configman

README

Go Configuration Manager Based on Viper

What is Viper?

Viper is a complete configuration solution for go applications including 12 factor apps.

What is configman?

TODO

Putting Values into Viper

Establishing Defaults

A good configuration system will support default values. A default value is not required for a key, but it's useful in the event that a key hasn’t been set via config file, environment variable, remote configuration or flag.

Examples:

viper.SetDefault("ContentDir", "content")
viper.SetDefault("LayoutDir", "layouts")
viper.SetDefault("Taxonomies", map[string]string{"tag": "tags", "category": "categories"})

Watching and re-reading config files

Viper supports the ability to have your application live read a config file while running.

Gone are the days of needing to restart a server to have a config take effect, viper powered applications can read an update to a config file while running and not miss a beat.

Simply tell the viper instance to watchConfig. Optionally you can provide a function for Viper to run each time a change occurs.

Make sure you add all of the configPaths prior to calling WatchConfig()

		viper.WatchConfig()
		viper.OnConfigChange(func(e fsnotify.Event) {
			fmt.Println("Config file changed:", e.Name)
		})

Reading Config from io.Reader

Viper predefines many configuration sources such as files, environment variables, flags, and remote K/V store, but you are not bound to them. You can also implement your own required configuration source and feed it to viper.

viper.SetConfigType("yaml") // or viper.SetConfigType("YAML")

// any approach to require this configuration into your program.
var yamlExample = []byte(`
Hacker: true
name: steve
hobbies:
- skateboarding
- snowboarding
- go
clothing:
  jacket: leather
  trousers: denim
age: 35
eyes : brown
beard: true
`)

viper.ReadConfig(bytes.NewBuffer(yamlExample))

viper.Get("name") // this would be "steve"

Setting Overrides

These could be from a command line flag, or from your own application logic.

viper.Set("Verbose", true)
viper.Set("LogFile", LogFile)

Registering and Using Aliases

Aliases permit a single value to be referenced by multiple keys

viper.RegisterAlias("loud", "Verbose")

viper.Set("verbose", true) // same result as next line
viper.Set("loud", true)   // same result as prior line

viper.GetBool("loud") // true
viper.GetBool("verbose") // true

Working with Environment Variables

Viper has full support for environment variables. This enables 12 factor applications out of the box. There are four methods that exist to aid working with ENV:

• AutomaticEnv()
• BindEnv(string...) : error
• SetEnvPrefix(string)
• SetEnvReplacer(string...) *strings.Replacer

When working with ENV variables, it’s important to recognize that Viper treats ENV variables as case sensitive.

Viper provides a mechanism to try to ensure that ENV variables are unique. By using SetEnvPrefix, you can tell Viper to use add a prefix while reading from the environment variables. Both BindEnv and AutomaticEnv will use this prefix.

BindEnv takes one or two parameters. The first parameter is the key name, the second is the name of the environment variable. The name of the environment variable is case sensitive. If the ENV variable name is not provided, then Viper will automatically assume that the key name matches the ENV variable name, but the ENV variable is IN ALL CAPS. When you explicitly provide the ENV variable name, it does not automatically add the prefix.

One important thing to recognize when working with ENV variables is that the value will be read each time it is accessed. Viper does not fix the value when the BindEnv is called.

AutomaticEnv is a powerful helper especially when combined with SetEnvPrefix. When called, Viper will check for an environment variable any time a viper.Get request is made. It will apply the following rules. It will check for a environment variable with a name matching the key uppercased and prefixed with the EnvPrefix if set.

SetEnvReplacer allows you to use a strings.Replacer object to rewrite Env keys to an extent. This is useful if you want to use - or something in your Get() calls, but want your environmental variables to use _ delimiters. An example of using it can be found in viper_test.go.

Env example

SetEnvPrefix("spf") // will be uppercased automatically
BindEnv("id")

os.Setenv("SPF_ID", "13") // typically done outside of the app

id := Get("id") // 13

Working with Flags

Viper has the ability to bind to flags. Specifically, Viper supports Pflags as used in the Cobra library.

