1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 // 5 // Protobuf representation of the UniquePosition class. 6 7 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change 8 // any fields in this file. 9 10 syntax = "proto2"; 11 12 option optimize_for = LITE_RUNTIME; 13 option retain_unknown_fields = true; 14 15 package sync_pb; 16 17 // A UniquePosition is a string of bytes. 18 // 19 // Unique positions are unique per-item, since they are guaranteed to end with a 20 // fixed-length suffix that is unique per-item. The position string may not end 21 // with a '\0' byte. 22 // 23 // Prior to the suffix is a series of arbitrary bytes of arbitrary length. 24 // Items under the same parent are positioned relative to each other by a 25 // lexicographic comparison of their UniquePosition values. 26 message UniquePosition { 27 // The uncompressed string of bytes representing the position. 28 optional bytes value = 1; 29 30 // The client may choose to write a compressed position to this field instead 31 // of populating the 'value' above. If it chooses to use compression, the 32 // 'value' field above must be empty. The position value will be compressed 33 // with gzip and stored in the compressed_value field. The position's 34 // uncompressed length must be specified and written to the 35 // uncompressed_length field. 36 optional bytes compressed_value = 2; 37 optional uint64 uncompressed_length = 3; 38 39 // This encoding uses compression scheme designed especially for unique 40 // positions. It has the property that X < Y precisely when Compressed(X) < 41 // Compressed(Y), which is very useful when the most common operation is to 42 // compare these positions against each other. Their values may remain 43 // compressed in memory. 44 // 45 // The compression scheme is implemented and documented in 46 // sync/internal_api/base/unique_position.cc. 47 // 48 // As of M30, this is the preferred encoding. Newer clients may continue to 49 // populate the 'value' and 'compressed_value' fields to ensure backwards 50 // compatibility, but they will always try to read from this field first. 51 optional bytes custom_compressed_v1 = 4; 52 } 53
