[NOD-88] Add getTopHeaders rpc command (#242)

* [NOD-88] Add getTopHeaders rpc command

* [NOD-88] Fix gofmt error

* [NOD-88] Remove unnecessary variable

* [NOD-88] Remove GetTopHeaders from rpcSyncMgr

blockdag/dag.go

@@ -1421,7 +1421,7 @@ func (dag *BlockDAG) locateBlockNodes(locator BlockLocator, hashStop *daghash.Ha
 	queue.pushSet(node.children)
 
 	visited := newSet()
-	for i := uint32(0); queue.Len() > 0 && i < maxEntries; i++ {
+	for queue.Len() > 0 && uint32(len(nodes)) < maxEntries {
 		var current *blockNode
 		current = queue.pop()
 		if !visited.contains(current) {
@@ -1474,6 +1474,32 @@ func (dag *BlockDAG) locateHeaders(locator BlockLocator, hashStop *daghash.Hash,
 	return headers
 }
 
+// GetTopHeaders returns the top wire.MaxBlockHeadersPerMsg block headers ordered by height.
+func (dag *BlockDAG) GetTopHeaders(startHash *daghash.Hash) ([]*wire.BlockHeader, error) {
+	startNode := &dag.virtual.blockNode
+	if startHash != nil {
+		startNode = dag.index.LookupNode(startHash)
+		if startNode == nil {
+			return nil, fmt.Errorf("Couldn't find the start hash %s in the dag", startHash)
+		}
+	}
+	headers := make([]*wire.BlockHeader, 0, startNode.blueScore)
+	queue := NewDownHeap()
+	queue.pushSet(startNode.parents)
+
+	visited := newSet()
+	for i := uint32(0); queue.Len() > 0 && len(headers) < wire.MaxBlockHeadersPerMsg; i++ {
+		var current *blockNode
+		current = queue.pop()
+		if !visited.contains(current) {
+			visited.add(current)
+			headers = append(headers, current.Header())
+			queue.pushSet(current.parents)
+		}
+	}
+	return headers, nil
+}
+
 // RLock locks the DAG's UTXO set for reading.
 func (dag *BlockDAG) RLock() {
 	dag.dagLock.RLock()

btcjson/btcdextcmds.go

@@ -90,6 +90,19 @@ func NewGetCurrentNetCmd() *GetCurrentNetCmd {
 	return &GetCurrentNetCmd{}
 }
 
+// GetTopHeadersCmd defined the getTopHeaders JSON-RPC command.
+type GetTopHeadersCmd struct {
+	StartHash *string `json:"startHash"`
+}
+
+// NewGetTopHeadersCmd returns a new instance which can be used to issue a
+// getTopHeaders JSON-RPC command.
+func NewGetTopHeadersCmd(startHash *string) *GetTopHeadersCmd {
+	return &GetTopHeadersCmd{
+		StartHash: startHash,
+	}
+}
+
 // GetHeadersCmd defines the getHeaders JSON-RPC command.
 //
 // NOTE: This is a btcsuite extension ported from
@@ -134,5 +147,6 @@ func init() {
 	MustRegisterCmd("getBestBlock", (*GetBestBlockCmd)(nil), flags)
 	MustRegisterCmd("getCurrentNet", (*GetCurrentNetCmd)(nil), flags)
 	MustRegisterCmd("getHeaders", (*GetHeadersCmd)(nil), flags)
+	MustRegisterCmd("getTopHeaders", (*GetTopHeadersCmd)(nil), flags)
 	MustRegisterCmd("version", (*VersionCmd)(nil), flags)
 }

btcjson/btcdextcmds_test.go

@@ -176,6 +176,34 @@ func TestBtcdExtCmds(t *testing.T) {
 				HashStop: "000000000000000000ba33b33e1fad70b69e234fc24414dd47113bff38f523f7",
 			},
 		},
+		{
+			name: "getTopHeaders",
+			newCmd: func() (interface{}, error) {
+				return btcjson.NewCmd("getTopHeaders")
+			},
+			staticCmd: func() interface{} {
+				return btcjson.NewGetTopHeadersCmd(
+					nil,
+				)
+			},
+			marshalled:   `{"jsonrpc":"1.0","method":"getTopHeaders","params":[],"id":1}`,
+			unmarshalled: &btcjson.GetTopHeadersCmd{},
+		},
+		{
+			name: "getTopHeaders - with start hash",
+			newCmd: func() (interface{}, error) {
+				return btcjson.NewCmd("getTopHeaders", "000000000000000000ba33b33e1fad70b69e234fc24414dd47113bff38f523f7")
+			},
+			staticCmd: func() interface{} {
+				return btcjson.NewGetTopHeadersCmd(
+					btcjson.String("000000000000000000ba33b33e1fad70b69e234fc24414dd47113bff38f523f7"),
+				)
+			},
+			marshalled: `{"jsonrpc":"1.0","method":"getTopHeaders","params":["000000000000000000ba33b33e1fad70b69e234fc24414dd47113bff38f523f7"],"id":1}`,
+			unmarshalled: &btcjson.GetTopHeadersCmd{
+				StartHash: btcjson.String("000000000000000000ba33b33e1fad70b69e234fc24414dd47113bff38f523f7"),
+			},
+		},
 		{
 			name: "version",
 			newCmd: func() (interface{}, error) {

rpcclient/extensions.go

@@ -275,6 +275,24 @@ func (r FutureGetHeadersResult) Receive() ([]wire.BlockHeader, error) {
 	return headers, nil
 }
 
