Add custom ice stdnet implementation (#754)

On Android, because of the hard SELinux policies can not list the
interfaces of the ICE package. Without it can not generate a host type
candidate. In this pull request, the list of interfaces comes via the Java
interface.

client/internal/stdnet/stdnet.go

@@ -0,0 +1,137 @@
+// Package stdnet is an extension of the pion's stdnet.
+// With it the list of the interface can come from external source.
+// More info: https://github.com/golang/go/issues/40569
+package stdnet
+
+import (
+	"fmt"
+	"net"
+	"strings"
+
+	"github.com/pion/transport/v2"
+	"github.com/pion/transport/v2/stdnet"
+	log "github.com/sirupsen/logrus"
+)
+
+// Net is an implementation of the net.Net interface
+// based on functions of the standard net package.
+type Net struct {
+	stdnet.Net
+	interfaces []*transport.Interface
+}
+
+// NewNet creates a new StdNet instance.
+func NewNet(iFaceDiscover IFaceDiscover) (*Net, error) {
+	n := &Net{}
+
+	return n, n.UpdateInterfaces(iFaceDiscover)
+}
+
+// UpdateInterfaces updates the internal list of network interfaces
+// and associated addresses.
+func (n *Net) UpdateInterfaces(iFaceDiscover IFaceDiscover) error {
+	ifacesString, err := iFaceDiscover.IFaces()
+	if err != nil {
+		return err
+	}
+	n.interfaces = parseInterfacesString(ifacesString)
+	return err
+}
+
+// Interfaces returns a slice of interfaces which are available on the
+// system
+func (n *Net) Interfaces() ([]*transport.Interface, error) {
+	return n.interfaces, nil
+}
+
+// InterfaceByIndex returns the interface specified by index.
+//
+// On Solaris, it returns one of the logical network interfaces
+// sharing the logical data link; for more precision use
+// InterfaceByName.
+func (n *Net) InterfaceByIndex(index int) (*transport.Interface, error) {
+	for _, ifc := range n.interfaces {
+		if ifc.Index == index {
+			return ifc, nil
+		}
+	}
+
+	return nil, fmt.Errorf("%w: index=%d", transport.ErrInterfaceNotFound, index)
+}
+
+// InterfaceByName returns the interface specified by name.
+func (n *Net) InterfaceByName(name string) (*transport.Interface, error) {
+	for _, ifc := range n.interfaces {
+		if ifc.Name == name {
+			return ifc, nil
+		}
+	}
+
+	return nil, fmt.Errorf("%w: %s", transport.ErrInterfaceNotFound, name)
+}
+
+func parseInterfacesString(interfaces string) []*transport.Interface {
+	ifs := []*transport.Interface{}
+
+	for _, iface := range strings.Split(interfaces, "\n") {
+		if strings.TrimSpace(iface) == "" {
+			continue
+		}
+
+		fields := strings.Split(iface, "|")
+		if len(fields) != 2 {
+			log.Warnf("parseInterfacesString: unable to split %q", iface)
+			continue
+		}
+
+		var name string
+		var index, mtu int
+		var up, broadcast, loopback, pointToPoint, multicast bool
+		_, err := fmt.Sscanf(fields[0], "%s %d %d %t %t %t %t %t",
+			&name, &index, &mtu, &up, &broadcast, &loopback, &pointToPoint, &multicast)
+		if err != nil {
+			log.Warnf("parseInterfacesString: unable to parse %q: %v", iface, err)
+			continue
+		}
+
+		newIf := net.Interface{
+			Name:  name,
+			Index: index,
+			MTU:   mtu,
+		}
+		if up {
+			newIf.Flags |= net.FlagUp
+		}
+		if broadcast {
+			newIf.Flags |= net.FlagBroadcast
+		}
+		if loopback {
+			newIf.Flags |= net.FlagLoopback
+		}
+		if pointToPoint {
+			newIf.Flags |= net.FlagPointToPoint
+		}
+		if multicast {
+			newIf.Flags |= net.FlagMulticast
+		}
+
+		ifc := transport.NewInterface(newIf)
+
+		addrs := strings.Trim(fields[1], " \n")
+		foundAddress := false
+		for _, addr := range strings.Split(addrs, " ") {
+			ip, ipNet, err := net.ParseCIDR(addr)
+			if err != nil {
+				log.Warnf("%s", err)
+				continue
+			}
+			ipNet.IP = ip
+			ifc.AddAddress(ipNet)
+			foundAddress = true
+		}
+		if foundAddress {
+			ifs = append(ifs, ifc)
+		}
+	}
+	return ifs
+}