go-config

go-config allows to initialize configuration in flexible way using from default, file, environment variables value.

Initialization

Done in three steps:

1. init with value from default tag
2. merge with config file if filepath is provided
3. override with environment variables which stored under envconfig tag

Supported file extensions

• json

Supported types

• Standard types: bool, float, int(uint), slice, string
• time.Duration, time.Time: full support with aliases config.Duration, config.Time
• Custom types, slice of custom types

Usage

Default value

type Server struct {
    Addr string `default:"localhost:8080"`
}

Environment value

type Server struct {
    Addr string `envconfig:"SERVER_ADDR"`
}

Combined default, json, env

type Server struct {
    Addr string `json:"addr" envconfig:"SERVER_ADDR" default:"localhost:8080"`
}

Slice

Default strings separator is comma.

REDIS_ADDR=127.0.0.1:6377,127.0.0.1:6378,127.0.0.1:6379

type Redis struct {
    Addrs []string `json:"addrs" envconfig:"REDIS_ADDR" default:"localhost:6378,localhost:6379"`
}

Slice of structs could be parsed from environment by defining envprefix.
Every ENV group override element stored at index of slice or append new one.
Sparse slices are not allowed.

var cfg struct {
...
Replicas []Postgres `json:"replicas" envprefix:"REPLICAS"`
...
}

Environment key should has next pattern:
${envprefix}_${index}_${envconfig} or ${envprefix}_${index}_${StructFieldName}

REPLICAS_0_POSTGRES_USER=replica REPLICAS_2_USER=replica

time.Duration, time.Time

In case using json file you have to use aliases config.Duration, config.Time, that properly unmarshal it self

type NATS struct {
    ...
    ReconnectInterval config.Duration `json:"reconnect_interval" envconfig:"NATS_RECONNECT_INTERVAL" default:"2s"`
}

Otherwise time.Duration, time.Time might be used directly:

var cfg struct {
    ReadTimeout  time.Duration `envconfig:"READ_TIMEOUT"  default:"1s"`
    WriteTimeout time.Duration `envconfig:"WRITE_TIMEOUT" default:"10s"`
}