Add DAGService.GetLinks() method and use it in the GC and elsewhere.

This method will use the (also new) LinkService if it is available to
retrieving just the links for a MerkleDAG without necessary having to
retrieve the underlying block.

For now the main benefit is that the pinner will not break when a block
becomes invalid due to a change in the backing file.  This is possible
because the metadata for a block (that includes the Links) is stored
separately and thus always available even if the backing file changes.

License: MIT
Signed-off-by: Kevin Atkinson <k@kevina.org>

core/commands/pin.go

@@ -328,12 +328,11 @@ func pinLsAll(typeStr string, ctx context.Context, n *core.IpfsNode) (map[string
 	if typeStr == "indirect" || typeStr == "all" {
 		set := cid.NewSet()
 		for _, k := range n.Pinning.RecursiveKeys() {
-			nd, err := n.DAG.Get(ctx, k)
+			links, err := n.DAG.GetLinks(ctx, k)
 			if err != nil {
 				return nil, err
 			}
-
-			err = dag.EnumerateChildren(n.Context(), n.DAG, nd, set.Visit, false)
+			err = dag.EnumerateChildren(n.Context(), n.DAG, links, set.Visit, false)
 			if err != nil {
 				return nil, err
 			}

core/core.go

@@ -94,14 +94,15 @@ type IpfsNode struct {
 	PrivateKey ic.PrivKey // the local node's private Key
 
 	// Services
-	Peerstore  pstore.Peerstore     // storage for other Peer instances
-	Blockstore bstore.GCBlockstore  // the block store (lower level)
-	Blocks     *bserv.BlockService  // the block service, get/add blocks.
-	DAG        merkledag.DAGService // the merkle dag service, get/add objects.
-	Resolver   *path.Resolver       // the path resolution system
-	Reporter   metrics.Reporter
-	Discovery  discovery.Service
-	FilesRoot  *mfs.Root
+	Peerstore   pstore.Peerstore     // storage for other Peer instances
+	Blockstore  bstore.GCBlockstore  // the block store (lower level)
+	Blocks      *bserv.BlockService  // the block service, get/add blocks.
+	DAG         merkledag.DAGService // the merkle dag service, get/add objects.
+	LinkService merkledag.LinkService
+	Resolver    *path.Resolver // the path resolution system
+	Reporter    metrics.Reporter
+	Discovery   discovery.Service
+	FilesRoot   *mfs.Root
 
 	// Online
 	PeerHost     p2phost.Host        // the network host (server+client)

core/corerepo/gc.go

@@ -90,7 +90,7 @@ func GarbageCollect(n *core.IpfsNode, ctx context.Context) error {
 	if err != nil {
 		return err
 	}
-	rmed, err := gc.GC(ctx, n.Blockstore, n.Pinning, roots)
+	rmed, err := gc.GC(ctx, n.Blockstore, n.LinkService, n.Pinning, roots)
 	if err != nil {
 		return err
 	}
@@ -113,7 +113,7 @@ func GarbageCollectAsync(n *core.IpfsNode, ctx context.Context) (<-chan *KeyRemo
 	if err != nil {
 		return nil, err
 	}
-	rmed, err := gc.GC(ctx, n.Blockstore, n.Pinning, roots)
+	rmed, err := gc.GC(ctx, n.Blockstore, n.LinkService, n.Pinning, roots)
 	if err != nil {
 		return nil, err
 	}

core/coreunix/add_test.go

@@ -98,7 +98,7 @@ func TestAddGCLive(t *testing.T) {
 	gcstarted := make(chan struct{})
 	go func() {
 		defer close(gcstarted)
-		gcchan, err := gc.GC(context.Background(), node.Blockstore, node.Pinning, nil)
+		gcchan, err := gc.GC(context.Background(), node.Blockstore, node.LinkService, node.Pinning, nil)
 		if err != nil {
 			log.Error("GC ERROR:", err)
 			errs <- err
@@ -162,7 +162,7 @@ func TestAddGCLive(t *testing.T) {
 	}
 
 	set := cid.NewSet()
-	err = dag.EnumerateChildren(ctx, node.DAG, root, set.Visit, false)
+	err = dag.EnumerateChildren(ctx, node.DAG, root.Links, set.Visit, false)
 	if err != nil {
 		t.Fatal(err)
 	}

merkledag/merkledag.go

@@ -23,6 +23,10 @@ type DAGService interface {
 	Get(context.Context, *cid.Cid) (*Node, error)
 	Remove(*Node) error
 
