rpc: add getblockheadercount call

See neo-project/neo-modules#504.

docs/rpc.md

@@ -40,6 +40,7 @@ which would yield the response:
 | `getblockcount` |
 | `getblockhash` |
 | `getblockheader` |
+| `getblockheadercount` |
 | `getblocksysfee` |
 | `getconnectioncount` |
 | `getcontractstate` |

pkg/rpc/client/rpc.go

@@ -155,6 +155,15 @@ func (c *Client) GetBlockHeader(hash util.Uint256) (*block.Header, error) {
 	return h, nil
 }
 
+// GetBlockHeaderCount returns the number of headers in the main chain.
+func (c *Client) GetBlockHeaderCount() (uint32, error) {
+	var resp uint32
+	if err := c.performRequest("getblockheadercount", request.NewRawParams(), &resp); err != nil {
+		return resp, err
+	}
+	return resp, nil
+}
+
 // GetBlockHeaderVerbose returns the corresponding block header information from Json format string
 // according to the specified script hash.
 func (c *Client) GetBlockHeaderVerbose(hash util.Uint256) (*result.Header, error) {

pkg/rpc/client/rpc_test.go

@@ -280,6 +280,18 @@ var rpcClientTestCases = map[string][]rpcClientTestCase{
 			},
 		},
 	},
+	"getblockheadercount": {
+		{
+			name: "positive",
+			invoke: func(c *Client) (interface{}, error) {
+				return c.GetBlockHeaderCount()
+			},
+			serverResponse: `{"jsonrpc":"2.0","id":1,"result":2021}`,
+			result: func(c *Client) interface{} {
+				return uint32(2021)
+			},
+		},
+	},
 	"getblocksysfee": {
 		{
 			name: "positive",

pkg/rpc/server/server.go

@@ -29,12 +29,12 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
 	"github.com/nspcc-dev/neo-go/pkg/io"
 	"github.com/nspcc-dev/neo-go/pkg/network"
-	"github.com/nspcc-dev/neo-go/pkg/services/oracle"
-	"github.com/nspcc-dev/neo-go/pkg/services/oracle/broadcaster"
 	"github.com/nspcc-dev/neo-go/pkg/rpc"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/request"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/response"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/response/result"
+	"github.com/nspcc-dev/neo-go/pkg/services/oracle"
+	"github.com/nspcc-dev/neo-go/pkg/services/oracle/broadcaster"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/callflag"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/manifest"
 	"github.com/nspcc-dev/neo-go/pkg/smartcontract/trigger"
@@ -99,6 +99,7 @@ var rpcHandlers = map[string]func(*Server, request.Params) (interface{}, *respon
 	"getblockcount":          (*Server).getBlockCount,
 	"getblockhash":           (*Server).getBlockHash,
 	"getblockheader":         (*Server).getBlockHeader,
+	"getblockheadercount":    (*Server).getBlockHeaderCount,
 	"getblocksysfee":         (*Server).getBlockSysFee,
 	"getcommittee":           (*Server).getCommittee,
 	"getconnectioncount":     (*Server).getConnectionCount,
@@ -433,6 +434,10 @@ func (s *Server) getBlockCount(_ request.Params) (interface{}, *response.Error)
 	return s.chain.BlockHeight() + 1, nil
 }
 
+func (s *Server) getBlockHeaderCount(_ request.Params) (interface{}, *response.Error) {
+	return s.chain.HeaderHeight() + 1, nil
+}
+
 func (s *Server) getConnectionCount(_ request.Params) (interface{}, *response.Error) {
 	return s.coreServer.PeerCount(), nil
 }

pkg/rpc/server/server_test.go

@@ -494,6 +494,15 @@ var rpcTestCases = map[string][]rpcTestCase{
 			fail:   true,
 		},
 	},
+	"getblockheadercount": {
+		{
+			params: "[]",
+			result: func(e *executor) interface{} {
+				v := int(e.chain.HeaderHeight() + 1)
+				return &v
+			},
+		},
+	},
 	"getblocksysfee": {
 		{
 			name:   "positive",