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loader.go
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loader.go
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package cfgenv
import (
"errors"
"fmt"
"github.com/go-andiamo/splitter"
"os"
"reflect"
"strconv"
"strings"
"time"
)
// LoadAs loads the specified T config struct type from environment vars
//
// the type of T must be a struct
//
// Use any options (such as PrefixOption, SeparatorOption, NamingOption or multiple CustomSetterOption) to alter
// loading behaviour
func LoadAs[T any](options ...any) (*T, error) {
var cfg T
if err := Load(&cfg, options...); err == nil {
return &cfg, nil
} else {
return nil, err
}
}
// Load loads a config struct from environment vars
//
// the supplied cfg arg must be a pointer to a struct
//
// Use any options (such as PrefixOption, SeparatorOption, NamingOption or multiple CustomSetterOption) to alter
// loading behaviour
func Load(cfg any, options ...any) error {
o, err := buildOpts(options...)
if err != nil {
return err
}
v := reflect.ValueOf(cfg)
if v.Kind() != reflect.Ptr {
return errors.New("cfg not a pointer")
} else {
v = v.Elem()
if v.Kind() != reflect.Struct {
return errors.New("cfg not a struct")
}
}
return loadStruct(v, o.prefix.GetPrefix(), o)
}
func buildOpts(options ...any) (*opts, error) {
result := &opts{
prefix: NewPrefix(""),
separator: NewSeparator("_"),
naming: defaultNamingOption,
}
countPfx := 0
countSep := 0
countNm := 0
countExpand := 0
for _, o := range options {
if o != nil {
used := false
if pfx, ok := o.(PrefixOption); ok {
used = true
result.prefix = pfx
countPfx++
}
if sep, ok := o.(SeparatorOption); ok {
used = true
result.separator = sep
countSep++
}
if nm, ok := o.(NamingOption); ok {
used = true
result.naming = nm
countNm++
}
if ex, ok := o.(ExpandOption); ok {
used = true
result.expand = ex
countExpand++
}
if cs, ok := o.(CustomSetterOption); ok {
used = true
result.customs = append(result.customs, cs)
}
if !used {
return nil, errors.New("invalid option")
}
}
}
if countPfx > 1 {
return nil, errors.New("multiple prefix options")
}
if countSep > 1 {
return nil, errors.New("multiple separator options")
}
if countNm > 1 {
return nil, errors.New("multiple naming options")
}
if countExpand > 1 {
return nil, errors.New("multiple expand options")
}
return result, nil
}
type opts struct {
prefix PrefixOption
separator SeparatorOption
naming NamingOption
expand ExpandOption
customs []CustomSetterOption
}
func loadStruct(v reflect.Value, prefix string, options *opts) error {
t := v.Type()
for f := 0; f < t.NumField(); f++ {
if fld := t.Field(f); fld.IsExported() {
fi, err := getFieldInfo(fld, options)
if err != nil {
return err
}
name := options.naming.BuildName(prefix, options.separator.GetSeparator(), fld, fi.name)
if fi.customSetter != nil {
raw, ok := os.LookupEnv(name)
if !ok && !fi.optional {
return fmt.Errorf("missing env var '%s'", name)
} else if !ok && fi.hasDefault {
raw = fi.defaultValue
}
if err = fi.customSetter.Set(fld, v.Field(f), raw); err != nil {
return err
}
} else if fi.isPrefixedMap {
pfx := addPrefixes(prefix, fi.prefix, options.separator.GetSeparator())
setPrefixMap(v.Field(f), pfx, options)
} else if fi.isStruct {
fv := v.Field(f)
if fi.pointer {
fvp := reflect.New(fv.Type().Elem())
fv.Set(fvp)
fv = fvp.Elem()
}
pfx := addPrefixes(prefix, fi.prefix, options.separator.GetSeparator())
if err = loadStruct(fv, pfx, options); err != nil {
return err
}
} else {
raw, ok := os.LookupEnv(name)
if !ok && !fi.optional {
return fmt.Errorf("missing env var '%s'", name)
} else if !ok && fi.hasDefault {
raw = fi.defaultValue
} else if !ok && fi.pointer {
continue
}
if options.expand != nil {
raw = options.expand.Expand(raw)
}
if err = setValue(name, raw, fld, fi, v.Field(f)); err != nil {
return err
}
}
}
}
return nil
}
var durationType = reflect.TypeOf(time.Duration(0))
func setValue(name string, raw string, fld reflect.StructField, fi *fieldInfo, fv reflect.Value) (err error) {
k := fv.Type().Kind()
if fi.pointer {
k = fv.Type().Elem().Kind()
}
switch k {
case reflect.String:
setStringValue(raw, fv, fi.pointer)
case reflect.Bool:
err = setBoolValue(name, raw, fv, fi.pointer)
case reflect.Int:
err = setIntValue[int](name, raw, fv, fi.pointer)
case reflect.Int8:
