diff --git a/blocks/blocksutil/block_generator.go b/blocks/blocksutil/block_generator.go
index d70f794702a..438eac1a5da 100644
--- a/blocks/blocksutil/block_generator.go
+++ b/blocks/blocksutil/block_generator.go
@@ -10,13 +10,13 @@ type BlockGenerator struct {
 	seq int
 }
 
-func (bg *BlockGenerator) Next() blocks.Block {
+func (bg *BlockGenerator) Next() *blocks.BasicBlock {
 	bg.seq++
 	return blocks.NewBlock([]byte(string(bg.seq)))
 }
 
-func (bg *BlockGenerator) Blocks(n int) []blocks.Block {
-	blocks := make([]blocks.Block, 0)
+func (bg *BlockGenerator) Blocks(n int) []*blocks.BasicBlock {
+	blocks := make([]*blocks.BasicBlock, 0)
 	for i := 0; i < n; i++ {
 		b := bg.Next()
 		blocks = append(blocks, b)
diff --git a/blockservice/blockservice.go b/blockservice/blockservice.go
index 3fb47aa0ba9..be84bb98ec5 100644
--- a/blockservice/blockservice.go
+++ b/blockservice/blockservice.go
@@ -4,6 +4,7 @@
 package blockservice
 
 import (
+	"context"
 	"errors"
 	"fmt"
 
@@ -11,7 +12,6 @@ import (
 	"github.com/ipfs/go-ipfs/blocks/blockstore"
 	exchange "github.com/ipfs/go-ipfs/exchange"
 
-	context "context"
 	logging "gx/ipfs/QmSpJByNKFX1sCsHBEp3R73FL4NF6FnQTEGyNAXHm2GS52/go-log"
 	cid "gx/ipfs/QmakyCk6Vnn16WEKjbkxieZmM2YLTzkFWizbmGowoYPjro/go-cid"
 )
@@ -23,77 +23,112 @@ var ErrNotFound = errors.New("blockservice: key not found")
 // BlockService is a hybrid block datastore. It stores data in a local
 // datastore and may retrieve data from a remote Exchange.
 // It uses an internal `datastore.Datastore` instance to store values.
-type BlockService struct {
-	// TODO don't expose underlying impl details
-	Blockstore blockstore.Blockstore
-	Exchange   exchange.Interface
+type BlockService interface {
+	Blockstore() blockstore.Blockstore
+	Exchange() exchange.Interface
+	AddBlock(o blocks.Block) (*cid.Cid, error)
+	AddBlocks(bs []blocks.Block) ([]*cid.Cid, error)
+	GetBlock(ctx context.Context, c *cid.Cid) (blocks.Block, error)
+	GetBlocks(ctx context.Context, ks []*cid.Cid) <-chan blocks.Block
+	DeleteBlock(o blocks.Block) error
+	Close() error
+}
+
+type blockService struct {
+	blockstore blockstore.Blockstore
+	exchange   exchange.Interface
+	// If checkFirst is true then first check that a block doesn't
+	// already exist to avoid republishing the block on the exchange.
+	checkFirst bool
 }
 
 // NewBlockService creates a BlockService with given datastore instance.
-func New(bs blockstore.Blockstore, rem exchange.Interface) *BlockService {
+func New(bs blockstore.Blockstore, rem exchange.Interface) BlockService {
+	if rem == nil {
+		log.Warning("blockservice running in local (offline) mode.")
+	}
+
+	return &blockService{
+		blockstore: bs,
+		exchange:   rem,
+		checkFirst: true,
+	}
+}
+
+// NewWriteThrough ceates a BlockService that guarantees writes will go
+// through to the blockstore and are not skipped by cache checks.
+func NewWriteThrough(bs blockstore.Blockstore, rem exchange.Interface) BlockService {
 	if rem == nil {
 		log.Warning("blockservice running in local (offline) mode.")
 	}
 
-	return &BlockService{
-		Blockstore: bs,
-		Exchange:   rem,
+	return &blockService{
+		blockstore: bs,
+		exchange:   rem,
+		checkFirst: false,
 	}
 }
 
