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// 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.

package gob

import (
        "bytes"
        "math"
        "reflect"
        "unsafe"
)

const uint64Size = int(unsafe.Sizeof(uint64(0)))

// 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        *bytes.Buffer
        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
}

func (enc *Encoder) newEncoderState(b *bytes.Buffer) *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
        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 {
                err := state.b.WriteByte(uint8(x))
                if err != nil {
                        error_(err)
                }
                return
        }
        i := uint64Size
        for x > 0 {
                state.buf[i] = uint8(x)
                x >>= 8
                i--
        }
        state.buf[i] = uint8(i - uint64Size) // = loop count, negated
        _, err := state.b.Write(state.buf[i : uint64Size+1])
        if err != nil {
                error_(err)
        }
}

// 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(uint64(x))
}

// encOp is the signature of an encoding operator for a given type.
type encOp func(i *encInstr, state *encoderState, p unsafe.Pointer)

// The 'instructions' of the encoding machine
type encInstr struct {
        op     encOp
        field  int     // field number
        indir  int     // how many pointer indirections to reach the value in the struct
        offset uintptr // offset in the structure of the field to encode
}

// 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 p indir times and returns the result.
func encIndirect(p unsafe.Pointer, indir int) unsafe.Pointer {
        for ; indir > 0; indir-- {
                p = *(*unsafe.Pointer)(p)
                if p == nil {
                        return unsafe.Pointer(nil)
                }
        }
        return p
}

// encBool encodes the bool with address p as an unsigned 0 or 1.
func encBool(i *encInstr, state *encoderState, p unsafe.Pointer) {
        b := *(*bool)(p)
        if b || state.sendZero {
                state.update(i)
                if b {
                        state.encodeUint(1)
                } else {
                        state.encodeUint(0)
                }
        }
}

// encInt encodes the int with address p.
func encInt(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := int64(*(*int)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

// encUint encodes the uint with address p.
func encUint(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uint)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

// encInt8 encodes the int8 with address p.
func encInt8(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := int64(*(*int8)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

// encUint8 encodes the uint8 with address p.
func encUint8(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uint8)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

// encInt16 encodes the int16 with address p.
func encInt16(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := int64(*(*int16)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

// encUint16 encodes the uint16 with address p.
func encUint16(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uint16)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

// encInt32 encodes the int32 with address p.
func encInt32(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := int64(*(*int32)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

// encUint encodes the uint32 with address p.
func encUint32(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uint32)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

// encInt64 encodes the int64 with address p.
func encInt64(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := *(*int64)(p)
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeInt(v)
        }
}

// encInt64 encodes the uint64 with address p.
func encUint64(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := *(*uint64)(p)
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

// encUintptr encodes the uintptr with address p.
func encUintptr(i *encInstr, state *encoderState, p unsafe.Pointer) {
        v := uint64(*(*uintptr)(p))
        if v != 0 || state.sendZero {
                state.update(i)
                state.encodeUint(v)
        }
}

// 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)
        var v uint64
        for i := 0; i < 8; i++ {
                v <<= 8
                v |= u & 0xFF
                u >>= 8
        }
        return v
}

// encFloat32 encodes the float32 with address p.
func encFloat32(i *encInstr, state *encoderState, p unsafe.Pointer) {
        f := *(*float32)(p)
        if f != 0 || state.sendZero {
                v := floatBits(float64(f))
                state.update(i)
                state.encodeUint(v)
        }
}

// encFloat64 encodes the float64 with address p.
func encFloat64(i *encInstr, state *encoderState, p unsafe.Pointer) {
        f := *(*float64)(p)
        if f != 0 || state.sendZero {
                state.update(i)
                v := floatBits(f)
                state.encodeUint(v)
        }
}

// encComplex64 encodes the complex64 with address p.
// Complex numbers are just a pair of floating-point numbers, real part first.
func encComplex64(i *encInstr, state *encoderState, p unsafe.Pointer) {
        c := *(*complex64)(p)
        if c != 0+0i || state.sendZero {
                rpart := floatBits(float64(real(c)))
                ipart := floatBits(float64(imag(c)))
                state.update(i)
                state.encodeUint(rpart)
                state.encodeUint(ipart)
        }
}

