| // 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. |
| // |
| // Protobuf representation of the UniquePosition class. |
| |
| // 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; |
| |
| // A UniquePosition is a string of bytes. |
| // |
| // Unique positions are unique per-item, since they are guaranteed to end with a |
| // fixed-length suffix that is unique per-item. The position string may not end |
| // with a '\0' byte. |
| // |
| // Prior to the suffix is a series of arbitrary bytes of arbitrary length. |
| // Items under the same parent are positioned relative to each other by a |
| // lexicographic comparison of their UniquePosition values. |
| message UniquePosition { |
| // The uncompressed string of bytes representing the position. |
| optional bytes value = 1; |
| |
| // The client may choose to write a compressed position to this field instead |
| // of populating the 'value' above. If it chooses to use compression, the |
| // 'value' field above must be empty. The position value will be compressed |
| // with gzip and stored in the compressed_value field. The position's |
| // uncompressed length must be specified and written to the |
| // uncompressed_length field. |
| optional bytes compressed_value = 2; |
| optional uint64 uncompressed_length = 3; |
| |
| // This encoding uses compression scheme designed especially for unique |
| // positions. It has the property that X < Y precisely when Compressed(X) < |
| // Compressed(Y), which is very useful when the most common operation is to |
| // compare these positions against each other. Their values may remain |
| // compressed in memory. |
| // |
| // The compression scheme is implemented and documented in |
| // sync/internal_api/base/unique_position.cc. |
| // |
| // As of M30, this is the preferred encoding. Newer clients may continue to |
| // populate the 'value' and 'compressed_value' fields to ensure backwards |
| // compatibility, but they will always try to read from this field first. |
| optional bytes custom_compressed_v1 = 4; |
| } |