summaryrefslogtreecommitdiffstats
path: root/src/encoding/gob/encode.go
blob: 8f8f170c1643c14e84b91a2271599bf15c718c9a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:generate go run encgen.go -output enc_helpers.go

package gob

import (
	"encoding"
	"encoding/binary"
	"math"
	"math/bits"
	"reflect"
	"sync"
)

const uint64Size = 8

type encHelper func(state *encoderState, v reflect.Value) bool

// encoderState is the global execution state of an instance of the encoder.
// Field numbers are delta encoded and always increase. The field
// number is initialized to -1 so 0 comes out as delta(1). A delta of
// 0 terminates the structure.
type encoderState struct {
	enc      *Encoder
	b        *encBuffer
	sendZero bool                 // encoding an array element or map key/value pair; send zero values
	fieldnum int                  // the last field number written.
	buf      [1 + uint64Size]byte // buffer used by the encoder; here to avoid allocation.
	next     *encoderState        // for free list
}

// encBuffer is an extremely simple, fast implementation of a write-only byte buffer.
// It never returns a non-nil error, but Write returns an error value so it matches io.Writer.
type encBuffer struct {
	data    []byte
	scratch [64]byte
}

var encBufferPool = sync.Pool{
	New: func() interface{} {
		e := new(encBuffer)
		e.data = e.scratch[0:0]
		return e
	},
}

func (e *encBuffer) writeByte(c byte) {
	e.data = append(e.data, c)
}

func (e *encBuffer) Write(p []byte) (int, error) {
	e.data = append(e.data, p...)
	return len(p), nil
}

func (e *encBuffer) WriteString(s string) {
	e.data = append(e.data, s...)
}

func (e *encBuffer) Len() int {
	return len(e.data)
}

func (e *encBuffer) Bytes() []byte {
	return e.data
}

func (e *encBuffer) Reset() {
	if len(e.data) >= tooBig {
		e.data = e.scratch[0:0]
	} else {
		e.data = e.data[0:0]
	}
}

func (enc *Encoder) newEncoderState(b *encBuffer) *encoderState {
	e := enc.freeList
	if e == nil {
		e = new(encoderState)
		e.enc = enc
	} else {
		enc.freeList = e.next
	}
	e.sendZero = false
	e.fieldnum = 0
	e.b = b
	if len(b.data) == 0 {
		b.data = b.scratch[0:0]
	}
	return e
}

func (enc *Encoder) freeEncoderState(e *encoderState) {
	e.next = enc.freeList
	enc.freeList = e
}

// Unsigned integers have a two-state encoding. If the number is less
// than 128 (0 through 0x7F), its value is written directly.
// Otherwise the value is written in big-endian byte order preceded
// by the byte length, negated.

// encodeUint writes an encoded unsigned integer to state.b.
func (state *encoderState) encodeUint(x uint64) {
	if x <= 0x7F {
		state.b.writeByte(uint8(x))
		return
	}

	binary.BigEndian.PutUint64(state.buf[1:], x)
	bc := bits.LeadingZeros64(x) >> 3      // 8 - bytelen(x)
	state.buf[bc] = uint8(bc - uint64Size) // and then we subtract 8 to get -bytelen(x)

	state.b.Write(state.buf[bc : uint64Size+1])
}

// encodeInt writes an encoded signed integer to state.w.
// The low bit of the encoding says whether to bit complement the (other bits of the)
// uint to recover the int.
func (state *encoderState) encodeInt(i int64) {
	var x uint64
	if i < 0 {
		x = uint64(^i<<1) | 1
	} else {
		x = uint64(i << 1)
	}
	state.encodeUint(x)
}

// encOp is the signature of an encoding operator for a given type.
type encOp func(i *encInstr, state *encoderState, v reflect.Value)

// The 'instructions' of the encoding machine
type encInstr struct {
	op    encOp
	field int   // field number in input
	index []int // struct index
	indir int   // how many pointer indirections to reach the value in the struct
}

// update emits a field number and updates the state to record its value for delta encoding.
// If the instruction pointer is nil, it does nothing
func (state *encoderState) update(instr *encInstr) {
	if instr != nil {
		state.encodeUint(uint64(instr.field - state.fieldnum))
		state.fieldnum = instr.field
	}
}

// Each encoder for a composite is responsible for handling any
// indirections associated with the elements of the data structure.
// If any pointer so reached is nil, no bytes are written. If the
// data item is zero, no bytes are written. Single values - ints,
// strings etc. - are indirected before calling their encoders.
// Otherwise, the output (for a scalar) is the field number, as an
// encoded integer, followed by the field data in its appropriate
// format.

