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119 lines
3.3 KiB
119 lines
3.3 KiB
// Copyright (C) MongoDB, Inc. 2017-present.
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may
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// not use this file except in compliance with the License. You may obtain
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// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
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package bson
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import (
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"errors"
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"fmt"
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"reflect"
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"sync"
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"go.mongodb.org/mongo-driver/bson/bsoncodec"
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"go.mongodb.org/mongo-driver/bson/bsonrw"
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)
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// ErrDecodeToNil is the error returned when trying to decode to a nil value
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var ErrDecodeToNil = errors.New("cannot Decode to nil value")
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// This pool is used to keep the allocations of Decoders down. This is only used for the Marshal*
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// methods and is not consumable from outside of this package. The Decoders retrieved from this pool
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// must have both Reset and SetRegistry called on them.
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var decPool = sync.Pool{
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New: func() interface{} {
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return new(Decoder)
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},
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}
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// A Decoder reads and decodes BSON documents from a stream. It reads from a bsonrw.ValueReader as
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// the source of BSON data.
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type Decoder struct {
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dc bsoncodec.DecodeContext
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vr bsonrw.ValueReader
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}
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// NewDecoder returns a new decoder that uses the DefaultRegistry to read from vr.
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func NewDecoder(vr bsonrw.ValueReader) (*Decoder, error) {
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if vr == nil {
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return nil, errors.New("cannot create a new Decoder with a nil ValueReader")
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}
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return &Decoder{
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dc: bsoncodec.DecodeContext{Registry: DefaultRegistry},
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vr: vr,
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}, nil
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}
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// NewDecoderWithContext returns a new decoder that uses DecodeContext dc to read from vr.
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func NewDecoderWithContext(dc bsoncodec.DecodeContext, vr bsonrw.ValueReader) (*Decoder, error) {
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if dc.Registry == nil {
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dc.Registry = DefaultRegistry
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}
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if vr == nil {
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return nil, errors.New("cannot create a new Decoder with a nil ValueReader")
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}
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return &Decoder{
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dc: dc,
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vr: vr,
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}, nil
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}
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// Decode reads the next BSON document from the stream and decodes it into the
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// value pointed to by val.
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//
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// The documentation for Unmarshal contains details about of BSON into a Go
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// value.
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func (d *Decoder) Decode(val interface{}) error {
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if unmarshaler, ok := val.(Unmarshaler); ok {
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// TODO(skriptble): Reuse a []byte here and use the AppendDocumentBytes method.
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buf, err := bsonrw.Copier{}.CopyDocumentToBytes(d.vr)
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if err != nil {
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return err
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}
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return unmarshaler.UnmarshalBSON(buf)
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}
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rval := reflect.ValueOf(val)
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switch rval.Kind() {
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case reflect.Ptr:
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if rval.IsNil() {
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return ErrDecodeToNil
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}
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rval = rval.Elem()
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case reflect.Map:
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if rval.IsNil() {
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return ErrDecodeToNil
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}
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default:
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return fmt.Errorf("argument to Decode must be a pointer or a map, but got %v", rval)
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}
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decoder, err := d.dc.LookupDecoder(rval.Type())
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if err != nil {
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return err
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}
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return decoder.DecodeValue(d.dc, d.vr, rval)
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}
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// Reset will reset the state of the decoder, using the same *DecodeContext used in
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// the original construction but using vr for reading.
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func (d *Decoder) Reset(vr bsonrw.ValueReader) error {
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d.vr = vr
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return nil
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}
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// SetRegistry replaces the current registry of the decoder with r.
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func (d *Decoder) SetRegistry(r *bsoncodec.Registry) error {
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d.dc.Registry = r
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return nil
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}
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// SetContext replaces the current registry of the decoder with dc.
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func (d *Decoder) SetContext(dc bsoncodec.DecodeContext) error {
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d.dc = dc
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return nil
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}
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