Connection string parsing errors incorrectly reported as "PG::UnableToSend: no connection to the server"

[edmorley]

Hi!

libpq's parsing of integer connection string parameters (such as connect_timeout) was made more strict in PostgreSQL 12:
postgres/postgres@e7a2217

However these new variants of error messages are not surfaced correctly by ruby-pg, which instead reports PG::UnableToSend: no connection to the server, making debugging harder.

STR

1. Install Docker and docker-compose

2. Create the following files:

   # docker-compose.yml
   testcase:
     build: .
     links:
       - db
   db:
     image: postgres:11.5-alpine

   # Dockerfile
   FROM ruby:2.6.5-buster
   
   RUN curl -fsSL https://www.postgresql.org/media/keys/ACCC4CF8.asc -o /etc/apt/trusted.gpg.d/pgdg.asc
   RUN echo 'deb http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main' > /etc/apt/sources.list.d/pgdg.list
   RUN apt-get update \
       && apt-get install -y --no-install-recommends libpq-dev \
       && rm -rf /var/lib/apt/lists/*
   
   RUN gem install pg
   
   COPY testcase.rb .
   CMD ["ruby", "testcase.rb"]

   # testcase.rb
   require "pg"
   
   connection_parameters = {
     host: "db",
     user: "postgres",
     connect_timeout: "15s",
   }
   
   conn = PG.connect(connection_parameters)
   conn.exec("SELECT 'test'") do |result|
     puts "Succeeded"
   end

3. docker-compose run testcase

4. docker-compose down

Expected

That the docker-compose run testcase fail with an error message that makes it clear that the connection parameters were incorrect. For example the original libpq error (that doesn't get propagated itself) says:
invalid integer value "15s" for keyword "connect_timeout"

Actual

$ docker-compose run testcase
Starting testcase-pg_db_1 ... done
Traceback (most recent call last):
	1: from testcase.rb:11:in `<main>'
testcase.rb:11:in `async_exec': no connection to the server (PG::UnableToSend)

[larskanis]

Thank you for the detailed description of the issue. I'll look at it.

[larskanis]

I submitted a patch to libpq, that fixes the issue: https://www.postgresql.org/message-id/a9b4cbd7-4ecb-06b2-ebd7-1739bbff3217%40greiz-reinsdorf.de

[edmorley]

Oh that's amazing, thank you :-) (The fix being in libpq also means we can pick it up without needing to wait for customers to update their app's pg gem, which really helps)

[larskanis]

This is fixed in libpq and will be part of PostgreSQL-12.1: postgres/postgres@ba19a6b

[edmorley]

@larskanis Many thanks!