request to clear all Chromium data from the server
  optional ClearUserDataMessage clear_user_data = 9;

  optional string store_birthday = 7; // Opaque store ID; if it changes, duck!
  // The client sets this if it detects a sync issue. The server will tell it
  // if it should perform a refresh.
  optional bool sync_problem_detected = 8 [default = false];

  // Client side state information for debugging purpose.
  // This is only sent on the first getupdates of every sync cycle,
  // as an optimization to save bandwidth.
  optional DebugInfo debug_info = 10;
};

message CommitResponse {
  enum ResponseType {
    SUCCESS = 1;
    CONFLICT = 2; // You're out of date; update and check your data
    // TODO(ncarter): What's the difference between RETRY and TRANSIENT_ERROR?
    RETRY = 3; // Someone has a conflicting, non-expired session open
    INVALID_MESSAGE = 4; // What the client sent was invalid, and trying again
                         // won't help.
    OVER_QUOTA = 5; // This operation would put you, or you are, over quota
    TRANSIENT_ERROR = 6; // Something went wrong; try again in a bit
  }
  repeated group EntryResponse = 1 {
    required ResponseType response_type = 2;

    // Sync servers may also return a new ID for an existing item, indicating
    // a new entry's been created to hold the data the client's sending up.
    optional string id_string = 3;

    // should be filled if our parent was assigned a new ID.
    optional string parent_id_string = 4;

    // This value is the same as the position_in_parent value returned within
    // the SyncEntity message in GetUpdatesResponse.
    optional int64 position_in_parent = 5;

    // The item's current version.
    optional int64 version = 6;

    // Allows the server to move-aside an entry as it's being committed.
    // This name is the same as the name field returned within the SyncEntity
    // message in GetUpdatesResponse.
    optional string name = 7;

    // This name is the same as the non_unique_name field returned within the
    // SyncEntity message in GetUpdatesResponse.
    optional string non_unique_name = 8;

    optional string error_message = 9;

  }
};

message GetUpdatesResponse {
  // New sync entries that the client should apply.
  repeated SyncEntity entries = 1;

  // If there are more changes on the server that weren't processed during this
  // GetUpdates request, the client should send another GetUpdates request and
  // use new_timestamp as the from_timestamp value within GetUpdatesMessage.
  //
  // This field has been deprecated and will be returned only to clients
  // that set the also-deprecated |from_timestamp| field in the update request.
  // Clients should use |from_progress_marker| and |new_progress_marker|
  // instead.
  optional int64 new_timestamp = 2;

  // DEPRECATED FIELD - server does not set this anymore.
  optional int64 deprecated_newest_timestamp = 3;

  // Approximate count of changes remaining - use this for UI feedback.
  // If present and zero, this estimate is firm: the server has no changes
  // after the current batch.
  optional int64 changes_remaining = 4;

  // Opaque, per-datatype timestamp-like tokens.  A client should use this
  // field in lieu of new_timestamp, which is deprecated in newer versions
  // of the protocol.  Clients should retain and persist the values returned
  // in this field, and present them back to the server to indicate the
  // starting point for future update requests.
  //
  // This will be sent only if the client provided |from_progress_marker|
  // in the update request.
  //
  // The server may provide a new progress marker even if this is the end of
  // the batch, or if there were no new updates on the server; and the client
  // must save these.  If the server does not provide a |new_progress_marker|
  // value for a particular datatype, when the request provided a
  // |from_progress_marker| value for that datatype, the client should
  // interpret this to mean "no change from the previous state" and retain its
  // previous progress-marker value for that datatype.
  //
  // Progress markers in the context of a response will never have the
  // |timestamp_token_for_migration| field set.
  repeated DataTypeProgressMarker new_progress_marker = 5;
};

// The metadata response for GetUpdatesMessage.  This response is sent when
// streaming is set to true in the request.  It is prefixed with a length
// delimiter, which is encoded in varint.
message GetUpdatesMetadataResponse {
  // Approximate count of changes remaining.  Detailed comment is available in
  // GetUpdatesResponse.
  optional int64 changes_remaining = 1;

  // Opaque, per-datatype timestamp-like tokens.  Detailed comment is available
  // in GetUpdatesResponse.
  repeated DataTypeProgressMarker new_progress_marker = 2;
};

// The streaming response message for GetUpdatesMessage.  This message is sent
// when streaming is set to true in the request.  There may be multiple
// GetUpdatesStreamingResponse messages in a response.  This type of messages
// is preceded by GetUpdatesMetadataResponse.  It is prefixed with a length
// delimiter, which is encoded in varint.
message GetUpdatesStreamingResponse {
  // New sync entries that the client should apply.
  repeated SyncEntity entries = 1;
};

