koanf (pronounced conf; a play on the Japanese Koan) is a library for reading configuration from different sources in different formats in Go applications. It is a cleaner, lighter alternative to spf13/viper with better abstractions and extensibility and fewer dependencies.
koanf comes with built in support for reading configuration from files, command line flags, and environment variables, and can parse JSON, YAML, TOML, and Hashicorp HCL.
go get -u github.com/knadh/koanf
- Concepts
- Reading config from files
- Reading from command line
- Reading environment variables
- Reading raw bytes
- Unmarshalling
- Unmarshalling with flat paths
- Setting default values
- Order of merge and key case senstivity
- Custom Providers and Parsers
- API
koanf.Provider
is a generic interface that provides configuration, for example, from files, enviornment variables, HTTP sources, or anywhere. The configuration can either be raw bytes that a parser can parse, or it can be a nested map[string]interface{} that can be directly loaded.koanf.Parser
is a generic interface that takes raw bytes, parses, and returns a nested map[string]interface{} representation. For example, JSON and YAML parsers.- Once loaded into koanf, configuration are values queried by a delimited key path syntax. eg:
app.server.port
. Any delimiter can be chosen. - Configuration from multiple sources can be loaded and merged into a koanf instance, for example, load from a file first and override certain values with flags from the command line.
With these two interface implementations, koanf can obtain configuration from multiple sources and parse any format and make it available to an application.
package main
import (
"fmt"
"log"
"github.com/knadh/koanf"
"github.com/knadh/koanf/parsers/json"
"github.com/knadh/koanf/parsers/yaml"
"github.com/knadh/koanf/providers/file"
)
// Global koanf instance. Use "." as the key path delimiter. This can be "/" or any character.
var k = koanf.New(".")
func main() {
// Load JSON config.
if err := k.Load(file.Provider("mock/mock.json"), json.Parser()); err != nil {
log.Fatalf("error loading config: %v", err)
}
// Load YAML config and merge into the previously loaded config (because we can).
k.Load(file.Provider("mock/mock.yaml"), yaml.Parser())
fmt.Println("parent's name is = ", k.String("parent1.name"))
fmt.Println("parent's ID is = ", k.Int("parent1.id"))
}
The following example shows the use of posflag.Provider
, a wrapper over spf13/pflag library, an advanced commandline lib. For Go's built in flag
package, use basicflag.Provider
.
package main
import (
"fmt"
"log"
"os"
"github.com/knadh/koanf"
"github.com/knadh/koanf/parsers/toml"
"github.com/knadh/koanf/providers/file"
"github.com/knadh/koanf/providers/posflag"
flag "github.com/spf13/pflag"
)
// Global koanf instance. Use "." as the key path delimiter. This can be "/" or any character.
var k = koanf.New(".")
func main() {
// Use the POSIX compliant pflag lib instead of Go's flag lib.
f := flag.NewFlagSet("config", flag.ContinueOnError)
f.Usage = func() {
fmt.Println(f.FlagUsages())
os.Exit(0)
}
// Path to one or more config files to load into koanf along with some config params.
f.StringSlice("conf", []string{"mock/mock.toml"}, "path to one or more .toml config files")
f.String("time", "2020-01-01", "a time string")
f.String("type", "xxx", "type of the app")
f.Parse(os.Args[1:])
// Load the config files provided in the commandline.
cFiles, _ := f.GetStringSlice("conf")
for _, c := range cFiles {
if err := k.Load(file.Provider(c), toml.Parser()); err != nil {
log.Fatalf("error loading file: %v", err)
}
}
// "time" and "type" may have been loaded from the config file, but
// they can still be overridden with the values from the command line.
// The bundled posflag.Provider takes a flagset from the spf13/pflag lib.
