chore(netlink): define own types with minimal fields

- Allow to swap `github.com/vishvananda/netlink`
- Allow to add build tags for each platform
- One step closer to development on non-Linux platforms

internal/netlink/link.go

@@ -2,36 +2,117 @@ package netlink
 
 import "github.com/vishvananda/netlink"
 
-type (
-	Link      = netlink.Link
-	Bridge    = netlink.Bridge
-	Wireguard = netlink.Wireguard
-)
+type Link struct {
+	Type      string
+	Name      string
+	Index     int
+	EncapType string
+	MTU       uint16
+
+	NetNsID int
+	TxQLen  int
+}
 
 func (n *NetLink) LinkList() (links []Link, err error) {
-	return netlink.LinkList()
+	netlinkLinks, err := netlink.LinkList()
+	if err != nil {
+		return nil, err
+	}
+
+	links = make([]Link, len(netlinkLinks))
+	for i := range netlinkLinks {
+		links[i] = netlinkLinkToLink(netlinkLinks[i])
+	}
+
+	return links, nil
 }
 
 func (n *NetLink) LinkByName(name string) (link Link, err error) {
-	return netlink.LinkByName(name)
+	netlinkLink, err := netlink.LinkByName(name)
+	if err != nil {
+		return Link{}, err
+	}
+
+	return netlinkLinkToLink(netlinkLink), nil
 }
 
 func (n *NetLink) LinkByIndex(index int) (link Link, err error) {
-	return netlink.LinkByIndex(index)
+	netlinkLink, err := netlink.LinkByIndex(index)
+	if err != nil {
+		return Link{}, err
+	}
+
+	return netlinkLinkToLink(netlinkLink), nil
 }
 
-func (n *NetLink) LinkAdd(link Link) (err error) {
-	return netlink.LinkAdd(link)
+func (n *NetLink) LinkAdd(link Link) (linkIndex int, err error) {
+	netlinkLink := linkToNetlinkLink(&link)
+	err = netlink.LinkAdd(netlinkLink)
+	if err != nil {
+		return 0, err
+	}
+	return netlinkLink.Attrs().Index, nil
 }
 
 func (n *NetLink) LinkDel(link Link) (err error) {
-	return netlink.LinkDel(link)
+	return netlink.LinkDel(linkToNetlinkLink(&link))
 }
 
-func (n *NetLink) LinkSetUp(link Link) (err error) {
-	return netlink.LinkSetUp(link)
+func (n *NetLink) LinkSetUp(link Link) (linkIndex int, err error) {
+	netlinkLink := linkToNetlinkLink(&link)
+	err = netlink.LinkSetUp(netlinkLink)
+	if err != nil {
+		return 0, err
+	}
+	return netlinkLink.Attrs().Index, nil
 }
 
 func (n *NetLink) LinkSetDown(link Link) (err error) {
-	return netlink.LinkSetDown(link)
+	return netlink.LinkSetDown(linkToNetlinkLink(&link))
+}
+
+type netlinkLinkImpl struct {
+	attrs    *netlink.LinkAttrs
+	linkType string
+}
+
+func (n *netlinkLinkImpl) Attrs() *netlink.LinkAttrs {
+	return n.attrs
+}
+
+func (n *netlinkLinkImpl) Type() string {
+	return n.linkType
+}
+
+func netlinkLinkToLink(netlinkLink netlink.Link) Link {
+	attributes := netlinkLink.Attrs()
+	return Link{
+		Type:      netlinkLink.Type(),
+		Name:      attributes.Name,
+		Index:     attributes.Index,
+		EncapType: attributes.EncapType,
+		MTU:       uint16(attributes.MTU),
+		NetNsID:   attributes.NetNsID,
+		TxQLen:    attributes.TxQLen,
+	}
+}
+
+// Warning: we must return `netlink.Link` and not `netlinkLinkImpl`
+// so that the vishvananda/netlink package can compare the returned
+// value against an untyped nil.
+func linkToNetlinkLink(link *Link) netlink.Link {
+	if link == nil {
+		return nil
+	}
+	return &netlinkLinkImpl{
+		linkType: link.Type,
+		attrs: &netlink.LinkAttrs{ // TODO get all original attributes
+			Name:      link.Name,
+			Index:     link.Index,
+			EncapType: link.EncapType,
+			MTU:       int(link.MTU),
+			NetNsID:   link.NetNsID,
+			TxQLen:    link.TxQLen,
+		},
+	}
 }