+func (bs *blockService) Blockstore() blockstore.Blockstore {
+	return bs.blockstore
+}
+
+func (bs *blockService) Exchange() exchange.Interface {
+	return bs.exchange
+}
+
 // AddBlock adds a particular block to the service, Putting it into the datastore.
 // TODO pass a context into this if the remote.HasBlock is going to remain here.
-func (s *BlockService) AddBlock(o blocks.Block) (*cid.Cid, error) {
-	// TODO: while this is a great optimization, we should think about the
-	// possibility of streaming writes directly to disk. If we can pass this object
-	// all the way down to the datastore without having to 'buffer' its data,
-	// we could implement a `WriteTo` method on it that could do a streaming write
-	// of the content, saving us (probably) considerable memory.
+func (s *blockService) AddBlock(o blocks.Block) (*cid.Cid, error) {
 	c := o.Cid()
-	has, err := s.Blockstore.Has(c)
-	if err != nil {
-		return nil, err
-	}
+	if s.checkFirst {
+		has, err := s.blockstore.Has(c)
+		if err != nil {
+			return nil, err
+		}
 
-	if has {
-		return c, nil
+		if has {
+			return c, nil
+		}
 	}
 
-	err = s.Blockstore.Put(o)
+	err := s.blockstore.Put(o)
 	if err != nil {
 		return nil, err
 	}
 
-	if err := s.Exchange.HasBlock(o); err != nil {
+	if err := s.exchange.HasBlock(o); err != nil {
 		return nil, errors.New("blockservice is closed")
 	}
 
 	return c, nil
 }
 
-func (s *BlockService) AddBlocks(bs []blocks.Block) ([]*cid.Cid, error) {
+func (s *blockService) AddBlocks(bs []blocks.Block) ([]*cid.Cid, error) {
 	var toput []blocks.Block
-	for _, b := range bs {
-		has, err := s.Blockstore.Has(b.Cid())
-		if err != nil {
-			return nil, err
-		}
-
-		if has {
-			continue
+	if s.checkFirst {
+		for _, b := range bs {
+			has, err := s.blockstore.Has(b.Cid())
+			if err != nil {
+				return nil, err
+			}
+			if has {
+				continue
+			}
+			toput = append(toput, b)
 		}
-
-		toput = append(toput, b)
+	} else {
+		toput = bs
 	}
 
-	err := s.Blockstore.PutMany(toput)
+	err := s.blockstore.PutMany(toput)
 	if err != nil {
 		return nil, err
 	}
 
 	var ks []*cid.Cid
 	for _, o := range toput {
-		if err := s.Exchange.HasBlock(o); err != nil {
+		if err := s.exchange.HasBlock(o); err != nil {
 			return nil, fmt.Errorf("blockservice is closed (%s)", err)
 		}
 
@@ -104,19 +139,19 @@ func (s *BlockService) AddBlocks(bs []blocks.Block) ([]*cid.Cid, error) {
 
 // GetBlock retrieves a particular block from the service,
 // Getting it from the datastore using the key (hash).
-func (s *BlockService) GetBlock(ctx context.Context, c *cid.Cid) (blocks.Block, error) {
+func (s *blockService) GetBlock(ctx context.Context, c *cid.Cid) (blocks.Block, error) {
 	log.Debugf("BlockService GetBlock: '%s'", c)
 
-	block, err := s.Blockstore.Get(c)
+	block, err := s.blockstore.Get(c)
 	if err == nil {
 		return block, nil
 	}
 
