Repository files navigation

Viper v2 feedback

Viper is heading towards v2 and we would love to hear whatyou would like to see in it. Share your thoughts here:https://forms.gle/R6faU74qPRPAzchZ9

Thank you!

Go configuration with fangs!

Many Go projects are built using Viper including:

• Hugo
• EMC RexRay
• Imgur’s Incus
• Nanobox/Nanopack
• Docker Notary
• BloomApi
• doctl
• Clairctl
• Mercure
• Meshery
• Bearer
• Coder
• Vitess

go get github.com/spf13/viper

Note: Viper usesGo Modules to manage dependencies.

Viper is a complete configuration solution for Go applications including12-Factor apps.It is designed to work within an application, and can handle all types of configuration needsand formats. It supports:

• setting defaults
• reading from JSON, TOML, YAML, HCL, envfile and Java properties config files
• live watching and re-reading of config files (optional)
• reading from environment variables
• reading from remote config systems (etcd or Consul), and watching changes
• reading from command line flags
• reading from buffer
• setting explicit values

Viper can be thought of as a registry for all of your applications configuration needs.

When building a modern application, you don’t want to worry aboutconfiguration file formats; you want to focus on building awesome software.Viper is here to help with that.

Viper does the following for you:

1. Find, load, and unmarshal a configuration file in JSON, TOML, YAML, HCL, INI, envfile or Java properties formats.
2. Provide a mechanism to set default values for your different configuration options.
3. Provide a mechanism to set override values for options specified through command line flags.
4. Provide an alias system to easily rename parameters without breaking existing code.
5. Make it easy to tell the difference between when a user has provided a command line or config file which is the same as the default.

Viper uses the following precedence order. Each item takes precedence over the item below it:

• explicit call toSet
• flag
• env
• config
• key/value store
• default

Important: Viper configuration keys are case insensitive.There are ongoing discussions about making that optional.

A good configuration system will support default values. A default value is notrequired for a key, but it’s useful in the event that a key hasn't been set viaconfig 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"})

Viper requires minimal configuration so it knows where to look for config files.Viper supports JSON, TOML, YAML, HCL, INI, envfile and Java Properties files. Viper can search multiple paths, butcurrently a single Viper instance only supports a single configuration file.Viper does not default to any configuration search paths leaving defaults decisionto an application.

Here is an example of how to use Viper to search for and read a configuration file.None of the specific paths are required, but at least one path should be providedwhere a configuration file is expected.

viper.SetConfigName("config")// name of config file (without extension)viper.SetConfigType("yaml")// REQUIRED if the config file does not have the extension in the nameviper.AddConfigPath("/etc/appname/")// path to look for the config file inviper.AddConfigPath("$HOME/.appname")// call multiple times to add many search pathsviper.AddConfigPath(".")// optionally look for config in the working directoryerr:=viper.ReadInConfig()// Find and read the config fileiferr!=nil {// Handle errors reading the config filepanic(fmt.Errorf("fatal error config file: %w",err))}

You can handle the specific case where no config file is found like this:

iferr:=viper.ReadInConfig();err!=nil {if_,ok:=err.(viper.ConfigFileNotFoundError);ok {// Config file not found; ignore error if desired}else {// Config file was found but another error was produced}}// Config file found and successfully parsed

NOTE [since 1.6]: You can also have a file without an extension and specify the format programmatically. For those configuration files that lie in the home of the user without any extension like.bashrc

Reading from config files is useful, but at times you want to store all modifications made at run time.For that, a bunch of commands are available, each with its own purpose:

• WriteConfig - writes the current viper configuration to the predefined path, if exists. Errors if no predefined path. Will overwrite the current config file, if it exists.
• SafeWriteConfig - writes the current viper configuration to the predefined path. Errors if no predefined path. Will not overwrite the current config file, if it exists.
• WriteConfigAs - writes the current viper configuration to the given filepath. Will overwrite the given file, if it exists.
• SafeWriteConfigAs - writes the current viper configuration to the given filepath. Will not overwrite the given file, if it exists.

As a rule of the thumb, everything marked with safe won't overwrite any file, but just create if not existent, whilst the default behavior is to create or truncate.

