bencode/encode.go

   1 package bencode
   2
   3 import (
   4         "io"
   5         "math/big"
   6         "reflect"
   7         "runtime"
   8         "sort"
   9         "strconv"
  10         "sync"
  11
  12         "github.com/anacrolix/missinggo"
  13 )
  14
  15 func isEmptyValue(v reflect.Value) bool {
  16         return missinggo.IsEmptyValue(v)
  17 }
  18
  19 type Encoder struct {
  20         w       io.Writer
  21         scratch [64]byte
  22 }
  23
  24 func (e *Encoder) Encode(v interface{}) (err error) {
  25         if v == nil {
  26                 return
  27         }
  28         defer func() {
  29                 if e := recover(); e != nil {
  30                         if _, ok := e.(runtime.Error); ok {
  31                                 panic(e)
  32                         }
  33                         var ok bool
  34                         err, ok = e.(error)
  35                         if !ok {
  36                                 panic(e)
  37                         }
  38                 }
  39         }()
  40         e.reflectValue(reflect.ValueOf(v))
  41         return nil
  42 }
  43
  44 type stringValues []reflect.Value
  45
  46 func (sv stringValues) Len() int           { return len(sv) }
  47 func (sv stringValues) Swap(i, j int)      { sv[i], sv[j] = sv[j], sv[i] }
  48 func (sv stringValues) Less(i, j int) bool { return sv.get(i) < sv.get(j) }
  49 func (sv stringValues) get(i int) string   { return sv[i].String() }
  50
  51 func (e *Encoder) write(s []byte) {
  52         _, err := e.w.Write(s)
  53         if err != nil {
  54                 panic(err)
  55         }
  56 }
  57
  58 func (e *Encoder) writeString(s string) {
  59         for s != "" {
  60                 n := copy(e.scratch[:], s)
  61                 s = s[n:]
  62                 e.write(e.scratch[:n])
  63         }
  64 }
  65
  66 func (e *Encoder) reflectString(s string) {
  67         e.writeStringPrefix(int64(len(s)))
  68         e.writeString(s)
  69 }
  70
  71 func (e *Encoder) writeStringPrefix(l int64) {
  72         b := strconv.AppendInt(e.scratch[:0], l, 10)
  73         e.write(b)
  74         e.writeString(":")
  75 }
  76
  77 func (e *Encoder) reflectByteSlice(s []byte) {
  78         e.writeStringPrefix(int64(len(s)))
  79         e.write(s)
  80 }
  81
  82 // Returns true if the value implements Marshaler interface and marshaling was
  83 // done successfully.
  84 func (e *Encoder) reflectMarshaler(v reflect.Value) bool {
  85         if !v.Type().Implements(marshalerType) {
  86                 if v.Kind() != reflect.Ptr && v.CanAddr() && v.Addr().Type().Implements(marshalerType) {
  87                         v = v.Addr()
  88                 } else {
  89                         return false
  90                 }
  91         }
  92         m := v.Interface().(Marshaler)
  93         data, err := m.MarshalBencode()
  94         if err != nil {
  95                 panic(&MarshalerError{v.Type(), err})
  96         }
  97         e.write(data)
  98         return true
  99 }
 100
 101 var bigIntType = reflect.TypeOf((*big.Int)(nil)).Elem()
 102
 103 func (e *Encoder) reflectValue(v reflect.Value) {
 104         if e.reflectMarshaler(v) {
 105                 return
 106         }
 107
 108         if v.Type() == bigIntType {
 109                 e.writeString("i")
 110                 bi := v.Interface().(big.Int)
 111                 e.writeString(bi.String())
 112                 e.writeString("e")
 113                 return
 114         }
 115
 116         switch v.Kind() {
 117         case reflect.Bool:
 118                 if v.Bool() {
 119                         e.writeString("i1e")
 120                 } else {
 121                         e.writeString("i0e")
 122                 }
 123         case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
 124                 e.writeString("i")
 125                 b := strconv.AppendInt(e.scratch[:0], v.Int(), 10)
 126                 e.write(b)
 127                 e.writeString("e")
 128         case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
 129                 e.writeString("i")
 130                 b := strconv.AppendUint(e.scratch[:0], v.Uint(), 10)
 131                 e.write(b)
 132                 e.writeString("e")
 133         case reflect.String:
 134                 e.reflectString(v.String())
 135         case reflect.Struct:
 136                 e.writeString("d")
 137                 for _, ef := range getEncodeFields(v.Type()) {
 138                         fieldValue := ef.i(v)
 139                         if !fieldValue.IsValid() {
 140                                 continue
 141                         }
 142                         if ef.omitEmpty && isEmptyValue(fieldValue) {
 143                                 continue
 144                         }
 145                         e.reflectString(ef.tag)
 146                         e.reflectValue(fieldValue)
 147                 }
 148                 e.writeString("e")
 149         case reflect.Map:
 150                 if v.Type().Key().Kind() != reflect.String {
 151                         panic(&MarshalTypeError{v.Type()})
 152                 }
 153                 if v.IsNil() {
 154                         e.writeString("de")
 155                         break
 156                 }
 157                 e.writeString("d")