+// GetTopHeadersAsync returns an instance of a type that can be used to get the result
+// of the RPC at some future time by invoking the Receive function on the returned instance.
+//
+// See GetTopHeaders for the blocking version and more details.
+func (c *Client) GetTopHeadersAsync(startHash *daghash.Hash) FutureGetHeadersResult {
+	var hash *string
+	if startHash != nil {
+		hash = btcjson.String(startHash.String())
+	}
+	cmd := btcjson.NewGetTopHeadersCmd(hash)
+	return c.sendCmd(cmd)
+}
+
+// GetTopHeaders sends a getTopHeaders rpc command to the server.
+func (c *Client) GetTopHeaders(startHash *daghash.Hash) ([]wire.BlockHeader, error) {
+	return c.GetTopHeadersAsync(startHash).Receive()
+}
+
 // GetHeadersAsync returns an instance of a type that can be used to get the result
 // of the RPC at some future time by invoking the Receive function on the returned instance.
 //

server/rpc/rpcserver.go

@@ -161,6 +161,7 @@ var rpcHandlersBeforeInit = map[string]commandHandler{
 	"getGenerate":           handleGetGenerate,
 	"getHashesPerSec":       handleGetHashesPerSec,
 	"getHeaders":            handleGetHeaders,
+	"getTopHeaders":         handleGetTopHeaders,
 	"getInfo":               handleGetInfo,
 	"getManualNodeInfo":     handleGetManualNodeInfo,
 	"getMempoolInfo":        handleGetMempoolInfo,
@@ -2289,6 +2290,39 @@ func handleGetHashesPerSec(s *Server, cmd interface{}, closeChan <-chan struct{}
 	return int64(s.cfg.CPUMiner.HashesPerSecond()), nil
 }
 
+// handleGetTopHeaders implements the getTopHeaders command.
+func handleGetTopHeaders(s *Server, cmd interface{}, closeChan <-chan struct{}) (interface{}, error) {
+	c := cmd.(*btcjson.GetTopHeadersCmd)
+
+	var startHash *daghash.Hash
+	if c.StartHash != nil {
+		startHash = &daghash.Hash{}
+		err := daghash.Decode(startHash, *c.StartHash)
+		if err != nil {
+			return nil, rpcDecodeHexError(*c.StartHash)
+		}
+	}
+	headers, err := s.cfg.DAG.GetTopHeaders(startHash)
+	if err != nil {
+		return nil, internalRPCError(err.Error(),
+			"Failed to get top headers")
+	}
+
+	// Return the serialized block headers as hex-encoded strings.
+	hexBlockHeaders := make([]string, len(headers))
+	var buf bytes.Buffer
+	for i, h := range headers {
+		err := h.Serialize(&buf)
+		if err != nil {
+			return nil, internalRPCError(err.Error(),
+				"Failed to serialize block header")
+		}
+		hexBlockHeaders[i] = hex.EncodeToString(buf.Bytes())
+		buf.Reset()
+	}
+	return hexBlockHeaders, nil
+}
+
 // handleGetHeaders implements the getHeaders command.
 //
 // NOTE: This is a btcsuite extension originally ported from

server/rpc/rpcserverhelp.go

@@ -402,6 +402,11 @@ var helpDescsEnUS = map[string]string{
 	"infoWalletResult-relayFee":        "The minimum relay fee for non-free transactions in BTC/KB",
 	"infoWalletResult-errors":          "Any current errors",
 
+	// GetTopHeadersCmd help.
+	"getTopHeaders--synopsis": "Returns the top block headers starting with the provided start hash (not inclusive)",
+	"getTopHeaders-startHash": "Block hash to stop including block headers for; if not found, all headers to the latest known block are returned.",
+	"getTopHeaders--result0":  "Serialized block headers of all located blocks, limited to some arbitrary maximum number of hashes (currently 2000, which matches the wire protocol headers message, but this is not guaranteed)",
+
 	// GetHeadersCmd help.
 	"getHeaders--synopsis":     "Returns block headers starting with the first known block hash from the request",
 	"getHeaders-blockLocators": "JSON array of hex-encoded hashes of blocks.  Headers are returned starting from the first known hash in this list",
@@ -707,6 +712,7 @@ var rpcResultTypes = map[string][]interface{}{
 	"getDifficulty":         {(*float64)(nil)},
 	"getGenerate":           {(*bool)(nil)},
 	"getHashesPerSec":       {(*float64)(nil)},
+	"getTopHeaders":         {(*[]string)(nil)},
 	"getHeaders":            {(*[]string)(nil)},
 	"getInfo":               {(*btcjson.InfoDAGResult)(nil)},
 	"getManualNodeInfo":     {(*string)(nil), (*btcjson.GetManualNodeInfoResult)(nil)},