+	// Return all links for a node, may be more effect than
+	// calling Get
+	GetLinks(context.Context, *cid.Cid) ([]*Link, error)
+
 	// GetDAG returns, in order, all the single leve child
 	// nodes of the passed in node.
 	GetMany(context.Context, []*cid.Cid) <-chan *NodeOption
@@ -30,8 +34,14 @@ type DAGService interface {
 	Batch() *Batch
 }
 
-func NewDAGService(bs *bserv.BlockService) DAGService {
-	return &dagService{bs}
+// A LinkService returns the links for a node if they are available
+// locally without having to retrieve the block from the datastore.
+type LinkService interface {
+	Get(*cid.Cid) ([]*Link, error)
+}
+
+func NewDAGService(bs *bserv.BlockService) *dagService {
+	return &dagService{Blocks: bs}
 }
 
 // dagService is an IPFS Merkle DAG service.
@@ -40,7 +50,8 @@ func NewDAGService(bs *bserv.BlockService) DAGService {
 // TODO: should cache Nodes that are in memory, and be
 //       able to free some of them when vm pressure is high
 type dagService struct {
-	Blocks *bserv.BlockService
+	Blocks      *bserv.BlockService
+	LinkService LinkService
 }
 
 // Add adds a node to the dagService, storing the block in the BlockService
@@ -93,6 +104,20 @@ func (n *dagService) Get(ctx context.Context, c *cid.Cid) (*Node, error) {
 	return res, nil
 }
 
+func (n *dagService) GetLinks(ctx context.Context, c *cid.Cid) ([]*Link, error) {
+	if n.LinkService != nil {
+		links, err := n.LinkService.Get(c)
+		if err == nil {
+			return links, nil
+		}
+	}
+	node, err := n.Get(ctx, c)
+	if err != nil {
+		return nil, err
+	}
+	return node.Links, nil
+}
+
 func (n *dagService) Remove(nd *Node) error {
 	return n.Blocks.DeleteObject(nd)
 }
@@ -366,11 +391,11 @@ func legacyCidFromLink(lnk *Link) *cid.Cid {
 // EnumerateChildren will walk the dag below the given root node and add all
 // unseen children to the passed in set.
 // TODO: parallelize to avoid disk latency perf hits?
-func EnumerateChildren(ctx context.Context, ds DAGService, root *Node, visit func(*cid.Cid) bool, bestEffort bool) error {
-	for _, lnk := range root.Links {
+func EnumerateChildren(ctx context.Context, ds DAGService, links []*Link, visit func(*cid.Cid) bool, bestEffort bool) error {
+	for _, lnk := range links {
 		c := legacyCidFromLink(lnk)
 		if visit(c) {
-			child, err := ds.Get(ctx, c)
+			children, err := ds.GetLinks(ctx, c)
 			if err != nil {
 				if bestEffort && err == ErrNotFound {
 					continue
@@ -378,7 +403,7 @@ func EnumerateChildren(ctx context.Context, ds DAGService, root *Node, visit fun
 					return err
 				}
 			}
-			err = EnumerateChildren(ctx, ds, child, visit, bestEffort)
+			err = EnumerateChildren(ctx, ds, children, visit, bestEffort)
 			if err != nil {
 				return err
 			}

merkledag/merkledag_test.go

@@ -241,7 +241,7 @@ func TestFetchGraph(t *testing.T) {
 
 	offline_ds := NewDAGService(bs)
 
