From 9437c3784a69f0bbee12dcc701e828170f046da5 Mon Sep 17 00:00:00 2001
From: Conner Fromknecht <conner@mit.edu>
Date: Wed, 18 Apr 2018 19:43:39 -0700
Subject: [PATCH] chain/rpc: impl FilterBlocks using gc filter rescan

---
 chain/rpc.go | 88 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 88 insertions(+)

diff --git a/chain/rpc.go b/chain/rpc.go
index fc40456..36c0f3e 100644
--- a/chain/rpc.go
+++ b/chain/rpc.go
@@ -13,9 +13,12 @@ import (
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/rpcclient"
+	"github.com/btcsuite/btcd/wire"
 	"github.com/btcsuite/btcutil"
 	"github.com/btcsuite/btcwallet/waddrmgr"
 	"github.com/btcsuite/btcwallet/wtxmgr"
+	"github.com/ltcsuite/ltcutil/gcs"
+	"github.com/ltcsuite/ltcutil/gcs/builder"
 )
 
 // RPCClient represents a persistent client connection to a bitcoin RPC server
@@ -163,6 +166,91 @@ func (c *RPCClient) BlockStamp() (*waddrmgr.BlockStamp, error) {
 	}
 }
 
+// FilterBlocks scans the blocks contained in the FilterBlocksRequest for any
+// addresses of interest. For each requested block, the corresponding compact
+// filter will first be checked for matches, skipping those that do not report
+// anything. If the filter returns a postive match, the full block will be
+// fetched and filtered. This method returns a FilterBlocksReponse for the first
+// block containing a matching address. If no matches are found in the range of
+// blocks requested, the returned response will be nil.
+func (c *RPCClient) FilterBlocks(
+	req *FilterBlocksRequest) (*FilterBlocksResponse, error) {
+
+	blockFilterer := NewBlockFilterer(c.chainParams, req)
+
+	// Construct the watchlist using the addresses and outpoints contained
+	// in the filter blocks request.
+	watchList, err := buildFilterBlocksWatchList(req)
+	if err != nil {
+		return nil, err
+	}
+
+	// Iterate over the requested blocks, fetching the compact filter for
+	// each one, and matching it against the watchlist generated above. If
+	// the filter returns a positive match, the full block is then requested
+	// and scanned for addresses using the block filterer.
+	for i, blk := range req.Blocks {
+		rawFilter, err := c.GetCFilter(&blk.Hash, wire.GCSFilterRegular)
+		if err != nil {
+			return nil, err
+		}
+
+		// Ensure the filter is large enough to be deserialized.
+		if len(rawFilter.Data) < 4 {
+			continue
+		}
+
+		filter, err := gcs.FromNBytes(builder.DefaultP, rawFilter.Data)
+		if err != nil {
+			return nil, err
+		}
+
+		// Skip any empty filters.
+		if filter.N() == 0 {
+			continue
+		}
+
+		key := builder.DeriveKey(&blk.Hash)
+		matched, err := filter.MatchAny(key, watchList)
+		if err != nil {
+			return nil, err
+		} else if !matched {
+			continue
+		}
+
+		log.Infof("Fetching block height=%d hash=%v",
+			blk.Height, blk.Hash)
+
+		rawBlock, err := c.GetBlock(&blk.Hash)
+		if err != nil {
+			return nil, err
+		}
+
+		if !blockFilterer.FilterBlock(rawBlock) {
+			continue
+		}
+
+		// If any external or internal addresses were detected in this
+		// block, we return them to the caller so that the rescan
+		// windows can widened with subsequent addresses. The
+		// `BatchIndex` is returned so that the caller can compute the
+		// *next* block from which to begin again.
+		resp := &FilterBlocksResponse{
+			BatchIndex:         uint32(i),
+			BlockMeta:          blk,
+			FoundExternalAddrs: blockFilterer.FoundExternal,
+			FoundInternalAddrs: blockFilterer.FoundInternal,
+			FoundOutPoints:     blockFilterer.FoundOutPoints,
+			RelevantTxns:       blockFilterer.RelevantTxns,
+		}
+
+		return resp, nil
+	}
+
+	// No addresses were found for this range.
+	return nil, nil
+}
+
 // parseBlock parses a btcws definition of the block a tx is mined it to the
 // Block structure of the wtxmgr package, and the block index.  This is done
 // here since rpcclient doesn't parse this nicely for us.