util: Add a terrible heuristic for getting ethernet devices

I don't know of a better way. This will have to do for now.

util/net.go

@@ -0,0 +1,64 @@
+// Mgmt
+// Copyright (C) 2013-2024+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+//
+// Additional permission under GNU GPL version 3 section 7
+//
+// If you modify this program, or any covered work, by linking or combining it
+// with embedded mcl code and modules (and that the embedded mcl code and
+// modules which link with this program, contain a copy of their source code in
+// the authoritative form) containing parts covered by the terms of any other
+// license, the licensors of this program grant you additional permission to
+// convey the resulting work. Furthermore, the licensors of this program grant
+// the original author, James Shubin, additional permission to update this
+// additional permission if he deems it necessary to achieve the goals of this
+// additional permission.
+
+package util
+
+import (
+	"strings"
+
+	"github.com/vishvananda/netlink"
+)
+
+// GetPhysicalEthernetDevices returns a link of physical ethernet devices. This
+// is a heuristic and I wish I knew the better way.
+//
+// XXX: Patches welcome!
+func GetPhysicalEthernetDevices() ([]string, error) {
+	devices := []string{}
+	links, err := netlink.LinkList()
+	if err != nil {
+		return nil, err
+	}
+	for _, link := range links {
+		// wifi, eth, and loopback all do this, bridges do not.
+		if link.Type() != "device" {
+			continue
+		}
+		name := link.Attrs().Name
+		if name == "lo" { // loopback
+			continue
+		}
+		if strings.HasPrefix(name, "w") { // heuristic, eg: wlp0s20f3
+			continue
+		}
+		devices = append(devices, name)
+	}
+
+	return devices, nil
+}