(dev/core#174) civicrm_cache - Allow storage of binary data

[totten]

Overview

In working on a PSR-16 provider based on the civicrm_cache table, the compliance test suite revealed that civicrm_cache.data was unable to store binary information. The cache is more useful if it can store binary data...

Before

• civicrm_cache.data is a MySQL longtext column storing the output of serialize($data).

After

• civicrm_cache.data is a MySQL longtext column storing the output of base64_encode(serialize($data)) (or, if you've just upgraded, possibly serialize($data)).

Technical Details

• The serialize format is not designed for transmission over strictly textual media. It's meant to differentiate among PHP data-types(eg array vs string vs int). If a string has binary content, then it's still binary content.
• The output of serialize() and base64_encode() are quite distinctive. Serialize makes heavy use of punctuation (;:{}), whereas base64 is dense alphanumeric (a-zA-Z0-9+/). We use this to pre-emptively deal with any weird edge-cases mixing new logic with old content (e.g. reading cached data in the old format in a pre-upgrade environment).
• This replaces (dev/core#174) civicrm_cache - Allow storage of binary data #12350. In testing some other work on top of (dev/core#174) civicrm_cache - Allow storage of binary data #12350, I encountered some character-set issues with using the binary column.

[civibot]

(Standard links)

• If this is your first pull-request for CiviCRM, please browse CONTRIBUTING.md for information about the development and testing processes.
• If you are reviewing this pull-request, you may wish to consult the test sites and the Review Standards (long template, short template).