404-solution / includes / ajax / ResponseCompressionSuppression.php

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

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1	<?php
2
3	if (!defined('ABSPATH')) {
4	exit;
5	}
6
7	/**
8	* Ask this response's transport not to compress or transform it, and report
9	* whether each request actually took effect.
10	*
11	* Two mechanisms, because two different parties compress. `Cache-Control:
12	* no-transform` asks an intermediary (LiteSpeed, Cloudflare, a caching reverse
13	* proxy) to leave the bytes alone; `zlib.output_compression` is PHP's own
14	* output handler. Suppressing one and not the other still yields a compressed
15	* response, so the two outcomes are reported separately and `applied` is the
16	* conjunction.
17	*
18	* BOTH are refusable at runtime, and neither refusal raises anything a caller
19	* would notice:
20	*
21	* - Once any byte of output has been emitted, headers_sent() is true, the
22	* header cannot be set, and ini_set() returns false for this directive with
23	* "Cannot change zlib.output_compression - headers already sent".
24	* - A host with ini_set in disable_functions refuses the second half outright
25	* (see ABJ_404_Solution_PhpRuntimeCapabilityAdapter), which is a live user
26	* environment, not a hypothetical one.
27	*
28	* The outcome is returned rather than discarded because the caller is a
29	* diagnostic instrument. A canary rung that suppressed nothing but reports
30	* itself as the suppressed rung does not merely lose a probe: it turns the
31	* ladder's central comparison -- adjacent rungs differing by exactly one
32	* variable -- into a comparison of a step against itself, while every consumer
33	* still reads it as evidence about compression.
34	*/
35	final class ABJ_404_Solution_ResponseCompressionSuppression {
36
37	/**
38	* Request suppression from both parties and report what each one did.
39	*
40	* @return array{noTransformHeader: bool, zlibOutputCompression: bool, applied: bool}
41	* `noTransformHeader`: the no-transform header was set on this response.
42	* `zlibOutputCompression`: PHP's output compression is now off (a
43	* directive that was already off still counts -- the state is what the
44	* probe depends on, not whether this call changed it).
45	* `applied`: both, so the response is genuinely unsuppressed-by-nobody.
46	*/
47	public static function apply(): array {
48	$noTransformHeader = false;
49	if (!headers_sent()) {
50	header('Cache-Control: no-transform');
51	$noTransformHeader = true;
52	}
53	// setIni() returns the PREVIOUS value on success and false on refusal,
54	// so `!== false` is the test: an empty-string previous value means the
55	// directive was already off, which is success, while a loose truthy
56	// check would read it as failure.
57	$zlibDisabled = ABJ_404_Solution_PhpRuntimeCapabilityAdapter::setIni(
58	array('directive' => 'zlib.output_compression', 'value' => '0')) !== false;
59
60	return array(
61	'noTransformHeader' => $noTransformHeader,
62	'zlibOutputCompression' => $zlibDisabled,
63	'applied' => $noTransformHeader && $zlibDisabled,
64	);
65	}
66	}
67