This commit removes the Go html2text lib that would automatically
convert all HTML messages to plaintext and add them as the alt
text body to outgoing e-mails. This lib also had memory leak
issues with certain kinds of HTML templates.
A new UI field for optionally adding an alt plaintext body to
a campaign is added. On enabling, it converts the HTML message in
the campaign editor into plaintext (using the textversionjs lib).
This introduces breaking changes in the campaigns table schema,
model, and template compilation.
This is a major feature that builds upon the `Messenger` interface
that has been in listmonk since its inception (with SMTP as the only
messenger). This commit introduces a new Messenger implementation, an
HTTP "postback", that can post campaign messages as a standard JSON
payload to arbitrary HTTP servers. These servers can in turn push them
to FCM, SMS, or any or any such upstream, enabling listmonk to be a
generic campaign messenger for any type of communication, not just
e-mails.
Postback HTTP endpoints can be defined in settings and they can be
selected on campaigns.
- Added as a setting in the settings UI.
- Refactor Messenger.Push() method to accept messenger.Message{}
instead of a growing number of positional arguments.
This is a major breaking change that moves away from having the
entire app configuration in external TOML files to settings being
in the database with a UI to update them dynamically.
The app loads all config into memory (app settings, SMTP conf)
on boot. "Hot" replacing them is complex and it's a fair tradeoff
to instead just restart the application as it is practically
instant.
A new `settings` table stores arbitrary string keys with a JSONB
value field which happens to support arbitrary types. After every
settings update, the app gracefully releases all resources
(HTTP server, DB pool, SMTP pool etc.) and restarts itself,
occupying the same PID. If there are any running campaigns, the
auto-restart doesn't happen and the user is prompted to invoke
it manually with a one-click button once all running campaigns
have been paused.
