internal/linux: Add NetlinkInterfaces

Signed-off-by: Stéphane Graber <stgraber@stgraber.org>
Sponsored-by: https://webdock.io

internal/linux/netlink.go

@@ -0,0 +1,99 @@
+//go:build linux
+
+package linux
+
+import (
+	"fmt"
+	"net"
+	"syscall"
+	"unsafe"
+)
+
+// NetlinkInterface returns a net.Interface extended to also contain its addresses.
+type NetlinkInterface struct {
+	net.Interface
+
+	Addresses []net.Addr
+}
+
+// NetlinkInterfaces performs a RTM_GETADDR call to get both
+func NetlinkInterfaces() ([]NetlinkInterface, error) {
+	// Grab the interface list.
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	// Initialize result slice.
+	netlinkIfaces := make([]NetlinkInterface, 0, len(ifaces))
+	for _, iface := range ifaces {
+		netlinkIfaces = append(netlinkIfaces, NetlinkInterface{iface, make([]net.Addr, 0)})
+	}
+
+	// Turn it into a map.
+	ifaceMap := make(map[int]*NetlinkInterface, len(ifaces))
+	for k, v := range netlinkIfaces {
+		ifaceMap[v.Index] = &netlinkIfaces[k] //nolint:typecheck
+	}
+
+	// Make the netlink call.
+	rib, err := syscall.NetlinkRIB(syscall.RTM_GETADDR, syscall.AF_UNSPEC)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to query RTM_GETADDR: %v", err)
+	}
+
+	messages, err := syscall.ParseNetlinkMessage(rib)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to parse RTM_GETADDR: %v", err)
+	}
+
+	for _, m := range messages {
+		if m.Header.Type == syscall.RTM_NEWADDR {
+			addrMessage := (*syscall.IfAddrmsg)(unsafe.Pointer(&m.Data[0]))
+
+			addrAttrs, err := syscall.ParseNetlinkRouteAttr(&m)
+			if err != nil {
+				return nil, fmt.Errorf("Failed to parse rotue attribute: %v", err)
+			}
+
+			ifi, ok := ifaceMap[int(addrMessage.Index)]
+			if ok {
+				ifi.Addresses = append(ifi.Addresses, newAddr(addrMessage, addrAttrs))
+			}
+		}
+	}
+
+	return netlinkIfaces, nil
+}
+
+// Variation of function of the same name from within Go source.
+func newAddr(ifam *syscall.IfAddrmsg, attrs []syscall.NetlinkRouteAttr) net.Addr {
+	var ipPointToPoint bool
+
+	// Seems like we need to make sure whether the IP interface
+	// stack consists of IP point-to-point numbered or unnumbered
+	// addressing.
+	for _, a := range attrs {
+		if a.Attr.Type == syscall.IFA_LOCAL {
+			ipPointToPoint = true
+			break
+		}
+	}
+
+	for _, a := range attrs {
+		if ipPointToPoint && a.Attr.Type == syscall.IFA_ADDRESS {
+			continue
+		}
+
+		switch ifam.Family {
+		case syscall.AF_INET:
+			return &net.IPNet{IP: net.IPv4(a.Value[0], a.Value[1], a.Value[2], a.Value[3]), Mask: net.CIDRMask(int(ifam.Prefixlen), 8*net.IPv4len)}
+		case syscall.AF_INET6:
+			ifa := &net.IPNet{IP: make(net.IP, net.IPv6len), Mask: net.CIDRMask(int(ifam.Prefixlen), 8*net.IPv6len)}
+			copy(ifa.IP, a.Value[:])
+			return ifa
+		}
+	}
+
+	return nil
+}