With two concurrent requests, it's possible to create two ballot lines
when only one of them should be created.
The reason is the code validating the line is not thread safe:
```
if ballot.amount_available(investment.heading) < investment.price.to_i
errors.add(:money, "insufficient funds")
end
```
If the second request executes this code after the first request has
executed it but before the first request has saved the record to the
database, both records will pass this validation and both will be saved
to the database.
So we need to introduce a lock. Now when the second request tries to
lock the ballot, it finds it's already locked by the first request, and
will wait for the transaction of the first request to finish before
checking whether there are sufficient funds.
Note we need to disable transactions during the test; otherwise the
second thread will wait for the first one to finish.
Also note that we need to update a couple of tests because records are
reloaded when they're locked.
In one case, reloading the ballot causes `ballot.user` to be `nil`,
since the user is hidden. So we hide the user after creating all its
associated records (which is the scenario that would take place in real
life).
In the other case, reloading the ballot causes `ballot.user` to reload
as well. So we need to reload the user object used in the test too so it
gets the updates done on `ballot.user`.
I haven't been able to reproduce this behavior in a system test. The
following test works with Rails 5.0, but it stopped working when we
moved to system tests in commit 9427f014. After that commit, for reasons
I haven't been able to debug (reintroducing truncation with
DatabaseClaner didn't seem to affect this test, and neither did
increasing the number of threads in Puma), the two AJAX requests
executed here are no longer simultaneous; the second request waits for
the first one to finish.
scenario "Race conditions with simultaneous requests", :js do
allow_any_instance_of(Budget::Ballot::Line).to receive(:check_sufficient_funds) do |object|
allow(object).to receive(:check_sufficient_funds).and_call_original
object.check_sufficient_funds
sleep 0.3
end
["First", "Second"].each do |title|
create(:budget_investment, :selected,
heading: california,
price: california.price,
title: title
)
end
login_as(user)
visit budget_investments_path(budget, heading_id: california.id)
within(".budget-investment", text: "First") { click_link "Vote" }
within(".budget-investment", text: "Second") { click_link "Vote" }
expect(page).to have_link "Remove vote"
expect(Budget::Ballot::Line.count).to eq 1
end
We were very inconsistent regarding these rules.
Personally I prefer no empty lines around blocks, clases, etc... as
recommended by the Ruby style guide [1], and they're the default values
in rubocop, so those are the settings I'm applying.
The exception is the `private` access modifier, since we were leaving
empty lines around it most of the time. That's the default rubocop rule
as well. Personally I don't have a strong preference about this one.
[1] https://rubystyle.guide/#empty-lines-around-bodies
Having exceptions is better than having silent bugs.
There are a few methods I've kept the same way they were.
The `RelatedContentScore#score_with_opposite` method is a bit peculiar:
it creates scores for both itself and the opposite related content,
which means the opposite related content will try to create the same
scores as well.
We've already got a test to check `Budget::Ballot#add_investment` when
creating a line fails ("Edge case voting a non-elegible investment").
Finally, the method `User#send_oauth_confirmation_instructions` doesn't
update the record when the email address isn't already present, leading
to the test "Try to register with the email of an already existing user,
when an unconfirmed email was provided by oauth" fo fail if we raise an
exception for an invalid user. That's because updating a user's email
doesn't update the database automatically, but instead a confirmation
email is sent.
There are also a few false positives for classes which don't have bang
methods (like the GraphQL classes) or destroying attachments.
For these reasons, I'm adding the rule with a "Refactor" severity,
meaning it's a rule we can break if necessary.
We're using `eq` and `match_array` in most places, but there were a few
places where we were still checking each element is included in the
array. This is a bit dangerous, because the array could have duplicate
elements, and we wouldn't detect them with `include`.
