source: code/trunk/vendor/google.golang.org/protobuf/internal/impl/convert.go@ 822

// Copyright 2018 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 impl

import (
        "fmt"
        "reflect"

        "google.golang.org/protobuf/reflect/protoreflect"
)

// unwrapper unwraps the value to the underlying value.
// This is implemented by List and Map.
type unwrapper interface {
        protoUnwrap() interface{}
}

// A Converter coverts to/from Go reflect.Value types and protobuf protoreflect.Value types.
type Converter interface {
        // PBValueOf converts a reflect.Value to a protoreflect.Value.
        PBValueOf(reflect.Value) protoreflect.Value

        // GoValueOf converts a protoreflect.Value to a reflect.Value.
        GoValueOf(protoreflect.Value) reflect.Value

        // IsValidPB returns whether a protoreflect.Value is compatible with this type.
        IsValidPB(protoreflect.Value) bool

        // IsValidGo returns whether a reflect.Value is compatible with this type.
        IsValidGo(reflect.Value) bool

        // New returns a new field value.
        // For scalars, it returns the default value of the field.
        // For composite types, it returns a new mutable value.
        New() protoreflect.Value

        // Zero returns a new field value.
        // For scalars, it returns the default value of the field.
        // For composite types, it returns an immutable, empty value.
        Zero() protoreflect.Value
}

// NewConverter matches a Go type with a protobuf field and returns a Converter
// that converts between the two. Enums must be a named int32 kind that
// implements protoreflect.Enum, and messages must be pointer to a named
// struct type that implements protoreflect.ProtoMessage.
//
// This matcher deliberately supports a wider range of Go types than what
// protoc-gen-go historically generated to be able to automatically wrap some
// v1 messages generated by other forks of protoc-gen-go.
func NewConverter(t reflect.Type, fd protoreflect.FieldDescriptor) Converter {
        switch {
        case fd.IsList():
                return newListConverter(t, fd)
        case fd.IsMap():
                return newMapConverter(t, fd)
        default:
                return newSingularConverter(t, fd)
        }
        panic(fmt.Sprintf("invalid Go type %v for field %v", t, fd.FullName()))
}

var (
        boolType    = reflect.TypeOf(bool(false))
        int32Type   = reflect.TypeOf(int32(0))
        int64Type   = reflect.TypeOf(int64(0))
        uint32Type  = reflect.TypeOf(uint32(0))
        uint64Type  = reflect.TypeOf(uint64(0))
        float32Type = reflect.TypeOf(float32(0))
        float64Type = reflect.TypeOf(float64(0))
        stringType  = reflect.TypeOf(string(""))
        bytesType   = reflect.TypeOf([]byte(nil))
        byteType    = reflect.TypeOf(byte(0))
)

var (
        boolZero    = protoreflect.ValueOfBool(false)
        int32Zero   = protoreflect.ValueOfInt32(0)
        int64Zero   = protoreflect.ValueOfInt64(0)
        uint32Zero  = protoreflect.ValueOfUint32(0)
        uint64Zero  = protoreflect.ValueOfUint64(0)
        float32Zero = protoreflect.ValueOfFloat32(0)
        float64Zero = protoreflect.ValueOfFloat64(0)
        stringZero  = protoreflect.ValueOfString("")
        bytesZero   = protoreflect.ValueOfBytes(nil)
)

