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Json source

Json source

This source allows conferer to read configuration from json files.

This uses the same facilities as the properties file to resolve the file name so it uses the "env" key to find out which file to use like config/${env}.json, so if it's set to production the file will be config/production.json. If no env key is set, "development" will be used.

There is a bit of interpretation since conferer's values are not a one to one mapping to json values.

{
    "some": {
        "key": "value"
    },
    "other": true,
    "list": [1, 2, {"k": "x"}]
}

Now this json file will result in only two keys;

• "some" not present
• "some.key" mapped to "value"
• "other" mapped to "true"
• "list.0" mapped to "1"
• "list.1" mapped to "2"
• "list.3.k" mapped to "x"

Note that:

• Since conferer's values always are string, the true becomes "true", conferer's FromConfig knows how to interpret this properly though (same as numbers and null).
• We traverse the tree until we find a primitive value.
• We don't define keys for nested values like "some" in this case.
• For list we define a key with its index and they can nest other values.
• The json file may only contain valid keys (lowercase ascii and numbers) otherwise an exception will be thrown.

Special _self key

Conferer allows setting some key and at the same time more specific keys at the same time.

For example setting:

somefile=myfile.png somefile.extension=jpg

is possible and when parsing File this will result in myfile.jpg (more specific wins)

Json cannot do that natively so we have the _self special key, which is interpreted as setting the value of the object while still allowing more specific keys to be set.

The example above in json would be:

{
    "somefile": {
        "_self": "myfile.png",
        "extension": "jpg"
    }
}

Special keys key

For nested values the magic keys key is present and has a comma separated list of the present keys

{
    "list": [3,4,5],
    "object": {"a": 1, "b": 7}
}

exposes

• "list" not present
• "list.0" mapped to "3"
• "list.keys" mapped to "0,1,2"
• "object" not present
• "object.a" mapped to "1"
• "object.keys" mapped to "a,b"

NOTE: The keys list is always sorted in lexicographical order, since aeson doesn't maintain the original order of keys, we sort it to be consistent.