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|
package main
import (
"fmt"
"strconv"
"strings"
"unicode"
)
type Decoder struct {
raw string
decoderFuncs []DecoderFunc
}
type DecoderFunc func(string) (any, int, error)
func NewDecoder(raw string) *Decoder {
d := &Decoder{raw: raw}
return d.WithDecoderFunc(d.decodeSlice).WithDecoderFunc(d.decodeMap).WithDecoderFunc(d.decodeString).WithDecoderFunc(d.decodeInteger)
}
func (d *Decoder) WithDecoderFunc(f DecoderFunc) *Decoder {
d.decoderFuncs = append(d.decoderFuncs, f)
return d
}
func (d *Decoder) Decode() (any, error) {
for _, f := range d.decoderFuncs {
if r, l, err := f(d.raw); l > 0 || err != nil {
return r, nil
}
}
return nil, fmt.Errorf("failed to decode value: %s", d.raw)
}
func (d *Decoder) decodeString(chunk string) (any, int, error) {
if !unicode.IsDigit(rune(chunk[0])) {
return "", 0, nil
}
var firstColonIndex int
for i := 0; i < len(chunk); i++ {
if chunk[i] == ':' {
firstColonIndex = i
break
}
}
lengthStr := chunk[:firstColonIndex]
length, err := strconv.Atoi(lengthStr)
if err != nil {
return "", 0, err
}
val := chunk[firstColonIndex+1 : firstColonIndex+1+length]
return val, length + 1 + len(lengthStr), nil
}
func (d *Decoder) decodeInteger(chunk string) (any, int, error) {
if rune(chunk[0]) != 'i' {
return 0, 0, nil
}
num, err := strconv.Atoi(chunk[1:strings.IndexByte(chunk, 'e')])
if err != nil {
return 0, 0, err
}
return num, len(strconv.Itoa(num)) + 2, nil
}
func (d *Decoder) decodeSlice(chunk string) (any, int, error) {
if rune(chunk[0]) != 'l' {
return nil, 0, nil
}
if rune(chunk[1]) == 'e' {
return []any{}, 2, nil
}
result := make([]any, 0, 32)
offset := 1
for rune(chunk[offset]) != 'e' {
for _, f := range d.decoderFuncs {
if v, l, err := f(chunk[offset:]); l > 0 {
if err != nil {
return nil, 0, err
}
result = append(result, v)
offset += l
break
}
}
}
return result, offset + 1, nil
}
func (d *Decoder) decodeMap(chunk string) (any, int, error) {
if rune(chunk[0]) != 'd' {
return nil, 0, nil
}
if rune(chunk[1]) == 'e' {
return map[string]any{}, 2, nil
}
result := make(map[string]any, 32)
offset := 1
for rune(chunk[offset]) != 'e' {
key, keyLen, err := d.decodeString(chunk[offset:])
if err != nil {
return nil, 0, err
}
if keyLen == 0 {
return nil, 0, fmt.Errorf("invalid bencoded map key length")
}
for _, f := range d.decoderFuncs {
if v, l, err := f(chunk[offset+keyLen:]); l > 0 {
if err != nil {
return nil, 0, err
}
result[key.(string)] = v
offset += keyLen + l
break
}
}
}
return result, offset + 1, nil
}
|
