Colour output on different terminals

[alexslade]

Weird one here... I'm slightly abusing Owl to render an interface for a MUD that is displayed over a LiveView, and I'm hitting a funny issue when deploying.

The ansi colour codes work fine on dev, when I'm usind a LiveScreen and updating a block, I observe its io_request message and the colour codes are present.

But when I do this in prod (Debian / Fly.io), the same messages contain no colour codes. I'm observing the raw data in logs:

dev

�[2K�[33Hello�[39m world

prod

�[2KHello world

(No colour codes)

Any pointers for what might be happening? I've been trying to debug this morning and my best guess is that Owl is doing some kind of terminal support check and disabling colours...

[fuelen]

Owl doesn't disable colours, Elixir does this by itself. Owl uses IO.ANSI.format/2:

owl/lib/owl/data.ex

Line 266 in 5b05678

|> IO.ANSI.format()

which uses IO.ANSI.enabled?/0 by default. Looks like IO.ANSI.enabled/0 returns false in prod.
You can enable it manually

owl/test/test_helper.exs

Line 1 in 5b05678

Application.put_env(:elixir, :ansi_enabled, true)

but this keep in mind that this change is global

[fuelen]

I think we can add an optional second parameter to Owl.Data.to_ansidata/1 so it behaves similarly to IO.ANSI.format/2 and you'd be able to force ANSI formatting even though it is disabled globally. Will it solve your issue?

[alexslade]

Thanks for the pointer, that's exactly the cause :)

I have no problem enabling ansi colours for this app, so that works for now. Happy to close this issue if you are.