Parse Json Array issue: Unable to unmarshal object

[NicoHood]

Hi,
I am not sure if this is an issue or if I just did something obvious wrong. Maybe you can help and other will see the post if they run into the same issue.

test.json

["London", "Johannesburg", "Windhoek"]

test.tmpl

{{ range $i, $city := (ds "cities") }}
{{ add 1 $i }}: {{ include "weather" (print $city "?0") }}
{{ end }}

command:

$ gomplate -d 'cities=test.json'  -d 'weather=https://wttr.in/?0' -H 'weather=User-Agent: curl' -f test.tmpl 

23:41:03 FTL  error="template: test.tmpl:1:23: executing \"test.tmpl\" at <ds \"cities\">: error calling ds: Unable to unmarshal object [\"London\", \"Johannesburg\", \"Windhoek\"]\n: yaml: unmarshal errors:\n  line 1: cannot unmarshal !!seq into map[string]interface {}"

It works if you use city: [...] in json and (ds "cities").city inside the template. But my json root object is not dict, it is an array, because I request it via REST api (common usecase).

Thanks :-)

[hairyhenderson]

Hi @NicoHood - thanks for logging this!

.json files are assumed to be of type application/json which gomplate interprets as a JSON object. If you want, you can override the type to application/array+json (which is a non-standard MIME type that gomplate understands) by appending ?type=application/array+json to the datasource's URL:

$ gomplate -d 'cities=test.json?type=application/array+json'  -d 'weather=https://wttr.in/?0' -H 'weather=User-Agent: curl' -f test.tmpl

1: Weather report: London

      \   /     Sunny
       .-.      20 °C
    ― (   ) ―   ↑ 15 km/h
       `-’      10 km
      /   \     0.4 mm


2: Weather report: Johannesburg

      \   /     Clear
       .-.      11..13 °C
    ― (   ) ―   ↓ 17 km/h
       `-’      10 km
      /   \     0.0 mm


3: Weather report: Windhoek

      \   /     Clear
       .-.      14 °C
    ― (   ) ―   ↑ 12 km/h
       `-’      10 km
      /   \     0.0 mm

See https://docs.gomplate.ca/datasources/#mime-types for more details, and especially https://docs.gomplate.ca/datasources/#overriding-mime-types

[NicoHood]

WTF, there is a special mime type for this!? That was new to me, thanks!

Edit: Maybe add this to your post or readme?

[hairyhenderson]

Edit: Maybe add this to your post or readme?

@NicoHood which post? which README? It's in the docs, as I linked.

[NicoHood]

Oh, my fault. I was referring to this post:
https://blog.hairyhenderson.ca/post/one_template_many_outputs/

It might be useful to add this note there, as it looks like a common usecase to connect a rest api to such a template. I was not aware that there is a special json array mime type, I thought it is all the same.

[hairyhenderson]

Oh, my fault. I was referring to this post:
https://blog.hairyhenderson.ca/post/one_template_many_outputs/

Wild - I didn't know anyone read those 😂

It might be useful to add this note there

Not sure that really makes sense... I didn't use a JSON array file as a datasource in that article directly, and where I did mention using datasources, I linked straight to the docs, which is where you'd find the answer.

I was not aware that there is a special json array mime type, I thought it is all the same.

It's is a bit of a hack TBH... JSON suffers from being a bit too general sometimes, and YAML even more so. So it's tough to make the right call when parsing sometimes. However, I have thought in the past about maybe attempting to parse as an array if the file can't be parsed as an object. I'll re-open this and just add a workaround to make this simpler.