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// Copyright (C) MongoDB, Inc. 2017-present.
//
// Licensed 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
package bson
import (
"errors"
"fmt"
"reflect"
"sync"
"go.mongodb.org/mongo-driver/bson/bsoncodec"
"go.mongodb.org/mongo-driver/bson/bsonrw"
)
// ErrDecodeToNil is the error returned when trying to decode to a nil value
var ErrDecodeToNil = errors.New("cannot Decode to nil value")
// This pool is used to keep the allocations of Decoders down. This is only used for the Marshal*
// methods and is not consumable from outside of this package. The Decoders retrieved from this pool
// must have both Reset and SetRegistry called on them.
var decPool = sync.Pool{
New: func() interface{} {
return new(Decoder)
},
}
// A Decoder reads and decodes BSON documents from a stream. It reads from a bsonrw.ValueReader as
// the source of BSON data.
type Decoder struct {
dc bsoncodec.DecodeContext
vr bsonrw.ValueReader
}
// NewDecoder returns a new decoder that uses the DefaultRegistry to read from vr.
func NewDecoder(vr bsonrw.ValueReader) (*Decoder, error) {
if vr == nil {
return nil, errors.New("cannot create a new Decoder with a nil ValueReader")
}
return &Decoder{
dc: bsoncodec.DecodeContext{Registry: DefaultRegistry},
vr: vr,
}, nil
}
// NewDecoderWithContext returns a new decoder that uses DecodeContext dc to read from vr.
func NewDecoderWithContext(dc bsoncodec.DecodeContext, vr bsonrw.ValueReader) (*Decoder, error) {
if dc.Registry == nil {
dc.Registry = DefaultRegistry
}
if vr == nil {
return nil, errors.New("cannot create a new Decoder with a nil ValueReader")
}
return &Decoder{
dc: dc,
vr: vr,
}, nil
}
// Decode reads the next BSON document from the stream and decodes it into the
// value pointed to by val.
//
// The documentation for Unmarshal contains details about of BSON into a Go
// value.
func (d *Decoder) Decode(val interface{}) error {
if unmarshaler, ok := val.(Unmarshaler); ok {
// TODO(skriptble): Reuse a []byte here and use the AppendDocumentBytes method.
buf, err := bsonrw.Copier{}.CopyDocumentToBytes(d.vr)
if err != nil {
return err
}
return unmarshaler.UnmarshalBSON(buf)
}
rval := reflect.ValueOf(val)
switch rval.Kind() {
case reflect.Ptr:
if rval.IsNil() {
return ErrDecodeToNil
}
rval = rval.Elem()
case reflect.Map:
if rval.IsNil() {
return ErrDecodeToNil
}
default:
return fmt.Errorf("argument to Decode must be a pointer or a map, but got %v", rval)
}
decoder, err := d.dc.LookupDecoder(rval.Type())
if err != nil {
return err
}
return decoder.DecodeValue(d.dc, d.vr, rval)
}
// Reset will reset the state of the decoder, using the same *DecodeContext used in
// the original construction but using vr for reading.
func (d *Decoder) Reset(vr bsonrw.ValueReader) error {
d.vr = vr
return nil
}
// SetRegistry replaces the current registry of the decoder with r.
func (d *Decoder) SetRegistry(r *bsoncodec.Registry) error {
d.dc.Registry = r
return nil
}
// SetContext replaces the current registry of the decoder with dc.
func (d *Decoder) SetContext(dc bsoncodec.DecodeContext) error {
d.dc = dc
return nil
}
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