err = setIntValue[int8](name, raw, fv, fi.pointer)
case reflect.Int16:
err = setIntValue[int16](name, raw, fv, fi.pointer)
case reflect.Int32:
err = setIntValue[int32](name, raw, fv, fi.pointer)
case reflect.Int64:
if fv.Type() == durationType {
err = setIntValue[time.Duration](name, raw, fv, fi.pointer)
} else {
err = setIntValue[int64](name, raw, fv, fi.pointer)
}
case reflect.Uint:
err = setUintValue[uint](name, raw, fv, fi.pointer)
case reflect.Uint8:
err = setUintValue[uint8](name, raw, fv, fi.pointer)
case reflect.Uint16:
err = setUintValue[uint16](name, raw, fv, fi.pointer)
case reflect.Uint32:
err = setUintValue[uint32](name, raw, fv, fi.pointer)
case reflect.Uint64:
err = setUintValue[uint64](name, raw, fv, fi.pointer)
case reflect.Float32:
err = setFloatValue[float32](name, raw, fv, fi.pointer)
case reflect.Float64:
err = setFloatValue[float64](name, raw, fv, fi.pointer)
case reflect.Slice:
err = setSlice(name, raw, fld, fi, fv)
case reflect.Map:
err = setMap(name, raw, fld, fi, fv)
}
return
}
func setSlice(name string, raw string, fld reflect.StructField, fi *fieldInfo, fv reflect.Value) error {
if raw != "" {
vs := strings.Split(raw, fi.delimiter)
sl := reflect.MakeSlice(fv.Type(), len(vs), len(vs))
for i, v := range vs {
if err := setValue(name, v, fld, fi, sl.Index(i)); err != nil {
return err
}
}
fv.Set(sl)
}
return nil
}
func setMap(name string, raw string, fld reflect.StructField, fi *fieldInfo, fv reflect.Value) error {
if raw != "" {
vs := strings.Split(raw, fi.delimiter)
m := reflect.MakeMap(fv.Type())
kt := fv.Type().Key()
vt := fv.Type().Elem()
for _, v := range vs {
kvp := strings.Split(v, fi.separator)
if len(kvp) != 2 {
return fmt.Errorf("env var '%s' contains invalid key/value pair - %s", name, v)
}
kv := reflect.New(kt).Elem()
if err := setValue(name, kvp[0], fld, fi, kv); err != nil {
return err
}
vv := reflect.New(vt).Elem()
if err := setValue(name, kvp[1], fld, fi, vv); err != nil {
return err
}
m.SetMapIndex(kv, vv)
}
fv.Set(m)
}
return nil
}
func setPrefixMap(fv reflect.Value, prefix string, options *opts) {
m := map[string]string{}
for _, e := range os.Environ() {
if strings.HasPrefix(e, prefix) {
ev := strings.SplitN(e, "=", 2)
if options.expand != nil {
m[ev[0][len(prefix):]] = options.expand.Expand(ev[1])
} else {
m[ev[0][len(prefix):]] = ev[1]
}
}
}
fv.Set(reflect.ValueOf(m))
}
func setStringValue(raw string, fv reflect.Value, isPtr bool) {
if isPtr {
fv.Set(reflect.ValueOf(&raw))
} else {
fv.Set(reflect.ValueOf(raw))
}
}
func setBoolValue(name string, raw string, fv reflect.Value, isPtr bool) error {
if b, bErr := strconv.ParseBool(raw); bErr == nil {
if isPtr {
fv.Set(reflect.ValueOf(&b))
} else {
fv.Set(reflect.ValueOf(b))
}
return nil
} else {
return fmt.Errorf("env var '%s' is not a bool", name)
}
}
func setIntValue[T int | int8 | int16 | int32 | int64 | time.Duration](name string, raw string, fv reflect.Value, isPtr bool) error {
if i, err := strconv.ParseInt(raw, 0, getBitSize(fv, isPtr)); err == nil {
if isPtr {
pv := T(i)
fv.Set(reflect.ValueOf(&pv))
} else {
fv.Set(reflect.ValueOf(T(i)))
}
return nil
} else {
return fmt.Errorf("env var '%s' is not an int", name)
}
}
func setUintValue[T uint | uint8 | uint16 | uint32 | uint64](name string, raw string, fv reflect.Value, isPtr bool) error {
if i, err := strconv.ParseUint(raw, 0, getBitSize(fv, isPtr)); err == nil {
if isPtr {
pv := T(i)
fv.Set(reflect.ValueOf(&pv))
} else {
fv.Set(reflect.ValueOf(T(i)))
}
return nil
} else {
return fmt.Errorf("env var '%s' is not an uint", name)
}
}
func setFloatValue[T float32 | float64](name string, raw string, fv reflect.Value, isPtr bool) error {
if f, err := strconv.ParseFloat(raw, getBitSize(fv, isPtr)); err == nil {
if isPtr {
pv := T(f)
fv.Set(reflect.ValueOf(&pv))
} else {
fv.Set(reflect.ValueOf(T(f)))
}
return nil
} else {
return fmt.Errorf("env var '%s' is not a float", name)
}
}
func getBitSize(fv reflect.Value, isPtr bool) int {
if isPtr {
return fv.Type().Elem().Bits()
}
return fv.Type().Bits()
}
func addPrefixes(currPfx, addPfx string, separator string) string {
if currPfx != "" && addPfx != "" {
return currPfx + separator + addPfx
} else if addPfx != "" {
return addPfx
}
return currPfx
}
var tagSplitter = splitter.MustCreateSplitter(',', splitter.DoubleQuotes, splitter.SingleQuotes).
