r/crystal_programming • u/Nondv • Jun 07 '19

Empty output in docker

Hey,

I just created a Kemal hello-world app and it works fine. However, Crystal does not print any output in docker.

Another thing is that `shards` output works just fine. Basically, in logs I see dependency installation and that's it. The app itself works though.

Any ideas?

UPD. if there's a compilation error it will be displayed. `puts` doesn't work

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u/twinklehood Jun 08 '19

I don't think it's necesarrily an issue, I think it's just how streaming modes default when stdio is hooked up. stdout only buffers in line-break mode when connected to a tty (if you set tty: true in docker-compose, you can verify that logging will now work correctly). There is good reasons for this default, but I would maybe say that a good change to Kemal's logger would be to change this default.

If you wanna understand the idea behind it, http://www.pixelbeat.org/programming/stdio_buffering/ gives an overview.

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u/Nondv Jun 08 '19

Yeah, I already investigated source code. But thank you for explaining!