// Passing the Koanf instance to posflag helps it deal with default command
// line flag values that are not present in conf maps from previously loaded
// providers.
if err := k.Load(posflag.Provider(f, ".", k), nil); err != nil {
log.Fatalf("error loading config: %v", err)
}
fmt.Println("time is = ", k.String("time"))
}
package main
import (
"fmt"
"log"
"strings"
"github.com/knadh/koanf"
"github.com/knadh/koanf/parsers/json"
"github.com/knadh/koanf/providers/env"
"github.com/knadh/koanf/providers/file"
)
// Global koanf instance. Use . as the key path delimiter. This can be / or anything.
var k = koanf.New(".")
func main() {
// Load JSON config.
if err := k.Load(file.Provider("mock/mock.json"), json.Parser()); err != nil {
log.Fatalf("error loading config: %v", err)
}
// Load environment variables and merge into the loaded config.
// "MYVAR" is the prefix to filter the env vars by.
// "." is the delimiter used to represent the key hierarchy in env vars.
// The (optional, or can be nil) function can be used to transform
// the env var names, for instance, to lowercase them.
//
// For example, env vars: MYVAR_TYPE and MYVAR_PARENT1_CHILD1_NAME
// will be merged into the "type" and the nested "parent1.child1.name"
// keys in the config file here as we lowercase the key,
// replace `_` with `.` and strip the MYVAR_ prefix so that
// only "parent1.child1.name" remains.
k.Load(env.Provider("MYVAR_", ".", func(s string) string {
return strings.Replace(strings.ToLower(
strings.TrimPrefix(s, "MYVAR_")), "_", ".", -1)
}), nil)
fmt.Println("name is = ", k.String("parent1.child1.name"))
}
The bundled rawbytes
Provider can be used to read arbitrary bytes from a source, like a database or an HTTP call.
package main
import (
"fmt"
"github.com/knadh/koanf"
"github.com/knadh/koanf/parsers/json"
"github.com/knadh/koanf/providers/rawbytes"
)
// Global koanf instance. Use . as the key path delimiter. This can be / or anything.
var k = koanf.New(".")
func main() {
b := []byte(`{"type": "rawbytes", "parent1": {"child1": {"type": "rawbytes"}}}`)
k.Load(rawbytes.Provider(b), json.Parser())
fmt.Println("type is = ", k.String("parent1.child1.type"))
}
Unmarshalling is useful when you want to copy a nested config map into a struct (like unmarshalling JSON) instead of accessing individual config values using gettor methods.
package main
import (
"fmt"
"log"
"github.com/knadh/koanf"
"github.com/knadh/koanf/parsers/json"
"github.com/knadh/koanf/providers/file"
)
// Global koanf instance. Use . as the key path delimiter. This can be / or anything.
var k = koanf.New(".")
func main() {
// Load JSON config.
if err := k.Load(file.Provider("mock/mock.json"), json.Parser()); err != nil {
log.Fatalf("error loading config: %v", err)
}
// Structure to unmarshal nested conf to.
type childStruct struct {
Name string `koanf:"name"`
Type string `koanf:"type"`
Empty map[string]string `koanf:"empty"`
GrandChild struct {
Ids []int `koanf:"ids"`
On bool `koanf:"on"`
} `koanf:"grandchild1"`
}
var out childStruct
// Quick unmarshal.
k.Unmarshal("parent1.child1", &out)
fmt.Println(out)
// Unmarshal with advanced config.
out = childStruct{}
k.UnmarshalWithConf("parent1.child1", &out, koanf.UnmarshalConf{Tag: "koanf"})
fmt.Println(out)
}
Sometimes it is necessary to unmarshal an assortment of keys from various nested structures into a flat target structure. This is possible with the UnmarshalConf.FlatPaths
flag.
package main
import (
"fmt"
"log"
"github.com/knadh/koanf"
"github.com/knadh/koanf/parsers/json"
"github.com/knadh/koanf/providers/file"
)
// Global koanf instance. Use . as the key path delimiter. This can be / or anything.
var k = koanf.New(".")
func main() {
// Load JSON config.
