Fix bug with long stream identifiers when using Postgres adapter

[palkan]

Fixes #28751.

PostgreSQL has a limit on identifiers length (63 chars, docs).

Provided fix minifies identifiers longer than 63 chars by hashing them with SHA1.
Although it has an impact on performance, I think, it's negligible.

It would be great to use non-cryptographic hash functions (such as Murmur or CityHash), but that would require adding new dependencies.

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[matthewd]

I'm fine with SHA1 -- it shouldn't be user-controlled data, so I see no risk of collision. And it's used for network communication, so the extra time spent hashing should indeed be negligible.

It does seem a bit unfortunate to leave it totally opaque, though... is it worth keeping the first 22 characters?

[matthewd]

👎

[palkan]

Could you, please, clarify?

That's an easiest way to handle blocking queue.pop calls in these tests (which cause a process to stuck forever).

Of course, it would be better to refactor the tests to not use blocking calls though.

Another idea is to "enhance" Queue#pop with built-in timeout through refinements:

refine Queue do
  def pop(timeout)
    while empty?
      sleep 0.1
      timeout -= 0.1
      return nil unless timeout > 0
    end
    super
  end
end

Or we can add custom queue class.

But either way, I think, we should be able to make tests fail (which is impossible now).

[matthewd]

❓

[palkan]

As I understand, we want to use the same DB configuration as in ActiveRecord tests (that's why we're using ARTest).

ARTest.config["arunit"] is always nil, 'cause databases config has nested structure (connections -> adapter -> id).

I'm using custom PostgreSQL credentials in config.yml, and it turned out that there is a bug here.

[palkan]

It can be extracted into a separate PR, 'cause it does nothing with the bug under consideration.

[palkan]

is it worth keeping the first 22 characters?

Keeping in mind that we're working with long GlobalIDs, I'm not sure that would help, 'cause in that case the prefix would contain only a part of a namespace, e.g. "gid://app/MySuperModule/SubModule/Person/5" => "gid://app/MySuperModul".

[palkan]

@matthewd Codebase was cleaned up. Anything else I can do to get it merged?

[matthewd]

Sorry I didn't reply on this earlier.

Beyond general concern about Timeout, allocating a single WAIT_WHEN_EXPECTING_EVENT to an arbitrarily-long block of code (which could, itself, contain one or more waits) doesn't really honour the implied contract. Tests failing when things are broken is certainly a good thing, though, so finding some way to make that true seems like a good idea. I think I'd still be hesitant for any "set up a subscription" helper to apply a surprise time limit on its contained block, though.

As for the ARTest thing -- yeah, I just couldn't work out why that was necessary for this change. If it's Just Wrong, we should definitely fix that. 🙈

[eric1234]

If someone needs this backported to a released version of Rails the following will work:

# Backport of https://github.com/rails/rails/commit/2bce7777b70efe81f45e4ae8dc61b25f1e18771e
require 'action_cable/subscription_adapter/postgresql'

module PostgresChannelShortener
  def broadcast channel, payload
    super channel_identifier(channel), payload
  end

  def subscribe channel, callback, success_callback=nil
    super channel_identifier(channel), callback, success_callback
  end

  def unsubscribe channel, callback
    super channel_identifier(channel), callback
  end

  private

  def channel_identifier channel
    channel.size > 63 ? Digest::SHA1.hexdigest(channel) : channel
  end
end
ActionCable::SubscriptionAdapter::PostgreSQL.prepend PostgresChannelShortener

I drop this in my lib directory then just require it from my config/application.rb file.