[Sync] Create new top-level sync/ directory

chrome/browser/sync/protocol/sync.proto

-// Copyright (c) 2012 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 "app_notification_specifics.proto";
-import "app_setting_specifics.proto";
-import "app_specifics.proto";
-import "autofill_specifics.proto";
-import "bookmark_specifics.proto";
-import "extension_setting_specifics.proto";
-import "extension_specifics.proto";
-import "nigori_specifics.proto";
-import "password_specifics.proto";
-import "preference_specifics.proto";
-import "search_engine_specifics.proto";
-import "session_specifics.proto";
-import "theme_specifics.proto";
-import "typed_url_specifics.proto";
-import "encryption.proto";
-import "sync_enums.proto";
-import "client_commands.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, define your message type, and add an optional field
-  // to the list below using the unique tag value you selected.
-  //
-  //  optional 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 fields.  In this
-  // way, it is possible to add new datatype fields without having
-  // to update the server.
-  //
-  // Note: The tag selection process is based on legacy versions of the
-  // protocol which used protobuf extensions. We have kept the process
-  // consistent as the old values cannot change.  The 5+ digit nature of the
-  // tags also makes them recognizable (individually and collectively) from
-  // noise in logs and debugging contexts, and creating a divergent subset of
-  // tags would only make things a bit more confusing.
-
-  optional AutofillSpecifics autofill = 31729;
-  optional BookmarkSpecifics bookmark = 32904;
-  optional PreferenceSpecifics preference = 37702;
-  optional TypedUrlSpecifics typed_url = 40781;
-  optional ThemeSpecifics theme = 41210;
-  optional AppNotification app_notification = 45184;
-  optional PasswordSpecifics password = 45873;
-  optional NigoriSpecifics nigori = 47745;
-  optional ExtensionSpecifics extension = 48119;
-  optional AppSpecifics app = 48364;
-  optional SessionSpecifics session = 50119;
-  optional AutofillProfileSpecifics autofill_profile = 63951;
-  optional SearchEngineSpecifics search_engine = 88610;
-  optional ExtensionSettingSpecifics extension_setting = 96159;
-  optional AppSettingSpecifics app_setting = 103656;
-}
-
-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.
-    DATATYPE_REFRESH = 11;    // A datatype has requested a refresh. This is
-                              // typically used when datatype's have custom
-                              // sync UI, e.g. sessions.
-  }
-
-  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 fields 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 field indicates that the
-  // client requests sync object types associated with that field.  This
-  // determination depends only on the presence of the field, not its
-  // contents -- thus clients should send empty messages as the field value.
-  // For backwards compatibility only bookmark objects will be sent to the
-  // client should requested_types not be present.
-  //
-  // requested_types may contain multiple EntitySpecifics fields -- 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 create the mobile bookmarks folder if it's not
-  // already created.  Should be set to true only by mobile clients.
-  optional bool create_mobile_bookmarks_folder = 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;
-
-    // Last modification time (in java time milliseconds).  Allows the server
-    // to override the client-supplied mtime during a commit operation.
-    optional int64 mtime = 10;
-  }
-};
-
-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;
-};
-
-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;
-
-  message Error {
-    optional SyncEnums.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 SyncEnums.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;
-};
-