Improve Linux performance of GetAllInterfaces

ifaddrs.go

@@ -240,7 +240,7 @@ func IfAttrs(selectorName string, ifAddrs IfAddrs) (string, error) {
 // available IP addresses on each interface and converts them to
 // sockaddr.IPAddrs, and returning the result as an array of IfAddr.
 func GetAllInterfaces() (IfAddrs, error) {
-	ifs, err := net.Interfaces()
+	ifs, err := NetInterfaces()
 	if err != nil {
 		return nil, err
 	}
@@ -259,10 +259,7 @@ func GetAllInterfaces() (IfAddrs, error) {
 				return IfAddrs{}, fmt.Errorf("unable to create an IP address from %q", addr.String())
 			}
 
-			ifAddr := IfAddr{
-				SockAddr:  ipAddr,
-				Interface: intf,
-			}
+			ifAddr := NewIfAddr(ipAddr, intf)
 			ifAddrs = append(ifAddrs, ifAddr)
 		}
 	}

net_default.go

@@ -0,0 +1,16 @@
+//go:build !linux
+// +build !linux
+
+package sockaddr
+
+import (
+	"net"
+)
+
+func NetInterfaces() ([]net.Interface, error) {
+	return net.Interfaces()
+}
+
+func NewIfAddr(addr IPAddr, intf net.Interface) IfAddr {
+	return IfAddr{addr, intf}
+}

net_linux.go

@@ -0,0 +1,91 @@
+package sockaddr
+
+import (
+	"net"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// LinuxNetInterface contains a net.Interface along with its associated []net.Addr.
+type LinuxNetInterface struct {
+	net.Interface
+	addrs []net.Addr
+}
+
+func (ifi *LinuxNetInterface) Addrs() ([]net.Addr, error) {
+	return ifi.addrs, nil
+}
+
+// NetInterfaces returns all net.Interfaces along with their associated []net.Addr.
+// This Linux optimization avoids a separate Netlink dump of addresses for each individual interface,
+// which is prohibitively slow on servers with large numbers of interfaces:
+// https://github.com/golang/go/issues/53660
+func NetInterfaces() ([]LinuxNetInterface, error) {
+	interfaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+	netInterfaces := make([]LinuxNetInterface, 0, len(interfaces))
+	for _, ifi := range interfaces {
+		netInterfaces = append(netInterfaces, LinuxNetInterface{ifi, make([]net.Addr, 0)})
+	}
+	ifMap := make(map[int]*LinuxNetInterface, len(netInterfaces))
+	for i, ifi := range netInterfaces {
+		ifMap[ifi.Index] = &netInterfaces[i]
+	}
+
+	tab, err := syscall.NetlinkRIB(syscall.RTM_GETADDR, syscall.AF_UNSPEC)
+	if err != nil {
+		return nil, os.NewSyscallError("NetlinkRIB", err)
+	}
+	msgs, err := syscall.ParseNetlinkMessage(tab)
+	if err != nil {
+		return nil, os.NewSyscallError("ParseNetLinkMessage", err)
+	}
+
+	for _, m := range msgs {
+		if m.Header.Type == syscall.RTM_NEWADDR {
+			ifam := (*syscall.IfAddrmsg)(unsafe.Pointer(&m.Data[0]))
+			attrs, err := syscall.ParseNetlinkRouteAttr(&m)
+			if err != nil {
+				return nil, os.NewSyscallError("ParseNetLinkRouteAttr", err)
+			}
+			if ifi, ok := ifMap[int(ifam.Index)]; ok {
+				ifi.addrs = append(ifi.addrs, newAddr(ifam, attrs))
+			}
+		}
+	}
+
+	return netInterfaces, err
+}
+
+// Vendored unexported function:
+// https://github.com/golang/go/blob/8bcc490667d4dd44c633c536dd463bbec0a3838f/src/net/interface_linux.go#L178-L203
+func newAddr(ifam *syscall.IfAddrmsg, attrs []syscall.NetlinkRouteAttr) net.Addr {
+	var ipPointToPoint bool
+	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
+}
+
+func NewIfAddr(addr IPAddr, intf LinuxNetInterface) IfAddr {
+	return IfAddr{addr, intf.Interface}
+}