-	if err == blockstore.ErrNotFound && s.Exchange != nil {
+	if err == blockstore.ErrNotFound && s.exchange != nil {
 		// TODO be careful checking ErrNotFound. If the underlying
 		// implementation changes, this will break.
 		log.Debug("Blockservice: Searching bitswap")
-		blk, err := s.Exchange.GetBlock(ctx, c)
+		blk, err := s.exchange.GetBlock(ctx, c)
 		if err != nil {
 			if err == blockstore.ErrNotFound {
 				return nil, ErrNotFound
@@ -137,13 +172,13 @@ func (s *BlockService) GetBlock(ctx context.Context, c *cid.Cid) (blocks.Block,
 // GetBlocks gets a list of blocks asynchronously and returns through
 // the returned channel.
 // NB: No guarantees are made about order.
-func (s *BlockService) GetBlocks(ctx context.Context, ks []*cid.Cid) <-chan blocks.Block {
+func (s *blockService) GetBlocks(ctx context.Context, ks []*cid.Cid) <-chan blocks.Block {
 	out := make(chan blocks.Block, 0)
 	go func() {
 		defer close(out)
 		var misses []*cid.Cid
 		for _, c := range ks {
-			hit, err := s.Blockstore.Get(c)
+			hit, err := s.blockstore.Get(c)
 			if err != nil {
 				misses = append(misses, c)
 				continue
@@ -160,7 +195,7 @@ func (s *BlockService) GetBlocks(ctx context.Context, ks []*cid.Cid) <-chan bloc
 			return
 		}
 
-		rblocks, err := s.Exchange.GetBlocks(ctx, misses)
+		rblocks, err := s.exchange.GetBlocks(ctx, misses)
 		if err != nil {
 			log.Debugf("Error with GetBlocks: %s", err)
 			return
@@ -178,11 +213,11 @@ func (s *BlockService) GetBlocks(ctx context.Context, ks []*cid.Cid) <-chan bloc
 }
 
 // DeleteBlock deletes a block in the blockservice from the datastore
-func (s *BlockService) DeleteBlock(o blocks.Block) error {
-	return s.Blockstore.DeleteBlock(o.Cid())
+func (s *blockService) DeleteBlock(o blocks.Block) error {
+	return s.blockstore.DeleteBlock(o.Cid())
 }
 
-func (s *BlockService) Close() error {
+func (s *blockService) Close() error {
 	log.Debug("blockservice is shutting down...")
-	return s.Exchange.Close()
+	return s.exchange.Close()
 }
diff --git a/blockservice/blockservice_test.go b/blockservice/blockservice_test.go
new file mode 100644
index 00000000000..d87a383e566
--- /dev/null
+++ b/blockservice/blockservice_test.go
@@ -0,0 +1,49 @@
+package blockservice
+
+import (
+	"testing"
+
+	"github.com/ipfs/go-ipfs/blocks"
+	"github.com/ipfs/go-ipfs/blocks/blockstore"
+	butil "github.com/ipfs/go-ipfs/blocks/blocksutil"
+	offline "github.com/ipfs/go-ipfs/exchange/offline"
+
+	ds "gx/ipfs/QmbzuUusHqaLLoNTDEVLcSF6vZDHZDLPC7p4bztRvvkXxU/go-datastore"
+	dssync "gx/ipfs/QmbzuUusHqaLLoNTDEVLcSF6vZDHZDLPC7p4bztRvvkXxU/go-datastore/sync"
+)
+
+func TestWriteThroughWorks(t *testing.T) {
+	bstore := &PutCountingBlockstore{
+		blockstore.NewBlockstore(dssync.MutexWrap(ds.NewMapDatastore())),
+		0,
+	}
+	bstore2 := blockstore.NewBlockstore(dssync.MutexWrap(ds.NewMapDatastore()))
+	exch := offline.Exchange(bstore2)
+	bserv := NewWriteThrough(bstore, exch)
+	bgen := butil.NewBlockGenerator()
+
+	block := bgen.Next()
+
+	t.Logf("PutCounter: %d", bstore.PutCounter)
+	bserv.AddBlock(block)
+	if bstore.PutCounter != 1 {
+		t.Fatalf("expected just one Put call, have: %d", bstore.PutCounter)
+	}
+
+	bserv.AddBlock(block)
+	if bstore.PutCounter != 2 {
+		t.Fatal("Put should have called again, should be 2 is: %d", bstore.PutCounter)
+	}
+}
+
+var _ blockstore.GCBlockstore = (*PutCountingBlockstore)(nil)
+
+type PutCountingBlockstore struct {
+	blockstore.GCBlockstore
+	PutCounter int
+}
+
+func (bs *PutCountingBlockstore) Put(block blocks.Block) error {
+	bs.PutCounter++
+	return bs.GCBlockstore.Put(block)
+}
diff --git a/blockservice/test/mock.go b/blockservice/test/mock.go
index 28e3a4e9912..622d1c8d689 100644
--- a/blockservice/test/mock.go
+++ b/blockservice/test/mock.go
@@ -9,13 +9,13 @@ import (
 )
 
