Source file src/pkg/encoding/xml/marshal.go
1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package xml 6 7 import ( 8 "bufio" 9 "bytes" 10 "fmt" 11 "io" 12 "reflect" 13 "strconv" 14 "strings" 15 "time" 16 ) 17 18 const ( 19 // A generic XML header suitable for use with the output of Marshal. 20 // This is not automatically added to any output of this package, 21 // it is provided as a convenience. 22 Header = `<?xml version="1.0" encoding="UTF-8"?>` + "\n" 23 ) 24 25 // Marshal returns the XML encoding of v. 26 // 27 // Marshal handles an array or slice by marshalling each of the elements. 28 // Marshal handles a pointer by marshalling the value it points at or, if the 29 // pointer is nil, by writing nothing. Marshal handles an interface value by 30 // marshalling the value it contains or, if the interface value is nil, by 31 // writing nothing. Marshal handles all other data by writing one or more XML 32 // elements containing the data. 33 // 34 // The name for the XML elements is taken from, in order of preference: 35 // - the tag on the XMLName field, if the data is a struct 36 // - the value of the XMLName field of type xml.Name 37 // - the tag of the struct field used to obtain the data 38 // - the name of the struct field used to obtain the data 39 // - the name of the marshalled type 40 // 41 // The XML element for a struct contains marshalled elements for each of the 42 // exported fields of the struct, with these exceptions: 43 // - the XMLName field, described above, is omitted. 44 // - a field with tag "-" is omitted. 45 // - a field with tag "name,attr" becomes an attribute with 46 // the given name in the XML element. 47 // - a field with tag ",attr" becomes an attribute with the 48 // field name in the in the XML element. 49 // - a field with tag ",chardata" is written as character data, 50 // not as an XML element. 51 // - a field with tag ",innerxml" is written verbatim, not subject 52 // to the usual marshalling procedure. 53 // - a field with tag ",comment" is written as an XML comment, not 54 // subject to the usual marshalling procedure. It must not contain 55 // the "--" string within it. 56 // - a field with a tag including the "omitempty" option is omitted 57 // if the field value is empty. The empty values are false, 0, any 58 // nil pointer or interface value, and any array, slice, map, or 59 // string of length zero. 60 // - a non-pointer anonymous struct field is handled as if the 61 // fields of its value were part of the outer struct. 62 // 63 // If a field uses a tag "a>b>c", then the element c will be nested inside 64 // parent elements a and b. Fields that appear next to each other that name 65 // the same parent will be enclosed in one XML element. 66 // 67 // See MarshalIndent for an example. 68 // 69 // Marshal will return an error if asked to marshal a channel, function, or map. 70 func Marshal(v interface{}) ([]byte, error) { 71 var b bytes.Buffer 72 if err := NewEncoder(&b).Encode(v); err != nil { 73 return nil, err 74 } 75 return b.Bytes(), nil 76 } 77 78 // MarshalIndent works like Marshal, but each XML element begins on a new 79 // indented line that starts with prefix and is followed by one or more 80 // copies of indent according to the nesting depth. 81 func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) { 82 var b bytes.Buffer 83 enc := NewEncoder(&b) 84 enc.prefix = prefix 85 enc.indent = indent 86 err := enc.marshalValue(reflect.ValueOf(v), nil) 87 enc.Flush() 88 if err != nil { 89 return nil, err 90 } 91 return b.Bytes(), nil 92 } 93 94 // An Encoder writes XML data to an output stream. 95 type Encoder struct { 96 printer 97 } 98 99 // NewEncoder returns a new encoder that writes to w. 100 func NewEncoder(w io.Writer) *Encoder { 101 return &Encoder{printer{Writer: bufio.NewWriter(w)}} 102 } 103 104 // Encode writes the XML encoding of v to the stream. 105 // 106 // See the documentation for Marshal for details about the conversion 107 // of Go values to XML. 108 func (enc *Encoder) Encode(v interface{}) error { 109 err := enc.marshalValue(reflect.ValueOf(v), nil) 110 enc.Flush() 111 return err 112 } 113 114 type printer struct { 115 *bufio.Writer 116 indent string 117 prefix string 118 depth int 119 indentedIn bool 120 } 121 122 // marshalValue writes one or more XML elements representing val. 123 // If val was obtained from a struct field, finfo must have its details. 