Hello Core,
Background: with Redmine-1.2 on Rails-2.3.11 we're experiencing a "500 Internal Server Error" every time a mail with invalid UTF-8 byte sequence is hitting the MailHandler (the exception comes from the DB complaining about invalid string in the INSERT statement.)
Since we do care about internal errors we've installed
exception_notification plugin and this results in mailbox flood for
our Redmine admins, coming from these internal errors. Besides that,
not being able to properly handle invalid input is just a shame. 
Now, most of the time (100% so far, to be honest,) these failing mails are spam, but it would be really nice if we could alleviate the problem by repairing the invalid byte sequences prior to passing params to the application. This far we have short of the options but disabling exceptions_notification, which is not what we'd really like to do.
It is my belief, that trying to fix this in the application realm isn't worth the effort: it has to be a core fix instead.
From what I can see, the problem has been noted in a more recent version of Rails:
https://github.com/rails/rails/blob/3-1-stable/actionpack/lib/action_dispatch/http/parameters.rb#L39
# TODO: Validate that the characters are UTF-8. If they aren't, # you'll get a weird error down the road, but our form handling # should really prevent that from happening def encode_params(params)
That's exactly what happens to us, and since the data isn't coming from a webform we don't enjoy the mentioned form handling.
I'd vote for a fix along the lines of Iconv.conv("#{$KCODE}//IGNORE", $KCODE, ...), but I'm not sure what would be a good place to apply that, more so that 2.3 and 3.x differ greatly in this regard, AFAICT.