404-solution / includes / ajax / CanarySizeTarget.php

CanarySizeTarget.php in 404 Solution trunk, at includes/ajax/CanarySizeTarget.php

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1	<?php
2
3	if (!defined('ABSPATH')) {
4	exit;
5	}
6
7	/**
8	* The byte count the canary size probes calibrate against, and where it came
9	* from.
10	*
11	* Split out of ABJ_404_Solution_AjaxCanaryStepRunner. Every other arm of that
12	* class emits a payload of a known size and times the round trip; this one
13	* emits nothing and times nothing. It answers a question about the SITE --
14	* how big is a real admin-table response here -- by arbitrating between two
15	* independent sources and naming which one answered. That is a policy
16	* decision, not a probe, and it sits beside the sources it arbitrates
17	* (ABJ_404_Solution_EncodedTableResponseSize,
18	* ABJ_404_Solution_MeasuredTableResponseSize) rather than among the probes
19	* that consume its answer.
20	*
21	* It lives in includes/ajax/ rather than includes/diagnostics/ because its
22	* fallback branch BUILDS a table response to measure it. deptrac's Diagnostics
23	* layer may not reach Presentation, and that rule is right: a class that
24	* renders a response has stopped being a recorder. This one genuinely does
25	* that, so it is classified where it belongs instead of being excepted from
26	* the rule. The recorded branch still reads only journal evidence.
27	*
28	* Recorded first, measured second, named either way. The recorded number is
29	* the exact size of the response that actually failed, so it always wins when
30	* it exists -- but it exists only on a site whose durable trace was already
31	* armed when the failure happened, and `debug_mode` is off by default on
32	* purpose (AjaxDiagnosticRequestPolicy::DIAGNOSTIC_TRACE_ACTIONS keeps
33	* `ajaxUpdatePaginationLinks` behind the 4.3.3 performance gate). The ladder
34	* self-arms, which is what gives the ladder its OWN evidence, but nothing can
35	* retroactively arm a request that has already run.
36	*
37	* So on the shipped default there is nothing to recover and the step used to
38	* answer with an absence, leaving the client to calibrate the whole size axis
39	* on a hardcoded default -- support report 2026-08-27 (Azure App Service,
40	* plugin 4.3.4) ran all ten steps and could neither confirm nor rule out size,
41	* because every probe ran at a size unrelated to this site's real response. A
42	* measurement is available on every site, so the absence is now the fallback's
43	* fallback.
44	*
45	* `realResponseRecordedSource` keeps the recorded channel's own answer whatever
46	* happens, so "measured because nothing was recorded" stays distinguishable
47	* from "measured because the trace named no table request" and from "recorded
48	* exactly". A number is never returned without the source that produced it.
49	*/
50	final class ABJ_404_Solution_CanarySizeTarget {
51
52	/**
53	* Resolve the calibration size for one browser session and subpage.
54	*
55	* Keyed rather than positional: a session id and a subpage are both
56	* strings, so positionally a transposed call would query the journal for a
57	* subpage and the table for a session, and return a confidently wrong byte
58	* count with a plausible-looking source beside it. PHP 7.4 is the floor
59	* here, so named arguments are unavailable.
60	*
61	* @param array{subpage: string, session_id: string} $inputs
62	* @param array<string, mixed> $context Mutated in place by the build's stages.
63	* @return array<string, mixed>
64	*/
65	public static function resolve(array $inputs, array &$context): array {
66	$sessionId = $inputs['session_id'];
67	$recorded = ABJ_404_Solution_AjaxStageDiagnostics::runStage($context, 'canary_size_target',
68	static function () use ($sessionId) {
69	return ABJ_404_Solution_EncodedTableResponseSize::forSession($sessionId);
70	});
71	if (is_int($recorded['bytes']) && $recorded['bytes'] > 0) {
72	return array(
73	'realResponseBytes' => $recorded['bytes'],
74	'realResponseBytesSource' => $recorded['source'],
75	'realResponseRequestId' => $recorded['request_id'],
76	'realResponseRecordedSource' => $recorded['source'],
77	);
78	}
79	// Deliberately NOT inside the stage above: the builder opens its own
80	// stage and trace stages are flat, so nesting would only mark
81	// canary_size_target `superseded`. See MeasuredTableResponseSize.
82	$measured = ABJ_404_Solution_MeasuredTableResponseSize::forSubpage($inputs['subpage'], $context);
83	return array(
84	'realResponseBytes' => $measured['bytes'],
85	'realResponseBytesSource' => $measured['source'],
86	// No request id: a measurement is of this site's table, not of any
87	// one request, and borrowing a request id would imply otherwise.
88	'realResponseRequestId' => '',
89	'realResponseRecordedSource' => $recorded['source'],
90	);
91	}
92	}
93