124 func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo) error { 125 if !val.IsValid() { 126 return nil 127 } 128 if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) { 129 return nil 130 } 131 132 kind := val.Kind() 133 typ := val.Type() 134 135 // Drill into pointers/interfaces 136 if kind == reflect.Ptr || kind == reflect.Interface { 137 if val.IsNil() { 138 return nil 139 } 140 return p.marshalValue(val.Elem(), finfo) 141 } 142 143 // Slices and arrays iterate over the elements. They do not have an enclosing tag. 144 if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 { 145 for i, n := 0, val.Len(); i < n; i++ { 146 if err := p.marshalValue(val.Index(i), finfo); err != nil { 147 return err 148 } 149 } 150 return nil 151 } 152 153 tinfo, err := getTypeInfo(typ) 154 if err != nil { 155 return err 156 } 157 158 // Precedence for the XML element name is: 159 // 1. XMLName field in underlying struct; 160 // 2. field name/tag in the struct field; and 161 // 3. type name 162 var xmlns, name string 163 if tinfo.xmlname != nil { 164 xmlname := tinfo.xmlname 165 if xmlname.name != "" { 166 xmlns, name = xmlname.xmlns, xmlname.name 167 } else if v, ok := val.FieldByIndex(xmlname.idx).Interface().(Name); ok && v.Local != "" { 168 xmlns, name = v.Space, v.Local 169 } 170 } 171 if name == "" && finfo != nil { 172 xmlns, name = finfo.xmlns, finfo.name 173 } 174 if name == "" { 175 name = typ.Name() 176 if name == "" { 177 return &UnsupportedTypeError{typ} 178 } 179 } 180 181 p.writeIndent(1) 182 p.WriteByte('<') 183 p.WriteString(name) 184 185 if xmlns != "" { 186 p.WriteString(` xmlns="`) 187 // TODO: EscapeString, to avoid the allocation. 188 Escape(p, []byte(xmlns)) 189 p.WriteByte('"') 190 } 191 192 // Attributes 193 for i := range tinfo.fields { 194 finfo := &tinfo.fields[i] 195 if finfo.flags&fAttr == 0 { 196 continue 197 } 198 fv := val.FieldByIndex(finfo.idx) 199 if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) { 200 continue 201 } 202 p.WriteByte(' ') 203 p.WriteString(finfo.name) 204 p.WriteString(`="`) 205 if err := p.marshalSimple(fv.Type(), fv); err != nil { 206 return err 207 } 208 p.WriteByte('"') 209 } 210 p.WriteByte('>') 211 212 if val.Kind() == reflect.Struct { 213 err = p.marshalStruct(tinfo, val) 214 } else { 215 err = p.marshalSimple(typ, val) 216 } 217 if err != nil { 218 return err 219 } 220 221 p.writeIndent(-1) 222 p.WriteByte('<') 223 p.WriteByte('/') 224 p.WriteString(name) 225 p.WriteByte('>') 226 227 return nil 228 } 229 230 var timeType = reflect.TypeOf(time.Time{}) 231 232 func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) error { 233 // Normally we don't see structs, but this can happen for an attribute. 234 if val.Type() == timeType { 235 p.WriteString(val.Interface().(time.Time).Format(time.RFC3339Nano)) 236 return nil 237 } 238 switch val.Kind() { 239 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: 240 p.WriteString(strconv.FormatInt(val.Int(), 10)) 241 case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr: 242 p.WriteString(strconv.FormatUint(val.Uint(), 10)) 243 case reflect.Float32, reflect.Float64: 244 p.WriteString(strconv.FormatFloat(val.Float(), 'g', -1, 64)) 245 case reflect.String: 246 // TODO: Add EscapeString. 247 Escape(p, []byte(val.String())) 248 case reflect.Bool: 249 p.WriteString(strconv.FormatBool(val.Bool())) 250 case reflect.Array: 251 // will be [...]byte 252 bytes := make([]byte, val.Len()) 253 for i := range bytes { 254 bytes[i] = val.Index(i).Interface().(byte) 255 } 256 Escape(p, bytes) 257 case reflect.Slice: 258 // will be []byte 259 Escape(p, val.Bytes()) 260 default: 261 return &UnsupportedTypeError{typ} 262 } 263 return nil 264 } 265 266 var ddBytes = []byte("--") 267 268 func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error { 269 if val.Type() == timeType { 270 p.WriteString(val.Interface().