Config Access

Config Access provides tools for loading, layering and accessing configuration files. It works with any configuration format that can be parsed into a map[string]interface{}, which includes Go's built in JSON parser and the most widely used YAML parsers.

This package provides a small subset of the functionality of larger configuration libraries like Viper, but has a fraction of the upstream dependencies. This package provides the configuration handling functionality for the Granitic microservices framework.

GoDoc for this package can be found here

Loading configuration

Config Access is agnostic of how your configuration is stored and parsed, as long as the result of parsing is a map[string]interface{}. For brevity, Config Access defines a type alias ConfigNode for map[string]interface{}.

For example, a JSON file could be loaded and parsed as:

  var config config_access.ConfigNode

  f, _ := os.Open("/your/config.json")
  b, _ := io.ReadAll(f)

  json.Unmarshal(bytes, &config)

Accessing configuration

Once loaded, Config Access provides a way of recovering individual configuration values while converting them to various Go builtin types through an interface called a Selector. Individual items are accessed using a dot delimited 'path' syntax.

  cs := new(config_access.DefaultSelector)
	
  if cs.PathExists("my.string") {
    s := cs.StringVal("my.string")		
  }

Methods exist to try and interpret configuration values as string, int, float64, bool, slices []interface{} and objects map[string]interface{}.

Layering and merging

Configuration sources can be merged together. The most common use case is to combine some base common configuration with configuration that is specific to a deployment environment.

  var base config_access.ConfigNode
  var prod config_access.ConfigNode

  f, _ := os.Open("/your/base-config.json")
  b, _ := io.ReadAll(f)

  json.Unmarshal(bytes, &base)

  f, _ = os.Open("/your/prod-config.json")
  b, _ = io.ReadAll(f)

  json.Unmarshal(bytes, &prod)
  
  combined := config_access.Merge(base, prod, false)

Injecting configuration

Configuration loaded into a ConfigNode can be used to populate the fields of a struct in one call:

  //Assume config previously loaded into variable config
  type Name struct {
    First string
    Middle []string
    Last string
  }
  
  var name Name

  ca.Populate("orderDetails.recipient", &name, config)