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row_decoder.go
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row_decoder.go
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// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package coder
import (
"fmt"
"io"
"reflect"
"github.com/apache/beam/sdks/go/pkg/beam/internal/errors"
)
// RowDecoderBuilder allows one to build Beam Schema row encoders for provided types.
type RowDecoderBuilder struct {
allFuncs map[reflect.Type]decoderProvider
ifaceFuncs []reflect.Type
// RequireAllFieldsExported when set to true will have the default decoder building fail if
// there are any unexported fields. When set false, unexported fields in default
// destination structs will be silently ignored when decoding.
// This has no effect on types with registered decoder providers.
RequireAllFieldsExported bool
}
type decoderProvider = func(reflect.Type) (func(io.Reader) (interface{}, error), error)
// Register accepts a provider to decode schema encoded values
// of that type.
//
// When decoding values, decoder functions produced by this builder will
// first check for exact type matches, then interfaces implemented by
// the type in recency order of registration, and then finally the
// default Beam Schema encoding behavior.
//
// TODO(BEAM-9615): Add final factory types. This interface is subject to change.
// Currently f must be a function func(reflect.Type) (func(io.Reader) (interface{}, error), error)
func (b *RowDecoderBuilder) Register(rt reflect.Type, f interface{}) {
fd, ok := f.(decoderProvider)
if !ok {
panic(fmt.Sprintf("%T isn't a supported decoder function type (passed with %v), currently expecting %T", f, rt, (decoderProvider)(nil)))
}
if rt.Kind() == reflect.Interface && rt.NumMethod() == 0 {
panic(fmt.Sprintf("interface type %v must have methods", rt))
}
if b.allFuncs == nil {
b.allFuncs = make(map[reflect.Type]decoderProvider)
}
b.allFuncs[rt] = fd
if rt.Kind() == reflect.Interface {
b.ifaceFuncs = append(b.ifaceFuncs, rt)
}
}
// Build constructs a Beam Schema coder for the given type, using any providers registered for
// itself or it's fields.
func (b *RowDecoderBuilder) Build(rt reflect.Type) (func(io.Reader) (interface{}, error), error) {
if err := rowTypeValidation(rt, true); err != nil {
return nil, err
}
return b.decoderForType(rt)
}
// decoderForType returns a decoder function for the struct or pointer to struct type.
func (b *RowDecoderBuilder) decoderForType(t reflect.Type) (func(io.Reader) (interface{}, error), error) {
// Check if there are any providers registered for this type, or that this type adheres to any interfaces.
f, addr, err := b.customFunc(t)
if err != nil {
return nil, err
}
if addr {
// We cannot deal with address of here, only in embedded fields, indices, and keys/values. So clear f and continue.
f = nil
}
if f != nil {
return f, nil
}
var isPtr bool
// Pointers become the value type for decomposition.
if t.Kind() == reflect.Ptr {
isPtr = true
t = t.Elem()
}
dec, err := b.decoderForStructReflect(t)
if err != nil {
return nil, err
}
if isPtr {
return func(r io.Reader) (interface{}, error) {
rv := reflect.New(t)
err := dec(rv.Elem(), r)
return rv.Interface(), errors.Wrapf(err, "decoding a *%v", t)
}, nil
}
return func(r io.Reader) (interface{}, error) {
rv := reflect.New(t)
err := dec(rv.Elem(), r)
return rv.Elem().Interface(), errors.Wrapf(err, "decoding a *%v", t)
}, nil
}
// decoderForStructReflect returns a reflection based decoder function for the
// given struct type.
func (b *RowDecoderBuilder) decoderForStructReflect(t reflect.Type) (func(reflect.Value, io.Reader) error, error) {
var coder typeDecoderReflect
coder.typ = t
for i := 0; i < t.NumField(); i++ {
i := i // avoid alias issues in the closures.
sf := t.Field(i)
isUnexported := sf.PkgPath != ""
if sf.Anonymous {
ft := sf.Type
if ft.Kind() == reflect.Ptr {
// If a struct embeds a pointer to an unexported type,
// it is not possible to set a newly allocated value
// since the field is unexported.
