diff --git a/core/coreapi/coreapi.go b/core/coreapi/coreapi.go
index b289bb38253..43cdd3565dc 100644
--- a/core/coreapi/coreapi.go
+++ b/core/coreapi/coreapi.go
@@ -5,10 +5,12 @@ import (
 
 	core "github.com/ipfs/go-ipfs/core"
 	coreiface "github.com/ipfs/go-ipfs/core/coreapi/interface"
+	namesys "github.com/ipfs/go-ipfs/namesys"
 	ipfspath "github.com/ipfs/go-ipfs/path"
 	uio "github.com/ipfs/go-ipfs/unixfs/io"
 
 	cid "gx/ipfs/QmcZfnkapfECQGcLZaf9B79NRg7cRa9EnZh4LSbkCzwNvY/go-cid"
+	ipld "gx/ipfs/Qme5bWv7wtjUNGsK2BNGVUFPKiuxWrsqrtvYwCLRw8YFES/go-ipld-format"
 )
 
 type CoreAPI struct {
@@ -49,12 +51,16 @@ func (api *CoreAPI) Object() coreiface.ObjectAPI {
 // ResolveNode resolves the path `p` using Unixfx resolver, gets and returns the
 // resolved Node.
 func (api *CoreAPI) ResolveNode(ctx context.Context, p coreiface.Path) (coreiface.Node, error) {
-	p, err := api.ResolvePath(ctx, p)
+	return resolveNode(ctx, api.node.DAG, api.node.Namesys, p)
+}
+
+func resolveNode(ctx context.Context, ng ipld.NodeGetter, nsys namesys.NameSystem, p coreiface.Path) (coreiface.Node, error) {
+	p, err := resolvePath(ctx, ng, nsys, p)
 	if err != nil {
 		return nil, err
 	}
 
-	node, err := api.node.DAG.Get(ctx, p.Cid())
+	node, err := ng.Get(ctx, p.Cid())
 	if err != nil {
 		return nil, err
 	}
@@ -65,17 +71,21 @@ func (api *CoreAPI) ResolveNode(ctx context.Context, p coreiface.Path) (coreifac
 // resolved path.
 // TODO: store all of ipfspath.Resolver.ResolvePathComponents() in Path
 func (api *CoreAPI) ResolvePath(ctx context.Context, p coreiface.Path) (coreiface.Path, error) {
+	return resolvePath(ctx, api.node.DAG, api.node.Namesys, p)
+}
+
+func resolvePath(ctx context.Context, ng ipld.NodeGetter, nsys namesys.NameSystem, p coreiface.Path) (coreiface.Path, error) {
 	if p.Resolved() {
 		return p, nil
 	}
 
 	r := &ipfspath.Resolver{
-		DAG:         api.node.DAG,
+		DAG:         ng,
 		ResolveOnce: uio.ResolveUnixfsOnce,
 	}
 
 	p2 := ipfspath.FromString(p.String())
-	node, err := core.Resolve(ctx, api.node.Namesys, r, p2)
+	node, err := core.Resolve(ctx, nsys, r, p2)
 	if err == core.ErrNoNamesys {
 		return nil, coreiface.ErrOffline
 	} else if err != nil {
diff --git a/core/coreapi/unixfs.go b/core/coreapi/unixfs.go
index f8a0ab23ac6..435fff309c7 100644
--- a/core/coreapi/unixfs.go
+++ b/core/coreapi/unixfs.go
@@ -6,6 +6,7 @@ import (
 
 	coreiface "github.com/ipfs/go-ipfs/core/coreapi/interface"
 	coreunix "github.com/ipfs/go-ipfs/core/coreunix"
+	dag "github.com/ipfs/go-ipfs/merkledag"
 	uio "github.com/ipfs/go-ipfs/unixfs/io"
 
 	cid "gx/ipfs/QmcZfnkapfECQGcLZaf9B79NRg7cRa9EnZh4LSbkCzwNvY/go-cid"
@@ -30,12 +31,14 @@ func (api *UnixfsAPI) Add(ctx context.Context, r io.Reader) (coreiface.Path, err
 
 // Cat returns the data contained by an IPFS or IPNS object(s) at path `p`.
 func (api *UnixfsAPI) Cat(ctx context.Context, p coreiface.Path) (coreiface.Reader, error) {
-	dagnode, err := api.core().ResolveNode(ctx, p)
+	ses := dag.NewSession(ctx, api.node.DAG)
+
+	dagnode, err := resolveNode(ctx, ses, api.node.Namesys, p)
 	if err != nil {
 		return nil, err
 	}
 
