Add request length check to json rpcs (#221)

* Add request length check to avoid ddos

* Add tests

rpc/jsonrpc/server/http_json_handler.go

@@ -15,6 +15,8 @@ import (
 
 // HTTP + JSON handler
 
+const REQUEST_BATCH_SIZE_LIMIT = 10
+
 // jsonrpc calls grab the given method's function info and runs reflect.Call
 func makeJSONRPCHandler(funcMap map[string]*RPCFunc, logger log.Logger) http.HandlerFunc {
 	return func(w http.ResponseWriter, hreq *http.Request) {
@@ -41,6 +43,11 @@ func makeJSONRPCHandler(funcMap map[string]*RPCFunc, logger log.Logger) http.Han
 		}
 
 		requests, err := parseRequests(b)
+		if len(requests) > REQUEST_BATCH_SIZE_LIMIT {
+			writeRPCResponse(w, logger, rpctypes.RPCRequest{}.MakeErrorf(
+				rpctypes.CodeParseError, "Batch size limit exceeded."))
+			return
+		}
 		if err != nil {
 			writeRPCResponse(w, logger, rpctypes.RPCRequest{}.MakeErrorf(
 				rpctypes.CodeParseError, "decoding request: %v", err))

rpc/jsonrpc/server/http_json_handler_test.go

@@ -3,6 +3,7 @@ package server
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -221,6 +222,67 @@ func TestRPCNotificationInBatch(t *testing.T) {
 	}
 }
 
+func TestRPCBatchLimit(t *testing.T) {
+	mux := testMux()
+	tests := []struct {
+		payload string
+		success bool
+	}{
+		{
+			`[
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]}
+			 ]`,
+			true,
+		},
+		{
+			`[
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]},
+				{"jsonrpc": "2.0","method":"c","id":"abc","params":["a","10"]}
+			 ]`,
+			false,
+		},
+	}
+	for i, tt := range tests {
+		req, _ := http.NewRequest("POST", "http://localhost/", strings.NewReader(tt.payload))
+		rec := httptest.NewRecorder()
+		mux.ServeHTTP(rec, req)
+		res := rec.Result()
+		// Always expecting back a JSONRPCResponse
+		assert.True(t, statusOK(res.StatusCode), "#%d: should always return 2XX", i)
+		blob, err := io.ReadAll(res.Body)
+
+		fmt.Printf("responses: %s\n", blob)
+		if err != nil {
+			t.Errorf("#%d: err reading body: %v", i, err)
+			continue
+		}
+		res.Body.Close()
+
+		var responses []rpctypes.RPCResponse
+		err = json.Unmarshal(blob, &responses)
+		if err != nil {
+			if tt.success {
+				t.Errorf("#%d: expected successful parsing of an RPCResponse\nblob: %s", i, blob)
+				continue
+			} else {
+				fmt.Printf("blob: %s, %d\n", responses, len(responses))
+				assert.Contains(t, string(blob), "Batch size limit exceeded.")
+			}
+		}
+
+	}
+}
+
 func TestUnknownRPCPath(t *testing.T) {
 	mux := testMux()
 	req, _ := http.NewRequest("GET", "http://localhost/unknownrpcpath", strings.NewReader(""))