net: add MarshalText/UnmarshalText to HardwareAddr

[maja42]

What version of Go are you using (go version)?

$ go version
go1.10 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What did you do?

I'm trying to unmarshal json content into net.IP and net.HardwareAddr.
Both types are actually of type []byte
Since net.IP implements json.Marshaler, it works as expected. However, net.HardwareAddr does not and fails with the error "illegal base64 data at input byte 2" (that's the position of the separator).

Here's an example:
https://play.golang.org/p/HOBBAyvpfrK

I found the google group discussion about adding the Marshaller to the net.IP type: https://groups.google.com/forum/#!topic/golang-nuts/io8aHJarm6U

What did you expect to see?

I expect net.HardwareAddr to be consistent with net.IP and implement json.Marshaler.
Strings in the form of "ab:cd:ef:ab:cd:ef" inside json should be parsable to MAC addresses.

[agnivade]

Considering there is a ParseMAC corresponding to ParseIP which is basically what the Unmarshaller for IP does, this seems like a reasonable request.

[rsc]

There are backwards compatibility concerns with adding MarshalText/UnmarshalText where they did not exist before. Was it possible to marshal these to JSON/Gob/XML before and then decode them back? If so, we can't break the old encoding. Or even if it was only possible to marshal, if that was a form other languages/tools knew, we can't change that either.

While we're on the topic, do we need to think about net.IPMask too?

[rsc]

Waiting for someone to dig into whether there are compatibility issues here.

[agnivade]

/cc @mikioh

[gopherbot]

Timed out in state WaitingForInfo. Closing.

(I am just a bot, though. Please speak up if this is a mistake or you have the requested information.)

[mikioh]

Just FYI.

As far as I can see/remember;

• textual representation for link- or below-layer identifiers varies,
• the existing net.ParseMAC accepts only a few well-known representations, IEEE and some vendors, for the sake of convenience,
• the existing net.HardwareAddr.String method returns the form described in IEEE Std 802-2001, Section 3.1.8 hexadecimal representation with the pick of "colons" instead of "hyphens",
• though, MAC-48 is now obsolete. IEEE RA states that "... octets separated by hyphens; the IEEE RA refers to this as the hexadecimal (hex) representation." in https://standards.ieee.org/content/dam/ieee-standards/standards/web/documents/tutorials/eui.pdf

[mikioh]

While we're on the topic, do we need to think about net.IPMask too?

Also net.IPNet? I don't think so. As shown in #30264, there is a need for flexible IP address printer but simple, single-form text marshaler and unmarshaler might not fit for the actual needs, not only for classical telco sectors but tech sectors.