// encIndirect dereferences pv indir times and returns the result.
func encIndirect(pv reflect.Value, indir int) reflect.Value {
	for ; indir > 0; indir-- {
		if pv.IsNil() {
			break
		}
		pv = pv.Elem()
	}
	return pv
}

// encBool encodes the bool referenced by v as an unsigned 0 or 1.
func encBool(i *encInstr, state *encoderState, v reflect.Value) {
	b := v.Bool()
	if b || state.sendZero {
		state.update(i)
		if b {
			state.encodeUint(1)
		} else {
			state.encodeUint(0)
		}
	}
}

// encInt encodes the signed integer (int int8 int16 int32 int64) referenced by v.
func encInt(i *encInstr, state *encoderState, v reflect.Value) {
	value := v.Int()
	if value != 0 || state.sendZero {
		state.update(i)
		state.encodeInt(value)
	}
}

// encUint encodes the unsigned integer (uint uint8 uint16 uint32 uint64 uintptr) referenced by v.
func encUint(i *encInstr, state *encoderState, v reflect.Value) {
	value := v.Uint()
	if value != 0 || state.sendZero {
		state.update(i)
		state.encodeUint(value)
	}
}

// floatBits returns a uint64 holding the bits of a floating-point number.
// Floating-point numbers are transmitted as uint64s holding the bits
// of the underlying representation. They are sent byte-reversed, with
// the exponent end coming out first, so integer floating point numbers
// (for example) transmit more compactly. This routine does the
// swizzling.
func floatBits(f float64) uint64 {
	u := math.Float64bits(f)
	return bits.ReverseBytes64(u)
}

// encFloat encodes the floating point value (float32 float64) referenced by v.
func encFloat(i *encInstr, state *encoderState, v reflect.Value) {
	f := v.Float()
	if f != 0 || state.sendZero {
		bits := floatBits(f)
		state.update(i)
		state.encodeUint(bits)
	}
}

// encComplex encodes the complex value (complex64 complex128) referenced by v.
// Complex numbers are just a pair of floating-point numbers, real part first.
func encComplex(i *encInstr, state *encoderState, v reflect.Value) {
	c := v.Complex()
	if c != 0+0i || state.sendZero {
		rpart := floatBits(real(c))
		ipart := floatBits(imag(c))
		state.update(i)
		state.encodeUint(rpart)
		state.encodeUint(ipart)
	}
}

// encUint8Array encodes the byte array referenced by v.
// Byte arrays are encoded as an unsigned count followed by the raw bytes.
func encUint8Array(i *encInstr, state *encoderState, v reflect.Value) {
	b := v.Bytes()
	if len(b) > 0 || state.sendZero {
		state.update(i)
		state.encodeUint(uint64(len(b)))
		state.b.Write(b)
	}
}

// encString encodes the string referenced by v.
// Strings are encoded as an unsigned count followed by the raw bytes.
func encString(i *encInstr, state *encoderState, v reflect.Value) {
	s := v.String()
	if len(s) > 0 || state.sendZero {
		state.update(i)
		state.encodeUint(uint64(len(s)))
		state.b.WriteString(s)
	}
}

// encStructTerminator encodes the end of an encoded struct
// as delta field number of 0.
func encStructTerminator(i *encInstr, state *encoderState, v reflect.Value) {
	state.encodeUint(0)
}

// Execution engine

// encEngine an array of instructions indexed by field number of the encoding
// data, typically a struct. It is executed top to bottom, walking the struct.
type encEngine struct {
	instr []encInstr
}

const singletonField = 0

// valid reports whether the value is valid and a non-nil pointer.
// (Slices, maps, and chans take care of themselves.)
func valid(v reflect.Value) bool {
	switch v.Kind() {
	case reflect.Invalid:
		return false
	case reflect.Ptr:
		return !v.IsNil()
	}
	return true
}

// encodeSingle encodes a single top-level non-struct value.
func (enc *Encoder) encodeSingle(b *encBuffer, engine *encEngine, value reflect.Value) {
	state := enc.newEncoderState(b)
	defer enc.freeEncoderState(state)
	state.fieldnum = singletonField
	// There is no surrounding struct to frame the transmission, so we must
	// generate data even if the item is zero. To do this, set sendZero.
	state.sendZero = true
	instr := &engine.instr[singletonField]
	if instr.indir > 0 {
		value = encIndirect(value, instr.indir)
	}
	if valid(value) {
		instr.op(instr, state, value)
	}
}

