util: Move socketset from net resource to util

Prepare the socketset api to be used outside of the scope the net
resource.

engine/resources/net.go

@@ -34,6 +34,7 @@ import (
 	"github.com/purpleidea/mgmt/engine/traits"
 	"github.com/purpleidea/mgmt/recwatch"
 	"github.com/purpleidea/mgmt/util"
+	"github.com/purpleidea/mgmt/util/socketset"
 
 	multierr "github.com/hashicorp/go-multierror"
 	errwrap "github.com/pkg/errors"
@@ -41,7 +42,6 @@ import (
 	// do not clean up spawned goroutines. Should be replaced when a suitable
 	// alternative is available.
 	"github.com/vishvananda/netlink"
-	"golang.org/x/sys/unix"
 )
 
 func init() {
@@ -195,11 +195,11 @@ func (obj *NetRes) Watch() error {
 	defer wg.Wait()
 
 	// create a netlink socket for receiving network interface events
-	conn, err := newSocketSet(rtmGrps, obj.socketFile)
+	conn, err := socketset.NewSocketSet(rtmGrps, obj.socketFile)
 	if err != nil {
 		return errwrap.Wrapf(err, "error creating socket set")
 	}
-	defer conn.shutdown() // close the netlink socket and unblock conn.receive()
+	defer conn.Shutdown() // close the netlink socket and unblock conn.receive()
 
 	// watch the systemd-networkd configuration file
 	recWatcher, err := recwatch.NewRecWatcher(obj.unitFilePath, false)
@@ -219,11 +219,11 @@ func (obj *NetRes) Watch() error {
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
-		defer conn.close() // close the pipe when we're done with it
+		defer conn.Close() // close the pipe when we're done with it
 		defer close(nlChan)
 		for {
 			// receive messages from the socket set
-			msgs, err := conn.receive()
+			msgs, err := conn.Receive()
 			if err != nil {
 				select {
 				case nlChan <- &nlChanStruct{
@@ -768,122 +768,3 @@ func (obj *iface) addrApplyAdd(objAddrs []string) error {
 	}
 	return nil
 }
-
-// socketSet is used to receive events from a socket and shut it down cleanly
-// when asked. It contains a socket for events and a pipe socket to unblock
-// receive on shutdown.
-type socketSet struct {
-	fdEvents int
-	fdPipe   int
-	pipeFile string
-}
-
-// newSocketSet returns a socketSet, initialized with the given parameters.
-func newSocketSet(groups uint32, file string) (*socketSet, error) {
-	// make a netlink socket file descriptor
-	fdEvents, err := unix.Socket(unix.AF_NETLINK, unix.SOCK_RAW, unix.NETLINK_ROUTE)
-	if err != nil {
-		return nil, errwrap.Wrapf(err, "error creating netlink socket")
-	}
-	// bind to the socket and add add the netlink groups we need to get events
-	if err := unix.Bind(fdEvents, &unix.SockaddrNetlink{
-		Family: unix.AF_NETLINK,
-		Groups: groups,
-	}); err != nil {
-		return nil, errwrap.Wrapf(err, "error binding netlink socket")
-	}
-
-	// create a pipe socket to unblock unix.Select when we close
-	fdPipe, err := unix.Socket(unix.AF_UNIX, unix.SOCK_RAW, unix.PROT_NONE)
-	if err != nil {
-		return nil, errwrap.Wrapf(err, "error creating pipe socket")
-	}
-	// bind the pipe to a file
-	if err = unix.Bind(fdPipe, &unix.SockaddrUnix{
-		Name: file,
-	}); err != nil {
-		return nil, errwrap.Wrapf(err, "error binding pipe socket")
-	}
-	return &socketSet{
-		fdEvents: fdEvents,
-		fdPipe:   fdPipe,
-		pipeFile: file,
-	}, nil
-}
-
-// shutdown closes the event file descriptor and unblocks receive by sending
-// a message to the pipe file descriptor. It must be called before close, and
-// should only be called once.
-func (obj *socketSet) shutdown() error {
-	// close the event socket so no more events are produced
-	if err := unix.Close(obj.fdEvents); err != nil {
-		return err
-	}
-	// send a message to the pipe to unblock select
-	return unix.Sendto(obj.fdPipe, nil, 0, &unix.SockaddrUnix{
-		Name: path.Join(obj.pipeFile),
-	})
-}
-
-// close closes the pipe file descriptor. It must only be called after
-// shutdown has closed fdEvents, and unblocked receive. It should only be
-// called once.
-func (obj *socketSet) close() error {
-	return unix.Close(obj.fdPipe)
-}
-
-// receive waits for bytes from fdEvents and parses them into a slice of
-// netlink messages. It will block until an event is produced, or shutdown
-// is called.
-func (obj *socketSet) receive() ([]syscall.NetlinkMessage, error) {
-	// Select will return when any fd in fdSet (fdEvents and fdPipe) is ready
-	// to read.
-	_, err := unix.Select(obj.nfd(), obj.fdSet(), nil, nil, nil)
-	if err != nil {
-		// if a system interrupt is caught
-		if err == unix.EINTR { // signal interrupt
-			return nil, nil
-		}
-		return nil, errwrap.Wrapf(err, "error selecting on fd")
-	}
-	// receive the message from the netlink socket into b
-	b := make([]byte, os.Getpagesize())
-	n, _, err := unix.Recvfrom(obj.fdEvents, b, unix.MSG_DONTWAIT) // non-blocking receive
-	if err != nil {
-		// if fdEvents is closed
-		if err == unix.EBADF { // bad file descriptor
-			return nil, nil
-		}
-		return nil, errwrap.Wrapf(err, "error receiving messages")
-	}
-	// if we didn't get enough bytes for a header, something went wrong
-	if n < unix.NLMSG_HDRLEN {
-		return nil, fmt.Errorf("received short header")
-	}
-	b = b[:n] // truncate b to message length
-	// use syscall to parse, as func does not exist in x/sys/unix
-	return syscall.ParseNetlinkMessage(b)
-}
-
-// nfd returns one more than the highest fd value in the struct, for use as as
-// the nfds parameter in select. It represents the file descriptor set maximum
-// size. See man select for more info.
-func (obj *socketSet) nfd() int {
-	if obj.fdEvents > obj.fdPipe {
-		return obj.fdEvents + 1
-	}
-	return obj.fdPipe + 1
-}
-
-// fdSet returns a bitmask representation of the integer values of fdEvents
-// and fdPipe. See man select for more info.
-func (obj *socketSet) fdSet() *unix.FdSet {
-	fdSet := &unix.FdSet{}
-	// Generate the bitmask representing the file descriptors in the socketSet.
-	// The rightmost bit corresponds to file descriptor zero, and each bit to
-	// the left represents the next file descriptor number in the sequence of
-	// all real numbers. E.g. the FdSet containing containing 0 and 4 is 10001.
-	fdSet.Bits[obj.fdEvents/64] |= 1 << uint(obj.fdEvents)
-	fdSet.Bits[obj.fdPipe/64] |= 1 << uint(obj.fdPipe)
-	return fdSet
-}