Like BindEnv, the value is not set when the binding method is called, but when it is accessed. This means you can bind as early as you want, even in an init() function.

The BindPFlag() method provides this functionality.

Example:

serverCmd.Flags().Int("port", 1138, "Port to run Application server on")
viper.BindPFlag("port", serverCmd.Flags().Lookup("port"))

The use of pflag in Viper does not preclude the use of other packages that use the flag package from the standard library. The pflag package can handle the flags defined for the flag package by importing these flags. This is accomplished by a calling a convenience function provided by the pflag package called AddGoFlagSet().

Example:

package main

import (
	"flag"
	"github.com/spf13/pflag"
)

func main() {
	pflag.CommandLine.AddGoFlagSet(flag.CommandLine)
	pflag.Parse()
    ...
}

Flag interfaces

Viper provides two Go interfaces to bind other flag systems if you don't use Pflags.

FlagValue represents a single flag. This is a very simple example on how to implement this interface:

type myFlag struct {}
func (f myFlag) HasChanged() bool { return false }
func (f myFlag) Name() string { return "my-flag-name" }
func (f myFlag) ValueString() string { return "my-flag-value" }
func (f myFlag) ValueType() string { return "string" }

Once your flag implements this interface, you can simply tell Viper to bind it:

viper.BindFlagValue("my-flag-name", myFlag{})

FlagValueSet represents a group of flags. This is a very simple example on how to implement this interface:

type myFlagSet struct {
	flags []myFlag
}

func (f myFlagSet) VisitAll(fn func(FlagValue)) {
	for _, flag := range flags {
		fn(flag)
	}
}

Once your flag set implements this interface, you can simply tell Viper to bind it:

fSet := myFlagSet{
	flags: []myFlag{myFlag{}, myFlag{}},
}
viper.BindFlagValues("my-flags", fSet)

Getting Values From Viper

In Viper, there are a few ways to get a value depending on the value's type. The following functions and methods exist:

• Get(key string) : interface{}
• GetBool(key string) : bool
• GetFloat64(key string) : float64
• GetInt(key string) : int
• GetString(key string) : string
• GetStringMap(key string) : map[string]interface{}
• GetStringMapString(key string) : map[string]string
• GetStringSlice(key string) : []string
• GetTime(key string) : time.Time
• GetDuration(key string) : time.Duration
• IsSet(key string) : bool

One important thing to recognize is that each Get function will return a zero value if it’s not found. To check if a given key exists, the IsSet() method has been provided.

Example:

viper.GetString("logfile") // case-insensitive Setting & Getting
if viper.GetBool("verbose") {
    fmt.Println("verbose enabled")
}

Accessing nested keys

The accessor methods also accept formatted paths to deeply nested keys. For example, if the following JSON file is loaded:

{
    "host": {
        "address": "localhost",
        "port": 5799
    },
    "datastore": {
        "metric": {
            "host": "127.0.0.1",
            "port": 3099
        },
        "warehouse": {
            "host": "198.0.0.1",
            "port": 2112
        }
    }
}

Viper can access a nested field by passing a . delimited path of keys:

GetString("datastore.metric.host") // (returns "127.0.0.1")

This obeys the precedence rules established above; the search for the path will cascade through the remaining configuration registries until found.

For example, given this configuration file, both datastore.metric.host and datastore.metric.port are already defined (and may be overridden). If in addition datastore.metric.protocol was defined in the defaults, Viper would also find it.

However, if datastore.metric was overridden (by a flag, an environment variable, the Set() method, …) with an immediate value, then all sub-keys of datastore.metric become undefined, they are “shadowed” by the higher-priority configuration level.

Lastly, if there exists a key that matches the delimited key path, its value will be returned instead. E.g.

{
    "datastore.metric.host": "0.0.0.0",
    "host": {
        "address": "localhost",
        "port": 5799
    },
    "datastore": {
        "metric": {
            "host": "127.0.0.1",
            "port": 3099
        },
        "warehouse": {
            "host": "198.0.0.1",
            "port": 2112
        }
    }
}

GetString("datastore.metric.host") // returns "0.0.0.0"

Extract sub-tree

Extract sub-tree from Viper.

