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common-issues.md

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Frequently Encountered Issues

These are fixes or information for common issues encountered by Go Driver users. If none of these are helpful, create a GODRIVER Jira ticket and we'll try to troubleshoot your issue!

WriteXXX can only write while positioned on a Element or Value but is positioned on a TopLevel

The bson.Marshal function requires a parameter that can be decoded into a BSON Document, i.e. a bson.D. Therefore the error message

WriteXXX can only write while positioned on a Element or Value but is positioned on a TopLevel

occurs when the input to bson.Marshal is something other than a BSON Document. Examples of this occurrence include

  • WriteString: the input into bson.Marshal is a string
  • WriteNull: the input into bson.Marshal is null
  • WriteInt32: the input into bson.Marshal is an integer

Many CRUD operations in the Go Driver use bson.Marshal under the hood, so it's possible to encounter this particular error without directly attempting to encode data. For example, when using a sort on FindOneAndUpdate this error can occur when not properly initializing the sort variable:

var sort bson.D // this is nil and will result in a WriteNull error
opts := options.FindOneAndUpdate().SetSort(sort)
update := bson.D{{"$inc", bson.D{{"x", 1}}}}
sr := coll.FindOneAndUpdate(ctx, bson.D{}, update)
if err := sr.Err(); err != nil {
	log.Fatalf("error getting single result: %v", err)
}

The above example is resolved by initializing the sort variable:

sort := bson.D{}

Convert BSON Document to JSON

There are a variety of marshalers that can be used to encode a BSON document as JSON, including MarshalExtJSON:

doc := bson.D{{"x", 1}}

jsonBytes, err := bson.MarshalExtJSON(doc, true, false)
if err != nil {
	log.Fatalf("error encoding json: %v", err)
}

m := make(map[string]interface{})
if err := json.Unmarshal(jsonBytes, &m); err != nil {
	log.Fatalf("error decoding json: %v", err)
}
fmt.Printf("json: %v\n", m)

Authentication Failed

When connecting to a MongoDB deployment with password authentication enabled, if your authentication information or configuration are incorrect, you may encounter an error message like:

connection() error occurred during connection handshake: auth error: sasl conversation error: unable to authenticate using mechanism "SCRAM-SHA-256": (AuthenticationFailed) Authentication failed.

That error can be caused by a number of issues. The error message intentionally omits the exact authentication failure reason (see the OWASP Authentication and Error Messages guidelines for an explanation). Possible causes of the error include:

  • Incorrect password.
  • Incorrect username.
  • Incorrect authentication database (i.e. authSource).

If you encounter an AuthenticationFailed error like the one above, check that the username and password in your connection string or SetAuth call are correct. In most cases, authSource does not need to be specified unless you are using a non-default authentication database (the default is "admin").