goext/confext/confParser.go

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package confext
import (
"errors"
"fmt"
"gogs.mikescher.com/BlackForestBytes/goext/timeext"
"math/bits"
"os"
"reflect"
"strconv"
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"strings"
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"time"
)
// ApplyEnvOverrides overrides field values from environment variables
//
// fields must be tagged with `env:"env_key"`
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//
// only works on exported fields
//
// fields without an env tag are ignored
// fields with an `env:"-"` tag are ignore
//
// sub-structs are recursively parsed (if they have an env tag) and the env-variable keys are delimited by the delim parameter
// sub-structs with `env:""` are also parsed, but the delimited is skipped (they are handled as if they were one level higher)
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func ApplyEnvOverrides[T any](prefix string, c *T, delim string) error {
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rval := reflect.ValueOf(c).Elem()
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return processEnvOverrides(rval, delim, prefix)
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}
func processEnvOverrides(rval reflect.Value, delim string, prefix string) error {
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rtyp := rval.Type()
for i := 0; i < rtyp.NumField(); i++ {
rsfield := rtyp.Field(i)
rvfield := rval.Field(i)
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if !rsfield.IsExported() {
continue
}
envkey, found := rsfield.Tag.Lookup("env")
if !found || envkey == "-" {
continue
}
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if rvfield.Kind() == reflect.Struct && rvfield.Type() != reflect.TypeOf(time.UnixMilli(0)) {
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subPrefix := prefix
if envkey != "" {
subPrefix = subPrefix + envkey + delim
}
err := processEnvOverrides(rvfield, delim, subPrefix)
if err != nil {
return err
}
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continue
}
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fullEnvKey := prefix + envkey
envval, efound := os.LookupEnv(fullEnvKey)
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if !efound {
continue
}
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if rvfield.Type().Kind() == reflect.Pointer {
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newval, err := parseEnvToValue(envval, fullEnvKey, rvfield.Type().Elem())
if err != nil {
return err
}
// converts reflect.Value to pointer
ptrval := reflect.New(rvfield.Type().Elem())
ptrval.Elem().Set(newval)
rvfield.Set(ptrval)
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fmt.Printf("[CONF] Overwrite config '%s' with '%s'\n", fullEnvKey, envval)
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} else {
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newval, err := parseEnvToValue(envval, fullEnvKey, rvfield.Type())
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if err != nil {
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return err
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}
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rvfield.Set(newval)
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fmt.Printf("[CONF] Overwrite config '%s' with '%s'\n", fullEnvKey, envval)
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}
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}
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return nil
}
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func parseEnvToValue(envval string, fullEnvKey string, rvtype reflect.Type) (reflect.Value, error) {
if rvtype == reflect.TypeOf("") {
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return reflect.ValueOf(envval), nil
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} else if rvtype == reflect.TypeOf(int(0)) {
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envint, err := strconv.ParseInt(envval, 10, bits.UintSize)
if err != nil {
return reflect.Value{}, errors.New(fmt.Sprintf("Failed to parse env-config variable '%s' to int (value := '%s')", fullEnvKey, envval))
}
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return reflect.ValueOf(int(envint)), nil
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} else if rvtype == reflect.TypeOf(int64(0)) {
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envint, err := strconv.ParseInt(envval, 10, 64)
if err != nil {
return reflect.Value{}, errors.New(fmt.Sprintf("Failed to parse env-config variable '%s' to int64 (value := '%s')", fullEnvKey, envval))
}
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return reflect.ValueOf(int64(envint)), nil
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} else if rvtype == reflect.TypeOf(int32(0)) {
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envint, err := strconv.ParseInt(envval, 10, 32)
if err != nil {
return reflect.Value{}, errors.New(fmt.Sprintf("Failed to parse env-config variable '%s' to int32 (value := '%s')", fullEnvKey, envval))
}
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return reflect.ValueOf(int32(envint)), nil
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} else if rvtype == reflect.TypeOf(int8(0)) {
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envint, err := strconv.ParseInt(envval, 10, 8)
if err != nil {
return reflect.Value{}, errors.New(fmt.Sprintf("Failed to parse env-config variable '%s' to int32 (value := '%s')", fullEnvKey, envval))
}
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return reflect.ValueOf(int8(envint)), nil
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} else if rvtype == reflect.TypeOf(time.Duration(0)) {
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dur, err := timeext.ParseDurationShortString(envval)
if err != nil {
return reflect.Value{}, errors.New(fmt.Sprintf("Failed to parse env-config variable '%s' to duration (value := '%s')", fullEnvKey, envval))
}
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return reflect.ValueOf(dur), nil
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} else if rvtype == reflect.TypeOf(time.UnixMilli(0)) {
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tim, err := time.Parse(time.RFC3339Nano, envval)
if err != nil {
return reflect.Value{}, errors.New(fmt.Sprintf("Failed to parse env-config variable '%s' to time.time (value := '%s')", fullEnvKey, envval))
}
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return reflect.ValueOf(tim), nil
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} else if rvtype.ConvertibleTo(reflect.TypeOf(int(0))) {
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envint, err := strconv.ParseInt(envval, 10, 8)
if err != nil {
return reflect.Value{}, errors.New(fmt.Sprintf("Failed to parse env-config variable '%s' to <%s, ,int> (value := '%s')", rvtype.Name(), fullEnvKey, envval))
}
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envcvl := reflect.ValueOf(envint).Convert(rvtype)
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return envcvl, nil
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} else if rvtype.ConvertibleTo(reflect.TypeOf(false)) {
if strings.TrimSpace(strings.ToLower(envval)) == "true" {
return reflect.ValueOf(true).Convert(rvtype), nil
} else if strings.TrimSpace(strings.ToLower(envval)) == "false" {
return reflect.ValueOf(false).Convert(rvtype), nil
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} else if strings.TrimSpace(strings.ToLower(envval)) == "1" {
return reflect.ValueOf(true).Convert(rvtype), nil
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} else if strings.TrimSpace(strings.ToLower(envval)) == "0" {
return reflect.ValueOf(false).Convert(rvtype), nil
} else {
return reflect.Value{}, errors.New(fmt.Sprintf("Failed to parse env-config variable '%s' to <%s, ,bool> (value := '%s')", rvtype.Name(), fullEnvKey, envval))
}
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} else if rvtype.ConvertibleTo(reflect.TypeOf("")) {
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envcvl := reflect.ValueOf(envval).Convert(rvtype)
return envcvl, nil
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} else {
return reflect.Value{}, errors.New(fmt.Sprintf("Unknown kind/type in config: [ %s | %s ]", rvtype.Kind().String(), rvtype.String()))
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}
}