 // Mocks returns |n| connected mock Blockservices
-func Mocks(n int) []*BlockService {
+func Mocks(n int) []BlockService {
 	net := tn.VirtualNetwork(mockrouting.NewServer(), delay.Fixed(0))
 	sg := bitswap.NewTestSessionGenerator(net)
 
 	instances := sg.Instances(n)
 
-	var servs []*BlockService
+	var servs []BlockService
 	for _, i := range instances {
 		servs = append(servs, New(i.Blockstore(), i.Exchange))
 	}
diff --git a/cmd/ipfs/init.go b/cmd/ipfs/init.go
index 3317acf9d4e..9d5acf9ce75 100644
--- a/cmd/ipfs/init.go
+++ b/cmd/ipfs/init.go
@@ -8,13 +8,13 @@ import (
 	"os"
 	"path"
 
+	context "context"
 	assets "github.com/ipfs/go-ipfs/assets"
 	cmds "github.com/ipfs/go-ipfs/commands"
 	core "github.com/ipfs/go-ipfs/core"
 	namesys "github.com/ipfs/go-ipfs/namesys"
 	config "github.com/ipfs/go-ipfs/repo/config"
 	fsrepo "github.com/ipfs/go-ipfs/repo/fsrepo"
-	context "context"
 )
 
 const (
diff --git a/core/core.go b/core/core.go
index b4ee113c93e..6c1507abd21 100644
--- a/core/core.go
+++ b/core/core.go
@@ -96,7 +96,7 @@ type IpfsNode struct {
 	// 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.
+	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
diff --git a/core/core_test.go b/core/core_test.go
index 86e8466756e..8f2414a5f5a 100644
--- a/core/core_test.go
+++ b/core/core_test.go
@@ -3,10 +3,10 @@ package core
 import (
 	"testing"
 
+	context "context"
 	"github.com/ipfs/go-ipfs/repo"
 	config "github.com/ipfs/go-ipfs/repo/config"
 	"github.com/ipfs/go-ipfs/thirdparty/testutil"
-	context "context"
 )
 
 func TestInitialization(t *testing.T) {
diff --git a/core/corerepo/stat.go b/core/corerepo/stat.go
index 637195c65c6..26810344fa1 100644
--- a/core/corerepo/stat.go
+++ b/core/corerepo/stat.go
@@ -3,9 +3,9 @@ package corerepo
 import (
 	"fmt"
 
+	context "context"
 	"github.com/ipfs/go-ipfs/core"
 	fsrepo "github.com/ipfs/go-ipfs/repo/fsrepo"
-	context "context"
 )
 
 type Stat struct {
diff --git a/core/coreunix/cat.go b/core/coreunix/cat.go
index 7ca6de802ab..af3f43952c3 100644
--- a/core/coreunix/cat.go
+++ b/core/coreunix/cat.go
@@ -1,10 +1,10 @@
 package coreunix
 
 import (
+	context "context"
 	core "github.com/ipfs/go-ipfs/core"
 	path "github.com/ipfs/go-ipfs/path"
 	uio "github.com/ipfs/go-ipfs/unixfs/io"
-	context "context"
 )
 
 func Cat(ctx context.Context, n *core.IpfsNode, pstr string) (*uio.DagReader, error) {
diff --git a/fuse/ipns/link_unix.go b/fuse/ipns/link_unix.go
index 04da5a74f7d..0ba9157f757 100644
--- a/fuse/ipns/link_unix.go
+++ b/fuse/ipns/link_unix.go
@@ -5,9 +5,9 @@ package ipns
 import (
 	"os"
 
