decoder.go

Documentation: go.mongodb.org/mongo-driver/bson

     1  // Copyright (C) MongoDB, Inc. 2017-present.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License"); you may
     4  // not use this file except in compliance with the License. You may obtain
     5  // a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
     6  
     7  package bson
     8  
     9  import (
    10  	"errors"
    11  	"fmt"
    12  	"reflect"
    13  	"sync"
    14  
    15  	"go.mongodb.org/mongo-driver/bson/bsoncodec"
    16  	"go.mongodb.org/mongo-driver/bson/bsonrw"
    17  )
    18  
    19  // ErrDecodeToNil is the error returned when trying to decode to a nil value
    20  var ErrDecodeToNil = errors.New("cannot Decode to nil value")
    21  
    22  // This pool is used to keep the allocations of Decoders down. This is only used for the Marshal*
    23  // methods and is not consumable from outside of this package. The Decoders retrieved from this pool
    24  // must have both Reset and SetRegistry called on them.
    25  var decPool = sync.Pool{
    26  	New: func() interface{} {
    27  		return new(Decoder)
    28  	},
    29  }
    30  
    31  // A Decoder reads and decodes BSON documents from a stream. It reads from a bsonrw.ValueReader as
    32  // the source of BSON data.
    33  type Decoder struct {
    34  	dc bsoncodec.DecodeContext
    35  	vr bsonrw.ValueReader
    36  
    37  	// We persist defaultDocumentM and defaultDocumentD on the Decoder to prevent overwriting from
    38  	// (*Decoder).SetContext.
    39  	defaultDocumentM bool
    40  	defaultDocumentD bool
    41  
    42  	binaryAsSlice     bool
    43  	useJSONStructTags bool
    44  	useLocalTimeZone  bool
    45  	zeroMaps          bool
    46  	zeroStructs       bool
    47  }
    48  
    49  // NewDecoder returns a new decoder that uses the DefaultRegistry to read from vr.
    50  func NewDecoder(vr bsonrw.ValueReader) (*Decoder, error) {
    51  	if vr == nil {
    52  		return nil, errors.New("cannot create a new Decoder with a nil ValueReader")
    53  	}
    54  
    55  	return &Decoder{
    56  		dc: bsoncodec.DecodeContext{Registry: DefaultRegistry},
    57  		vr: vr,
    58  	}, nil
    59  }
    60  
    61  // NewDecoderWithContext returns a new decoder that uses DecodeContext dc to read from vr.
    62  //
    63  // Deprecated: Use [NewDecoder] and use the Decoder configuration methods set the desired unmarshal
    64  // behavior instead.
    65  func NewDecoderWithContext(dc bsoncodec.DecodeContext, vr bsonrw.ValueReader) (*Decoder, error) {
    66  	if dc.Registry == nil {
    67  		dc.Registry = DefaultRegistry
    68  	}
    69  	if vr == nil {
    70  		return nil, errors.New("cannot create a new Decoder with a nil ValueReader")
    71  	}
    72  
    73  	return &Decoder{
    74  		dc: dc,
    75  		vr: vr,
    76  	}, nil
    77  }
    78  
    79  // Decode reads the next BSON document from the stream and decodes it into the
    80  // value pointed to by val.
    81  //
    82  // See [Unmarshal] for details about BSON unmarshaling behavior.
    83  func (d *Decoder) Decode(val interface{}) error {
    84  	if unmarshaler, ok := val.(Unmarshaler); ok {
    85  		// TODO(skriptble): Reuse a []byte here and use the AppendDocumentBytes method.