// A user-identifying struct.  For a given Google account the email and display
// name can change, but obfuscated_id should be constant.
// The obfuscated id is optional because at least one planned use of the proto
// (sharing) does not require it.
message UserIdentification {
  required string email = 1;  // the user's full primary email address.
  optional string display_name = 2;  // the user's display name.
  optional string obfuscated_id = 3;  // an obfuscated, opaque user id.
};

message AuthenticateResponse {
  // Optional only for backward compatibility.
  optional UserIdentification user = 1;
};

message ThrottleParameters {
  // Deprecated. Remove this from the server side.
  required int32 min_measure_payload_size = 1;
  required double target_utilization = 2;
  required double measure_interval_max = 3;
  required double measure_interval_min = 4;
  required double observation_window = 5;
};

// A command from the server instructing the client to update settings or
// perform some operation.
message ClientCommand {
  // Time to wait before sending any requests to the server.
  optional int32 set_sync_poll_interval = 1;  // in seconds
  optional int32 set_sync_long_poll_interval = 2;  // in seconds

  optional int32 max_commit_batch_size = 3;

  // Number of seconds to delay between a sessions
  // action and sending a commit message to the
  // server
  optional int32 sessions_commit_delay_seconds = 4;

  // Number of seconds to delay before the throttled client should retry.
  optional int32 throttle_delay_seconds = 5;
};

message ClientToServerResponse {
  optional CommitResponse commit = 1;
  optional GetUpdatesResponse get_updates = 2;
  optional AuthenticateResponse authenticate = 3;
  optional ClearUserDataResponse clear_user_data = 9;
  optional GetUpdatesMetadataResponse stream_metadata = 10;
  // If GetUpdatesStreamingResponse is contained in the ClientToServerResponse,
  // none of the other fields (error_code and etc) will be set.
  optional GetUpdatesStreamingResponse stream_data = 11;

  enum ErrorType {
    SUCCESS            = 0;
    ACCESS_DENIED      = 1;   // Returned when the user doesn't have access to
                              // store (instead of HTTP 401).
    NOT_MY_BIRTHDAY    = 2;   // Returned when the server and client disagree on
                              // the store birthday.
    THROTTLED          = 3;   // Returned when the store has exceeded the
                              // allowed bandwidth utilization.
    AUTH_EXPIRED       = 4;   // Auth token or cookie has expired.
    USER_NOT_ACTIVATED = 5;   // User doesn't have the Chrome bit set on that
                              // Google Account.
    AUTH_INVALID       = 6;   // Auth token or cookie is otherwise invalid.
    CLEAR_PENDING      = 7;   // A clear of the user data is pending (e.g.
                              // initiated by privacy request).  Client should
                              // come back later.
    TRANSIENT_ERROR    = 8;   // A transient error occured (eg. backend
                              // timeout). Client should try again later.
    MIGRATION_DONE     = 9;   // Migration has finished for one or more data
                              // types.  Client should clear the cache for
                              // these data types only and then re-sync with
                              // a server. The migrated datatypes are in the
                              // |migrated_datatype_ids| field.
    UNKNOWN            = 100; // Unknown value. This should never be explicitly
                              // used; it is the default value when an
                              // out-of-date client parses a value it doesn't
                              // recognize.
  }

  message Error {
    optional ErrorType error_type       = 1 [default = UNKNOWN];
    optional string error_description   = 2;
    optional string url                 = 3;
    enum Action {
      UPGRADE_CLIENT              = 0; // Upgrade the client to latest version.
      CLEAR_USER_DATA_AND_RESYNC  = 1; // Clear user data from dashboard and
                                       // setup sync again.
      ENABLE_SYNC_ON_ACCOUNT      = 2; // The administrator needs to enable sync
                                       // on the account.
      STOP_AND_RESTART_SYNC       = 3; // Stop sync and set up sync again.
      DISABLE_SYNC_ON_CLIENT      = 4; // Wipe the client of all sync data and
                                       // stop syncing.
      UNKNOWN_ACTION              = 5; // This is the default.
    }
    optional Action action              = 4 [default = UNKNOWN_ACTION];

    // Currently only meaningful if |error_type| is throttled. If this field
    // is absent then the whole client (all datatypes) is throttled.
    repeated int32 error_data_type_ids = 5;
  }

  optional Error error = 13;

  // Up until protocol_version 24, the default was SUCCESS which made it
  // impossible to add new enum values since older clients would parse any
  // out-of-range value as SUCCESS. Starting with 25, unless explicitly set,
  // the error_code will be UNKNOWN so that clients know when they're
  // out-of-date. Note also that when using protocol_version < 25,
  // TRANSIENT_ERROR is not supported. Instead, the server sends back a HTTP
  // 400 error code. This is deprecated now.
  optional ErrorType error_code = 4 [default = UNKNOWN];
  optional string error_message = 5;

  // Opaque store ID; if it changes, the contents of the client's cache
  // is meaningless to this server.  This happens most typically when
  // you switch from one storage backend instance (say, a test instance)
  // to another (say, the official instance).
  optional string store_birthday = 6;

  optional ClientCommand client_command = 7;
  optional ProfilingData profiling_data = 8;

  // The data types whose storage has been migrated.  Present when the value of
  // error_code is MIGRATION_DONE.
  repeated int32 migrated_data_type_id = 12;
};