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