package scfg
import (
"encoding"
"fmt"
"io"
"reflect"
"strconv"
)
// Decoder reads and decodes an scfg document from an input stream.
type Decoder struct {
r io.Reader
}
// NewDecoder returns a new decoder which reads from r.
func NewDecoder(r io.Reader) *Decoder {
return &Decoder{r}
}
// Decode reads scfg document from the input and stores it in the value pointed
// to by v.
//
// If v is nil or not a pointer, Decode returns an error.
//
// Blocks can be unmarshaled to:
//
// - Maps. Each directive is unmarshaled into a map entry. The map key must
// be a string.
// - Structs. Each directive is unmarshaled into a struct field.
//
// Duplicate directives are not allowed, unless the struct field or map value
// is a slice of values representing a directive: structs or maps.
//
// Directives can be unmarshaled to:
//
// - Maps. The children block is unmarshaled into the map. Parameters are not
// allowed.
// - Structs. The children block is unmarshaled into the struct. Parameters
// are allowed if one of the struct fields contains the "param" option in
// its tag.
// - Slices. Parameters are unmarshaled into the slice. Children blocks are
// not allowed.
// - Arrays. Parameters are unmarshaled into the array. The number of
// parameters must match exactly the length of the array. Children blocks
// are not allowed.
// - Strings, booleans, integers, floating-point values, values implementing
// encoding.TextUnmarshaler. Only a single parameter is allowed and is
// unmarshaled into the value. Children blocks are not allowed.
//
// The decoding of each struct field can be customized by the format string
// stored under the "scfg" key in the struct field's tag. The tag contains the
// name of the field possibly followed by a comma-separated list of options.
// The name may be empty in order to specify options without overriding the
// default field name. As a special case, if the field name is "-", the field
// is ignored. The "param" option specifies that directive parameters are
// stored in this field (the name must be empty).
func (dec *Decoder) Decode(v interface{}) error {
block, err := Read(dec.r)
if err != nil {
return err
}
rv := reflect.ValueOf(v)
if rv.Kind() != reflect.Ptr || rv.IsNil() {
return fmt.Errorf("scfg: invalid value for unmarshaling")
}
return unmarshalBlock(block, rv)
}
func unmarshalBlock(block Block, v reflect.Value) error {
v = unwrapPointers(v)
t := v.Type()
dirsByName := make(map[string][]*Directive, len(block))
for _, dir := range block {
dirsByName[dir.Name] = append(dirsByName[dir.Name], dir)
}
switch v.Kind() {
case reflect.Map:
if t.Key().Kind() != reflect.String {
return fmt.Errorf("scfg: map key type must be string")
}
if v.IsNil() {
v.Set(reflect.MakeMap(t))
} else if v.Len() > 0 {
clearMap(v)
}
for name, dirs := range dirsByName {
mv := reflect.New(t.Elem()).Elem()
if err := unmarshalDirectiveList(dirs, mv); err != nil {
return err
}
v.SetMapIndex(reflect.ValueOf(name), mv)
}
case reflect.Struct:
si, err := getStructInfo(t)
if err != nil {
return err
}
for name, dirs := range dirsByName {
fieldIndex, ok := si.children[name]
if !ok {
return newUnmarshalDirectiveError(dirs[0], "unknown directive")
}
fv := v.Field(fieldIndex)
if err := unmarshalDirectiveList(dirs, fv); err != nil {
return err
}
}
default:
return fmt.Errorf("scfg: unsupported type for unmarshaling blocks: %v", t)
}
return nil
}
func unmarshalDirectiveList(dirs []*Directive, v reflect.Value) error {
v = unwrapPointers(v)
t := v.Type()
if v.Kind() != reflect.Slice || !isDirectiveType(t.Elem()) {
if len(dirs) > 1 {
return newUnmarshalDirectiveError(dirs[1], "directive must not be specified more than once")
}
return unmarshalDirective(dirs[0], v)
}
sv := reflect.MakeSlice(t, len(dirs), len(dirs))
for i, dir := range dirs {
if err := unmarshalDirective(dir, sv.Index(i)); err != nil {
return err
}
}
v.Set(sv)
return nil
}
// isDirectiveType checks whether a type can only be unmarshaled as a
// directive, not as a parameter. Accepting too many types here would result in
// ambiguities, see:
// https://lists.sr.ht/~emersion/public-inbox/%3C20230629132458.152205-1-contact%40emersion.fr%3E#%3Ch4Y2peS_YBqY3ar4XlmPDPiNBFpYGns3EBYUx3_6zWEhV2o8_-fBQveRujGADWYhVVCucHBEryFGoPtpC3d3mQ-x10pWnFogfprbQTSvtxc=@emersion.fr%3E
func isDirectiveType(t reflect.Type) bool {
for t.Kind() == reflect.Ptr {
t = t.Elem()
}
textUnmarshalerType := reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
if reflect.PtrTo(t).Implements(textUnmarshalerType) {
return false
