write blocks retrieved from the exchange to the blockstore

This follows the change in bitswap where that responsibility was removed.

blockservice.go

@@ -249,6 +249,11 @@ func getBlock(ctx context.Context, c cid.Cid, bs blockstore.Blockstore, fget fun
 		if err != nil {
 			return nil, err
 		}
+		// also write in the blockstore for caching
+		err = bs.Put(ctx, blk)
+		if err != nil {
+			return nil, err
+		}
 		logger.Debugf("BlockService.BlockFetched %s", c)
 		return blk, nil
 	}
@@ -326,6 +331,15 @@ func getBlocks(ctx context.Context, ks []cid.Cid, bs blockstore.Blockstore, fget
 
 		for b := range rblocks {
 			logger.Debugf("BlockService.BlockFetched %s", b.Cid())
+
+			// also write in the blockstore for caching
+			// TODO: for performance reason, it might make sense to batch those writes
+			err = bs.Put(ctx, b)
+			if err != nil {
+				logger.Errorf("could not write blocks from the network to the blockstore: %s", err)
+				return
+			}
+
 			select {
 			case out <- b:
 			case <-ctx.Done():