Not all email clients are formatting the `ping.body` contents uniformly. Even using different applications from the same email provider results in a different display of the `ping.body` contents. There are two basic issues:
* Not all email clients are honoring the fixed-width font that should be used inside `<pre>` tags. Using fixed-width font is listed in the definition on https://www.w3schools.com/tags/tag_pre.asp
* Not all email clients are displaying the text with a 1em line height. This was a recent change to the healthchecks WebUI in 9fd9c8e4ef but is not part of the definition of the `<pre>` tag. I'd like to add this to the emails to make Healthchecks more uniform between the website and the email notification.
Gmail Webmail:
- [x] Is using fixed-width font
- [ ] Line height is set by the webmail client to 18px
Gmail Android App:
- [ ] Text is not fixed-width
- [ ] Line height has extra padding
ProtonMail Webmail:
- [x] Is using fixed-width font
- [x] Line height is correct
ProtonMail Android:
- [ ] Text is not fixed width
- [ ] Line height has extra padding
The testing I performed is not extensive, but it does show how multiple clients are displaying the contents differently. To make the display of the `ping.body` more uniform I'd like to add a bit of formatting information to the `<pre>` tag.
Problem: if you use uBlock Origin, and enable the
"Fanboy's Social" filter list, Healthchecks does not show
Telegram or WhatsApp icons. This is because the filter list
contains "##.icon-telegram" and "##.icon-whatsapp" entries.
This commit changes the CSS class prefix to "ic-". So we're
now using icon classes like "ic-telegram" and "ic-whatsapp".
As a bonus, we save 2 bytes in HTML per displayed icon :-)
Previously, I had changed the default value to "", to force
users to set the SECRET_KEY value (the app refuses to start
if SECRET_KEY is empty).
The problem with that is, out of the box, with the default
configuration, the tests also don't run and complain about the
empty SECRET_KEY.
So, a compromise: revert back to the default value "---".
At runtime, if SECRET_KEY has the default value, show a warning
at the top of every page.