For example, viper represents:

app:
  cache1:
    max-items: 100
    item-size: 64
  cache2:
    max-items: 200
    item-size: 80

After executing:

subv := viper.Sub("app.cache1")

subv represents:

max-items: 100
item-size: 64

Suppose we have:

func NewCache(cfg *Viper) *Cache {...}

which creates a cache based on config information formatted as subv. Now it's easy to create these 2 caches separately as:

cfg1 := viper.Sub("app.cache1")
cache1 := NewCache(cfg1)

cfg2 := viper.Sub("app.cache2")
cache2 := NewCache(cfg2)

Unmarshaling

You also have the option of Unmarshaling all or a specific value to a struct, map, etc.

There are two methods to do this:

• Unmarshal(rawVal interface{}) : error
• UnmarshalKey(key string, rawVal interface{}) : error

Example:

type config struct {
	Port int
	Name string
	PathMap string `mapstructure:"path_map"`
}

var C config

err := Unmarshal(&C)
if err != nil {
	t.Fatalf("unable to decode into struct, %v", err)
}

Viper or Vipers?

Viper comes ready to use out of the box. There is no configuration or initialization needed to begin using Viper. Since most applications will want to use a single central repository for their configuration, the viper package provides this. It is similar to a singleton.

In all of the examples above, they demonstrate using viper in it's singleton style approach.

Working with multiple vipers

You can also create many different vipers for use in your application. Each will have it’s own unique set of configurations and values. Each can read from a different config file, key value store, etc. All of the functions that viper package supports are mirrored as methods on a viper.

Example:

x := viper.New()
y := viper.New()

x.SetDefault("ContentDir", "content")
y.SetDefault("ContentDir", "foobar")

//...

When working with multiple vipers, it is up to the user to keep track of the different vipers.

Q & A

Q: Why not INI files?

A: Ini files are pretty awful. There’s no standard format, and they are hard to validate. Viper is designed to work with JSON, TOML or YAML files. If someone really wants to add this feature, I’d be happy to merge it. It’s easy to specify which formats your application will permit.

Q: Why is it called “Viper”?

A: Viper is designed to be a companion to Cobra. While both can operate completely independently, together they make a powerful pair to handle much of your application foundation needs.

Q: Why is it called “Cobra”?

A: Is there a better name for a commander?

Documentation

Index

• type ConfigChangeListener
• type ConfigManager

Types

type ConfigChangeListener

type ConfigChangeListener interface {
	OnConfigChanged()
}

type ConfigManager

type ConfigManager interface {
	Get(string) interface{}
	GetString(string) string
	GetBool(string) bool
	GetInt(string) int
	GetInt64(string) int64
	GetFloat64(string) float64
	GetTime(string) time.Time
	GetDuration(string) time.Duration
	GetStringSlice(string) []string
	GetStringMap(string) map[string]interface{}
	GetStringMapString(string) map[string]string
	GetStringMapStringSlice(string) map[string][]string
	GetSizeInBytes(string) uint

	Set(key string, value interface{})

	IsSet(key string) bool
	InConfig(key string) bool
	AllKeys() []string
	SetDefault(key string, value interface{})

	// Sub returns new Config instance representing a sub tree of this instance.
	Sub(key string) ConfigManager

	// Unmarshal unmarshals the config into a Struct. Make sure that the tags
	// on the fields of the structure are properly set.
	Unmarshal(rawVal interface{}) error
	// UnmarshalKey takes a single key and unmarshals it into a Struct.
	UnmarshalKey(key string, rawVal interface{}) error

	// RegisterAlias provides another accessor for the same key.
	// This enables one to change a name without breaking the application
	RegisterAlias(alias string, key string)

	WatchConfig() error
	AddToChangeListeners(ConfigChangeListener)
	RemoveFromChangeListeners(ConfigChangeListener)
}