QoL feature - select best interface on current system

When generating a default config instead of using a canned value like "eth0", hypd will isntead look at what interfaces the system has and make a best guess based on progressively narrowing filters.

hypd/configuration/configuration.go

@@ -57,8 +57,16 @@ func LoadConfiguration(configFilePath string) (*HypdConfiguration, error) {
 }
 
 func DefaultConfig() *HypdConfiguration {
+	var ifaceString string
+	iface, err := getDefaultNIC()
+	if err == nil {
+		ifaceString = iface.Name
+	} else {
+		ifaceString = "enp0s3" // fallback to fixed value
+	}
+
 	return &HypdConfiguration{
-		NetworkInterface:      "enp0s3",
+		NetworkInterface:      ifaceString,
 		PreSharedKeyDirectory: "./secrets/",
 		SuccessAction:         "iptables -A INPUT -p tcp -s %s --dport 22 -j ACCEPT",
 		TimeoutSeconds:        1440,

hypd/configuration/defaultNIC.go

@@ -0,0 +1,81 @@
+package configuration
+
+import (
+	"fmt"
+	"net"
+)
+
+// QoL feature to try and detect the best NIC for hyp
+func getDefaultNIC() (*net.Interface, error) {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get network interfaces on this system: %v", err)
+	}
+	if len(ifaces) < 1 {
+		return nil, fmt.Errorf("this system has no network interfaces: %v", err)
+	}
+
+	// Just pick one to start
+	selectedIface := ifaces[0]
+	filteredIfaces := make([]net.Interface, 0)
+
+	// Check for ethernet addresses
+	for _, iface := range ifaces {
+		if len(iface.HardwareAddr) == 6 {
+			selectedIface = iface
+			filteredIfaces = append(filteredIfaces, iface)
+		}
+	}
+	ifaces = filteredIfaces
+	filteredIfaces = make([]net.Interface, 0)
+
+	// Check for interfaces that are up and not loopbacks
+	for _, iface := range ifaces {
+		if iface.Flags&net.FlagUp != 0 && iface.Flags&net.FlagRunning != 0 && iface.Flags&net.FlagLoopback == 0 {
+			selectedIface = iface
+			filteredIfaces = append(filteredIfaces, iface)
+		}
+	}
+	ifaces = filteredIfaces
+	filteredIfaces = make([]net.Interface, 0)
+
+	// Check for interfaces that have IPv4 addresses assigned
+	for _, iface := range ifaces {
+		addresses, err := iface.Addrs()
+		if err != nil {
+			continue
+		}
+		for _, address := range addresses {
+			ip, _, err := net.ParseCIDR(address.String())
+			if err != nil {
+				continue
+			}
+			if ip.To4() != nil {
+				selectedIface = iface
+				filteredIfaces = append(filteredIfaces, iface)
+			}
+		}
+	}
+	ifaces = filteredIfaces
+	filteredIfaces = nil
+
+	// Check for interfaces that have non RFC1918 addresses assigned
+	for _, iface := range ifaces {
+		addresses, err := iface.Addrs()
+		if err != nil {
+			continue
+		}
+		for _, address := range addresses {
+			ip, _, err := net.ParseCIDR(address.String())
+			if err != nil {
+				continue
+			}
+			if !ip.IsPrivate() {
+				selectedIface = iface
+
+			}
+		}
+	}
+
+	return &selectedIface, nil // TBD
+}