From 2e9a052f62757ff46d79e5f856e6dcae0284d8aa Mon Sep 17 00:00:00 2001
From: hannahhoward <hannah@hannahhoward.net>
Date: Thu, 19 Mar 2020 17:16:26 -0700
Subject: [PATCH] fix(chainsync): support longer graphsync fetches with loop

---
 chain/blocksync/graphsync_client.go | 63 ++++++++++++++++++-----------
 1 file changed, 40 insertions(+), 23 deletions(-)

diff --git a/chain/blocksync/graphsync_client.go b/chain/blocksync/graphsync_client.go
index 5d4af01cb..6fadb44b2 100644
--- a/chain/blocksync/graphsync_client.go
+++ b/chain/blocksync/graphsync_client.go
@@ -41,6 +41,9 @@ const (
 
 	// field index of values array AMT node
 	amtNodeValuesFieldIndex = 2
+
+	// maximum depth per traversal
+	maxRequestLength = 50
 )
 
 var blockHeadersSelector, fullSelector ipld.Node
@@ -132,15 +135,6 @@ func (bs *BlockSync) fetchBlocksGraphSync(ctx context.Context, p peer.ID, req *B
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 
-	sel := selectorForRequest(req)
-
-	// TODO:
-	for _, c := range req.Start {
-		if _, err := bs.bserv.GetBlock(ctx, c); err != nil {
-			return nil, xerrors.Errorf("failed to fetch blocks: %w")
-		}
-	}
-
 	immediateTsSelector := firstTipsetSelector(req)
 
 	// Do this because we can only request one root at a time
@@ -150,20 +144,43 @@ func (bs *BlockSync) fetchBlocksGraphSync(ctx context.Context, p peer.ID, req *B
 		}
 	}
 
-	// execute the selector forreal
-	if err := bs.executeGsyncSelector(ctx, p, req.Start[0], sel); err != nil {
-		return nil, err
+	var totalDepth uint64 = 0
+	var nextReq BlockSyncRequest = *req
+	var wholeChain []*BSTipSet
+	var reachedGenesis bool
+	for totalDepth < req.RequestLength && !reachedGenesis {
+		if nextReq.RequestLength > maxRequestLength {
+			nextReq.RequestLength = maxRequestLength
+		}
+
+		sel := selectorForRequest(&nextReq)
+
+		// execute the selector forreal
+		if err := bs.executeGsyncSelector(ctx, p, req.Start[0], sel); err != nil {
+			return nil, err
+		}
+
+		// Now pull the data we fetched out of the chainstore (where it should now be persisted)
+		tempcs := store.NewChainStore(bs.bserv.Blockstore(), datastore.NewMapDatastore(), nil)
+
+		opts := ParseBSOptions(req.Options)
+		tsk := types.NewTipSetKey(req.Start...)
+		chain, err := collectChainSegment(tempcs, tsk, req.RequestLength, opts)
+		if err != nil {
+			return nil, xerrors.Errorf("failed to load chain data from chainstore after successful graphsync response (start = %v): %w", req.Start, err)
+		}
+		wholeChain = append(wholeChain, chain...)
+		totalDepth += nextReq.RequestLength
+		nextCids := make([]cid.Cid, 0, len(chain[len(chain)-1].Blocks))
+		for _, blk := range chain[len(chain)-1].Blocks {
+			if blk.Height == 0 || blk.Parents == nil {
+				reachedGenesis = true
+			}
+			nextCids = append(nextCids, blk.Cid())
+		}
+		nextReq.Start = nextCids
+		nextReq.RequestLength = req.RequestLength - totalDepth
 	}
 
-	// Now pull the data we fetched out of the chainstore (where it should now be persisted)
-	tempcs := store.NewChainStore(bs.bserv.Blockstore(), datastore.NewMapDatastore(), nil)
-
-	opts := ParseBSOptions(req.Options)
-	tsk := types.NewTipSetKey(req.Start...)
-	chain, err := collectChainSegment(tempcs, tsk, req.RequestLength, opts)
-	if err != nil {
-		return nil, xerrors.Errorf("failed to load chain data from chainstore after successful graphsync response (start = %v): %w", req.Start, err)
-	}
-
-	return &BlockSyncResponse{Chain: chain}, nil
+	return &BlockSyncResponse{Chain: wholeChain}, nil
 }