//
// See https://golang.org/issue/21357
//
// Since the values are created by this package reflectively,
// there's no work around like pre-allocating the field
// manually.
if isUnexported {
return nil, errors.Errorf("cannot make schema decoder for type %v as it has an embedded field of a pointer to an unexported type %v. See https://golang.org/issue/21357", t, ft.Elem())
}
ft = ft.Elem()
}
if isUnexported && ft.Kind() != reflect.Struct {
// Ignore embedded fields of unexported non-struct types.
continue
}
// Do not ignore embedded fields of unexported struct types
// since they may have exported fields.
} else if isUnexported {
if b.RequireAllFieldsExported {
return nil, errors.Errorf("cannot make schema decoder for type %v as it has unexported fields such as %s.", t, sf.Name)
}
// Silently ignore, since we can't do anything about it.
// Add a no-op coder to fill in field index
coder.fields = append(coder.fields, typeDecoderFieldReflect{decode: func(rv reflect.Value, r io.Reader) error {
return nil
}})
continue
}
dec, err := b.decoderForSingleTypeReflect(sf.Type)
if err != nil {
return nil, err
}
coder.fields = append(coder.fields, dec)
}
return func(rv reflect.Value, r io.Reader) error {
nf, nils, err := ReadRowHeader(r)
if err != nil {
return err
}
if nf != len(coder.fields) {
return errors.Errorf("schema[%v] changed: got %d fields, want %d fields", coder.typ, nf, len(coder.fields))
}
for i, f := range coder.fields {
if IsFieldNil(nils, i) {
continue
}
fv := rv.Field(i)
if f.addr {
fv = fv.Addr()
}
if err := f.decode(fv, r); err != nil {
return err
}
}
return nil
}, nil
}
func reflectDecodeBool(rv reflect.Value, r io.Reader) error {
v, err := DecodeBool(r)
if err != nil {
return errors.Wrap(err, "error decoding bool field")
}
rv.SetBool(v)
return nil
}
func reflectDecodeByte(rv reflect.Value, r io.Reader) error {
b, err := DecodeByte(r)
if err != nil {
return errors.Wrap(err, "error decoding single byte field")
}
rv.SetUint(uint64(b))
return nil
}
func reflectDecodeString(rv reflect.Value, r io.Reader) error {
v, err := DecodeStringUTF8(r)
if err != nil {
return errors.Wrap(err, "error decoding string field")
}
rv.SetString(v)
return nil
}
func reflectDecodeInt(rv reflect.Value, r io.Reader) error {
v, err := DecodeVarInt(r)
if err != nil {
return errors.Wrap(err, "error decoding varint field")
}
rv.SetInt(v)
return nil
}
func reflectDecodeUint(rv reflect.Value, r io.Reader) error {
v, err := DecodeVarUint64(r)
if err != nil {
return errors.Wrap(err, "error decoding varint field")
}
rv.SetUint(v)
return nil
}
func reflectDecodeFloat(rv reflect.Value, r io.Reader) error {
v, err := DecodeDouble(r)
if err != nil {
return errors.Wrap(err, "error decoding double field")
}
rv.SetFloat(v)
return nil
}
func reflectDecodeByteSlice(rv reflect.Value, r io.Reader) error {
b, err := DecodeBytes(r)
if err != nil {
return errors.Wrap(err, "error decoding []byte field")
}
rv.SetBytes(b)
return nil
}
// customFunc returns nil if no custom func exists for this type.
// If an error is returned, coder construction should be aborted.
func (b *RowDecoderBuilder) customFunc(t reflect.Type) (func(io.Reader) (interface{}, error), bool, error) {
if fact, ok := b.allFuncs[t]; ok {
f, err := fact(t)
if err != nil {
return nil, false, err
}
return f, false, nil
}
// Check satisfaction of interface types in reverse registration order.
pt := reflect.PtrTo(t)
for i := len(b.ifaceFuncs) - 1; i >= 0; i-- {
it := b.ifaceFuncs[i]
if ok := t.Implements(it); ok {
if fact, ok := b.allFuncs[it]; ok {
f, err := fact(t)
if err != nil {
return nil, false, err
}
return f, false, nil
}
}
// This can occur when the type uses a pointer receiver but it is included as a value in a struct field.