// encComplex128 encodes the complex128 with address p.
func encComplex128(i *encInstr, state *encoderState, p unsafe.Pointer) {
        c := *(*complex128)(p)
        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 slice whose header has address p.
// Byte arrays are encoded as an unsigned count followed by the raw bytes.
func encUint8Array(i *encInstr, state *encoderState, p unsafe.Pointer) {
        b := *(*[]byte)(p)
        if len(b) > 0 || state.sendZero {
                state.update(i)
                state.encodeUint(uint64(len(b)))
                state.b.Write(b)
        }
}

// encString encodes the string whose header has address p.
// Strings are encoded as an unsigned count followed by the raw bytes.
func encString(i *encInstr, state *encoderState, p unsafe.Pointer) {
        s := *(*string)(p)
        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, p unsafe.Pointer) {
        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

// encodeSingle encodes a single top-level non-struct value.
func (enc *Encoder) encodeSingle(b *bytes.Buffer, engine *encEngine, basep uintptr) {
        state := enc.newEncoderState(b)
        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]
        p := unsafe.Pointer(basep) // offset will be zero
        if instr.indir > 0 {
                if p = encIndirect(p, instr.indir); p == nil {
                        return
                }
        }
        instr.op(instr, state, p)
        enc.freeEncoderState(state)
}

// encodeStruct encodes a single struct value.
func (enc *Encoder) encodeStruct(b *bytes.Buffer, engine *encEngine, basep uintptr) {
        state := enc.newEncoderState(b)
        state.fieldnum = -1
        for i := 0; i < len(engine.instr); i++ {
                instr := &engine.instr[i]
                p := unsafe.Pointer(basep + instr.offset)
                if instr.indir > 0 {
                        if p = encIndirect(p, instr.indir); p == nil {
                                continue
                        }
                }
                instr.op(instr, state, p)
        }
        enc.freeEncoderState(state)
}

// encodeArray encodes the array whose 0th element is at p.
func (enc *Encoder) encodeArray(b *bytes.Buffer, p uintptr, op encOp, elemWid uintptr, elemIndir int, length int) {
        state := enc.newEncoderState(b)
        state.fieldnum = -1
        state.sendZero = true
        state.encodeUint(uint64(length))
        for i := 0; i < length; i++ {
                elemp := p
                up := unsafe.Pointer(elemp)
                if elemIndir > 0 {
                        if up = encIndirect(up, elemIndir); up == nil {
                                errorf("encodeArray: nil element")
                        }
                        elemp = uintptr(up)
                }
                op(nil, state, unsafe.Pointer(elemp))
                p += uintptr(elemWid)
        }
        enc.freeEncoderState(state)
}

// 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, unsafe.Pointer(unsafeAddr(v)))
}

// encodeMap encodes a map as unsigned count followed by key:value pairs.
// Because map internals are not exposed, we must use reflection rather than
// addresses.
func (enc *Encoder) encodeMap(b *bytes.Buffer, 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 *bytes.Buffer, iv reflect.Value) {
        state := enc.newEncoderState(b)
        state.fieldnum = -1
        state.sendZero = true
        if iv.IsNil() {
                state.encodeUint(0)
                return
        }

        ut := userType(iv.Elem().Type())
        name, ok := concreteTypeToName[ut.base]
        if !ok {
                errorf("type not registered for interface: %s", ut.base)
        }
        // Send the name.
        state.encodeUint(uint64(len(name)))
        _, err := state.b.WriteString(name)
        if err != nil {
                error_(err)
        }
        // 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 := new(bytes.Buffer)
        data.Write(spaceForLength)
        enc.encode(data, iv.Elem(), ut)
        if enc.err != nil {
                error_(enc.err)
        }
        enc.popWriter()
        enc.writeMessage(b, data)
        if enc.err != nil {
                error_(err)
        }
        enc.freeEncoderState(state)
}

