Casting Go interface to struct

Wed, 20 Feb 2019 10:30:51 -0700

I was using an excellent go icmp library recently. I got hung up on dealing with a received MessageBody type that I knew was really an Echo type, but I could not refer to the fields in the Echo struct. I think my C/C++/Python background got in my way here.

After a bit of head scratching, I noticed the MessageBody type was defined an an interface and the Echo type was defined as a struct. Ah! A clue! I bet I can cast an interface type to a struct type.

Thusly:

switch rxMsg.Type {
case ipv4.ICMPTypeEchoReply:
    body, _ := rxMsg.Body.(*icmp.Echo)

where rxMsg.Body is the received icmp.MessageBody interface and body is the desired icmp.Echo struct.

Insert blinding flash o' light here. Using an interface definition, this Go icmp library author allows the library user to easily convert an received message body into its appropriate struct equivalent. Whoa. That sort of power was not so obvious to me when I first read about the Go interface.

Simple defer'd Error Handling in Go

Fri, 15 Feb 2019 10:47:00 -0700

I recently wrote a Go func that starts off by opening a network listening connection and defers closing that connection.

connection, err := icmp.ListenPacket(...)
if err != nil {
    panic(err)
}
defer connection.Close()

The defer'd connection.Close()returns an error, but how to capture and do something with that error if it occurs?

A solution was not so obvious to me. Thankfully I stumbled upon a very comprehensive and detailed answer.A bit of overkill (for my purposes) that led me to this simple implementation.

    connection, err := icmp.ListenPacket(...)
    if err != nil {
        panic(err)
    }
    defer func() {
        err = connection.Close()
        if err != nil {
            fmt.Printf("%v\n", err)
        }
    }()

Thank you most kindly pocketgophers. Life is good.

David Pointer

Casting Go interface to struct

Simple defer'd Error Handling in Go