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coder.go
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coder.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 beam
import (
"encoding/json"
"fmt"
"reflect"
"github.com/apache/beam/sdks/go/pkg/beam/core/graph/coder"
"github.com/apache/beam/sdks/go/pkg/beam/core/runtime/coderx"
"github.com/apache/beam/sdks/go/pkg/beam/core/typex"
"github.com/apache/beam/sdks/go/pkg/beam/core/util/reflectx"
"github.com/golang/protobuf/proto"
)
func init() {
RegisterFunction(JSONDec)
RegisterFunction(JSONEnc)
RegisterFunction(ProtoEnc)
RegisterFunction(ProtoDec)
}
// Coder defines how to encode and decode values of type 'A' into byte streams.
// Coders are attached to PCollections of the same type. For PCollections
// consumed by GBK, the attached coders are required to be deterministic.
type Coder struct {
coder *coder.Coder
}
// IsValid returns true iff the Coder is valid. Any use of an invalid Coder
// will result in a panic.
func (c Coder) IsValid() bool {
return c.coder != nil
}
// Type returns the full type 'A' of elements the coder can encode and decode.
// 'A' must be a concrete full type, such as int or KV<int,string>.
func (c Coder) Type() FullType {
if !c.IsValid() {
panic("Invalid Coder")
}
return c.coder.T
}
func (c Coder) String() string {
if c.coder == nil {
return "$"
}
return c.coder.String()
}
// TODO(herohde) 4/4/2017: for convenience, we use the magic json coding
// everywhere. To be replaced by Coder registry, sharing, etc.
// TODO: select optimal coder based on type, notably handling int, string, etc.
// TODO(herohde) 7/11/2017: figure out best way to let transformation use
// coders (like passert). For now, we just allow them to grab in the internal
// coder. Maybe it's cleaner to pull Encode/Decode into beam instead, if
// adequate. The issue is that we would need non-windowed coding. Maybe focus on
// coder registry and construction: then type -> coder might be adequate.
// UnwrapCoder returns the internal coder.
func UnwrapCoder(c Coder) *coder.Coder {
return c.coder
}
// NewCoder infers a Coder for any bound full type.
func NewCoder(t FullType) Coder {
c, err := inferCoder(t)
if err != nil {
panic(err) // for now
}
return Coder{c}
}
var protoMessageType = reflect.TypeOf((*proto.Message)(nil)).Elem()
func inferCoder(t FullType) (*coder.Coder, error) {
switch t.Class() {
case typex.Concrete, typex.Container:
switch t.Type() {
case reflectx.Int, reflectx.Int8, reflectx.Int16, reflectx.Int32, reflectx.Int64:
c, err := coderx.NewVarIntZ(t.Type())
if err != nil {
return nil, err
}
return &coder.Coder{Kind: coder.Custom, T: t, Custom: c}, nil
case reflectx.Uint, reflectx.Uint8, reflectx.Uint16, reflectx.Uint32, reflectx.Uint64:
c, err := coderx.NewVarUintZ(t.Type())
if err != nil {
return nil, err
}
return &coder.Coder{Kind: coder.Custom, T: t, Custom: c}, nil
case reflectx.Float32, reflectx.Float64:
c, err := coderx.NewFloat(t.Type())
if err != nil {
return nil, err
}
return &coder.Coder{Kind: coder.Custom, T: t, Custom: c}, nil
case reflectx.String, reflectx.ByteSlice:
// TODO(BEAM-3580): we should stop encoding string using the bytecoder. It forces
// conversions at runtime in inconvenient places.
return &coder.Coder{Kind: coder.Bytes, T: t}, nil
default:
// TODO(BEAM-3306): the coder registry should be consulted here for user
// specified types and their coders.
if t.Type().Implements(protoMessageType) {
c, err := newProtoCoder(t.Type())
if err != nil {
return nil, err
}
return &coder.Coder{Kind: coder.Custom, T: t, Custom: c}, nil
}
c, err := newJSONCoder(t.Type())
if err != nil {
return nil, err
}
return &coder.Coder{Kind: coder.Custom, T: t, Custom: c}, nil
}
case typex.Composite:
c, err := inferCoders(t.Components())
if err != nil {
return nil, err
}
switch t.Type() {
case typex.KVType:
return &coder.Coder{Kind: coder.KV, T: t, Components: c}, nil
case typex.CoGBKType:
return &coder.Coder{Kind: coder.CoGBK, T: t, Components: c}, nil
case typex.WindowedValueType:
// TODO(herohde) 4/15/2018: do we ever infer W types now that PCollections
// are non-windowed? We either need to know the windowing strategy or
// we should remove this case.
return &coder.Coder{Kind: coder.WindowedValue, T: t, Components: c, Window: coder.NewGlobalWindow()}, nil
default:
panic(fmt.Sprintf("Unexpected composite type: %v", t))
}
default:
panic(fmt.Sprintf("Unexpected type: %v", t))
}
}
func inferCoders(list []FullType) ([]*coder.Coder, error) {
var ret []*coder.Coder
for _, t := range list {
c, err := inferCoder(t)
if err != nil {
return nil, err
}
ret = append(ret, c)
}
return ret, nil
}
// TODO(herohde) 4/5/2017: decide whether we want an Encoded form. For now,
// we'll use exploded form coders only using typex.T. We might also need a
// form that doesn't require LengthPrefix'ing to cut up the bytestream from
// the FnHarness.
// ProtoEnc marshals the supplied proto.Message.
func ProtoEnc(in T) ([]byte, error) {
return proto.Marshal(in.(proto.Message))
}
// ProtoDec unmarshals the supplied bytes into an instance of the supplied
// proto.Message type.
func ProtoDec(t reflect.Type, in []byte) (T, error) {
val := reflect.New(t.Elem()).Interface().(proto.Message)
if err := proto.Unmarshal(in, val); err != nil {
return nil, err
}
return val, nil
}
func newProtoCoder(t reflect.Type) (*coder.CustomCoder, error) {
c, err := coder.NewCustomCoder("proto", t, ProtoEnc, ProtoDec)
if err != nil {
return nil, fmt.Errorf("invalid coder: %v", err)
}
return c, nil
}
// Concrete and universal custom coders both have a similar signature.
// Conversion is handled by reflection.
// JSONEnc encodes the supplied value in JSON.
func JSONEnc(in T) ([]byte, error) {
return json.Marshal(in)
}
// JSONDec decodes the supplied JSON into an instance of the supplied type.
func JSONDec(t reflect.Type, in []byte) (T, error) {
val := reflect.New(t)
if err := json.Unmarshal(in, val.Interface()); err != nil {
return nil, err
}
return val.Elem().Interface(), nil
}
func newJSONCoder(t reflect.Type) (*coder.CustomCoder, error) {
c, err := coder.NewCustomCoder("json", t, JSONEnc, JSONDec)
if err != nil {
return nil, fmt.Errorf("invalid coder: %v", err)
}
return c, nil
}