-	r, err := uio.NewDagReader(ctx, dagnode, api.node.DAG)
+	r, err := uio.NewDagReader(ctx, dagnode, ses)
 	if err == uio.ErrIsDir {
 		return nil, coreiface.ErrIsDir
 	} else if err != nil {
diff --git a/merkledag/errservice.go b/merkledag/errservice.go
new file mode 100644
index 00000000000..a8cd237379d
--- /dev/null
+++ b/merkledag/errservice.go
@@ -0,0 +1,41 @@
+package merkledag
+
+import (
+	"context"
+
+	cid "gx/ipfs/QmcZfnkapfECQGcLZaf9B79NRg7cRa9EnZh4LSbkCzwNvY/go-cid"
+	ipld "gx/ipfs/Qme5bWv7wtjUNGsK2BNGVUFPKiuxWrsqrtvYwCLRw8YFES/go-ipld-format"
+)
+
+// ErrorService implements ipld.DAGService, returning 'Err' for every call.
+type ErrorService struct {
+	Err error
+}
+
+var _ ipld.DAGService = (*ErrorService)(nil)
+
+func (cs *ErrorService) Add(ctx context.Context, nd ipld.Node) error {
+	return cs.Err
+}
+
+func (cs *ErrorService) AddMany(ctx context.Context, nds []ipld.Node) error {
+	return cs.Err
+}
+
+func (cs *ErrorService) Get(ctx context.Context, c *cid.Cid) (ipld.Node, error) {
+	return nil, cs.Err
+}
+
+func (cs *ErrorService) GetMany(ctx context.Context, cids []*cid.Cid) <-chan *ipld.NodeOption {
+	ch := make(chan *ipld.NodeOption)
+	close(ch)
+	return ch
+}
+
+func (cs *ErrorService) Remove(ctx context.Context, c *cid.Cid) error {
+	return cs.Err
+}
+
+func (cs *ErrorService) RemoveMany(ctx context.Context, cids []*cid.Cid) error {
+	return cs.Err
+}
diff --git a/merkledag/merkledag.go b/merkledag/merkledag.go
index fd66fb26974..1ee6ccfb671 100644
--- a/merkledag/merkledag.go
+++ b/merkledag/merkledag.go
@@ -146,6 +146,11 @@ func (sg *sesGetter) GetMany(ctx context.Context, keys []*cid.Cid) <-chan *ipld.
 	return getNodesFromBG(ctx, sg.bs, keys)
 }
 