A small examples section:

viper.WriteConfig()// writes current config to predefined path set by 'viper.AddConfigPath()' and 'viper.SetConfigName'viper.SafeWriteConfig()viper.WriteConfigAs("/path/to/my/.config")viper.SafeWriteConfigAs("/path/to/my/.config")// will error since it has already been writtenviper.SafeWriteConfigAs("/path/to/my/.other_config")

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 andnot 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 callingWatchConfig()

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

Viper predefines many configuration sources such as files, environmentvariables, flags, and remote K/V store, but you are not bound to them. You canalso 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.varyamlExample= []byte(`Hacker: truename: stevehobbies:- skateboarding- snowboarding- goclothing:  jacket: leather  trousers: denimage: 35eyes : brownbeard: true`)viper.ReadConfig(bytes.NewBuffer(yamlExample))viper.Get("name")// this would be "steve"

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

viper.Set("Verbose",true)viper.Set("LogFile",LogFile)viper.Set("host.port",5899)// set subset

Aliases permit a single value to be referenced by multiple keys

viper.RegisterAlias("loud","Verbose")viper.Set("verbose",true)// same result as next lineviper.Set("loud",true)// same result as prior lineviper.GetBool("loud")// trueviper.GetBool("verbose")// true

Viper has full support for environment variables. This enables 12 factorapplications out of the box. There are five methods that exist to aid workingwith ENV:

• AutomaticEnv()
• BindEnv(string...) : error
• SetEnvPrefix(string)
• SetEnvKeyReplacer(string...) *strings.Replacer
• AllowEmptyEnv(bool)

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

Viper provides a mechanism to try to ensure that ENV variables are unique. ByusingSetEnvPrefix, you can tell Viper to use a prefix while reading fromthe environment variables. BothBindEnv andAutomaticEnv will use thisprefix.

BindEnv takes one or more parameters. The first parameter is the key name, therest are the name of the environment variables to bind to this key. If more thanone are provided, they will take precedence in the specified order. The name ofthe environment variable is case sensitive. If the ENV variable name is not provided, thenViper will automatically assume that the ENV variable matches the following format: prefix + "_" + the key name in ALL CAPS. When you explicitly provide the ENV variable name (the second parameter),itdoes not automatically add the prefix. For example if the second parameter is "id",Viper will look for the ENV variable "ID".

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

AutomaticEnv is a powerful helper especially when combined withSetEnvPrefix. When called, Viper will check for an environment variable anytime aviper.Get request is made. It will apply the following rules. It willcheck for an environment variable with a name matching the key uppercased andprefixed with theEnvPrefix if set.

SetEnvKeyReplacer allows you to use astrings.Replacer object to rewrite Envkeys to an extent. This is useful if you want to use- or something in yourGet() calls, but want your environmental variables to use_ delimiters. Anexample of using it can be found inviper_test.go.

Alternatively, you can useEnvKeyReplacer withNewWithOptions factory function.UnlikeSetEnvKeyReplacer, it accepts aStringReplacer interface allowing you to write custom string replacing logic.

By default empty environment variables are considered unset and will fall back tothe next configuration source. To treat empty environment variables as set, usetheAllowEmptyEnv method.

SetEnvPrefix("spf")// will be uppercased automaticallyBindEnv("id")os.Setenv("SPF_ID","13")// typically done outside of the appid:=Get("id")// 13

Viper has the ability to bind to flags. Specifically, Viper supportsPflagsas used in theCobra library.

LikeBindEnv, the value is not set when the binding method is called, but whenit is accessed. This means you can bind as early as you want, even in aninit() function.

For individual flags, theBindPFlag() method provides this functionality.

Example:

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

You can also bind an existing set of pflags (pflag.FlagSet):

Example:

pflag.Int("flagname",1234,"help message for flagname")pflag.Parse()viper.BindPFlags(pflag.CommandLine)i:=viper.GetInt("flagname")// retrieve values from viper instead of pflag

The use ofpflag in Viper does not precludethe use of other packages that use theflagpackage from the standard library. The pflag package can handle the flagsdefined for the flag package by importing these flags. This is accomplishedby a calling a convenience function provided by the pflag package calledAddGoFlagSet().

Example:

package mainimport ("flag""github.com/spf13/pflag")funcmain() {// using standard library "flag" packageflag.Int("flagname",1234,"help message for flagname")pflag.CommandLine.AddGoFlagSet(flag.CommandLine)pflag.Parse()viper.BindPFlags(pflag.CommandLine)i:=viper.GetInt("flagname")// retrieve value from viper// ...}

Viper provides two Go interfaces to bind other flag systems if you don’t usePflags.

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

typemyFlagstruct {}func (fmyFlag)HasChanged()bool {returnfalse }func (fmyFlag)Name()string {return"my-flag-name" }func (fmyFlag)ValueString()string {return"my-flag-value" }func (fmyFlag)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:

typemyFlagSetstruct {flags []myFlag}func (fmyFlagSet)VisitAll(fnfunc(FlagValue)) {for_,flag:=rangeflags {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)

To enable remote support in Viper, do a blank import of theviper/remotepackage:

import _ "github.com/spf13/viper/remote"

Viper will read a config string (as JSON, TOML, YAML, HCL or envfile) retrieved from a pathin a Key/Value store such as etcd or Consul. These values take precedence overdefault values, but are overridden by configuration values retrieved from disk,flags, or environment variables.

