fix(bitswap) keep interface the same

changing the bitswap interace breaks tests and makes things a bit
difficult going forward. I think I have a temporary solution to replace
the async method.

this commit partially reverts changes from:

ec50703395098f75946f0bad01816cc54ab18a58

https://github.com/jbenet/go-ipfs/commit/ec50703395098f75946f0bad01816cc54ab18a58

bitswap.go

@@ -2,7 +2,6 @@ package bitswap
 
 import (
 	"errors"
-	"fmt"
 
 	context "github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
 	ds "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/datastore.go"
@@ -66,17 +65,13 @@ func (bs *bitswap) Block(parent context.Context, k u.Key) (*blocks.Block, error)
 	// TODO add to wantlist
 	promise := bs.notifications.Subscribe(ctx, k)
 
-	// const maxProviders = 20
-	// using non-async version for now.
-	peersToQuery, err := bs.routing.FindProviders(ctx, k)
-	if err != nil {
-		return nil, fmt.Errorf("No providers found for %d (%v)", k, err)
-	}
+	const maxProviders = 20
+	peersToQuery := bs.routing.FindProvidersAsync(ctx, k, maxProviders)
 
 	go func() {
 		message := bsmsg.New()
 		message.AppendWanted(k)
-		for _, iiiii := range peersToQuery {
+		for iiiii := range peersToQuery {
 			// u.DOut("bitswap got peersToQuery: %s\n", iiiii)
 			go func(p *peer.Peer) {
 				response, err := bs.sender.SendRequest(ctx, p, message)

network/interface.go

@@ -46,11 +46,7 @@ type NetMessageService interface {
 // TODO rename -> Router?
 type Routing interface {
 	// FindProvidersAsync returns a channel of providers for the given key
-	// FindProvidersAsync(context.Context, u.Key, int) <-chan *peer.Peer
-	// ^--- removed this for now because has some bugs apparently.
-
-	// FindProviders returns the providers for the given key
-	FindProviders(context.Context, u.Key) ([]*peer.Peer, error)
+	FindProvidersAsync(context.Context, u.Key, int) <-chan *peer.Peer
 
 	// Provide provides the key to the network
 	Provide(context.Context, u.Key) error