How can you decode multiple message types with golang websockets?

Question

I have a go program using the (relatively) standard go.net/websocket‎ library. I'm trying to receive and decode messages from a web page that have a different structure for each type of message, i.e.

{type: "messagetype", msg: { /* structure different for each message type */ } }

Is there any way to do a "partial" decode of the message, only checking the type field before proceeding to decode the actual message into a go struct?

Would this necessitate writing a custom Codec, a'la JSON, that delegates to the JSON codec for the message itself?

Answer 1

Use json.RawMessage to delay the decoding, eg

struct {
    type string
    msg  json.RawMessage
}

json.RawMessage is an alias for []byte which you can then further decode as you wish.