-	err = EnumerateChildren(context.Background(), offline_ds, root, func(_ *cid.Cid) bool { return true }, false)
+	err = EnumerateChildren(context.Background(), offline_ds, root.Links, func(_ *cid.Cid) bool { return true }, false)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -258,7 +258,7 @@ func TestEnumerateChildren(t *testing.T) {
 	}
 
 	set := cid.NewSet()
-	err = EnumerateChildren(context.Background(), ds, root, set.Visit, false)
+	err = EnumerateChildren(context.Background(), ds, root.Links, set.Visit, false)
 	if err != nil {
 		t.Fatal(err)
 	}

pin/gc/gc.go

@@ -24,11 +24,12 @@ var log = logging.Logger("gc")
 //
 // The routine then iterates over every block in the blockstore and
 // deletes any block that is not found in the marked set.
-func GC(ctx context.Context, bs bstore.GCBlockstore, pn pin.Pinner, bestEffortRoots []*cid.Cid) (<-chan key.Key, error) {
+func GC(ctx context.Context, bs bstore.GCBlockstore, ls dag.LinkService, pn pin.Pinner, bestEffortRoots []*cid.Cid) (<-chan key.Key, error) {
 	unlocker := bs.GCLock()
 
 	bsrv := bserv.New(bs, offline.Exchange(bs))
 	ds := dag.NewDAGService(bsrv)
+	ds.LinkService = ls
 
 	gcs, err := ColoredSet(ctx, pn, ds, bestEffortRoots)
 	if err != nil {
@@ -74,13 +75,13 @@ func GC(ctx context.Context, bs bstore.GCBlockstore, pn pin.Pinner, bestEffortRo
 func Descendants(ctx context.Context, ds dag.DAGService, set key.KeySet, roots []*cid.Cid, bestEffort bool) error {
 	for _, c := range roots {
 		set.Add(key.Key(c.Hash()))
-		nd, err := ds.Get(ctx, c)
+		links, err := ds.GetLinks(ctx, c)
 		if err != nil {
 			return err
 		}
 
 		// EnumerateChildren recursively walks the dag and adds the keys to the given set
-		err = dag.EnumerateChildren(ctx, ds, nd, func(c *cid.Cid) bool {
+		err = dag.EnumerateChildren(ctx, ds, links, func(c *cid.Cid) bool {
 			k := key.Key(c.Hash())
 			seen := set.Has(k)
 			if seen {

pin/pin.go

@@ -279,12 +279,12 @@ func (p *pinner) isPinnedWithType(c *cid.Cid, mode PinMode) (string, bool, error
 
 	// Default is Indirect
 	for _, rc := range p.recursePin.Keys() {
-		rnd, err := p.dserv.Get(context.Background(), rc)
+		links, err := p.dserv.GetLinks(context.Background(), rc)
 		if err != nil {
 			return "", false, err
 		}
 
-		has, err := hasChild(p.dserv, rnd, k)
+		has, err := hasChild(p.dserv, links, k)
 		if err != nil {
 			return "", false, err
 		}
@@ -317,11 +317,11 @@ func (p *pinner) CheckIfPinned(cids ...*cid.Cid) ([]Pinned, error) {
 	// Now walk all recursive pins to check for indirect pins
 	var checkChildren func(*cid.Cid, *cid.Cid) error
 	checkChildren = func(rk, parentKey *cid.Cid) error {
-		parent, err := p.dserv.Get(context.Background(), parentKey)
+		links, err := p.dserv.GetLinks(context.Background(), parentKey)
 		if err != nil {
 			return err
 		}
-		for _, lnk := range parent.Links {
+		for _, lnk := range links {
 			c := cid.NewCidV0(lnk.Hash)
 
 			if toCheck.Has(c) {
@@ -521,19 +521,19 @@ func (p *pinner) PinWithMode(c *cid.Cid, mode PinMode) {
 	}
 }
 
-func hasChild(ds mdag.DAGService, root *mdag.Node, child key.Key) (bool, error) {
-	for _, lnk := range root.Links {
+func hasChild(ds mdag.DAGService, links []*mdag.Link, child key.Key) (bool, error) {
+	for _, lnk := range links {
 		c := cid.NewCidV0(lnk.Hash)
 		if key.Key(c.Hash()) == child {
 			return true, nil
 		}
 
-		nd, err := ds.Get(context.Background(), c)
+		children, err := ds.GetLinks(context.Background(), c)
 		if err != nil {
 			return false, err
 		}
 
-		has, err := hasChild(ds, nd, child)
+		has, err := hasChild(ds, children, child)
 		if err != nil {
 			return false, err
 		}