func newSingularConverter(t reflect.Type, fd protoreflect.FieldDescriptor) Converter {
        defVal := func(fd protoreflect.FieldDescriptor, zero protoreflect.Value) protoreflect.Value {
                if fd.Cardinality() == protoreflect.Repeated {
                        // Default isn't defined for repeated fields.
                        return zero
                }
                return fd.Default()
        }
        switch fd.Kind() {
        case protoreflect.BoolKind:
                if t.Kind() == reflect.Bool {
                        return &boolConverter{t, defVal(fd, boolZero)}
                }
        case protoreflect.Int32Kind, protoreflect.Sint32Kind, protoreflect.Sfixed32Kind:
                if t.Kind() == reflect.Int32 {
                        return &int32Converter{t, defVal(fd, int32Zero)}
                }
        case protoreflect.Int64Kind, protoreflect.Sint64Kind, protoreflect.Sfixed64Kind:
                if t.Kind() == reflect.Int64 {
                        return &int64Converter{t, defVal(fd, int64Zero)}
                }
        case protoreflect.Uint32Kind, protoreflect.Fixed32Kind:
                if t.Kind() == reflect.Uint32 {
                        return &uint32Converter{t, defVal(fd, uint32Zero)}
                }
        case protoreflect.Uint64Kind, protoreflect.Fixed64Kind:
                if t.Kind() == reflect.Uint64 {
                        return &uint64Converter{t, defVal(fd, uint64Zero)}
                }
        case protoreflect.FloatKind:
                if t.Kind() == reflect.Float32 {
                        return &float32Converter{t, defVal(fd, float32Zero)}
                }
        case protoreflect.DoubleKind:
                if t.Kind() == reflect.Float64 {
                        return &float64Converter{t, defVal(fd, float64Zero)}
                }
        case protoreflect.StringKind:
                if t.Kind() == reflect.String || (t.Kind() == reflect.Slice && t.Elem() == byteType) {
                        return &stringConverter{t, defVal(fd, stringZero)}
                }
        case protoreflect.BytesKind:
                if t.Kind() == reflect.String || (t.Kind() == reflect.Slice && t.Elem() == byteType) {
                        return &bytesConverter{t, defVal(fd, bytesZero)}
                }
        case protoreflect.EnumKind:
                // Handle enums, which must be a named int32 type.
                if t.Kind() == reflect.Int32 {
                        return newEnumConverter(t, fd)
                }
        case protoreflect.MessageKind, protoreflect.GroupKind:
                return newMessageConverter(t)
        }
        panic(fmt.Sprintf("invalid Go type %v for field %v", t, fd.FullName()))
}

type boolConverter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *boolConverter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfBool(v.Bool())
}
func (c *boolConverter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(v.Bool()).Convert(c.goType)
}
func (c *boolConverter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(bool)
        return ok
}
func (c *boolConverter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *boolConverter) New() protoreflect.Value  { return c.def }
func (c *boolConverter) Zero() protoreflect.Value { return c.def }

type int32Converter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *int32Converter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfInt32(int32(v.Int()))
}
func (c *int32Converter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(int32(v.Int())).Convert(c.goType)
}
func (c *int32Converter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(int32)
        return ok
}
func (c *int32Converter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *int32Converter) New() protoreflect.Value  { return c.def }
func (c *int32Converter) Zero() protoreflect.Value { return c.def }

type int64Converter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *int64Converter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfInt64(int64(v.Int()))
}
func (c *int64Converter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(int64(v.Int())).Convert(c.goType)
}
func (c *int64Converter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(int64)
        return ok
}
func (c *int64Converter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *int64Converter) New() protoreflect.Value  { return c.def }
func (c *int64Converter) Zero() protoreflect.Value { return c.def }

type uint32Converter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *uint32Converter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfUint32(uint32(v.Uint()))
}
func (c *uint32Converter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(uint32(v.Uint())).Convert(c.goType)
}
func (c *uint32Converter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(uint32)
        return ok
}
func (c *uint32Converter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *uint32Converter) New() protoreflect.Value  { return c.def }
func (c *uint32Converter) Zero() protoreflect.Value { return c.def }

type uint64Converter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *uint64Converter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfUint64(uint64(v.Uint()))
}
func (c *uint64Converter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(uint64(v.Uint())).Convert(c.goType)
}
func (c *uint64Converter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(uint64)
        return ok
}
func (c *uint64Converter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *uint64Converter) New() protoreflect.Value  { return c.def }
func (c *uint64Converter) Zero() protoreflect.Value { return c.def }

type float32Converter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *float32Converter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfFloat32(float32(v.Float()))
}
func (c *float32Converter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(float32(v.Float())).Convert(c.goType)
}
func (c *float32Converter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(float32)
        return ok
}
func (c *float32Converter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *float32Converter) New() protoreflect.Value  { return c.def }
func (c *float32Converter) Zero() protoreflect.Value { return c.def }

type float64Converter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *float64Converter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfFloat64(float64(v.Float()))
}
func (c *float64Converter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(float64(v.Float())).Convert(c.goType)
}
func (c *float64Converter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(float64)
        return ok
}
func (c *float64Converter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *float64Converter) New() protoreflect.Value  { return c.def }
func (c *float64Converter) Zero() protoreflect.Value { return c.def }

type stringConverter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *stringConverter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfString(v.Convert(stringType).String())
}
func (c *stringConverter) GoValueOf(v protoreflect.Value) reflect.Value {
        // pref.Value.String never panics, so we go through an interface
        // conversion here to check the type.
        s := v.Interface().(string)
        if c.goType.Kind() == reflect.Slice && s == "" {
                return reflect.Zero(c.goType) // ensure empty string is []byte(nil)
        }
        return reflect.ValueOf(s).Convert(c.goType)
}
func (c *stringConverter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(string)
        return ok
}
func (c *stringConverter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *stringConverter) New() protoreflect.Value  { return c.def }
func (c *stringConverter) Zero() protoreflect.Value { return c.def }

