New in 1.5, Golang's JSON decoder type has a new method that provides a streaming interface for decoding a JSON document: Token. It also interoperates with the existing functionality of Decode, which will continue a decode operation already started with Decoder.Token. - see example at https://golang.org/pkg/encoding/json/#Decoder.Decode

The added Token function will allow us to read and validate opening and closing brackets for JSON arrays. This will eliminate the need for the separatorReader in mongoimport.