    86  		buf, err := bsonrw.Copier{}.CopyDocumentToBytes(d.vr)
    87  		if err != nil {
    88  			return err
    89  		}
    90  		return unmarshaler.UnmarshalBSON(buf)
    91  	}
    92  
    93  	rval := reflect.ValueOf(val)
    94  	switch rval.Kind() {
    95  	case reflect.Ptr:
    96  		if rval.IsNil() {
    97  			return ErrDecodeToNil
    98  		}
    99  		rval = rval.Elem()
   100  	case reflect.Map:
   101  		if rval.IsNil() {
   102  			return ErrDecodeToNil
   103  		}
   104  	default:
   105  		return fmt.Errorf("argument to Decode must be a pointer or a map, but got %v", rval)
   106  	}
   107  	decoder, err := d.dc.LookupDecoder(rval.Type())
   108  	if err != nil {
   109  		return err
   110  	}
   111  
   112  	if d.defaultDocumentM {
   113  		d.dc.DefaultDocumentM()
   114  	}
   115  	if d.defaultDocumentD {
   116  		d.dc.DefaultDocumentD()
   117  	}
   118  	if d.binaryAsSlice {
   119  		d.dc.BinaryAsSlice()
   120  	}
   121  	if d.useJSONStructTags {
   122  		d.dc.UseJSONStructTags()
   123  	}
   124  	if d.useLocalTimeZone {
   125  		d.dc.UseLocalTimeZone()
   126  	}
   127  	if d.zeroMaps {
   128  		d.dc.ZeroMaps()
   129  	}
   130  	if d.zeroStructs {
   131  		d.dc.ZeroStructs()
   132  	}
   133  
   134  	return decoder.DecodeValue(d.dc, d.vr, rval)
   135  }
   136  
   137  // Reset will reset the state of the decoder, using the same *DecodeContext used in
   138  // the original construction but using vr for reading.
   139  func (d *Decoder) Reset(vr bsonrw.ValueReader) error {
   140  	// TODO:(GODRIVER-2719): Remove error return value.
   141  	d.vr = vr
   142  	return nil
   143  }
   144  
   145  // SetRegistry replaces the current registry of the decoder with r.
   146  func (d *Decoder) SetRegistry(r *bsoncodec.Registry) error {
   147  	// TODO:(GODRIVER-2719): Remove error return value.
   148  	d.dc.Registry = r
   149  	return nil
   150  }
   151  
   152  // SetContext replaces the current registry of the decoder with dc.
   153  //
   154  // Deprecated: Use the Decoder configuration methods to set the desired unmarshal behavior instead.
   155  func (d *Decoder) SetContext(dc bsoncodec.DecodeContext) error {
   156  	// TODO:(GODRIVER-2719): Remove error return value.
   157  	d.dc = dc
   158  	return nil
   159  }
   160  
   161  // DefaultDocumentM causes the Decoder to always unmarshal documents into the primitive.M type. This
   162  // behavior is restricted to data typed as "interface{}" or "map[string]interface{}".
   163  func (d *Decoder) DefaultDocumentM() {
   164  	d.defaultDocumentM = true
   165  }
   166  
   167  // DefaultDocumentD causes the Decoder to always unmarshal documents into the primitive.D type. This
   168  // behavior is restricted to data typed as "interface{}" or "map[string]interface{}".
   169  func (d *Decoder) DefaultDocumentD() {
   170  	d.defaultDocumentD = true
   171  }
   172  
   173  // AllowTruncatingDoubles causes the Decoder to truncate the fractional part of BSON "double" values
   174  // when attempting to unmarshal them into a Go integer (int, int8, int16, int32, or int64) struct
   175  // field. The truncation logic does not apply to BSON "decimal128" values.
   176  func (d *Decoder) AllowTruncatingDoubles() {
   177  	d.dc.Truncate = true
   178  }
   179  
   180  // BinaryAsSlice causes the Decoder to unmarshal BSON binary field values that are the "Generic" or
   181  // "Old" BSON binary subtype as a Go byte slice instead of a primitive.Binary.
   182  func (d *Decoder) BinaryAsSlice() {
   183  	d.binaryAsSlice = true
   184  }
   185  
   186  // UseJSONStructTags causes the Decoder to fall back to using the "json" struct tag if a "bson"
   187  // struct tag is not specified.
   188  func (d *Decoder) UseJSONStructTags() {
   189  	d.useJSONStructTags = true
   190  }
   191  
   192  // UseLocalTimeZone causes the Decoder to unmarshal time.Time values in the local timezone instead
   193  // of the UTC timezone.
   194  func (d *Decoder) UseLocalTimeZone() {
   195  	d.useLocalTimeZone = true
   196  }
   197  
   198  // ZeroMaps causes the Decoder to delete any existing values from Go maps in the destination value
   199  // passed to Decode before unmarshaling BSON documents into them.
   200  func (d *Decoder) ZeroMaps() {
   201  	d.zeroMaps = true
   202  }
   203  
   204  // ZeroStructs causes the Decoder to delete any existing values from Go structs in the destination
   205  // value passed to Decode before unmarshaling BSON documents into them.
   206  func (d *Decoder) ZeroStructs() {
   207  	d.zeroStructs = true
   208  }
   209
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