if err := k.Load(file.Provider("mock/mock.json"), json.Parser()); err != nil {
log.Fatalf("error loading config: %v", err)
}
type rootFlat struct {
Type string `koanf:"type"`
Empty map[string]string `koanf:"empty"`
Parent1Name string `koanf:"parent1.name"`
Parent1ID int `koanf:"parent1.id"`
Parent1Child1Name string `koanf:"parent1.child1.name"`
Parent1Child1Type string `koanf:"parent1.child1.type"`
Parent1Child1Empty map[string]string `koanf:"parent1.child1.empty"`
Parent1Child1Grandchild1IDs []int `koanf:"parent1.child1.grandchild1.ids"`
Parent1Child1Grandchild1On bool `koanf:"parent1.child1.grandchild1.on"`
}
// Unmarshal the whole root with FlatPaths: True.
var o1 rootFlat
k.UnmarshalWithConf("", &o1, koanf.UnmarshalConf{Tag: "koanf", FlatPaths: true})
fmt.Println(o1)
// Unmarshal a child structure of "parent1".
type subFlat struct {
Name string `koanf:"name"`
ID int `koanf:"id"`
Child1Name string `koanf:"child1.name"`
Child1Type string `koanf:"child1.type"`
Child1Empty map[string]string `koanf:"child1.empty"`
Child1Grandchild1IDs []int `koanf:"child1.grandchild1.ids"`
Child1Grandchild1On bool `koanf:"child1.grandchild1.on"`
}
var o2 subFlat
k.UnmarshalWithConf("parent1", &o2, koanf.UnmarshalConf{Tag: "koanf", FlatPaths: true})
fmt.Println(o2)
}
The bundled confmap
provider takes a map[string]interface{}
that can be loaded into a koanf instance. Thus, koanf does not provide any special functions to set default values but uses the Provider interface to enable it.
package main
import (
"fmt"
"log"
"github.com/knadh/koanf"
"github.com/knadh/koanf/providers/confmap"
"github.com/knadh/koanf/providers/file"
"github.com/knadh/koanf/parsers/json"
"github.com/knadh/koanf/parsers/yaml"
)
// Global koanf instance. Use "." as the key path delimiter. This can be "/" or any character.
var k = koanf.New(".")
func main() {
// Load default values using the confmap provider.
// We provide a flat map with the "." delimiter.
// A nested map can be loaded by setting the delimiter to an empty string "".
k.Load(confmap.Provider(map[string]interface{}{
"parent1.name": "Default Name",
"parent3.name": "New name here",
}, "."), nil)
// Load JSON config on top of the default values.
if err := k.Load(file.Provider("mock/mock.json"), json.Parser()); err != nil {
log.Fatalf("error loading config: %v", err)
}
// Load YAML config and merge into the previously loaded config (because we can).
k.Load(file.Provider("mock/mock.yaml"), yaml.Parser())
fmt.Println("parent's name is = ", k.String("parent1.name"))
fmt.Println("parent's ID is = ", k.Int("parent1.id"))
}
- Config keys are case sensitive in koanf. For example,
app.server.port
andAPP.SERVER.port
are not the same. - koanf does not impose any ordering on loading config from various providers. Every successive
Load()
orLoad()
merges new config into existing config. That means it is possible to load environment variables first, then files on top of it, and then command line variables on top of it, or any such order.
A Provider can provide a nested map[string]interface{} config that can be loaded into koanf with koanf.Load()
or raw bytes that can be parsed with a Parser (loaded using koanf.Load()
.
Writing Providers and Parsers are easy. See the bundled implementations in the providers
and parses
directory.
