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env.go
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package env
import (
"encoding"
"errors"
"fmt"
"io/ioutil"
"net/url"
"os"
"reflect"
"strconv"
"strings"
"time"
)
// nolint: gochecknoglobals
var (
// ErrNotAStructPtr is returned if you pass something that is not a pointer to a
// Struct to Parse
ErrNotAStructPtr = errors.New("env: expected a pointer to a Struct")
defaultBuiltInParsers = map[reflect.Kind]ParserFunc{
reflect.Bool: func(v string) (interface{}, error) {
return strconv.ParseBool(v)
},
reflect.String: func(v string) (interface{}, error) {
return v, nil
},
reflect.Int: func(v string) (interface{}, error) {
i, err := strconv.ParseInt(v, 10, 32)
return int(i), err
},
reflect.Int16: func(v string) (interface{}, error) {
i, err := strconv.ParseInt(v, 10, 16)
return int16(i), err
},
reflect.Int32: func(v string) (interface{}, error) {
i, err := strconv.ParseInt(v, 10, 32)
return int32(i), err
},
reflect.Int64: func(v string) (interface{}, error) {
return strconv.ParseInt(v, 10, 64)
},
reflect.Int8: func(v string) (interface{}, error) {
i, err := strconv.ParseInt(v, 10, 8)
return int8(i), err
},
reflect.Uint: func(v string) (interface{}, error) {
i, err := strconv.ParseUint(v, 10, 32)
return uint(i), err
},
reflect.Uint16: func(v string) (interface{}, error) {
i, err := strconv.ParseUint(v, 10, 16)
return uint16(i), err
},
reflect.Uint32: func(v string) (interface{}, error) {
i, err := strconv.ParseUint(v, 10, 32)
return uint32(i), err
},
reflect.Uint64: func(v string) (interface{}, error) {
i, err := strconv.ParseUint(v, 10, 64)
return i, err
},
reflect.Uint8: func(v string) (interface{}, error) {
i, err := strconv.ParseUint(v, 10, 8)
return uint8(i), err
},
reflect.Float64: func(v string) (interface{}, error) {
return strconv.ParseFloat(v, 64)
},
reflect.Float32: func(v string) (interface{}, error) {
f, err := strconv.ParseFloat(v, 32)
return float32(f), err
},
}
defaultTypeParsers = map[reflect.Type]ParserFunc{
reflect.TypeOf(url.URL{}): func(v string) (interface{}, error) {
u, err := url.Parse(v)
if err != nil {
return nil, fmt.Errorf("unable to parse URL: %v", err)
}
return *u, nil
},
reflect.TypeOf(time.Nanosecond): func(v string) (interface{}, error) {
s, err := time.ParseDuration(v)
if err != nil {
return nil, fmt.Errorf("unable to parse duration: %v", err)
}
return s, err
},
}
)
// ParserFunc defines the signature of a function that can be used within `CustomParsers`
type ParserFunc func(v string) (interface{}, error)
// Parse parses a struct containing `env` tags and loads its values from
// environment variables.
func Parse(v interface{}) error {
return ParseWithFuncs(v, map[reflect.Type]ParserFunc{})
}
// ParseWithFuncs is the same as `Parse` except it also allows the user to pass
// in custom parsers.
func ParseWithFuncs(v interface{}, funcMap map[reflect.Type]ParserFunc) error {
ptrRef := reflect.ValueOf(v)
if ptrRef.Kind() != reflect.Ptr {
return ErrNotAStructPtr
}
ref := ptrRef.Elem()
if ref.Kind() != reflect.Struct {
return ErrNotAStructPtr
}
var parsers = defaultTypeParsers
for k, v := range funcMap {
parsers[k] = v
}
return doParse(ref, parsers)
}
func doParse(ref reflect.Value, funcMap map[reflect.Type]ParserFunc) error {
var refType = ref.Type()
for i := 0; i < refType.NumField(); i++ {
refField := ref.Field(i)
if !refField.CanSet() {
continue
}
if reflect.Ptr == refField.Kind() && !refField.IsNil() {
err := ParseWithFuncs(refField.Interface(), funcMap)
if err != nil {
return err
}
continue
}
if reflect.Struct == refField.Kind() && refField.CanAddr() && refField.Type().Name() == "" {
err := Parse(refField.Addr().Interface())
if err != nil {
return err
}
continue
}
refTypeField := refType.Field(i)
value, err := get(refTypeField)
if err != nil {
return err
}
if value == "" {
if reflect.Struct == refField.Kind() {
if err := doParse(refField, funcMap); err != nil {
return err
}
}
continue
}
if err := set(refField, refTypeField, value, funcMap); err != nil {
return err
}
}
return nil
}
func get(field reflect.StructField) (val string, err error) {
var required bool
var exists bool
var loadFile bool
var expand = strings.EqualFold(field.Tag.Get("envExpand"), "true")
var unset = strings.EqualFold(field.Tag.Get("envUnset"), "true")
key, opts := parseKeyForOption(field.Tag.Get("env"))
for _, opt := range opts {
switch opt {
case "":
break
case "file":
loadFile = true
case "required":
required = true
default:
return "", fmt.Errorf("env: tag option %q not supported", opt)
}
}
defaultValue := field.Tag.Get("envDefault")
val, exists = getOr(key, defaultValue)
if expand {
val = os.ExpandEnv(val)
}
if unset {
defer os.Unsetenv(key)
}
if required && !exists {
return "", fmt.Errorf(`env: required environment variable %q is not set`, key)
}
if loadFile && val != "" {
filename := val
val, err = getFromFile(filename)
if err != nil {
return "", fmt.Errorf(`env: could not load content of file "%s" from variable %s: %v`, filename, key, err)
}
}
return val, err
}
// split the env tag's key into the expected key and desired option, if any.