type bytesConverter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func (c *bytesConverter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        if c.goType.Kind() == reflect.String && v.Len() == 0 {
                return protoreflect.ValueOfBytes(nil) // ensure empty string is []byte(nil)
        }
        return protoreflect.ValueOfBytes(v.Convert(bytesType).Bytes())
}
func (c *bytesConverter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(v.Bytes()).Convert(c.goType)
}
func (c *bytesConverter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().([]byte)
        return ok
}
func (c *bytesConverter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}
func (c *bytesConverter) New() protoreflect.Value  { return c.def }
func (c *bytesConverter) Zero() protoreflect.Value { return c.def }

type enumConverter struct {
        goType reflect.Type
        def    protoreflect.Value
}

func newEnumConverter(goType reflect.Type, fd protoreflect.FieldDescriptor) Converter {
        var def protoreflect.Value
        if fd.Cardinality() == protoreflect.Repeated {
                def = protoreflect.ValueOfEnum(fd.Enum().Values().Get(0).Number())
        } else {
                def = fd.Default()
        }
        return &enumConverter{goType, def}
}

func (c *enumConverter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        return protoreflect.ValueOfEnum(protoreflect.EnumNumber(v.Int()))
}

func (c *enumConverter) GoValueOf(v protoreflect.Value) reflect.Value {
        return reflect.ValueOf(v.Enum()).Convert(c.goType)
}

func (c *enumConverter) IsValidPB(v protoreflect.Value) bool {
        _, ok := v.Interface().(protoreflect.EnumNumber)
        return ok
}

func (c *enumConverter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}

func (c *enumConverter) New() protoreflect.Value {
        return c.def
}

func (c *enumConverter) Zero() protoreflect.Value {
        return c.def
}

type messageConverter struct {
        goType reflect.Type
}

func newMessageConverter(goType reflect.Type) Converter {
        return &messageConverter{goType}
}

func (c *messageConverter) PBValueOf(v reflect.Value) protoreflect.Value {
        if v.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", v.Type(), c.goType))
        }
        if c.isNonPointer() {
                if v.CanAddr() {
                        v = v.Addr() // T => *T
                } else {
                        v = reflect.Zero(reflect.PtrTo(v.Type()))
                }
        }
        if m, ok := v.Interface().(protoreflect.ProtoMessage); ok {
                return protoreflect.ValueOfMessage(m.ProtoReflect())
        }
        return protoreflect.ValueOfMessage(legacyWrapMessage(v))
}

func (c *messageConverter) GoValueOf(v protoreflect.Value) reflect.Value {
        m := v.Message()
        var rv reflect.Value
        if u, ok := m.(unwrapper); ok {
                rv = reflect.ValueOf(u.protoUnwrap())
        } else {
                rv = reflect.ValueOf(m.Interface())
        }
        if c.isNonPointer() {
                if rv.Type() != reflect.PtrTo(c.goType) {
                        panic(fmt.Sprintf("invalid type: got %v, want %v", rv.Type(), reflect.PtrTo(c.goType)))
                }
                if !rv.IsNil() {
                        rv = rv.Elem() // *T => T
                } else {
                        rv = reflect.Zero(rv.Type().Elem())
                }
        }
        if rv.Type() != c.goType {
                panic(fmt.Sprintf("invalid type: got %v, want %v", rv.Type(), c.goType))
        }
        return rv
}

func (c *messageConverter) IsValidPB(v protoreflect.Value) bool {
        m := v.Message()
        var rv reflect.Value
        if u, ok := m.(unwrapper); ok {
                rv = reflect.ValueOf(u.protoUnwrap())
        } else {
                rv = reflect.ValueOf(m.Interface())
        }
        if c.isNonPointer() {
                return rv.Type() == reflect.PtrTo(c.goType)
        }
        return rv.Type() == c.goType
}

func (c *messageConverter) IsValidGo(v reflect.Value) bool {
        return v.IsValid() && v.Type() == c.goType
}

func (c *messageConverter) New() protoreflect.Value {
        if c.isNonPointer() {
                return c.PBValueOf(reflect.New(c.goType).Elem())
        }
        return c.PBValueOf(reflect.New(c.goType.Elem()))
}

func (c *messageConverter) Zero() protoreflect.Value {
        return c.PBValueOf(reflect.Zero(c.goType))
}

// isNonPointer reports whether the type is a non-pointer type.
// This never occurs for generated message types.
func (c *messageConverter) isNonPointer() bool {
        return c.goType.Kind() != reflect.Ptr
}