// encodeStruct encodes a single struct value.
func (enc *Encoder) encodeStruct(b *encBuffer, engine *encEngine, value reflect.Value) {
	if !valid(value) {
		return
	}
	state := enc.newEncoderState(b)
	defer enc.freeEncoderState(state)
	state.fieldnum = -1
	for i := 0; i < len(engine.instr); i++ {
		instr := &engine.instr[i]
		if i >= value.NumField() {
			// encStructTerminator
			instr.op(instr, state, reflect.Value{})
			break
		}
		field := value.FieldByIndex(instr.index)
		if instr.indir > 0 {
			field = encIndirect(field, instr.indir)
			// TODO: Is field guaranteed valid? If so we could avoid this check.
			if !valid(field) {
				continue
			}
		}
		instr.op(instr, state, field)
	}
}

// encodeArray encodes an array.
func (enc *Encoder) encodeArray(b *encBuffer, value reflect.Value, op encOp, elemIndir int, length int, helper encHelper) {
	state := enc.newEncoderState(b)
	defer enc.freeEncoderState(state)
	state.fieldnum = -1
	state.sendZero = true
	state.encodeUint(uint64(length))
	if helper != nil && helper(state, value) {
		return
	}
	for i := 0; i < length; i++ {
		elem := value.Index(i)
		if elemIndir > 0 {
			elem = encIndirect(elem, elemIndir)
			// TODO: Is elem guaranteed valid? If so we could avoid this check.
			if !valid(elem) {
				errorf("encodeArray: nil element")
			}
		}
		op(nil, state, elem)
	}
}

// encodeReflectValue is a helper for maps. It encodes the value v.
func encodeReflectValue(state *encoderState, v reflect.Value, op encOp, indir int) {
	for i := 0; i < indir && v.IsValid(); i++ {
		v = reflect.Indirect(v)
	}
	if !v.IsValid() {
		errorf("encodeReflectValue: nil element")
	}
	op(nil, state, v)
}

// encodeMap encodes a map as unsigned count followed by key:value pairs.
func (enc *Encoder) encodeMap(b *encBuffer, mv reflect.Value, keyOp, elemOp encOp, keyIndir, elemIndir int) {
	state := enc.newEncoderState(b)
	state.fieldnum = -1
	state.sendZero = true
	keys := mv.MapKeys()
	state.encodeUint(uint64(len(keys)))
	for _, key := range keys {
		encodeReflectValue(state, key, keyOp, keyIndir)
		encodeReflectValue(state, mv.MapIndex(key), elemOp, elemIndir)
	}
	enc.freeEncoderState(state)
}

// encodeInterface encodes the interface value iv.
// To send an interface, we send a string identifying the concrete type, followed
// by the type identifier (which might require defining that type right now), followed
// by the concrete value. A nil value gets sent as the empty string for the name,
// followed by no value.
func (enc *Encoder) encodeInterface(b *encBuffer, iv reflect.Value) {
	// Gobs can encode nil interface values but not typed interface
	// values holding nil pointers, since nil pointers point to no value.
	elem := iv.Elem()
	if elem.Kind() == reflect.Ptr && elem.IsNil() {
		errorf("gob: cannot encode nil pointer of type %s inside interface", iv.Elem().Type())
	}
	state := enc.newEncoderState(b)
	state.fieldnum = -1
	state.sendZero = true
	if iv.IsNil() {
		state.encodeUint(0)
		return
	}

	ut := userType(iv.Elem().Type())
	namei, ok := concreteTypeToName.Load(ut.base)
	if !ok {
		errorf("type not registered for interface: %s", ut.base)
	}
	name := namei.(string)

	// Send the name.
	state.encodeUint(uint64(len(name)))
	state.b.WriteString(name)
	// Define the type id if necessary.
	enc.sendTypeDescriptor(enc.writer(), state, ut)
	// Send the type id.
	enc.sendTypeId(state, ut)
	// Encode the value into a new buffer. Any nested type definitions
	// should be written to b, before the encoded value.
	enc.pushWriter(b)
	data := encBufferPool.Get().(*encBuffer)
	data.Write(spaceForLength)
	enc.encode(data, elem, ut)
	if enc.err != nil {
		error_(enc.err)
	}
	enc.popWriter()
	enc.writeMessage(b, data)
	data.Reset()
	encBufferPool.Put(data)
	if enc.err != nil {
		error_(enc.err)
	}
	enc.freeEncoderState(state)
}

