Crash when datasource is not specified

[bartmeuris]

Currently, when a datasource is specified in the template, but not on the CLI, gomplate crashes with a nil dereference error, which can easily be reproduced with:

echo '{{(datasource "test")}}' | ./gomplate

Tested with gomplate version 1.2.4 on Ubuntu 14.04.

In my opinion it shouldn't crash like that in the first place, but it would also be nice if there was a possibility to test within the template if specific datasources are specified/available before trying to access them.

Right now I solved this by wrapping gomplate and assigning a dummy file/source externally - but that's not really a clean solution in my opinion.

[hairyhenderson]

HI @bartmeuris, thanks for reporting this! For sure it's not great to get a nasty crash. It'd certainly be a good idea to error out in a more user-friendly way.

it would also be nice if there was a possibility to test within the template if specific datasources are specified/available before trying to access them.

Just so I'm clear, would something like this work for you?

{{ if datasource-available "test" }}
{{datasource "test"}}
{{ end }}

[bartmeuris]

Something like your proposed datasource-available would be good, although it should then be clarified what "available" means then. Does it only mean it's specified on the cli, or that the file/url/vault connection/... is valid? If no validation is performed, a datasource-exists would maybe be a better name, unless you want to keep the option open for future validation behind the scenes and start off with a simpler implementation.

[hairyhenderson]

Yeah, good point. I'll start looking at a datasource-exists function.

Just out of curiosity, is this more a usability thing, or do you have a real-world need to be able to render a template either with or without a datasource defined?

[hairyhenderson]

@bartmeuris - just in case you don't see the notification, I've got a PR for this in #94 - please let me know if that seems good to you! 🙂

[bartmeuris]

To satisfy your curiosity, yes I have an actual use-case for this.

I'm building a Wildfly docker image for our java-dev's, with a 'basic' default configuration that could satisfy 90% of the projects of our Java team. This implies that it requires some basic customization options, and this tool is very helpful in that :) Most is done through environment variables, but that's not suitable for everything, which is when in some situations I required the datasources and encountered this problem.

This way I'll be able to just test if a specific file is provided by the dev and append the datasource flag to the cli options of gomplate, and won't have to provide an empty file (which is what I do now).

[hairyhenderson]

@bartmeuris ok! awesome! I'm glad that gomplate is useful for you 😁