Terraform: jsondecode function

[matti]

jsonencode could be used as a way to pass lists and maps to module if there was a jsondecode function (or jsonparse etc).

[ckyoog]

And better support nested map and list.

[apparentlymart]

Hi @matti and @ckyoog! This is an old issue, but I have some news about it!

The current configuration language can't support a function like this because it has no way to model a function whose return type depends on its input value.

For a little while now we've been working on a revamp of the configuration language to address a number of shortcomings and limitations, and this is one of the things the new implementation can now support.

We're going to be rolling this new implementation out cautiously because it's a big change that will almost definitely contain some small breaking changes that we need to manage. However, we are planning to release an opt-in preview version of it soon to gather feedback and find as many bugs as possible. This initial release should include the new jsondecode function, though it will still be subject to some limitations initially since it will take a few steps to update all of Terraform's internals to support the new system.

[ckyoog]

Thank you @apparentlymart! It's really a good news! I can't wait to see what brilliant features the new implementation can bring to us.

[matti]

just found out that @ewbankkit has done this: https://github.com/EvilSuperstars/terraform-provider-jsondecode

[matti]

"The subset of JSON that can be decoded is limited - boolean, number, string, object with string values and array of strings." - see tests: https://github.com/EvilSuperstars/terraform-provider-jsondecode/blob/master/decode/data_source_decode_test.go

[matti]

I also gave a try, not as good, but might help someone https://github.com/matti/terraform-json-map

[robinbowes]

Is jsondecode due to be released in 0.12 ?

[ewbankkit]

I'm hoping that _Reliable JSON syntax_ promised here will give us what we need.

[robinbowes]

That's not the same as being able to process json.

[apparentlymart]

Although it's not included in the list in the article there, jsondecode is planned to be in the 0.12 release, along with improvements to jsonencode allowing it to work with arbitrarily-nested types rather than just with lists and maps of strings.

@robinbowes is correct that this is something separate than "Reliable JSON syntax", which is about Terraform's handling of its own configuration files written in JSON format (.tf.json files, in other words).

[robinbowes]

@apparentlymart Do you have any idea when 0.12 will be released? Is it days/weeks/months away?

[apparentlymart]

There are more details on the 0.12 release in the announcement blog post.

[robinbowes]

"later this summer" - some time before mid-Sept? :)

One thing that occurred to me - will providers also be updated for 0.12?

For example, I'd like to use the http provider to pull JSON from an api, but unless it's been re-written for 0.12 then it won't support the more complex JSON structures.

[chrisminton]

The http provider JSON use-case is one I am interested in too

[apparentlymart]

The http provider just returns the raw body string from the response, so it shouldn't need any changes itself to support reading JSON values. Instead, you'd pass its result through jsondecode(...) to get the data structure out.

[apparentlymart]

I just tried the following in v0.12.0-alpha1:

output "foo" {
  value = jsondecode(<<EOT
{
  "foo": "bar",
  "baz": ["boop"]
}
EOT
  )
}

$ terraform apply

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

foo = {
  "baz" = [
    "boop",
  ]
  "foo" = "bar"
}

The jsondecode function is available for experimental use in the v0.12.0-alpha1 release and will be included in the eventual v0.12.0 final release.

Thanks for filing this feature request, and for the patience while we got through the groundwork to make a function like this possible.

[udondan]

Already commented on https://github.com/terraform-providers/terraform-provider-aws/issues/4789 but also related here:

Here's a partial solution for Terraform v0.11 without any dependencies:

variable json_input {
  default = <<EOT
{
  "foo": "bar",
  "baz": "boop"
}
EOT
}

data "external" "helper" {
  program = ["echo", "${var.json_input}"]
}

data.external.helper.result is the full map stored in secret_string and elements can be accessed as data.external.helper.result["example"]

Or throw it into a module and return the whole map as output:

output "parsed" {
  value = "${data.external.helper.result}"
}

$ terraform apply
data.external.helper: Refreshing state...

Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

parsed = {
  baz = boop
  foo = bar
}

The only limitation is, that the external data provider can apparently not deal with arrays. So only works with json maps...

json: cannot unmarshal array into Go value of type string

[hashibot[bot]]

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