// isZero reports whether the value is the zero of its type.
func isZero(val reflect.Value) bool {
	switch val.Kind() {
	case reflect.Array:
		for i := 0; i < val.Len(); i++ {
			if !isZero(val.Index(i)) {
				return false
			}
		}
		return true
	case reflect.Map, reflect.Slice, reflect.String:
		return val.Len() == 0
	case reflect.Bool:
		return !val.Bool()
	case reflect.Complex64, reflect.Complex128:
		return val.Complex() == 0
	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Ptr:
		return val.IsNil()
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return val.Int() == 0
	case reflect.Float32, reflect.Float64:
		return val.Float() == 0
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return val.Uint() == 0
	case reflect.Struct:
		for i := 0; i < val.NumField(); i++ {
			if !isZero(val.Field(i)) {
				return false
			}
		}
		return true
	}
	panic("unknown type in isZero " + val.Type().String())
}

// encGobEncoder encodes a value that implements the GobEncoder interface.
// The data is sent as a byte array.
func (enc *Encoder) encodeGobEncoder(b *encBuffer, ut *userTypeInfo, v reflect.Value) {
	// TODO: should we catch panics from the called method?

	var data []byte
	var err error
	// We know it's one of these.
	switch ut.externalEnc {
	case xGob:
		data, err = v.Interface().(GobEncoder).GobEncode()
	case xBinary:
		data, err = v.Interface().(encoding.BinaryMarshaler).MarshalBinary()
	case xText:
		data, err = v.Interface().(encoding.TextMarshaler).MarshalText()
	}
	if err != nil {
		error_(err)
	}
	state := enc.newEncoderState(b)
	state.fieldnum = -1
	state.encodeUint(uint64(len(data)))
	state.b.Write(data)
	enc.freeEncoderState(state)
}

var encOpTable = [...]encOp{
	reflect.Bool:       encBool,
	reflect.Int:        encInt,
	reflect.Int8:       encInt,
	reflect.Int16:      encInt,
	reflect.Int32:      encInt,
	reflect.Int64:      encInt,
	reflect.Uint:       encUint,
	reflect.Uint8:      encUint,
	reflect.Uint16:     encUint,
	reflect.Uint32:     encUint,
	reflect.Uint64:     encUint,
	reflect.Uintptr:    encUint,
	reflect.Float32:    encFloat,
	reflect.Float64:    encFloat,
	reflect.Complex64:  encComplex,
	reflect.Complex128: encComplex,
	reflect.String:     encString,
}

// encOpFor returns (a pointer to) the encoding op for the base type under rt and
// the indirection count to reach it.
func encOpFor(rt reflect.Type, inProgress map[reflect.Type]*encOp, building map[*typeInfo]bool) (*encOp, int) {
	ut := userType(rt)
	// If the type implements GobEncoder, we handle it without further processing.
	if ut.externalEnc != 0 {
		return gobEncodeOpFor(ut)
	}
	// If this type is already in progress, it's a recursive type (e.g. map[string]*T).
	// Return the pointer to the op we're already building.
	if opPtr := inProgress[rt]; opPtr != nil {
		return opPtr, ut.indir
	}
	typ := ut.base
	indir := ut.indir
	k := typ.Kind()
	var op encOp
	if int(k) < len(encOpTable) {
		op = encOpTable[k]
	}
	if op == nil {
		inProgress[rt] = &op
		// Special cases
		switch t := typ; t.Kind() {
		case reflect.Slice:
			if t.Elem().Kind() == reflect.Uint8 {
				op = encUint8Array
				break
			}
			// Slices have a header; we decode it to find the underlying array.
			elemOp, elemIndir := encOpFor(t.Elem(), inProgress, building)
			helper := encSliceHelper[t.Elem().Kind()]
			op = func(i *encInstr, state *encoderState, slice reflect.Value) {
				if !state.sendZero && slice.Len() == 0 {
					return
				}
				state.update(i)
				state.enc.encodeArray(state.b, slice, *elemOp, elemIndir, slice.Len(), helper)
			}
		case reflect.Array:
			// True arrays have size in the type.
			elemOp, elemIndir := encOpFor(t.Elem(), inProgress, building)
			helper := encArrayHelper[t.Elem().Kind()]
			op = func(i *encInstr, state *encoderState, array reflect.Value) {
				state.update(i)
				state.enc.encodeArray(state.b, array, *elemOp, elemIndir, array.Len(), helper)
			}
		case reflect.Map:
			keyOp, keyIndir := encOpFor(t.Key(), inProgress, building)
			elemOp, elemIndir := encOpFor(t.Elem(), inProgress, building)
			op = func(i *encInstr, state *encoderState, mv reflect.Value) {
				// We send zero-length (but non-nil) maps because the
				// receiver might want to use the map.  (Maps don't use append.)
				if !state.sendZero && mv.IsNil() {
					return
				}
				state.update(i)
				state.enc.encodeMap(state.b, mv, *keyOp, *elemOp, keyIndir, elemIndir)
			}
		case reflect.Struct:
			// Generate a closure that calls out to the engine for the nested type.
			getEncEngine(userType(typ), building)
			info := mustGetTypeInfo(typ)
			op = func(i *encInstr, state *encoderState, sv reflect.Value) {
				state.update(i)
				// indirect through info to delay evaluation for recursive structs
				enc := info.encoder.Load().(*encEngine)
				state.enc.encodeStruct(state.b, enc, sv)
			}
		case reflect.Interface:
			op = func(i *encInstr, state *encoderState, iv reflect.Value) {
				if !state.sendZero && (!iv.IsValid() || iv.IsNil()) {
					return
				}
				state.update(i)
				state.enc.encodeInterface(state.b, iv)
			}
		}
	}
	if op == nil {
		errorf("can't happen: encode type %s", rt)
	}
	return &op, indir
}