Viper supports multiple hosts. To use, pass a list of endpoints separated by;. For examplehttp://127.0.0.1:4001;http://127.0.0.1:4002.

Viper usescrypt to retrieveconfiguration from the K/V store, which means that you can store yourconfiguration values encrypted and have them automatically decrypted if you havethe correct gpg keyring. Encryption is optional.

You can use remote configuration in conjunction with local configuration, orindependently of it.

crypt has a command-line helper that you can use to put configurations in yourK/V store.crypt defaults to etcd onhttp://127.0.0.1:4001.

$ go get github.com/sagikazarmark/crypt/bin/crypt$ cryptset -plaintext /config/hugo.json /Users/hugo/settings/config.json

Confirm that your value was set:

$ crypt get -plaintext /config/hugo.json

See thecrypt documentation for examples of how to set encrypted values, orhow to use Consul.

viper.AddRemoteProvider("etcd","http://127.0.0.1:4001","/config/hugo.json")viper.SetConfigType("json")// because there is no file extension in a stream of bytes, supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop", "env", "dotenv"err:=viper.ReadRemoteConfig()

viper.AddRemoteProvider("etcd3","http://127.0.0.1:4001","/config/hugo.json")viper.SetConfigType("json")// because there is no file extension in a stream of bytes, supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop", "env", "dotenv"err:=viper.ReadRemoteConfig()

You need to set a key to Consul key/value storage with JSON value containing your desired config.For example, create a Consul key/value store keyMY_CONSUL_KEY with value:

{"port":8080,"hostname":"myhostname.com"}

viper.AddRemoteProvider("consul","localhost:8500","MY_CONSUL_KEY")viper.SetConfigType("json")// Need to explicitly set this to jsonerr:=viper.ReadRemoteConfig()fmt.Println(viper.Get("port"))// 8080fmt.Println(viper.Get("hostname"))// myhostname.com

viper.AddRemoteProvider("firestore","google-cloud-project-id","collection/document")viper.SetConfigType("json")// Config's format: "json", "toml", "yaml", "yml"err:=viper.ReadRemoteConfig()

Of course, you're allowed to useSecureRemoteProvider also

viper.AddRemoteProvider("nats","nats://127.0.0.1:4222","myapp.config")viper.SetConfigType("json")err:=viper.ReadRemoteConfig()

viper.AddSecureRemoteProvider("etcd","http://127.0.0.1:4001","/config/hugo.json","/etc/secrets/mykeyring.gpg")viper.SetConfigType("json")// because there is no file extension in a stream of bytes,  supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop", "env", "dotenv"err:=viper.ReadRemoteConfig()

// alternatively, you can create a new viper instance.varruntime_viper=viper.New()runtime_viper.AddRemoteProvider("etcd","http://127.0.0.1:4001","/config/hugo.yml")runtime_viper.SetConfigType("yaml")// because there is no file extension in a stream of bytes, supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop", "env", "dotenv"// read from remote config the first time.err:=runtime_viper.ReadRemoteConfig()// unmarshal configruntime_viper.Unmarshal(&runtime_conf)// open a goroutine to watch remote changes forevergofunc(){for {time.Sleep(time.Second*5)// delay after each request// currently, only tested with etcd supporterr:=runtime_viper.WatchRemoteConfig()iferr!=nil {log.Errorf("unable to read remote config: %v",err)continue}// unmarshal new config into our runtime config struct. you can also use channel// to implement a signal to notify the system of the changesruntime_viper.Unmarshal(&runtime_conf)}}()

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) : any
• GetBool(key string) : bool
• GetFloat64(key string) : float64
• GetInt(key string) : int
• GetIntSlice(key string) : []int
• GetString(key string) : string
• GetStringMap(key string) : map[string]any
• GetStringMapString(key string) : map[string]string
• GetStringSlice(key string) : []string
• GetTime(key string) : time.Time
• GetDuration(key string) : time.Duration
• IsSet(key string) : bool
• AllSettings() : map[string]any

One important thing to recognize is that each Get function will return a zerovalue if it’s not found. To check if a given key exists, theIsSet() methodhas been provided.

The zero value will also be returned if the value is set, but fails to parseas the requested type.

Example:

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

The accessor methods also accept formatted paths to deeply nested keys. Forexample, 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 pathwill cascade through the remaining configuration registries until found.

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

However, ifdatastore.metric was overridden (by a flag, an environment variable,theSet() method, …) with an immediate value, then all sub-keys ofdatastore.metric become undefined, they are “shadowed” by the higher-priorityconfiguration level.

Viper can access array indices by using numbers in the path. For example:

{"host":{"address":"localhost","ports":[5799,6029]},"datastore":{"metric":{"host":"127.0.0.1","port":3099},"warehouse":{"host":"198.0.0.1","port":2112}}}GetInt("host.ports.1")// returns 6029

Lastly, if there exists a key that matches the delimited key path, its valuewill 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"

When developing reusable modules, it's often useful to extract a subset of the configurationand pass it to a module. This way the module can be instantiated more than once, with different configurations.