 158                 sv := stringValues(v.MapKeys())
 159                 sort.Sort(sv)
 160                 for _, key := range sv {
 161                         e.reflectString(key.String())
 162                         e.reflectValue(v.MapIndex(key))
 163                 }
 164                 e.writeString("e")
 165         case reflect.Slice, reflect.Array:
 166                 e.reflectSequence(v)
 167         case reflect.Interface:
 168                 e.reflectValue(v.Elem())
 169         case reflect.Ptr:
 170                 if v.IsNil() {
 171                         v = reflect.Zero(v.Type().Elem())
 172                 } else {
 173                         v = v.Elem()
 174                 }
 175                 e.reflectValue(v)
 176         default:
 177                 panic(&MarshalTypeError{v.Type()})
 178         }
 179 }
 180
 181 func (e *Encoder) reflectSequence(v reflect.Value) {
 182         // Use bencode string-type
 183         if v.Type().Elem().Kind() == reflect.Uint8 {
 184                 if v.Kind() != reflect.Slice {
 185                         // Can't use []byte optimization
 186                         if !v.CanAddr() {
 187                                 e.writeStringPrefix(int64(v.Len()))
 188                                 for i := 0; i < v.Len(); i++ {
 189                                         var b [1]byte
 190                                         b[0] = byte(v.Index(i).Uint())
 191                                         e.write(b[:])
 192                                 }
 193                                 return
 194                         }
 195                         v = v.Slice(0, v.Len())
 196                 }
 197                 s := v.Bytes()
 198                 e.reflectByteSlice(s)
 199                 return
 200         }
 201         if v.IsNil() {
 202                 e.writeString("le")
 203                 return
 204         }
 205         e.writeString("l")
 206         for i, n := 0, v.Len(); i < n; i++ {
 207                 e.reflectValue(v.Index(i))
 208         }
 209         e.writeString("e")
 210 }
 211
 212 type encodeField struct {
 213         i         func(v reflect.Value) reflect.Value
 214         tag       string
 215         omitEmpty bool
 216 }
 217
 218 type encodeFieldsSortType []encodeField
 219
 220 func (ef encodeFieldsSortType) Len() int           { return len(ef) }
 221 func (ef encodeFieldsSortType) Swap(i, j int)      { ef[i], ef[j] = ef[j], ef[i] }
 222 func (ef encodeFieldsSortType) Less(i, j int) bool { return ef[i].tag < ef[j].tag }
 223
 224 var (
 225         typeCacheLock     sync.RWMutex
 226         encodeFieldsCache = make(map[reflect.Type][]encodeField)
 227 )
 228
 229 func getEncodeFields(t reflect.Type) []encodeField {
 230         typeCacheLock.RLock()
 231         fs, ok := encodeFieldsCache[t]
 232         typeCacheLock.RUnlock()
 233         if ok {
 234                 return fs
 235         }
 236         fs = makeEncodeFields(t)
 237         typeCacheLock.Lock()
 238         defer typeCacheLock.Unlock()
 239         encodeFieldsCache[t] = fs
 240         return fs
 241 }
 242
 243 func makeEncodeFields(t reflect.Type) (fs []encodeField) {
 244         for _i, n := 0, t.NumField(); _i < n; _i++ {
 245                 i := _i
 246                 f := t.Field(i)
 247                 if f.PkgPath != "" {
 248                         continue
 249                 }
 250                 if f.Anonymous {
 251                         t := f.Type
 252                         if t.Kind() == reflect.Ptr {
 253                                 t = t.Elem()
 254                         }
 255                         anonEFs := makeEncodeFields(t)
 256                         for aefi := range anonEFs {
 257                                 anonEF := anonEFs[aefi]
 258                                 bottomField := anonEF
 259                                 bottomField.i = func(v reflect.Value) reflect.Value {
 260                                         v = v.Field(i)
 261                                         if v.Kind() == reflect.Ptr {
 262                                                 if v.IsNil() {
 263                                                         // This will skip serializing this value.
 264                                                         return reflect.Value{}
 265                                                 }
 266                                                 v = v.Elem()
 267                                         }
 268                                         return anonEF.i(v)
 269                                 }
 270                                 fs = append(fs, bottomField)
 271                         }
 272                         continue
 273                 }
 274                 var ef encodeField
 275                 ef.i = func(v reflect.Value) reflect.Value {
 276                         return v.Field(i)
 277                 }
 278                 ef.tag = f.Name
 279
 280                 tv := getTag(f.Tag)
 281                 if tv.Ignore() {
 282                         continue
 283                 }
 284                 if tv.Key() != "" {
 285                         ef.tag = tv.Key()
 286                 }
 287                 ef.omitEmpty = tv.OmitEmpty()
 288                 fs = append(fs, ef)
 289         }
 290         fss := encodeFieldsSortType(fs)
 291         sort.Sort(fss)
 292         return fs
 293 }