libnet/d/bridge: don't parse the MacAddress netlabel

[akerouanton]

- What I did

Libnet's method (*Network).createEndpoint() is already parsing this netlabel to set the field ep.iface.mac. Later on, this same method invoke the driver's method CreateEndpoint with an InterfaceInfo arg and an options arg (an opaque map of driver opts).

The InterfaceInfo interface contains a MacAddress() method that returns ep.iface.mac. And the opaque map may contain the key netlabel.MacAddress.

Prior to this change, the bridge driver was calling MacAddress(). If no value was returned, it'd fall back to the option set in the options map, or generate a MAC address based on the IP address.

However, the expected type of the options value is a net.HardwareAddr. This is what's set by the daemon when handing over the endpoint config to libnet controller. If the value is a string, as is the case if the MAC address is provided through EndpointsSettings.DriverOpts, it produces an error.

As such, the opaque option and the MacAddress() are necessarily the same -- either nothing or a net.HardwareAddr. No need to keep both.

Moreover, the struct endpointConfiguration was only used to store that netlabel value. Drop it too.

- How I did it

Careful static code analysis.

- How to verify it

CI and tests.

Or manually:

$ docker run --rm -it --network testnet --mac-address 02:42:ac:13:00:12 nicolaka/netshoot ip -brief link show
$ docker run --rm -it --network=name=testnet,driver-opt=com.docker.network.endpoint.macaddress=60:3e:5f:35:9a:e4 nicolaka/netshoot ip -brief link show

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Where is com.docker.network.endpoint.macaddress now parsed/handled after this PR? Or is the interface that's created the mechanism to pass that on?

(It was confusing a bit that com.docker.network.endpoint. reads as passing options for the endpoint but CreateEndpoint no longer accepting options, other than "by proxy" through the interface)

[akerouanton]

Where is com.docker.network.endpoint.macaddress now parsed/handled after this PR?

First, the MacAddress sent through the API is added the generic options by buildCreateEndpointOptions:

moby/daemon/network.go

Lines 843 to 849 in cd08d37

	if epConfig.DesiredMacAddress != "" {
	mac, err := net.ParseMAC(epConfig.DesiredMacAddress)
	if err != nil {
	return nil, err
	}
	genericOptions[netlabel.MacAddress] = mac
	}

Then, (*Controller).CreateEndpoint() parses these generic options and sets ep.iface.mac:

moby/libnetwork/network.go

Lines 1170 to 1174 in cd08d37

	if opt, ok := ep.generic[netlabel.MacAddress]; ok {
	if mac, ok := opt.(net.HardwareAddr); ok {
	ep.iface.mac = mac
	}
	}

Then, driver's CreateEndpoint is called with ep.Iface() (= ep.iface) passed as 3rd arg:

moby/libnetwork/network.go

Line 1115 in cd08d37

err = d.CreateEndpoint(n.id, ep.id, ep.Iface(), ep.generic)

Finally, the bridge driver initializes endpoint.macAddress from ifInfo.MacAdress() (which returns ep.iface.macAddress):

moby/libnetwork/drivers/bridge/bridge_linux.go

Line 1072 in cd08d37

endpoint.macAddress = ifInfo.MacAddress()

Now, if you're wondering what happens when com.docker.network.endpoint.macaddress is passed as a 'driver opt' (ie. docker run --network=name=testnet,driver-opt=com.docker.network.endpoint.macaddress=...), it was producing the following error and is now silently ignored (ie. the same way as unknown labels):

$ docker run --rm -it --network=name=testnet,driver-opt=com.docker.network.endpoint.macaddress=60:3e:5f:35:9a:e4 nicolaka/netshoot ip -brief link show
docker: Error response from daemon: failed to create endpoint inspiring_galileo on network testnet: trying to create an endpoint with an invalid endpoint configuration.