// isZero returns 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.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 *bytes.Buffer, v reflect.Value) {
        // TODO: should we catch panics from the called method?
        // We know it's a GobEncoder, so just call the method directly.
        data, err := v.Interface().(GobEncoder).GobEncode()
        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:       encInt8,
        reflect.Int16:      encInt16,
        reflect.Int32:      encInt32,
        reflect.Int64:      encInt64,
        reflect.Uint:       encUint,
        reflect.Uint8:      encUint8,
        reflect.Uint16:     encUint16,
        reflect.Uint32:     encUint32,
        reflect.Uint64:     encUint64,
        reflect.Uintptr:    encUintptr,
        reflect.Float32:    encFloat32,
        reflect.Float64:    encFloat64,
        reflect.Complex64:  encComplex64,
        reflect.Complex128: encComplex128,
        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 (enc *Encoder) encOpFor(rt reflect.Type, inProgress map[reflect.Type]*encOp) (*encOp, int) {
        ut := userType(rt)
        // If the type implements GobEncoder, we handle it without further processing.
        if ut.isGobEncoder {
                return enc.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, indir := enc.encOpFor(t.Elem(), inProgress)
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                slice := (*reflect.SliceHeader)(p)
                                if !state.sendZero && slice.Len == 0 {
                                        return
                                }
                                state.update(i)
                                state.enc.encodeArray(state.b, slice.Data, *elemOp, t.Elem().Size(), indir, int(slice.Len))
                        }
                case reflect.Array:
                        // True arrays have size in the type.
                        elemOp, indir := enc.encOpFor(t.Elem(), inProgress)
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                state.update(i)
                                state.enc.encodeArray(state.b, uintptr(p), *elemOp, t.Elem().Size(), indir, t.Len())
                        }
                case reflect.Map:
                        keyOp, keyIndir := enc.encOpFor(t.Key(), inProgress)
                        elemOp, elemIndir := enc.encOpFor(t.Elem(), inProgress)
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                // Maps cannot be accessed by moving addresses around the way
                                // that slices etc. can.  We must recover a full reflection value for
                                // the iteration.
                                v := reflect.ValueOf(unsafe.Unreflect(t, unsafe.Pointer(p)))
                                mv := reflect.Indirect(v)
                                // 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.
                        enc.getEncEngine(userType(typ))
                        info := mustGetTypeInfo(typ)
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                state.update(i)
                                // indirect through info to delay evaluation for recursive structs
                                state.enc.encodeStruct(state.b, info.encoder, uintptr(p))
                        }
                case reflect.Interface:
                        op = func(i *encInstr, state *encoderState, p unsafe.Pointer) {
                                // Interfaces transmit the name and contents of the concrete
                                // value they contain.
                                v := reflect.ValueOf(unsafe.Unreflect(t, unsafe.Pointer(p)))
                                iv := reflect.Indirect(v)
                                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 (enc *Encoder) 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, p unsafe.Pointer) {
                var v reflect.Value
                if ut.encIndir == -1 {
                        // Need to climb up one level to turn value into pointer.
                        v = reflect.ValueOf(unsafe.Unreflect(rt, unsafe.Pointer(&p)))
                } else {
                        v = reflect.ValueOf(unsafe.Unreflect(rt, p))
                }
                if !state.sendZero && isZero(v) {
                        return
                }
                state.update(i)
                state.enc.encodeGobEncoder(state.b, 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 (enc *Encoder) compileEnc(ut *userTypeInfo) *encEngine {
        srt := ut.base
        engine := new(encEngine)
        seen := make(map[reflect.Type]*encOp)
        rt := ut.base
        if ut.isGobEncoder {
                rt = ut.user
        }
        if !ut.isGobEncoder &&
                srt.Kind() == reflect.Struct {
                for fieldNum, wireFieldNum := 0, 0; fieldNum < srt.NumField(); fieldNum++ {
                        f := srt.Field(fieldNum)
                        if !isExported(f.Name) {
                                continue
                        }
                        op, indir := enc.encOpFor(f.Type, seen)
                        engine.instr = append(engine.instr, encInstr{*op, wireFieldNum, indir, uintptr(f.Offset)})
                        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, 0, 0})
        } else {
                engine.instr = make([]encInstr, 1)
                op, indir := enc.encOpFor(rt, seen)
                engine.instr[0] = encInstr{*op, singletonField, indir, 0} // offset is zero
        }
        return engine
}

// getEncEngine returns the engine to compile the type.
// typeLock must be held (or we're in initialization and guaranteed single-threaded).
func (enc *Encoder) getEncEngine(ut *userTypeInfo) *encEngine {
        info, err1 := getTypeInfo(ut)
        if err1 != nil {
                error_(err1)
        }
        if info.encoder == nil {
                // mark this engine as underway before compiling to handle recursive types.
                info.encoder = new(encEngine)
                info.encoder = enc.compileEnc(ut)
        }
        return info.encoder
}

// lockAndGetEncEngine is a function that locks and compiles.
// This lets us hold the lock only while compiling, not when encoding.
func (enc *Encoder) lockAndGetEncEngine(ut *userTypeInfo) *encEngine {
        typeLock.Lock()
        defer typeLock.Unlock()
        return enc.getEncEngine(ut)
}

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