Reason to not instantiate header when processing message?

[tprestegard]

If an incoming message doesn't have any headers, Msg.Header is nil (see here). This means if you want to modify the headers in a handler, you have to check if it is nil and instantiate it first. E.g.,

conn.Subscribe("my.subject", func(msg *Msg) {
    if msg.Header == nil {
        msg.Header = make(Header)
    }
    msg.Header.Set("my.header", "my.value")
    // Do something with msg
})

It's not at all a big deal, just a bit tedious and I found it surprising, especially since NewMsg instantiates the Header field. I was wondering if there is a reason for this (maybe minimizing memory usage?) or whether it would be reasonable to change the behavior.

[wallyqs]

Headers were not originally in the protocol but yes the reason would have been minimizing memory usage when introducing the feature. NewMsg helper was also added around the same time.

[tprestegard]

Makes sense, thanks!