}
switch t.Kind() {
case reflect.Struct, reflect.Map:
return true
default:
return false
}
}
func unmarshalDirective(dir *Directive, v reflect.Value) error {
v = unwrapPointers(v)
t := v.Type()
if v.CanAddr() {
if _, ok := v.Addr().Interface().(encoding.TextUnmarshaler); ok {
if len(dir.Children) != 0 {
return newUnmarshalDirectiveError(dir, "directive requires zero children")
}
return unmarshalParamList(dir, v)
}
}
switch v.Kind() {
case reflect.Map:
if len(dir.Params) > 0 {
return newUnmarshalDirectiveError(dir, "directive requires zero parameters")
}
if err := unmarshalBlock(dir.Children, v); err != nil {
return err
}
case reflect.Struct:
si, err := getStructInfo(t)
if err != nil {
return err
}
if si.param >= 0 {
if err := unmarshalParamList(dir, v.Field(si.param)); err != nil {
return err
}
} else {
if len(dir.Params) > 0 {
return newUnmarshalDirectiveError(dir, "directive requires zero parameters")
}
}
if err := unmarshalBlock(dir.Children, v); err != nil {
return err
}
default:
if len(dir.Children) != 0 {
return newUnmarshalDirectiveError(dir, "directive requires zero children")
}
if err := unmarshalParamList(dir, v); err != nil {
return err
}
}
return nil
}
func unmarshalParamList(dir *Directive, v reflect.Value) error {
switch v.Kind() {
case reflect.Slice:
t := v.Type()
sv := reflect.MakeSlice(t, len(dir.Params), len(dir.Params))
for i, param := range dir.Params {
if err := unmarshalParam(param, sv.Index(i)); err != nil {
return newUnmarshalParamError(dir, i, err)
}
}
v.Set(sv)
case reflect.Array:
if len(dir.Params) != v.Len() {
return newUnmarshalDirectiveError(dir, fmt.Sprintf("directive requires exactly %v parameters", v.Len()))
}
for i, param := range dir.Params {
if err := unmarshalParam(param, v.Index(i)); err != nil {
return newUnmarshalParamError(dir, i, err)
}
}
default:
if len(dir.Params) != 1 {
return newUnmarshalDirectiveError(dir, "directive requires exactly one parameter")
}
if err := unmarshalParam(dir.Params[0], v); err != nil {
return newUnmarshalParamError(dir, 0, err)
}
}
return nil
}
func unmarshalParam(param string, v reflect.Value) error {
v = unwrapPointers(v)
t := v.Type()
// TODO: improve our logic following:
// https://cs.opensource.google/go/go/+/refs/tags/go1.21.5:src/encoding/json/decode.go;drc=b9b8cecbfc72168ca03ad586cc2ed52b0e8db409;l=421
if v.CanAddr() {
if v, ok := v.Addr().Interface().(encoding.TextUnmarshaler); ok {
return v.UnmarshalText([]byte(param))
}
}
switch v.Kind() {
case reflect.String:
v.Set(reflect.ValueOf(param))
case reflect.Bool:
switch param {
case "true":
v.Set(reflect.ValueOf(true))
case "false":
v.Set(reflect.ValueOf(false))
default:
return fmt.Errorf("invalid bool parameter %q", param)
}
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
i, err := strconv.ParseInt(param, 10, t.Bits())
if err != nil {
return fmt.Errorf("invalid %v parameter: %v", t, err)
}
v.Set(reflect.ValueOf(i).Convert(t))
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
u, err := strconv.ParseUint(param, 10, t.Bits())
if err != nil {
return fmt.Errorf("invalid %v parameter: %v", t, err)
}
v.Set(reflect.ValueOf(u).Convert(t))
case reflect.Float32, reflect.Float64:
f, err := strconv.ParseFloat(param, t.Bits())
if err != nil {
return fmt.Errorf("invalid %v parameter: %v", t, err)
}
v.Set(reflect.ValueOf(f).Convert(t))
default:
return fmt.Errorf("unsupported type for unmarshaling parameter: %v", t)
}
return nil
}
func unwrapPointers(v reflect.Value) reflect.Value {
for v.Kind() == reflect.Ptr {
if v.IsNil() {
v.Set(reflect.New(v.Type().Elem()))
}
v = v.Elem()
}
return v
}
func clearMap(v reflect.Value) {
for _, k := range v.MapKeys() {
v.SetMapIndex(k, reflect.Value{})
}
}
type unmarshalDirectiveError struct {
lineno int
name string
msg string
}
func newUnmarshalDirectiveError(dir *Directive, msg string) *unmarshalDirectiveError {
return &unmarshalDirectiveError{
name: dir.Name,
lineno: dir.lineno,
msg: msg,
}
}
func (err *unmarshalDirectiveError) Error() string {
return fmt.Sprintf("line %v, directive %q: %v", err.lineno, err.name, err.msg)
}
type unmarshalParamError struct {
lineno int
directive string
paramIndex int
err error
}
func newUnmarshalParamError(dir *Directive, paramIndex int, err error) *unmarshalParamError {
return &unmarshalParamError{
directive: dir.Name,
lineno: dir.lineno,
paramIndex: paramIndex,
err: err,
}
}
func (err *unmarshalParamError) Error() string {
return fmt.Sprintf("line %v, directive %q, parameter %v: %v", err.lineno, err.directive, err.paramIndex+1, err.err)
}