// gobEncodeOpFor returns the op for a type that is known to implement GobEncoder.
func gobEncodeOpFor(ut *userTypeInfo) (*encOp, int) {
	rt := ut.user
	if ut.encIndir == -1 {
		rt = reflect.PtrTo(rt)
	} else if ut.encIndir > 0 {
		for i := int8(0); i < ut.encIndir; i++ {
			rt = rt.Elem()
		}
	}
	var op encOp
	op = func(i *encInstr, state *encoderState, v reflect.Value) {
		if ut.encIndir == -1 {
			// Need to climb up one level to turn value into pointer.
			if !v.CanAddr() {
				errorf("unaddressable value of type %s", rt)
			}
			v = v.Addr()
		}
		if !state.sendZero && isZero(v) {
			return
		}
		state.update(i)
		state.enc.encodeGobEncoder(state.b, ut, v)
	}
	return &op, int(ut.encIndir) // encIndir: op will get called with p == address of receiver.
}

// compileEnc returns the engine to compile the type.
func compileEnc(ut *userTypeInfo, building map[*typeInfo]bool) *encEngine {
	srt := ut.base
	engine := new(encEngine)
	seen := make(map[reflect.Type]*encOp)
	rt := ut.base
	if ut.externalEnc != 0 {
		rt = ut.user
	}
	if ut.externalEnc == 0 && srt.Kind() == reflect.Struct {
		for fieldNum, wireFieldNum := 0, 0; fieldNum < srt.NumField(); fieldNum++ {
			f := srt.Field(fieldNum)
			if !isSent(&f) {
				continue
			}
			op, indir := encOpFor(f.Type, seen, building)
			engine.instr = append(engine.instr, encInstr{*op, wireFieldNum, f.Index, indir})
			wireFieldNum++
		}
		if srt.NumField() > 0 && len(engine.instr) == 0 {
			errorf("type %s has no exported fields", rt)
		}
		engine.instr = append(engine.instr, encInstr{encStructTerminator, 0, nil, 0})
	} else {
		engine.instr = make([]encInstr, 1)
		op, indir := encOpFor(rt, seen, building)
		engine.instr[0] = encInstr{*op, singletonField, nil, indir}
	}
	return engine
}

// getEncEngine returns the engine to compile the type.
func getEncEngine(ut *userTypeInfo, building map[*typeInfo]bool) *encEngine {
	info, err := getTypeInfo(ut)
	if err != nil {
		error_(err)
	}
	enc, ok := info.encoder.Load().(*encEngine)
	if !ok {
		enc = buildEncEngine(info, ut, building)
	}
	return enc
}

func buildEncEngine(info *typeInfo, ut *userTypeInfo, building map[*typeInfo]bool) *encEngine {
	// Check for recursive types.
	if building != nil && building[info] {
		return nil
	}
	info.encInit.Lock()
	defer info.encInit.Unlock()
	enc, ok := info.encoder.Load().(*encEngine)
	if !ok {
		if building == nil {
			building = make(map[*typeInfo]bool)
		}
		building[info] = true
		enc = compileEnc(ut, building)
		info.encoder.Store(enc)
	}
	return enc
}

func (enc *Encoder) encode(b *encBuffer, value reflect.Value, ut *userTypeInfo) {
	defer catchError(&enc.err)
	engine := getEncEngine(ut, nil)
	indir := ut.indir
	if ut.externalEnc != 0 {
		indir = int(ut.encIndir)
	}
	for i := 0; i < indir; i++ {
		value = reflect.Indirect(value)
	}
	if ut.externalEnc == 0 && value.Type().Kind() == reflect.Struct {
		enc.encodeStruct(b, engine, value)
	} else {
		enc.encodeSingle(b, engine, value)
	}
}