1. DESCRIPTION

go-config-extender is a utility that helps to work with config files: it loads a JSON config file and overrides values by setting environment variables. This is useful when we are having, i.e., Dockerfile or docker-compose, consider that we are having application config file config.json and we have to override log level or db username+passord based on values in an .env file.

2. Requirements

To make this thing work, we have to do the following:

1. We have to separate "normal" environment variables from technical (those using for such override);
2. We should have some relation between JSON properties in config and env variable.

Considering these two restrictions, we decided to have a variable's name pattern that allows it to meet all these requirements.

consider following example of config:

{
    "server": {
        "schema": "http",
        "address": "0.0.0.0",
        "port": 8182,
        "secret_file": "./keyfile"
    },
    "logging": {
        "level": "debug",
        "appenders": [
            {
                "type": "rolling_file",
                "enabled": true,
                "level": "debug",
                "destination": {
                    "file": "./logs/ferrum.log",
                    "max_size": 100,
                    "max_age": 5,
                    "max_backups": 5,
                    "local_time": true
                }
            },
            {
                "type": "console",
                "enabled": true,
                "level": "debug"
            }
        ],
        "http_log": true,
        "http_console_out": true
    },
    "data_source": {
        "type": "redis",
        "source": "redis:6379",
        "credentials": {
            "username": "ferrum_db",
            "password": "FeRRuM000"
        },
        "options": {
            "namespace": "ferrum_1",
            "db_number": "0"
        }
    }
}

And we would like to override:

1. logging.level -> env variable __logging.level
2. data_source.username -> env variable __data_source.username
3. data_source.password -> env variable __data_source.password

What methods this package have:

1. LoadConfig [T any] (configFile string) (T, error) for loading without overriding
2. LoadConfigWithEnv [T any] (configFile string) (T, error) for loading with override

3. Full example

A full example could be found in the test TestLoadJSONConfigWithEnvOverride test_file In This test were set 3 variables of different types: bool, int and float

Real App usage will be shown later after this package Release && usage in Ferrum Community Authorization Server