An Extensible Config Package, supporting the usage idioms of Spring Boot, dotnet and Node "config" in Go

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Introduction

An extensible config package, supporting the usage elements of Spring Boot and Node "config", including:

json, yaml and Java property files,
cascading value over-rides using, GO_ENV, GO_APP_INSTANCE and GO_PROFILES_ACTIVE
placeholder resolution (or variable expansion),
encrypted values (via github.com/alt-golang/gosypt),
url fetching
environment variables (via config.get("env.MY_VAR"),
command line parameters (via config.get("args.MY_ARG")
and default (or fallback) values,

Usage

To use the module, import the module as so:

import  ( "github.com/alt-golang/config") ;

config.Get('key');
config.Get('nested.key');
config.GetAs('nested.key',&SomeStruct);
config.GetWithDefault('unknown','use this instead'); // this does not throw an error

File Loading and Precedence

The module follows the file loading and precedence rules of the popular Node config defaults, with additional rules in the style of Spring Boot.

By default, files are loaded from the working directory, or from the config folder if a default., production., or local-development.** file is detected (after the Node "config" idiom). The NODE_CONFIG_DIR variable can be specified to change the default.

Files are over-ridden from the indicated folder in the following order:

config.( json | yml | yaml | props | properties )
default.( json | yml | yaml | props | properties )
application.( json | yml | yaml | props | properties )
appsettings.( json | yml | yaml | props | properties )
{GO_ENV}.( json | yml | yaml | props | properties )
appsettings.{GO_ENV}.( json | yml | yaml | props | properties )
{GO_ENV}-{GO_APP_INSTANCE}.( json | yml | yaml | props | properties )
appsettings.{GO_ENV}.{GO_APP_INSTANCE}.( json | yml | yaml | props | properties )
application-{GO_PROFILES_ACTIVE[0]}.( json | yml | yaml | props | properties )
application-{GO_PROFILES_ACTIVE[1]}.( json | yml | yaml | props | properties )
environment variables (over-ridden into env)
commandline arguments (over-ridden into args)

Environment variables and command line arguments, will over-ride values found in files, for example env.MY_VAR=someValue in a application.properties file, or

local-development.yaml

env:
  MY_VAR: someValue

will be over-ridden only if it exists on the host system, negating the need for setting local development environment variables or arguments.

Placeholders, encrypted values, and remote config

Config values that include the common ${placeholder} syntax, will resolve the inline placeholders, so the config.get('placeholder')' path below will return start.one.two.end.

Config values that start with the prefix enc. will be decrypted with the gosypt package port, with the AES 16,32,64 byte passphrase being sourced from the GO_CONFIG_PASSPHRASE environment variable.

Config values that start with the prefix url. are be fetched and resolved , and HTTP options can be specified as in the example config file.

config.yaml


  "key": "value"
  "one" : "one"
  "placeholder": "start.${one}.${nested.two}.end"
  "placeholderEncrypted": "start.${nested.encrypted}.end"
  "nested" : 
    "key" : "value"
    "two" : "two"
    "placeholder": "start.${one}.${nested.two}.end"
    "encrypted" : "enc.pxQ6z9s/LRpGB+4ddJ8bsq8RqELmhVU2"
    "encryptedWithSecret" : "enc./emLGkD3cbfqoSPijGZ0jh1p1SYIHQeJ"
  "jsonplaceholder": 
    "todos": "url.https://jsonplaceholder.typicode.com/todos/1"
  "fetchWithOpts" : 
    "url": "url.https://jsonplaceholder.typicode.com/todos/1"
    "method": "get",
    "body": "{}"
    "headers":
      "Authorization": "Basic dXNlcjpwYXNz"
      "Content-Type": "application/json"