55 lines
1.4 KiB
Go
55 lines
1.4 KiB
Go
package main
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import (
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"os"
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"reflect"
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"strings"
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)
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// EnvOptions holds program options loaded from the process environment
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type EnvOptions map[string]interface{}
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// LoadEnvForStruct loads environment variables for each field in an options
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// struct passed into it.
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//
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// Fields in the options struct must have an `env` and `cfg` tag to be read
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// from the environment
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func (cfg EnvOptions) LoadEnvForStruct(options interface{}) {
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val := reflect.ValueOf(options)
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var typ reflect.Type
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if val.Kind() == reflect.Ptr {
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typ = val.Elem().Type()
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} else {
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typ = val.Type()
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}
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for i := 0; i < typ.NumField(); i++ {
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// pull out the struct tags:
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// flag - the name of the command line flag
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// deprecated - (optional) the name of the deprecated command line flag
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// cfg - (optional, defaults to underscored flag) the name of the config file option
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field := typ.Field(i)
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fieldV := reflect.Indirect(val).Field(i)
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if field.Type.Kind() == reflect.Struct && field.Anonymous {
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cfg.LoadEnvForStruct(fieldV.Interface())
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continue
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}
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flagName := field.Tag.Get("flag")
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envName := field.Tag.Get("env")
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cfgName := field.Tag.Get("cfg")
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if cfgName == "" && flagName != "" {
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cfgName = strings.Replace(flagName, "-", "_", -1)
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}
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if envName == "" || cfgName == "" {
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// resolvable fields must have the `env` and `cfg` struct tag
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continue
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}
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v := os.Getenv(envName)
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if v != "" {
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cfg[cfgName] = v
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}
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}
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}
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