+	"context"
 	"github.com/ipfs/go-ipfs/Godeps/_workspace/src/bazil.org/fuse"
 	"github.com/ipfs/go-ipfs/Godeps/_workspace/src/bazil.org/fuse/fs"
-	"context"
 )
 
 type Link struct {
diff --git a/fuse/node/mount_test.go b/fuse/node/mount_test.go
index 2651d460504..5ecc9076186 100644
--- a/fuse/node/mount_test.go
+++ b/fuse/node/mount_test.go
@@ -9,13 +9,13 @@ import (
 	"testing"
 	"time"
 
+	context "context"
 	core "github.com/ipfs/go-ipfs/core"
 	ipns "github.com/ipfs/go-ipfs/fuse/ipns"
 	mount "github.com/ipfs/go-ipfs/fuse/mount"
 	namesys "github.com/ipfs/go-ipfs/namesys"
 	offroute "github.com/ipfs/go-ipfs/routing/offline"
 	ci "github.com/ipfs/go-ipfs/thirdparty/testutil/ci"
-	context "context"
 )
 
 func maybeSkipFuseTests(t *testing.T) {
diff --git a/importer/helpers/helpers.go b/importer/helpers/helpers.go
index 0bec405a54a..bfde68214a6 100644
--- a/importer/helpers/helpers.go
+++ b/importer/helpers/helpers.go
@@ -3,10 +3,10 @@ package helpers
 import (
 	"fmt"
 
+	"context"
 	chunk "github.com/ipfs/go-ipfs/importer/chunk"
 	dag "github.com/ipfs/go-ipfs/merkledag"
 	ft "github.com/ipfs/go-ipfs/unixfs"
-	"context"
 )
 
 // BlockSizeLimit specifies the maximum size an imported block can have.
diff --git a/merkledag/merkledag.go b/merkledag/merkledag.go
index b9431522b07..5d2cd36dcfc 100644
--- a/merkledag/merkledag.go
+++ b/merkledag/merkledag.go
@@ -41,7 +41,7 @@ type LinkService interface {
 	GetOfflineLinkService() LinkService
 }
 
-func NewDAGService(bs *bserv.BlockService) *dagService {
+func NewDAGService(bs bserv.BlockService) *dagService {
 	return &dagService{Blocks: bs}
 }
 
@@ -51,7 +51,7 @@ 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
 }
 
 // Add adds a node to the dagService, storing the block in the BlockService
@@ -113,8 +113,8 @@ func (n *dagService) GetLinks(ctx context.Context, c *cid.Cid) ([]*Link, error)
 }
 
 func (n *dagService) GetOfflineLinkService() LinkService {
-	if n.Blocks.Exchange.IsOnline() {
-		bsrv := bserv.New(n.Blocks.Blockstore, offline.Exchange(n.Blocks.Blockstore))
+	if n.Blocks.Exchange().IsOnline() {
+		bsrv := bserv.New(n.Blocks.Blockstore(), offline.Exchange(n.Blocks.Blockstore()))
 		return NewDAGService(bsrv)
 	} else {
 		return n
diff --git a/merkledag/merkledag_test.go b/merkledag/merkledag_test.go
index 006c8b5ca07..bc909353278 100644
--- a/merkledag/merkledag_test.go
+++ b/merkledag/merkledag_test.go
@@ -237,7 +237,7 @@ func TestFetchGraph(t *testing.T) {
 	}
 
 	// create an offline dagstore and ensure all blocks were fetched
-	bs := bserv.New(bsis[1].Blockstore, offline.Exchange(bsis[1].Blockstore))
+	bs := bserv.New(bsis[1].Blockstore(), offline.Exchange(bsis[1].Blockstore()))
 
 	offline_ds := NewDAGService(bs)