(time.Time).Format(time.RFC3339Nano)) 271 return nil 272 } 273 s := parentStack{printer: p} 274 for i := range tinfo.fields { 275 finfo := &tinfo.fields[i] 276 if finfo.flags&(fAttr|fAny) != 0 { 277 continue 278 } 279 vf := val.FieldByIndex(finfo.idx) 280 switch finfo.flags & fMode { 281 case fCharData: 282 switch vf.Kind() { 283 case reflect.String: 284 Escape(p, []byte(vf.String())) 285 case reflect.Slice: 286 if elem, ok := vf.Interface().([]byte); ok { 287 Escape(p, elem) 288 } 289 } 290 continue 291 292 case fComment: 293 k := vf.Kind() 294 if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) { 295 return fmt.Errorf("xml: bad type for comment field of %s", val.Type()) 296 } 297 if vf.Len() == 0 { 298 continue 299 } 300 p.writeIndent(0) 301 p.WriteString("<!--") 302 dashDash := false 303 dashLast := false 304 switch k { 305 case reflect.String: 306 s := vf.String() 307 dashDash = strings.Index(s, "--") >= 0 308 dashLast = s[len(s)-1] == '-' 309 if !dashDash { 310 p.WriteString(s) 311 } 312 case reflect.Slice: 313 b := vf.Bytes() 314 dashDash = bytes.Index(b, ddBytes) >= 0 315 dashLast = b[len(b)-1] == '-' 316 if !dashDash { 317 p.Write(b) 318 } 319 default: 320 panic("can't happen") 321 } 322 if dashDash { 323 return fmt.Errorf(`xml: comments must not contain "--"`) 324 } 325 if dashLast { 326 // "--->" is invalid grammar. Make it "- -->" 327 p.WriteByte(' ') 328 } 329 p.WriteString("-->") 330 continue 331 332 case fInnerXml: 333 iface := vf.Interface() 334 switch raw := iface.(type) { 335 case []byte: 336 p.Write(raw) 337 continue 338 case string: 339 p.WriteString(raw) 340 continue 341 } 342 343 case fElement: 344 s.trim(finfo.parents) 345 if len(finfo.parents) > len(s.stack) { 346 if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() { 347 s.push(finfo.parents[len(s.stack):]) 348 } 349 } 350 } 351 if err := p.marshalValue(vf, finfo); err != nil { 352 return err 353 } 354 } 355 s.trim(nil) 356 return nil 357 } 358 359 func (p *printer) writeIndent(depthDelta int) { 360 if len(p.prefix) == 0 && len(p.indent) == 0 { 361 return 362 } 363 if depthDelta < 0 { 364 p.depth-- 365 if p.indentedIn { 366 p.indentedIn = false 367 return 368 } 369 p.indentedIn = false 370 } 371 p.WriteByte('\n') 372 if len(p.prefix) > 0 { 373 p.WriteString(p.prefix) 374 } 375 if len(p.indent) > 0 { 376 for i := 0; i < p.depth; i++ { 377 p.WriteString(p.indent) 378 } 379 } 380 if depthDelta > 0 { 381 p.depth++ 382 p.indentedIn = true 383 } 384 } 385 386 type parentStack struct { 387 *printer 388 stack []string 389 } 390 391 // trim updates the XML context to match the longest common prefix of the stack 392 // and the given parents. A closing tag will be written for every parent 393 // popped. Passing a zero slice or nil will close all the elements. 394 func (s *parentStack) trim(parents []string) { 395 split := 0 396 for ; split < len(parents) && split < len(s.stack); split++ { 397 if parents[split] != s.stack[split] { 398 break 399 } 400 } 401 for i := len(s.stack) - 1; i >= split; i-- { 402 s.writeIndent(-1) 403 s.WriteString("</") 404 s.WriteString(s.stack[i]) 405 s.WriteByte('>') 406 } 407 s.stack = parents[:split] 408 } 409 410 // push adds parent elements to the stack and writes open tags. 411 func (s *parentStack) push(parents []string) { 412 for i := 0; i < len(parents); i++ { 413 s.writeIndent(1) 414 s.WriteByte('<') 415 s.WriteString(parents[i]) 416 s.WriteByte('>') 417 } 418 s.stack = append(s.stack, parents...) 419 } 420 421 // A MarshalXMLError is returned when Marshal encounters a type 422 // that cannot be converted into XML. 423 type UnsupportedTypeError struct { 424 Type reflect.Type 425 } 426 427 func (e *UnsupportedTypeError) Error() string { 428 return "xml: unsupported type: " + e.Type.String() 429 } 430 431 func isEmptyValue(v reflect.Value) bool { 432 switch v.Kind() { 433 case reflect.Array, reflect.Map, reflect.Slice, reflect.String: 434 return v.Len() == 0 435 case reflect.Bool: 436 return !v.Bool() 437 case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: 438 return v.Int() == 0 439 case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr: 440 return v.Uint() == 0 441 case reflect.Float32, reflect.Float64: 442 return v.Float() == 0 443 case reflect.Interface, reflect.Ptr: 444 return v.IsNil() 445 } 446 return false 447 }