feat(bitswap) impl offline exchange

bitswap/offline.go

+package bitswap
+
+import (
+	"errors"
+	"time"
+
+	blocks "github.com/jbenet/go-ipfs/blocks"
+	u "github.com/jbenet/go-ipfs/util"
+)
+
+func NewOfflineExchange() Exchange {
+	return &offlineExchange{}
+}
+
+// offlineExchange implements the Exchange interface but doesn't return blocks.
+// For use in offline mode.
+type offlineExchange struct {
+}
+
+// Block returns nil to signal that a block could not be retrieved for the
+// given key.
+// NB: This function may return before the timeout expires.
+func (_ *offlineExchange) Block(k u.Key, timeout time.Duration) (*blocks.Block, error) {
+	return nil, errors.New("Block unavailable. Operating in offline mode")
+}
+
+// HasBlock always returns nil.
+func (_ *offlineExchange) HasBlock(*blocks.Block) error {
+	return nil
+}

bitswap/offline_test.go

+package bitswap
+
+import (
+	"testing"
+	"time"
+
+	u "github.com/jbenet/go-ipfs/util"
+	testutil "github.com/jbenet/go-ipfs/util/testutil"
+)
+
+func TestBlockReturnsErr(t *testing.T) {
+	off := NewOfflineExchange()
+	_, err := off.Block(u.Key("foo"), time.Second)
+	if err != nil {
+		return // as desired
+	}
+	t.Fail()
+}
+
+func TestHasBlockReturnsNil(t *testing.T) {
+	off := NewOfflineExchange()
+	block := testutil.NewBlockOrFail(t, "data")
+	err := off.HasBlock(&block)
+	if err != nil {
+		t.Fatal("")
+	}
+}