+// Session returns a NodeGetter using a new session for block fetches.
+func (ds *dagService) Session(ctx context.Context) ipld.NodeGetter {
+	return &sesGetter{bserv.NewSession(ctx, ds.Blocks)}
+}
+
 // FetchGraph fetches all nodes that are children of the given node
 func FetchGraph(ctx context.Context, root *cid.Cid, serv ipld.DAGService) error {
 	var ng ipld.NodeGetter = serv
diff --git a/merkledag/readonly.go b/merkledag/readonly.go
new file mode 100644
index 00000000000..1fd48eff95c
--- /dev/null
+++ b/merkledag/readonly.go
@@ -0,0 +1,20 @@
+package merkledag
+
+import (
+	"fmt"
+
+	ipld "gx/ipfs/Qme5bWv7wtjUNGsK2BNGVUFPKiuxWrsqrtvYwCLRw8YFES/go-ipld-format"
+)
+
+// ErrReadOnly is used when a read-only datastructure is written to.
+var ErrReadOnly = fmt.Errorf("cannot write to readonly DAGService")
+
+// NewReadOnlyDagService takes a NodeGetter, and returns a full DAGService
+// implementation that returns ErrReadOnly when its 'write' methods are
+// invoked.
+func NewReadOnlyDagService(ng ipld.NodeGetter) ipld.DAGService {
+	return &ComboService{
+		Read:  ng,
+		Write: &ErrorService{ErrReadOnly},
+	}
+}
diff --git a/merkledag/readonly_test.go b/merkledag/readonly_test.go
new file mode 100644
index 00000000000..86ea86cdad9
--- /dev/null
+++ b/merkledag/readonly_test.go
@@ -0,0 +1,64 @@
+package merkledag_test
+
+import (
+	"context"
+	"testing"
+
+	. "github.com/ipfs/go-ipfs/merkledag"
+	dstest "github.com/ipfs/go-ipfs/merkledag/test"
+
+	cid "gx/ipfs/QmcZfnkapfECQGcLZaf9B79NRg7cRa9EnZh4LSbkCzwNvY/go-cid"
+	ipld "gx/ipfs/Qme5bWv7wtjUNGsK2BNGVUFPKiuxWrsqrtvYwCLRw8YFES/go-ipld-format"
+)
+
+func TestReadonlyProperties(t *testing.T) {
+	ds := dstest.Mock()
+	ro := NewReadOnlyDagService(ds)
+
+	ctx := context.Background()
+	nds := []ipld.Node{
+		NewRawNode([]byte("foo1")),
+		NewRawNode([]byte("foo2")),
+		NewRawNode([]byte("foo3")),
+		NewRawNode([]byte("foo4")),
+	}
+	cids := []*cid.Cid{
+		nds[0].Cid(),
+		nds[1].Cid(),
+		nds[2].Cid(),
+		nds[3].Cid(),
+	}
+
+	// add to the actual underlying datastore
+	if err := ds.Add(ctx, nds[2]); err != nil {
+		t.Fatal(err)
+	}
+	if err := ds.Add(ctx, nds[3]); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ro.Add(ctx, nds[0]); err != ErrReadOnly {
+		t.Fatal("expected ErrReadOnly")
+	}
+	if err := ro.Add(ctx, nds[2]); err != ErrReadOnly {
+		t.Fatal("expected ErrReadOnly")
+	}
+
+	if err := ro.AddMany(ctx, nds[0:1]); err != ErrReadOnly {
+		t.Fatal("expected ErrReadOnly")
+	}
+
+	if err := ro.Remove(ctx, cids[3]); err != ErrReadOnly {
+		t.Fatal("expected ErrReadOnly")
+	}
+	if err := ro.RemoveMany(ctx, cids[1:2]); err != ErrReadOnly {
+		t.Fatal("expected ErrReadOnly")
+	}
+
+	if _, err := ro.Get(ctx, cids[0]); err != ipld.ErrNotFound {
+		t.Fatal("expected ErrNotFound")
+	}
+	if _, err := ro.Get(ctx, cids[3]); err != nil {
+		t.Fatal(err)
+	}
+}
diff --git a/merkledag/rwservice.go b/merkledag/rwservice.go
new file mode 100644
index 00000000000..1252d248e4e
--- /dev/null
+++ b/merkledag/rwservice.go
@@ -0,0 +1,41 @@
+package merkledag
+
+import (
+	"context"
+
+	cid "gx/ipfs/QmcZfnkapfECQGcLZaf9B79NRg7cRa9EnZh4LSbkCzwNvY/go-cid"
+	ipld "gx/ipfs/Qme5bWv7wtjUNGsK2BNGVUFPKiuxWrsqrtvYwCLRw8YFES/go-ipld-format"
+)
+
+// ComboService implements ipld.DAGService, using 'Read' for all fetch methods,
+// and 'Write' for all methods that add new objects.
+type ComboService struct {
+	Read  ipld.NodeGetter
+	Write ipld.DAGService
+}
+
+var _ ipld.DAGService = (*ComboService)(nil)
+
+func (cs *ComboService) Add(ctx context.Context, nd ipld.Node) error {
+	return cs.Write.Add(ctx, nd)
+}
+
+func (cs *ComboService) AddMany(ctx context.Context, nds []ipld.Node) error {
+	return cs.Write.AddMany(ctx, nds)
+}
+
+func (cs *ComboService) Get(ctx context.Context, c *cid.Cid) (ipld.Node, error) {
+	return cs.Read.Get(ctx, c)
+}
+
+func (cs *ComboService) GetMany(ctx context.Context, cids []*cid.Cid) <-chan *ipld.NodeOption {
+	return cs.Read.GetMany(ctx, cids)
+}
+
+func (cs *ComboService) Remove(ctx context.Context, c *cid.Cid) error {
+	return cs.Write.Remove(ctx, c)
+}
+
+func (cs *ComboService) RemoveMany(ctx context.Context, cids []*cid.Cid) error {
+	return cs.Write.RemoveMany(ctx, cids)
+}
diff --git a/merkledag/session.go b/merkledag/session.go
new file mode 100644
index 00000000000..fe0df24d0ec
--- /dev/null
+++ b/merkledag/session.go
@@ -0,0 +1,21 @@
+package merkledag
+
+import (
+	"context"
+
+	ipld "gx/ipfs/Qme5bWv7wtjUNGsK2BNGVUFPKiuxWrsqrtvYwCLRw8YFES/go-ipld-format"
+)
+
+// SessionMaker is an object that can generate a new fetching session.
+type SessionMaker interface {
+	Session(context.Context) ipld.NodeGetter
+}
+
+// NewSession returns a session backed NodeGetter if the given NodeGetter
+// implements SessionMaker.
+func NewSession(ctx context.Context, g ipld.NodeGetter) ipld.NodeGetter {
+	if sm, ok := g.(SessionMaker); ok {
+		return sm.Session(ctx)
+	}
+	return g
+}
diff --git a/path/resolver.go b/path/resolver.go
index 2609454a45c..4106e87885e 100644
--- a/path/resolver.go
+++ b/path/resolver.go
@@ -35,9 +35,9 @@ func (e ErrNoLink) Error() string {
 // TODO: now that this is more modular, try to unify this code with the
 //       the resolvers in namesys
 type Resolver struct {
-	DAG ipld.DAGService
+	DAG ipld.NodeGetter
 
