Merge pull request #4709 from ipfs/feat/session-exchanges

Add exchange.SessionExchange interface for exchanges that support sessions

blockservice/blockservice.go

@@ -10,7 +10,6 @@ import (
 	"io"
 
 	exchange "github.com/ipfs/go-ipfs/exchange"
-	bitswap "github.com/ipfs/go-ipfs/exchange/bitswap"
 
 	logging "gx/ipfs/QmRb5jh8z2E8hMGN2tkvs1yHynUanqnZ3UeKwgN1i9P1F8/go-log"
 	blockstore "gx/ipfs/QmTVDM4LCSUMFNQzbDLL9zQwp8usE6QHymFdh3h8vL9v6b/go-ipfs-blockstore"
@@ -107,19 +106,22 @@ func (s *blockService) Exchange() exchange.Interface {
 	return s.exchange
 }
 
-// NewSession creates a bitswap session that allows for controlled exchange of
-// wantlists to decrease the bandwidth overhead.
+// NewSession creates a new session that allows for
+// controlled exchange of wantlists to decrease the bandwidth overhead.
+// If the current exchange is a SessionExchange, a new exchange
+// session will be created. Otherwise, the current exchange will be used
+// directly.
 func NewSession(ctx context.Context, bs BlockService) *Session {
-	exchange := bs.Exchange()
-	if bswap, ok := exchange.(*bitswap.Bitswap); ok {
-		ses := bswap.NewSession(ctx)
+	exch := bs.Exchange()
+	if sessEx, ok := exch.(exchange.SessionExchange); ok {
+		ses := sessEx.NewSession(ctx)
 		return &Session{
 			ses: ses,
 			bs:  bs.Blockstore(),
 		}
 	}
 	return &Session{
-		ses: exchange,
+		ses: exch,
 		bs:  bs.Blockstore(),
 	}
 }

exchange/interface.go

-// package exchange defines the IPFS exchange interface
+// Package exchange defines the IPFS exchange interface
 package exchange
 
 import (
@@ -10,8 +10,7 @@ import (
 	cid "gx/ipfs/QmcZfnkapfECQGcLZaf9B79NRg7cRa9EnZh4LSbkCzwNvY/go-cid"
 )
 
-// Any type that implements exchange.Interface may be used as an IPFS block
-// exchange protocol.
+// Interface defines the functionality of the IPFS block exchange protocol.
 type Interface interface { // type Exchanger interface
 	Fetcher
 
@@ -30,3 +29,10 @@ type Fetcher interface {
 	GetBlock(context.Context, *cid.Cid) (blocks.Block, error)
 	GetBlocks(context.Context, []*cid.Cid) (<-chan blocks.Block, error)
 }
+
+// SessionExchange is an exchange.Interface which supports
+// sessions.
+type SessionExchange interface {
+	Interface
+	NewSession(context.Context) Interface
+}