Exchange don't add blocks on their own anymore

Follows:
- ipfs/go-ipfs-exchange-interface#23
- ipfs/go-bitswap#571


This commit was moved from ipfs/go-ipfs-exchange-offline@678648a

exchange/offline/offline.go

@@ -34,9 +34,10 @@ func (e *offlineExchange) GetBlock(ctx context.Context, k cid.Cid) (blocks.Block
 	return blk, err
 }
 
-// HasBlock always returns nil.
-func (e *offlineExchange) HasBlock(ctx context.Context, b blocks.Block) error {
-	return e.bs.Put(ctx, b)
+// NotifyNewBlocks tells the exchange that new blocks are available and can be served.
+func (e *offlineExchange) NotifyNewBlocks(ctx context.Context, blocks ...blocks.Block) error {
+	// as an offline exchange we have nothing to do
+	return nil
 }
 
 // Close always returns nil.
@@ -71,7 +72,3 @@ func (e *offlineExchange) GetBlocks(ctx context.Context, ks []cid.Cid) (<-chan b
 	}()
 	return out, nil
 }
-
-func (e *offlineExchange) IsOnline() bool {
-	return false
-}

exchange/offline/offline_test.go

@@ -28,13 +28,14 @@ func TestHasBlockReturnsNil(t *testing.T) {
 	ex := Exchange(store)
 	block := blocks.NewBlock([]byte("data"))
 
-	err := ex.HasBlock(context.Background(), block)
-	if err != nil {
-		t.Fail()
+	// we don't need to do that for the test, but that illustrate the normal workflow
+	if err := store.Put(context.Background(), block); err != nil {
+		t.Fatal(err)
 	}
 
-	if _, err := store.Get(context.Background(), block.Cid()); err != nil {
-		t.Fatal(err)
+	err := ex.NotifyNewBlocks(context.Background(), block)
+	if err != nil {
+		t.Fail()
 	}
 }
 
@@ -46,7 +47,10 @@ func TestGetBlocks(t *testing.T) {
 	expected := g.Blocks(2)
 
 	for _, b := range expected {
-		if err := ex.HasBlock(context.Background(), b); err != nil {
+		if err := store.Put(context.Background(), b); err != nil {
+			t.Fatal(err)
+		}
+		if err := ex.NotifyNewBlocks(context.Background(), b); err != nil {
 			t.Fail()
 		}
 	}