Package | Provider | Description |
---|---|---|
providers/file | file.Provider(filepath string) |
Reads a file and returns the raw bytes to be parsed. |
providers/basicflag | basicflag.Provider(f *flag.FlagSet, delim string) |
Takes an stdlib flag.FlagSet |
providers/posflag | posflag.Provider(f *pflag.FlagSet, delim string) |
Takes an spft3/pflag.FlagSet (advanced POSIX compatiable flags with multiple types) and provides a nested config map based on delim. |
providers/env | env.Provider(prefix, delim string, f func(s string) string) |
Takes an optional prefix to filter env variables by, an optional function that takes and returns a string to transform env variables, and returns a nested config map based on delim. |
providers/confmap | confmap.Provider(mp map[string]interface{}, delim string) |
Takes a premade map[string]interface{} conf map. If delim is provided, the keys are assumed to be flattened, thus unflattened using delim. |
providers/rawbytes | rawbytes.Provider(b []byte) |
Takes a raw []byte slice to be parsed with a koanf.Parser |
Package | Parser | Description |
---|---|---|
parsers/json | json.Parser() |
Parses JSON bytes into a nested map |
parsers/yaml | yaml.Parser() |
Parses YAML bytes into a nested map |
parsers/toml | toml.Parser() |
Parses TOML bytes into a nested map |
parsers/hcl | hcl.Parser(flattenSlices bool) |
Parses Hashicorp HCL bytes into a nested map. flattenSlices is recommended to be set to true. Read more. |
Method | Description |
---|---|
Load(p Provider, pa Parser) error |
Loads config from a Provider. If a koanf.Parser is provided, the config is assumed to be raw bytes that's then parsed with the Parser. |
Keys() []string |
Returns the list of flattened key paths that can be used to access config values |
KeyMap() map[string][]string |
Returns a map of all possible key path combinations possible in the loaded nested conf map |
All() map[string]interface{} |
Returns a flat map of flattened key paths and their corresponding config values |
Raw() map[string]interface{} |
Returns a copy of the raw nested conf map |
Print() |
Prints a human readable copy of the flattened key paths and their values for debugging |
Sprint() |
Returns a human readable copy of the flattened key paths and their values for debugging |
Cut(path string) *Koanf |
Cuts the loaded nested conf map at the given path and returns a new Koanf instance with the children |
Copy() *Koanf |
Returns a copy of the Koanf instance |
Merge(*Koanf) |
Merges the config map of a Koanf instance into the current instance |
Unmarshal(path string, o interface{}) error |
Scans the given nested key path into a given struct (like json.Unmarshal) where fields are denoted by the koanf tag |
UnmarshalWithConf(path string, o interface{}, c UnmarshalConf) error |
Like Unmarshal but with customizable options |
Get(path string) interface{} |
Returns the value for the given key path, and if it doesn’t exist, returns nil |
Exists(path string) bool |
Returns true if the given key path exists in the conf map |
Int64(path string) int64 |
|
Int64s(path string) []int64 |
|
Int64Map(path string) map[string]int64 |
|
Int(path string) int |
|
Ints(path string) []int |
|
IntMap(path string) map[string]int |
|
Float64(path string) float64 |
|
Float64s(path string) []float64 |
|
Float64Map(path string) map[string]float64 |
|
Duration(path string) time.Duration |
Returns the time.Duration value of the given key path if it’s numeric (attempts a parse+convert if string) |
Time(path, layout string) time.Time |
Parses the string value of the the given key path with the given layout format and returns time.Time. If the key path is numeric, treats it as a UNIX timestamp and returns its time.Time. |
String(path string) string |
|
Strings(path string) []string |
|
StringMap(path string) map[string]string |
|
Byte(path string) []byte |
|
Bool(path string) bool |
|
Bools(path string) []bool |
|
BoolMap(path string) map[string]bool |
|
MapKeys(path string) []string |
Returns the list of keys in any map |
koanf is a light weight alternative to the popular spf13/viper. It does not aim to do everything viper does (such as mutating config maps and writing them back to files), but provides simpler primitives for reading and accessing configuration. It was written as a result of multiple stumbling blocks encountered with some of viper's fundamental flaws.
- viper breaks JSON, YAML, TOML, HCL language specs by forcibly lowercasing keys.
- Tightly couples config parsing with file extensions.
- Has poor semantics and abstractions. Commandline, env, file etc. and various parses are hardcoded in the core. There are no primitives that can be extended.
- Pulls a large number of third party dependencies into the core package. For instance, even if you do not use YAML or flags, the dependencies are still pulled as a result of the coupling.
- Imposes arbitrary ordering conventions (eg: flag -> env -> config etc.)
Get()
returns references to slices and maps. Mutations made outside change the underlying values inside the conf map.- Does non-idiomatic things such as throwing away O(1) on flat maps.
- There are a large number of open issues.