mirror of
https://github.com/block/buzz.git
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76 lines
2.5 KiB
Dart
76 lines
2.5 KiB
Dart
import 'dart:convert';
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import 'read_state_format.dart';
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/// Packs frontiers without evicting a key or moving an existing carrier.
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///
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/// [previous] is the durably saved placement, including empty reusable slots.
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/// The caller must persist the returned placement and its slot IDs before any
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/// publication. Override groups and their frontiers belong in [primary].
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/// A capacity error leaves the caller's previous placement untouched.
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List<Map<String, int>> packReadStateContexts(
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Map<String, int> frontiers, {
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required String clientId,
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List<Map<String, int>> previous = const [],
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Map<String, int> primary = const {},
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int maxBytes = readStatePlaintextBytes,
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}) {
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int size(Map<String, int> contexts) => utf8
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.encode(
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jsonEncode(
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ReadStateBlob(clientId: clientId, contexts: contexts).toJson(),
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),
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)
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.length;
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bool fits(Map<String, int> contexts) =>
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contexts.length <= 10000 && size(contexts) <= maxBytes;
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final slots = <Map<String, int>>[
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for (final old in previous)
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{
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for (final key in old.keys)
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if (frontiers.containsKey(key) && !primary.containsKey(key))
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key: frontiers[key]!,
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},
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];
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if (slots.isEmpty) slots.add({});
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slots.first.addAll(primary);
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for (final slot in slots) {
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if (!fits(slot)) {
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throw StateError('Read-state slot exceeds its plaintext budget');
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}
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}
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final assigned = {for (final slot in slots) ...slot.keys};
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final keys = frontiers.keys.where((key) => !assigned.contains(key)).toList()
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..sort();
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final sizes = slots.map(size).toList();
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final emptySize = size({});
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// Account for the exact compact JSON entry and its optional comma without
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// repeatedly serializing every full slot for each incoming key.
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for (final key in keys) {
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final value = frontiers[key]!;
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final bytes = utf8.encode(jsonEncode(key)).length + 1 + '$value'.length;
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var placed = false;
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for (var index = 0; index < slots.length; index++) {
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final slot = slots[index];
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final cost = bytes + (slot.isEmpty ? 0 : 1);
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if (slot.length < 10000 && sizes[index] + cost <= maxBytes) {
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slot[key] = value;
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sizes[index] += cost;
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placed = true;
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break;
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}
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}
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if (!placed) {
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if (emptySize + bytes > maxBytes) {
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throw StateError('Read-state entry exceeds its plaintext budget');
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}
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slots.add({key: value});
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sizes.add(emptySize + bytes);
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}
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}
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return [
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for (final slot in slots)
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{for (final key in slot.keys.toList()..sort()) key: slot[key]!},
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];
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}
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