multi: Modify CFHeaders message to have a PrevFilterHeader field.

server.go

@@ -788,13 +788,28 @@ func (sp *serverPeer) OnGetCFHeaders(_ *peer.Peer, msg *wire.MsgGetCFHeaders) {
 		return
 	}
 
+	startHeight := int32(msg.StartHeight)
+	maxResults := wire.MaxCFHeadersPerMsg
+
+	// If StartHeight is positive, fetch the predecessor block hash so we can
+	// populate the PrevFilterHeader field.
+	if msg.StartHeight > 0 {
+		startHeight--
+		maxResults++
+	}
+
 	// Fetch the hashes from the block index.
-	hashList, err := sp.server.chain.HeightToHashRange(int32(msg.StartHeight),
-		&msg.StopHash, wire.MaxCFHeadersPerMsg)
+	hashList, err := sp.server.chain.HeightToHashRange(startHeight,
+		&msg.StopHash, maxResults)
 	if err != nil {
 		peerLog.Debugf("Invalid getcfheaders request: %v", err)
 	}
-	if len(hashList) == 0 {
+
+	// This is possible if StartHeight is one greater that the height of
+	// StopHash, and we pull a valid range of hashes including the previous
+	// filter header.
+	if len(hashList) == 0 || (msg.StartHeight > 0 && len(hashList) == 1) {
+		peerLog.Debug("No results for getcfheaders request")
 		return
 	}
 
@@ -815,6 +830,37 @@ func (sp *serverPeer) OnGetCFHeaders(_ *peer.Peer, msg *wire.MsgGetCFHeaders) {
 
 	// Generate cfheaders message and send it.
 	headersMsg := wire.NewMsgCFHeaders()
+
+	// Populate the PrevFilterHeader field.
+	if msg.StartHeight > 0 {
+		prevBlockHash := &hashList[0]
+
+		// Fetch the raw committed filter header bytes from the
+		// database.
+		headerBytes, err := sp.server.cfIndex.FilterHeaderByBlockHash(
+			prevBlockHash, msg.FilterType)
+		if err != nil {
+			peerLog.Errorf("Error retrieving CF header: %v", err)
+			return
+		}
+		if len(headerBytes) == 0 {
+			peerLog.Warnf("Could not obtain CF header for %v", prevBlockHash)
+			return
+		}
+
+		// Deserialize the hash into PrevFilterHeader.
+		err = headersMsg.PrevFilterHeader.SetBytes(headerBytes)
+		if err != nil {
+			peerLog.Warnf("Committed filter header deserialize "+
+				"failed: %v", err)
+			return
+		}
+
+		hashList = hashList[1:]
+		filterHeaders = filterHeaders[1:]
+	}
+
+	// Populate HeaderHashes.
 	for i, headerBytes := range filterHeaders {
 		if len(headerBytes) == 0 {
 			peerLog.Warnf("Could not obtain CF header for %v", hashList[i])

wire/message_test.go

@@ -106,7 +106,7 @@ func TestMessage(t *testing.T) {
 		{msgGetCFilters, msgGetCFilters, pver, MainNet, 61},
 		{msgGetCFHeaders, msgGetCFHeaders, pver, MainNet, 61},
 		{msgCFilter, msgCFilter, pver, MainNet, 65},
-		{msgCFHeaders, msgCFHeaders, pver, MainNet, 58},
+		{msgCFHeaders, msgCFHeaders, pver, MainNet, 90},
 	}
 
 	t.Logf("Running %d tests", len(tests))

wire/msgcfheaders.go

@@ -27,9 +27,10 @@ const (
 // of committed filter headers per message is currently 2000. See
 // MsgGetCFHeaders for details on requesting the headers.
 type MsgCFHeaders struct {
-	StopHash     chainhash.Hash
-	FilterType   FilterType
-	HeaderHashes []*chainhash.Hash
+	FilterType       FilterType
+	StopHash         chainhash.Hash
+	PrevFilterHeader chainhash.Hash
+	HeaderHashes     []*chainhash.Hash
 }
 
 // AddCFHeader adds a new committed filter header to the message.
@@ -47,14 +48,20 @@ func (msg *MsgCFHeaders) AddCFHeader(headerHash *chainhash.Hash) error {
 // BtcDecode decodes r using the bitcoin protocol encoding into the receiver.
 // This is part of the Message interface implementation.
 func (msg *MsgCFHeaders) BtcDecode(r io.Reader, pver uint32, _ MessageEncoding) error {
-	// Read stop hash
-	err := readElement(r, &msg.StopHash)
+	// Read filter type
+	err := readElement(r, &msg.FilterType)
 	if err != nil {
 		return err
 	}
 
-	// Read filter type
-	err = readElement(r, &msg.FilterType)
+	// Read stop hash
+	err = readElement(r, &msg.StopHash)
+	if err != nil {
+		return err
+	}
+
+	// Read prev filter header
+	err = readElement(r, &msg.PrevFilterHeader)
 	if err != nil {
 		return err
 	}
@@ -91,14 +98,20 @@ func (msg *MsgCFHeaders) BtcDecode(r io.Reader, pver uint32, _ MessageEncoding)
 // BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
 // This is part of the Message interface implementation.
 func (msg *MsgCFHeaders) BtcEncode(w io.Writer, pver uint32, _ MessageEncoding) error {
-	// Write stop hash
-	err := writeElement(w, msg.StopHash)
+	// Write filter type
+	err := writeElement(w, msg.FilterType)
 	if err != nil {
 		return err
 	}
 
-	// Write filter type
-	err = writeElement(w, msg.FilterType)
+	// Write stop hash
+	err = writeElement(w, msg.StopHash)
+	if err != nil {
+		return err
+	}
+
+	// Write prev filter header
+	err = writeElement(w, msg.PrevFilterHeader)
 	if err != nil {
 		return err
 	}
@@ -154,7 +167,7 @@ func (msg *MsgCFHeaders) Command() string {
 func (msg *MsgCFHeaders) MaxPayloadLength(pver uint32) uint32 {
 	// Hash size + filter type + num headers (varInt) +
 	// (header size * max headers).
-	return chainhash.HashSize + 1 + MaxVarIntPayload +
+	return 1 + chainhash.HashSize + chainhash.HashSize + MaxVarIntPayload +
 		(MaxCFHeaderPayload * MaxCFHeadersPerMsg)
 }