-	ResolveOnce func(ctx context.Context, ds ipld.DAGService, nd ipld.Node, names []string) (*ipld.Link, []string, error)
+	ResolveOnce func(ctx context.Context, ds ipld.NodeGetter, nd ipld.Node, names []string) (*ipld.Link, []string, error)
 }
 
 // NewBasicResolver constructs a new basic resolver.
@@ -124,7 +124,7 @@ func (s *Resolver) ResolvePath(ctx context.Context, fpath Path) (ipld.Node, erro
 
 // ResolveSingle simply resolves one hop of a path through a graph with no
 // extra context (does not opaquely resolve through sharded nodes)
-func ResolveSingle(ctx context.Context, ds ipld.DAGService, nd ipld.Node, names []string) (*ipld.Link, []string, error) {
+func ResolveSingle(ctx context.Context, ds ipld.NodeGetter, nd ipld.Node, names []string) (*ipld.Link, []string, error) {
 	return nd.ResolveLink(names)
 }
 
diff --git a/unixfs/io/dagreader.go b/unixfs/io/dagreader.go
index e92223230bc..c6e9cf0d9b3 100644
--- a/unixfs/io/dagreader.go
+++ b/unixfs/io/dagreader.go
@@ -34,7 +34,7 @@ type ReadSeekCloser interface {
 
 // NewDagReader creates a new reader object that reads the data represented by
 // the given node, using the passed in DAGService for data retreival
-func NewDagReader(ctx context.Context, n ipld.Node, serv ipld.DAGService) (DagReader, error) {
+func NewDagReader(ctx context.Context, n ipld.Node, serv ipld.NodeGetter) (DagReader, error) {
 	switch n := n.(type) {
 	case *mdag.RawNode:
 		return NewBufDagReader(n.RawData()), nil
diff --git a/unixfs/io/pbdagreader.go b/unixfs/io/pbdagreader.go
index 8745798a335..0c6bee8326f 100644
--- a/unixfs/io/pbdagreader.go
+++ b/unixfs/io/pbdagreader.go
@@ -17,7 +17,7 @@ import (
 
 // DagReader provides a way to easily read the data contained in a dag.
 type pbDagReader struct {
-	serv ipld.DAGService
+	serv ipld.NodeGetter
 
 	// the node being read
 	node *mdag.ProtoNode
@@ -51,7 +51,7 @@ type pbDagReader struct {
 var _ DagReader = (*pbDagReader)(nil)
 
 // NewPBFileReader constructs a new PBFileReader.
-func NewPBFileReader(ctx context.Context, n *mdag.ProtoNode, pb *ftpb.Data, serv ipld.DAGService) *pbDagReader {
+func NewPBFileReader(ctx context.Context, n *mdag.ProtoNode, pb *ftpb.Data, serv ipld.NodeGetter) *pbDagReader {
 	fctx, cancel := context.WithCancel(ctx)
 	curLinks := getLinkCids(n)
 	return &pbDagReader{
diff --git a/unixfs/io/resolve.go b/unixfs/io/resolve.go
index a06e29ca33b..26d360bb377 100644
--- a/unixfs/io/resolve.go
+++ b/unixfs/io/resolve.go
@@ -12,7 +12,7 @@ import (
 
 // ResolveUnixfsOnce resolves a single hop of a path through a graph in a
 // unixfs context. This includes handling traversing sharded directories.
-func ResolveUnixfsOnce(ctx context.Context, ds ipld.DAGService, nd ipld.Node, names []string) (*ipld.Link, []string, error) {
+func ResolveUnixfsOnce(ctx context.Context, ds ipld.NodeGetter, nd ipld.Node, names []string) (*ipld.Link, []string, error) {
 	switch nd := nd.(type) {
 	case *dag.ProtoNode:
 		upb, err := ft.FromBytes(nd.Data())
@@ -28,7 +28,8 @@ func ResolveUnixfsOnce(ctx context.Context, ds ipld.DAGService, nd ipld.Node, na
 
 		switch upb.GetType() {
 		case ft.THAMTShard:
-			s, err := hamt.NewHamtFromDag(ds, nd)
+			rods := dag.NewReadOnlyDagService(ds)
+			s, err := hamt.NewHamtFromDag(rods, nd)
 			if err != nil {
 				return nil, nil, err
 			}