AddDefaultOptions(splitter.Trim(" "), splitter.IgnoreEmpties)
var eqSplitter = splitter.MustCreateSplitter('=', splitter.DoubleQuotes, splitter.SingleQuotes).
AddDefaultOptions(splitter.Trim(" "))
func getFieldInfo(fld reflect.StructField, options *opts) (*fieldInfo, error) {
result, err := checkFieldType(fld, options)
if err != nil {
return nil, err
}
if tag, ok := fld.Tag.Lookup("env"); ok {
parts, err := tagSplitter.Split(tag)
if err != nil {
return nil, fmt.Errorf("invalid tag '%s' on field '%s'", tag, fld.Name)
}
for _, s := range parts {
if pts, _ := eqSplitter.Split(s); len(pts) == 2 {
switch pts[0] {
case "default":
result.hasDefault = true
result.defaultValue = unquoted(pts[1])
continue
case "prefix":
result.prefix = pts[1]
if fld.Type.Kind() == reflect.Map {
result.isPrefixedMap = fld.Type.Elem().Kind() == reflect.String && fld.Type.Key().Kind() == reflect.String
}
if !result.isPrefixedMap && !result.isStruct {
return nil, fmt.Errorf("cannot use env tag 'prefix' on field '%s' (only for structs or map[string]string)", fld.Name)
}
continue
case "separator", "sep":
result.separator = unquoted(pts[1])
continue
case "delimiter", "delim":
result.delimiter = unquoted(pts[1])
continue
}
return nil, fmt.Errorf("invalid tag '%s' on field '%s'", s, fld.Name)
} else if len(pts) == 1 {
switch s {
case "optional":
result.optional = true
case "default", "prefix", "separator", "sep", "delimiter", "delim":
return nil, fmt.Errorf("cannot use env tag '%s' without value on field '%s' (use quotes if necessary)", s, fld.Name)
default:
result.name = unquoted(s)
}
} else {
return nil, fmt.Errorf("invalid tag '%s' on field '%s'", s, fld.Name)
}
}
}
return result, nil
}
func unquoted(s string) string {
if (strings.HasPrefix(s, `"`) && strings.HasSuffix(s, `"`)) ||
(strings.HasPrefix(s, `'`) && strings.HasSuffix(s, `'`)) {
return s[1 : len(s)-1]
}
return s
}
func checkFieldType(fld reflect.StructField, options *opts) (*fieldInfo, error) {
isPtr := false
k := fld.Type.Kind()
if isPtr = k == reflect.Pointer; isPtr {
k = fld.Type.Elem().Kind()
}
result := &fieldInfo{
pointer: isPtr,
optional: isPtr,
separator: ":",
delimiter: ",",
}
for _, c := range options.customs {
if ok := c.IsApplicable(fld); ok {
result.customSetter = c
return result, nil
}
}
if isNativeType(k) {
return result, nil
}
switch k {
case reflect.Slice:
if isPtr {
return nil, fmt.Errorf("field '%s' has unsupported type - %s", fld.Name, fld.Type.String())
} else {
// check slice item type...
it := fld.Type.Elem()
if it.Kind() == reflect.Pointer {
it = it.Elem()
}
if !isNativeType(it.Kind()) {
return nil, fmt.Errorf("field '%s' has unsupported slice item type", fld.Name)
}
}
case reflect.Map:
if isPtr {
return nil, fmt.Errorf("field '%s' has unsupported type - %s", fld.Name, fld.Type.String())
} else {
// check map item type...
it := fld.Type.Elem()
if it.Kind() == reflect.Pointer {
it = it.Elem()
}
if !isNativeType(it.Kind()) {
return nil, fmt.Errorf("field '%s' has unsupported map item type", fld.Name)
} else {
// check map key type...
it = fld.Type.Key()
if !isNativeType(it.Kind()) {
return nil, fmt.Errorf("field '%s' has unsupported map key type", fld.Name)
}
}
}
case reflect.Struct:
result.isStruct = true
default:
return nil, fmt.Errorf("field '%s' has unsupported type - %s", fld.Name, fld.Type.String())
}
return result, nil
}
func isNativeType(k reflect.Kind) bool {
switch k {
case reflect.String, reflect.Bool,
reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
reflect.Float32, reflect.Float64:
return true
}
return false
}
type fieldInfo struct {
name string
optional bool
pointer bool
hasDefault bool
defaultValue string
prefix string
isStruct bool
isPrefixedMap bool
customSetter CustomSetterOption
separator string
delimiter string
}