GODRIVER-3436 Avoid initializing null data given custom decoder

[prestonvasquez]

GODRIVER-3436

Summary

If the value reader is null, prevent DefaultValueDecoders from initializing a pointer to the zero value.

Background & Motivation

The current behavior will lead to unexpected results:

ill instantiate a pointer field decoded from null data if the user defines a UnmarshalBSONValue. For example:

package main

import (
	"fmt"

	"go.mongodb.org/mongo-driver/v2/bson"
	"go.mongodb.org/mongo-driver/x/bsonx/bsoncore"
)

type DBInt64 int64

type Product struct {
	TotalForSell *DBInt64 `json:"total_for_sell" bson:"total_for_sell,omitempty"`
}

func (i *DBInt64) UnmarshalBSONValue(t bson.Type, value []byte) error {
	return nil
}

func main() {
	idx, doc := bsoncore.AppendDocumentStart(nil)
	doc = bsoncore.AppendNullElement(doc, "total_for_sell")

	doc, err := bsoncore.AppendDocumentEnd(doc, idx)
	if err != nil {
		panic(err)
	}

	bytes := bson.Raw(doc)

	got := Product{}
	if err := bson.Unmarshal(bytes, &got); err != nil {
		panic(err)
	}

	if got.TotalForSell != nil {
		fmt.Println("null value decoded as non-nil")
	}
}

Output:

❯ go run custom_type_with_pointer.go
null value decoded as non-nil

[mongodb-drivers-pr-bot]

API Change Report

./v2/mongo

incompatible changes

##Connect: changed from func(...*./v2/mongo/options.ClientOptions) (*Client, error) to func(..../v2/mongo/options.Lister[./v2/mongo/options.ClientOptions]) (*Client, error)

./v2/mongo/options

incompatible changes

(*AutoEncryptionOptions).SetBypassAutoEncryption: removed
(*AutoEncryptionOptions).SetBypassQueryAnalysis: removed
(*AutoEncryptionOptions).SetEncryptedFieldsMap: removed
(*AutoEncryptionOptions).SetExtraOptions: removed
(*AutoEncryptionOptions).SetKeyVaultClientOptions: removed
(*AutoEncryptionOptions).SetKeyVaultNamespace: removed
(*AutoEncryptionOptions).SetKmsProviders: removed
(*AutoEncryptionOptions).SetSchemaMap: removed
(*AutoEncryptionOptions).SetTLSConfig: removed
(*ClientOptions).ApplyURI: removed
(*ClientOptions).SetAppName: removed
(*ClientOptions).SetAuth: removed
(*ClientOptions).SetAutoEncryptionOptions: removed
(*ClientOptions).SetBSONOptions: removed
(*ClientOptions).SetCompressors: removed
(*ClientOptions).SetConnectTimeout: removed
(*ClientOptions).SetDialer: removed
(*ClientOptions).SetDirect: removed
(*ClientOptions).SetDisableOCSPEndpointCheck: removed
(*ClientOptions).SetDriverInfo: removed
(*ClientOptions).SetHTTPClient: removed
(*ClientOptions).SetHeartbeatInterval: removed
(*ClientOptions).SetHosts: removed
(*ClientOptions).SetLoadBalanced: removed
(*ClientOptions).SetLocalThreshold: removed
(*ClientOptions).SetLoggerOptions: removed
(*ClientOptions).SetMaxConnIdleTime: removed
(*ClientOptions).SetMaxConnecting: removed
(*ClientOptions).SetMaxPoolSize: removed
(*ClientOptions).SetMinPoolSize: removed
(*ClientOptions).SetMonitor: removed
(*ClientOptions).SetPoolMonitor: removed
(*ClientOptions).SetReadConcern: removed
(*ClientOptions).SetReadPreference: removed
(*ClientOptions).SetRegistry: removed
(*ClientOptions).SetReplicaSet: removed
(*ClientOptions).SetRetryReads: removed
(*ClientOptions).SetRetryWrites: removed
(*ClientOptions).SetSRVMaxHosts: removed
(*ClientOptions).SetSRVServiceName: removed
(*ClientOptions).SetServerAPIOptions: removed
(*ClientOptions).SetServerMonitor: removed
(*ClientOptions).SetServerMonitoringMode: removed
(*ClientOptions).SetServerSelectionTimeout: removed
(*ClientOptions).SetTLSConfig: removed
(*ClientOptions).SetTimeout: removed
(*ClientOptions).SetWriteConcern: removed
(*ClientOptions).SetZlibLevel: removed
(*ClientOptions).SetZstdLevel: removed
(*ClientOptions).Validate: removed
(*LoggerOptions).SetComponentLevel: removed
(*LoggerOptions).SetMaxDocumentLength: removed
(*LoggerOptions).SetSink: removed
(*ServerAPIOptions).SetDeprecationErrors: removed
(*ServerAPIOptions).SetStrict: removed
AutoEncryption: changed from func() *AutoEncryptionOptions to func() *AutoEncryptionOptionsBuilder
AutoEncryptionOptions.KeyVaultClientOptions: changed from *ClientOptions to Lister[ClientOptions]
Client: changed from func() *ClientOptions to func() *ClientOptionsBuilder
ClientOptions.AutoEncryptionOptions: changed from *AutoEncryptionOptions to Lister[AutoEncryptionOptions]
ClientOptions.LoggerOptions: changed from *LoggerOptions to Lister[LoggerOptions]
ClientOptions.ServerAPIOptions: changed from *ServerAPIOptions to Lister[ServerAPIOptions]
Logger: changed from func() *LoggerOptions to func() *LoggerOptionsBuilder
MergeClientOptions: removed
ServerAPI: changed from func(ServerAPIVersion) *ServerAPIOptions to func(ServerAPIVersion) *ServerAPIOptionsBuilder

compatible changes

AutoEncryptionOptionsBuilder: added
ClientOptionsBuilder: added
LoggerOptionsBuilder: added
ServerAPIOptionsBuilder: added

./v2/x/mongo/driver/topology

incompatible changes

##ConvertToDriverAPIOptions: changed from func(*./v2/mongo/options.ServerAPIOptions) *./v2/x/mongo/driver.ServerAPIOptions to func(./v2/mongo/options.Lister[./v2/mongo/options.ServerAPIOptions]) ./v2/x/mongo/driver.ServerAPIOptions
##NewConfig: changed from func(./v2/mongo/options.ClientOptions, *./v2/x/mongo/driver/session.ClusterClock) (Config, error) to func(./v2/mongo/options.ClientOptionsBuilder, *./v2/x/mongo/driver/session.ClusterClock) (*Config, error)

compatible changes

NewConfigFromOptions: added

[matthewdale]

Looks good! 👍