404-solution / includes / database / TableReadinessGate.php

TableReadinessGate.php in 404 Solution trunk, at includes/database/TableReadinessGate.php

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1	<?php
2
3	if (!defined('ABSPATH')) {
4	exit;
5	}
6
7	require_once __DIR__ . '/DatabaseTableNameResolver.php';
8
9	/**
10	* Decides whether a read may be skipped because its table is definitely absent.
11	*
12	* A fresh install genuinely does not have the plugin's tables until the upgrade
13	* runs, so callers that would otherwise aggregate over them ask here first.
14	* The whole point of this class is the distinction the underlying probe makes
15	* and a boolean cannot: SHOW TABLES LIKE returns nothing both when the engine
16	* looked and found nothing AND when the query never ran at all -- a lost
17	* connection, a revoked SHOW grant, a driver that does not speak the statement.
18	*
19	* Only an engine that ANSWERED "no such table" earns a suppressed read. A probe
20	* that could not be answered reports NOT absent, so the caller goes ahead: if
21	* the table really is gone that costs one error the centralized handler already
22	* knows how to log, repair and retry, which is strictly better than a confident
23	* wrong answer produced by a query nobody ran and therefore nobody logged.
24	*
25	* Keeping that policy here rather than in each caller is what makes the wrong
26	* reading unavailable: the tri-state constants stay an implementation detail,
27	* and a caller can only ask the question whose answer is safe to act on.
28	*
29	* A table observed PRESENT is remembered for the life of this instance, keyed
30	* by its fully-resolved name so a multisite blog switch cannot reuse another
31	* blog's answer. Any other outcome is deliberately re-probed, so an in-request
32	* repair can make later reads available without rebuilding the service graph.
33	*
34	* This is a schema-metadata collaborator: it issues one metadata probe and
35	* holds no business or presentation logic.
36	*/
37	class ABJ_404_Solution_TableReadinessGate {
38
39	/** @var ABJ_404_Solution_DatabaseQueryInterface */
40	private $dbCore;
41
42	/** @var ABJ_404_Solution_DatabaseTableNameResolver */
43	private $tableNameResolver;
44
45	/** @var array<string, bool> Resolved table name => observed present. */
46	private $observedPresent = array();
47
48	/**
49	* @param ABJ_404_Solution_DatabaseQueryInterface $dbCore Supplies table-name replacement.
50	* @param ABJ_404_Solution_DatabaseTableNameResolver $tableNameResolver Runs the probe.
51	*/
52	public function __construct(
53	ABJ_404_Solution_DatabaseQueryInterface $dbCore,
54	ABJ_404_Solution_DatabaseTableNameResolver $tableNameResolver
55	) {
56	$this->dbCore = $dbCore;
57	$this->tableNameResolver = $tableNameResolver;
58	}
59
60	/**
61	* Whether the engine positively reported this table as not existing.
62	*
63	* Asked in the negative on purpose, so that the answer a caller acts on is
64	* the only one that is safe to act on. False means "not known to be
65	* absent", which covers both a table that is there and a probe that could
66	* not be answered -- in both cases the caller should do its work.
67	*
68	* @param string $tableToken Unresolved token, e.g. '{wp_abj404_redirects}'.
69	*/
70	public function isKnownAbsent(string $tableToken): bool {
71	$table = $this->dbCore->doTableNameReplacements($tableToken);
72	if (!empty($this->observedPresent[$table])) {
73	return false;
74	}
75
76	$status = $this->tableNameResolver->tableExistenceStatus($table);
77	if ($status === ABJ_404_Solution_DatabaseTableNameResolver::TABLE_PRESENT) {
78	$this->observedPresent[$table] = true;
79	return false;
80	}
81
82	return $status === ABJ_404_Solution_DatabaseTableNameResolver::TABLE_ABSENT;
83	}
84	}
85