For example, an application might use multiple different cache stores for different purposes:

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

We could pass the cache name to a module (eg.NewCache("cache1")),but it would require weird concatenation for accessing config keys and would be less separated from the global config.

So instead of doing that let's pass a Viper instance to the constructor that represents a subset of the configuration:

cache1Config:=viper.Sub("cache.cache1")ifcache1Config==nil {// Sub returns nil if the key cannot be foundpanic("cache configuration not found")}cache1:=NewCache(cache1Config)

Note: Always check the return value ofSub. It returnsnil if a key cannot be found.

Internally, theNewCache function can addressmax-items anditem-size keys directly:

funcNewCache(v*Viper)*Cache {return&Cache{MaxItems:v.GetInt("max-items"),ItemSize:v.GetInt("item-size"),}}

The resulting code is easy to test, since it's decoupled from the main config structure,and easier to reuse (for the same reason).

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 any) : error
• UnmarshalKey(key string, rawVal any) : error

Example:

typeconfigstruct {PortintNamestringPathMapstring`mapstructure:"path_map"`}varCconfigerr:=viper.Unmarshal(&C)iferr!=nil {t.Fatalf("unable to decode into struct, %v",err)}

If you want to unmarshal configuration where the keys themselves contain dot (the default key delimiter),you have to change the delimiter:

v:=viper.NewWithOptions(viper.KeyDelimiter("::"))v.SetDefault("chart::values",map[string]any{"ingress":map[string]any{"annotations":map[string]any{"traefik.frontend.rule.type":"PathPrefix","traefik.ingress.kubernetes.io/ssl-redirect":"true",},},})typeconfigstruct {Chartstruct{Valuesmap[string]any}}varCconfigv.Unmarshal(&C)

Viper also supports unmarshaling into embedded structs:

/*Example config:module:    enabled: true    token: 89h3f98hbwf987h3f98wenf89ehf*/typeconfigstruct {Modulestruct {EnabledboolmoduleConfig`mapstructure:",squash"`}}// moduleConfig could be in a module specific packagetypemoduleConfigstruct {Tokenstring}varCconfigerr:=viper.Unmarshal(&C)iferr!=nil {t.Fatalf("unable to decode into struct, %v",err)}

Viper usesgithub.com/go-viper/mapstructure under the hood for unmarshaling values which usesmapstructure tags by default.

A frequently requested feature for Viper is adding more value formats and decoders.For example, parsing character (dot, comma, semicolon, etc) separated strings into slices.

This is already available in Viper using mapstructure decode hooks.

Read more about the details inthis blog post.

You may need to marshal all the settings held in viper into a string rather than write them to a file.You can use your favorite format's marshaller with the config returned byAllSettings().

import (yaml"gopkg.in/yaml.v2"// ...)funcyamlStringSettings()string {c:=viper.AllSettings()bs,err:=yaml.Marshal(c)iferr!=nil {log.Fatalf("unable to marshal config to YAML: %v",err)}returnstring(bs)}

Viper comes with a global instance (singleton) out of the box.

Although it makes setting up configuration easy,using it is generally discouraged as it makes testing harder and can lead to unexpected behavior.

The best practice is to initialize a Viper instance and pass that around when necessary.

The global instanceMAY be deprecated in the future.See#1855 for more details.

You can also create many different vipers for use in your application. Each willhave its own unique set of configurations and values. Each can read from adifferent config file, key value store, etc. All of the functions that viperpackage 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 thedifferent vipers.

A: Viper is designed to be acompaniontoCobra. While both can operate completelyindependently, together they make a powerful pair to handle much of yourapplication foundation needs.

Is there a better name for acommander?

tl;dr: No.

Viper merges configuration from various sources, many of which are either case insensitive or uses different casing than the rest of the sources (eg. env vars).In order to provide the best experience when using multiple sources, the decision has been made to make all keys case insensitive.

There has been several attempts to implement case sensitivity, but unfortunately it's not that trivial. We might take a stab at implementing it inViper v2, but despite the initial noise, it does not seem to be requested that much.

You can vote for case sensitivity by filling out this feedback form:https://forms.gle/R6faU74qPRPAzchZ9

No, you will need to synchronize access to the viper yourself (for example by using thesync package). Concurrent reads and writes can cause a panic.

SeeTROUBLESHOOTING.md.

For an optimal developer experience, it is recommended to installNix anddirenv.

Alternatively, installGo on your computer then runmake deps to install the rest of the dependencies.

Run the test suite:

maketest

Run linters:

make lint# pass -j option to run them in parallel

Some linter violations can automatically be fixed:

make fmt

The project is licensed under theMIT License.