BUG: trying to downcast TCPSocket+ (Crystal::VirtualType) <- TCPSocket (Crystal::NonGenericClassType)

zw963 · November 15, 2024, 12:15pm

Hi, i get an unable to understand compiler output again.

Error target procodile failed to compile:
BUG: trying to downcast TCPSocket+ (Crystal::VirtualType) <- TCPSocket (Crystal::NonGenericClassType) (Exception)
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Error: you've found a bug in the Crystal compiler. Please open an issue, including source code that will allow us to reproduce the bug: https://github.com/crystal-lang/crystal/issues

You can reproduce this issue on add_proxy_feature_back branch of procodile_cr

1. git clone https://github.com/crystal-china/procodile_cr.git
2.  cd procodile_cr
3. git checkout add_proxy_feature_back
4.  git reset --hard 8a3de19   # only if current git hash is not same
5. shards build

It’s seem like issue raised from a very unexpected place by this code, but, i have no idea of what happens

More context: current branch is adding the missing proxy feature back to Crystal fork. (reference original Ruby version code), it still WIP and not work anyway, but the really issue is, give me this error message is really useless for developer understand what happens.

Thanks.

sol.vin · November 15, 2024, 2:59pm

Is there a reason you need to sleep here? This may be considered sloppy depending on who you ask.

This is a bug, however, I find one line particularly interesting:

github.com

crystal-china/procodile_cr/blob/691ef3d30fd8a8ec61e1c77b1cd35735ea0d3c12/src/procodile/tcp_proxy.cr#L103


      
          
          def handle_client(client, server)
            process = @listeners[server]
            instances = @supervisor.processes[process]? || [] of Instance
          
            if instances.empty?
              Procodile.log nil, "proxy", "There are no processes running for #{process.name}"
            else
              instance = instances.sample
          
              backend_socket = TCPSocket.new("127.0.0.1", instance.port) rescue nil
          
              if backend_socket.nil?
                Procodile.log nil, "proxy", "Could not connect to #{instance.description}:#{instance.port}"
          
                return
              end
          
              readers = {backend: backend_socket, client: client}
          
              readers.values.each do |io|

I have never seen rescue used like this and it’s not even documented in Exception handling - Crystal …

Is it possible the bug comes from that? Try using begin..end instead and see if that helps?

zw963 · November 15, 2024, 4:47pm

Yes, it is probably not documented, but it is quite common usage when write Ruby, it works too with Crystal.

Is there a reason you need to sleep here?

No, i remove it.

Is it possible the bug comes from that?

No, after i reduce the code, i found this exception come from a very unexpected place.

github.com

crystal-china/procodile_cr/blob/8a3de19ca0b95fc16ad1f830bf928788e2bd088a/src/procodile/tcp_proxy.cr#L117


      
          
          #   return
          # end
          
          readers = {client: client}
          
          readers.values.each do |io|
            spawn do
              loop do
                readers.keys.each do |key|
                  p! io
                  # next unless readers[key] == io
                  # opposite_side = (key == :client) ? :backend : :client
          
                  # Original ruby version code <==
          
                  # if io.eof?
                  #   readers[opposite_side].shutdown(Socket::SHUT_WR) rescue nil
                  #   readers.delete(opposite_side)
                  # else
                  #   readers[opposite_side].write(io.readpartial(1024)) rescue nil

Please pull the latest 8a3de19 on add_proxy_feature_back branch to reproduce this.