vmarchese/go-confignet

go-confignet

The module is freely inspired by asp.net Configuration framework. The responsibility for reading the configuration rests with one or more configuration providers. Configuration providers read configuration data from key-value pairs (map[string]string) using a variety of configuration sources:

• Json Files
• Yaml Files
• Environment Variables
• Command line arguments
• Azure Key Vault
• Splitted Secrets
• Custom providers

The usage of the module consists in few simple steps:

• Create the struct which represents the configuration
• Create a configuration builder
• Add one or more configuration providers, each one with his configuration
• Build the configuration to retrieve a configuration struct
• Invoke the Configuration.Bind function to apply the configuration to your custom object

Configuration example

type MyConfig struct {
    Obj1 SubObj
}

type SubObj struct {
    PropertyString string
    PropertyInt    int
    PropertyInt8   int8
    PropertyInt16  int16
    PropertyInt64  int64
    PropertyBool   bool
    Time           time.Time
}

Usage example:

var confBuilder confignet.IConfigurationBuilder = &confignet.ConfigurationBuilder{}

// AddDefaultConfigurationProviders will add:
// 1. JsonConfigurationProvider: default file name app.json
// 2. YamlConfigurationProvider: default file name app.yaml
// 3. EnvConfigurationProvider
// 4. CmdLineConfigurationProvider
// 5. KeyvaultConfigurationProvider: connection settings will be retrieved from the environment variables:
//      AZURE_TENANT_ID
//      AZURE_CLIENT_ID
//      AZURE_CLIENT_SECRET
//      AZURE_CLIENT_CERTIFICATE_PATH
//      AZURE_USERNAME
//      AZURE_PASSWORD
confBuilder.AddDefaultConfigurationProviders()

conf := confBuilder.Build()

myCfg := MyConfig{}
conf.Bind("config", &myCfg)

Configuration Provider

A configuration provider is responsible for reading the configuration from a specific source. It must implement the following interface:

// IConfigurationProvider is configuration provider interface
type IConfigurationProvider interface {
 Load()
 GetData() map[string]string
 GetSeparator() string
}

Load function

"Load" function is invoked by the configuration builder when the "build" function is called. The function loads the configuration and stores the information in a map of type map[string]string. The key of the map contains the configuration name, the value of the map the value of the configuration. Usually the execution of the function should be safe, it means that should never throw an error. Yaml and Json configuration providers, for instance, write in the standard error stream the reason if they cannot find the file or if is not able to read it correctly.

Configuration keys:

• Are case-sensitive. For example, ConnectionString and connectionstring are treated as different keys.
• If a key and value is set in more than one configuration providers, the value from the last provider added is used.
• Hierarchical configuration must be represented in flat way in the map. The key will be made concatenating all chained properties with a specific separator. The separator is specific of every configuration provider.

Configuration values:

• Are strings.

Let's take as example the configuration:

type MyConfig struct {
  Obj1 struct {
    PropertyString string
    PropertyInt    int
    PropertyBool   bool
    Time           time.Time
    Obj2           struct {
       PropertyInt int
    }
  }
  PropertyString string
  PropertyInt    int
  PropertyBool   bool
  Time           time.Time
}

Let's assume that the configuration provider uses ":" as separator, the map will contain:

OOP dotted notation (myConfig struct)	Map Key	Map Value
myConfig.PropertyString	PropertyString	"text"
myConfig.PropertyInt	PropertyInt	"3"
myConfig.PropertyBool	PropertyBool	"true"
myConfig.Time	Time	"2022-01-01"
myConfig.Obj1.PropertyString	Obj1:PropertyString	"text2"
myConfig.Obj1.PropertyInt	Obj1:PropertyInt	"55"
myConfig.Obj1.PropertyBool	Obj1:PropertyBool	"false"
myConfig.Obj1.Time	Obj1:Time	"2022-05-01"
myConfig.Obj1.Obj2.PropertyInt	Obj1:Obj2:PropertyInt	"33"

GetData function

"GetData" function must return the map populated by the "Load" function

GetSeparator function

"GetSeparator" function must return the separator used by the configuration provider.

Built-in Configuration Providers

Json

JSONConfigurationProvider loads configuration from JSON file. It uses "." (dot) as separator for hierarchical configuration. It exposes just one public property: the file path. If the path is not provided the default value "app.json" is used.

// JSONConfigurationProvider loads configuration from JSON file key-value pairs
type JSONConfigurationProvider struct {
   FilePath string
}

Example:

{
  "config": {
    "PropertyInt8": 45,
    "Obj1": {
      "PropertyString": "TestObj1",
      "PropertyInt": 1,
      "PropertyBool": true,
      "Time": "2022-01-01"
    }
  }
}

Map:

Map Key	Map Value
config.PropertyInt8	"45"
config.Obj1.PropertyString	"TestObj1"
config.Obj1.PropertyInt	"1"
config.Obj1.PropertyBool	"true"
config.Obj1.Time	"2022-01-01"

Yaml

YamlConfigurationProvider loads configuration from YAML file. It uses "." (dot) as separator for hierarchical configuration. It exposes just one public property: the file path. If the path is not provided the default value "app.yaml" is used.

// YamlConfigurationProvider loads configuration from YAML file key-value pairs
type YamlConfigurationProvider struct {
  FilePath string
}

Example:

config:
  PropertyInt8: 45
  Obj1:
    PropertyString: "TestObj1"
    PropertyInt: 1
    PropertyBool: true

Map:

Map Key	Map Value
config.PropertyInt8	"45"
config.Obj1.PropertyString	"TestObj1"
config.Obj1.PropertyInt	"1"
config.Obj1.PropertyBool	"true"

Environment variables

EnvConfigurationProvider loads configuration from environment variables. It uses "__" (double underscore) as separator for hierarchical configuration. It exposes the following properties that change the behavior of the provider.

// EnvConfigurationProvider loads configuration from environment variables
type EnvConfigurationProvider struct {
  Prefix       string
  RemovePrefix bool
}

Properties:

• Prefix (optional): if set only the environment variables starting with the Prefix value will be loaded. E.g.:
  • Prefix value: "secrets"
  • Environment Variables:
    • secrets__cred__password=pwd123
    • cred__username=test1
  • Map: only secrets__cred__password is loaded
    • Key: secrets__cred__password
    • Value: pwd123
• RemovePrefix (optional): It is ignored if Prefix is not set. If set to true the environment variable will be added to the map removing from the key the prefix value and the first separator. E.g. using as example the previous settings:
  • RemovePrefix: true
  • Map: only secrets__cred__password is loaded
    • Key: cred__password
    • Value: pwd123

Example:

# Environment variables
export config__PropertyInt8=45
export config__Obj1__PropertyString=TestObj1
export config__Obj1__PropertyInt=1
export config__Obj1__PropertyBool=true

Map:

Map Key	Map Value
config__PropertyInt8	"45"
config__Obj1__PropertyString	"TestObj1"
config__Obj1__PropertyInt	"1"
config__Obj1__PropertyBool	"true"

Command line arguments

Azure Key Vault