if ok := pt.Implements(it); ok {
if fact, ok := b.allFuncs[it]; ok {
f, err := fact(pt)
if err != nil {
return nil, true, err
}
return f, true, nil
}
}
}
return nil, false, nil
}
// decoderForSingleTypeReflect returns a reflection based decoder function for the
// given type.
func (b *RowDecoderBuilder) decoderForSingleTypeReflect(t reflect.Type) (typeDecoderFieldReflect, error) {
// Check if there are any providers registered for this type, or that this type adheres to any interfaces.
dec, addr, err := b.customFunc(t)
if err != nil {
return typeDecoderFieldReflect{}, err
}
if dec != nil {
return typeDecoderFieldReflect{
decode: func(v reflect.Value, r io.Reader) error {
elm, err := dec(r)
if err != nil {
return err
}
if addr {
v.Elem().Set(reflect.ValueOf(elm).Elem())
} else {
v.Set(reflect.ValueOf(elm))
}
return nil
},
addr: addr,
}, nil
}
switch t.Kind() {
case reflect.Struct:
dec, err := b.decoderForStructReflect(t)
return typeDecoderFieldReflect{decode: dec}, err
case reflect.Bool:
return typeDecoderFieldReflect{decode: reflectDecodeBool}, nil
case reflect.Uint8:
return typeDecoderFieldReflect{decode: reflectDecodeByte}, nil
case reflect.String:
return typeDecoderFieldReflect{decode: reflectDecodeString}, nil
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return typeDecoderFieldReflect{decode: reflectDecodeInt}, nil
case reflect.Uint, reflect.Uint64, reflect.Uint32, reflect.Uint16:
return typeDecoderFieldReflect{decode: reflectDecodeUint}, nil
case reflect.Float32, reflect.Float64:
return typeDecoderFieldReflect{decode: reflectDecodeFloat}, nil
case reflect.Ptr:
decf, err := b.decoderForSingleTypeReflect(t.Elem())
if err != nil {
return typeDecoderFieldReflect{}, err
}
return typeDecoderFieldReflect{decode: func(rv reflect.Value, r io.Reader) error {
rv.Set(reflect.New(t.Elem()))
if !decf.addr {
rv = rv.Elem()
}
return decf.decode(rv, r)
}}, nil
case reflect.Slice:
// Special case handling for byte slices.
if t.Elem().Kind() == reflect.Uint8 {
return typeDecoderFieldReflect{decode: reflectDecodeByteSlice}, nil
}
decf, err := b.containerDecoderForType(t.Elem())
if err != nil {
return typeDecoderFieldReflect{}, err
}
return typeDecoderFieldReflect{decode: iterableDecoderForSlice(t, decf)}, nil
case reflect.Array:
decf, err := b.containerDecoderForType(t.Elem())
if err != nil {
return typeDecoderFieldReflect{}, err
}
return typeDecoderFieldReflect{decode: iterableDecoderForArray(t, decf)}, nil
case reflect.Map:
decK, err := b.containerDecoderForType(t.Key())
if err != nil {
return typeDecoderFieldReflect{}, err
}
decV, err := b.containerDecoderForType(t.Elem())
if err != nil {
return typeDecoderFieldReflect{}, err
}
return typeDecoderFieldReflect{decode: mapDecoder(t, decK, decV)}, nil
}
return typeDecoderFieldReflect{}, errors.Errorf("unable to decode type: %v", t)
}
func (b *RowDecoderBuilder) containerDecoderForType(t reflect.Type) (typeDecoderFieldReflect, error) {
dec, err := b.decoderForSingleTypeReflect(t)
if err != nil {
return typeDecoderFieldReflect{}, err
}
if t.Kind() == reflect.Ptr {
return typeDecoderFieldReflect{decode: containerNilDecoder(dec.decode), addr: dec.addr}, nil
}
return dec, nil
}
type typeDecoderReflect struct {
typ reflect.Type
fields []typeDecoderFieldReflect
}
type typeDecoderFieldReflect struct {
decode func(reflect.Value, io.Reader) error
// If true the decoder is expecting us to pass it the address
// of the field value (i.e. &foo.bar) and not the field value (i.e. foo.bar).
addr bool
}