func parseKeyForOption(key string) (string, []string) {
opts := strings.Split(key, ",")
return opts[0], opts[1:]
}
func getFromFile(filename string) (value string, err error) {
b, err := ioutil.ReadFile(filename)
return string(b), err
}
func getOr(key, defaultValue string) (value string, exists bool) {
value, exists = os.LookupEnv(key)
if !exists {
value = defaultValue
}
return value, exists
}
func set(field reflect.Value, sf reflect.StructField, value string, funcMap map[reflect.Type]ParserFunc) error {
if field.Kind() == reflect.Slice {
return handleSlice(field, value, sf, funcMap)
}
var tm = asTextUnmarshaler(field)
if tm != nil {
var err = tm.UnmarshalText([]byte(value))
return newParseError(sf, err)
}
var typee = sf.Type
var fieldee = field
if typee.Kind() == reflect.Ptr {
typee = typee.Elem()
fieldee = field.Elem()
}
parserFunc, ok := funcMap[typee]
if ok {
val, err := parserFunc(value)
if err != nil {
return newParseError(sf, err)
}
fieldee.Set(reflect.ValueOf(val))
return nil
}
parserFunc, ok = defaultBuiltInParsers[typee.Kind()]
if ok {
val, err := parserFunc(value)
if err != nil {
return newParseError(sf, err)
}
fieldee.Set(reflect.ValueOf(val).Convert(typee))
return nil
}
return newNoParserError(sf)
}
func handleSlice(field reflect.Value, value string, sf reflect.StructField, funcMap map[reflect.Type]ParserFunc) error {
var separator = sf.Tag.Get("envSeparator")
if separator == "" {
separator = ","
}
var parts = strings.Split(value, separator)
var typee = sf.Type.Elem()
if typee.Kind() == reflect.Ptr {
typee = typee.Elem()
}
if _, ok := reflect.New(typee).Interface().(encoding.TextUnmarshaler); ok {
return parseTextUnmarshalers(field, parts, sf)
}
parserFunc, ok := funcMap[typee]
if !ok {
parserFunc, ok = defaultBuiltInParsers[typee.Kind()]
if !ok {
return newNoParserError(sf)
}
}
var result = reflect.MakeSlice(sf.Type, 0, len(parts))
for _, part := range parts {
r, err := parserFunc(part)
if err != nil {
return newParseError(sf, err)
}
var v = reflect.ValueOf(r).Convert(typee)
if sf.Type.Elem().Kind() == reflect.Ptr {
v = reflect.New(typee)
v.Elem().Set(reflect.ValueOf(r).Convert(typee))
}
result = reflect.Append(result, v)
}
field.Set(result)
return nil
}
func asTextUnmarshaler(field reflect.Value) encoding.TextUnmarshaler {
if reflect.Ptr == field.Kind() {
if field.IsNil() {
field.Set(reflect.New(field.Type().Elem()))
}
} else if field.CanAddr() {
field = field.Addr()
}
tm, ok := field.Interface().(encoding.TextUnmarshaler)
if !ok {
return nil
}
return tm
}
func parseTextUnmarshalers(field reflect.Value, data []string, sf reflect.StructField) error {
s := len(data)
elemType := field.Type().Elem()
slice := reflect.MakeSlice(reflect.SliceOf(elemType), s, s)
for i, v := range data {
sv := slice.Index(i)
kind := sv.Kind()
if kind == reflect.Ptr {
sv = reflect.New(elemType.Elem())
} else {
sv = sv.Addr()
}
tm := sv.Interface().(encoding.TextUnmarshaler)
if err := tm.UnmarshalText([]byte(v)); err != nil {
return newParseError(sf, err)
}
if kind == reflect.Ptr {
slice.Index(i).Set(sv)
}
}
field.Set(slice)
return nil
}
func newParseError(sf reflect.StructField, err error) error {
if err == nil {
return nil
}
return parseError{
sf: sf,
err: err,
}
}
type parseError struct {
sf reflect.StructField
err error
}
func (e parseError) Error() string {
return fmt.Sprintf(`env: parse error on field "%s" of type "%s": %v`, e.sf.Name, e.sf.Type, e.err)
}
func newNoParserError(sf reflect.StructField) error {
return fmt.Errorf(`env: no parser found for field "%s" of type "%s"`, sf.Name, sf.Type)
}