Installation redirect loop when the php session directory is not writable

[benhaynes]

From directus created by override2k : directus/directus#2169

Version Info

• Directus version and branch (Or commit hash): aba7727
• PHP version: 7.1
• MySQL version: 5.7
• Web server: nginx
• OS name and version: Ubuntu 16.04

Expected Behavior

When the php session directory is not writable by the webserver, will be nice to obtain a warning about that in the installation requeriments step.

Actual Behavior

The installation process enters into a redirect loop that gets aborted by the browser. With this, the user cannot proceed the installation.

Steps to Reproduce

1. Set the php session directory without write permission for the webserver
2. Try to launch directus installation process

Schema Dump, Logs, or Screenshots

The bug is caused as php is unable to save session data, all the previous step progress is lost.

So when the installation reaches step 1 and the function install_can_do() checks if previous steps are pending (install.functions.php:123), the check fails, isPending() is always returning false for step 0, causing the installation program to reditect to step 0 again.

This derives into an infinite loop between step 0 and 1.