{"id":28005,"date":"2017-09-13T11:39:32","date_gmt":"2017-09-13T09:39:32","guid":{"rendered":"https:\/\/mamchenkov.net\/wordpress\/?p=28005"},"modified":"2017-09-13T12:12:53","modified_gmt":"2017-09-13T10:12:53","slug":"php-limit-on-maximum-form-fields","status":"publish","type":"post","link":"https:\/\/mamchenkov.net\/wordpress\/2017\/09\/13\/php-limit-on-maximum-form-fields\/","title":{"rendered":"PHP limit on maximum form fields"},"content":{"rendered":"\n

We had an interesting issue to debug at work today.\u00a0 One of the screens in our application features a form with a whole lot of checkboxes.\u00a0 It’s in the access control module, where the administrator of the system can manage user permissions for each module of the system.\u00a0 Here’s the screenshot just to give you an idea.<\/p>\n

\"\"<\/a><\/p>\n

This is not the pretties user interface (yet), but it sort of works.\u00a0 Every module can be expanded or collapsed, and inside each modules all checkboxes can be checked and unchecked easily.<\/p>\n

The problem that we had wasn’t user interface related.\u00a0 It was something else.\u00a0 The number of modules and permission checkboxes varies from system to system.\u00a0 This is based on each particular system setup.\u00a0 Now, on some of these systems, it was reported that some permissions are not being saved.<\/p>\n

The problem is not new, but it was slowly escalating with more and more clients reporting it.\u00a0 So, today we dived into it and found the cause of it.\u00a0 \u00a0Since PHP 5.3.9 there is a new runtime configuration setting: max_input_vars<\/a>, with default value of 1.000:<\/p>\n

max_input_vars<\/code>integer<\/a><\/span><\/p>\n

How many\u00a0input variables<\/a>\u00a0may be accepted (limit is applied to $_GET, $_POST and $_COOKIE superglobal separately). Use of this directive mitigates the possibility of denial of service attacks which use hash collisions. If there are more input variables than specified by this directive, an\u00a0E_WARNING<\/code><\/strong>\u00a0is issued, and further input variables are truncated from the request.<\/p>\n<\/blockquote>\n

So, on the systems, where the form contains more than a thousand checkboxes, PHP was only bringing in the first thousand and skipping the rest, causing not all permissions being saved properly.<\/p>\n

Increasing the value in runtime configuration is one way to solve it.\u00a0 But since we have a rather dynamic system and don’t always control the runtime configuration (client hosting), we opted for a different solution.\u00a0 As per this StackOverflow thread<\/a>, it’s a much more future-proof solution to combine the values into a single field.\u00a0 Either simple concatenate, or JSON-encode the values on form submit, and send them all as a single field value.\u00a0 Then just split or JSON-decode on the server before processing and you are done.<\/p>\n

P.S.: The extra bit that made the troubleshooting so much more difficult was that for some reason we were not seeing the PHP warning in logs.<\/p>\n

 <\/p>\n\n","protected":false},"excerpt":{"rendered":"\n

We had an interesting issue to debug at work today.\u00a0 One of the screens in our application features a form with a whole lot of checkboxes.\u00a0 It’s in the access control module, where the administrator of the system can manage user permissions for each module of the system.\u00a0 Here’s the screenshot just to give you … Continue reading PHP limit on maximum form fields<\/span><\/a><\/p>\n\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"PHP limit on maximum form fields #WebDev #PHP","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false,"_links_to":"","_links_to_target":""},"categories":[1,18,62,1334],"tags":[38,1330],"keyring_services":[],"class_list":["post-28005","post","type-post","status-publish","format-standard","hentry","category-general","category-programming","category-technology","category-web-work","tag-php","tag-web-development"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t