Add header spam protection

src/main.h

@@ -3,6 +3,9 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+// Header spam protection by Qtum
+// Copyright (c) 2016-2019 The Qtum developers
+
 #ifndef BITCOIN_MAIN_H
 #define BITCOIN_MAIN_H
 
@@ -139,6 +142,13 @@ static const bool DEFAULT_TESTSAFEMODE = false;
 /** Default for using fee filter */
 static const bool DEFAULT_FEEFILTER = true;
 
+/** Default for -headerspamfilter, use header spam filter */
+static const bool DEFAULT_HEADER_SPAM_FILTER = true;
+/** Default for -headerspamfiltermaxsize, maximum size of the list of indexes in the header spam filter */
+static const unsigned int DEFAULT_HEADER_SPAM_FILTER_MAX_SIZE = 500;
+/** Default for -headerspamfiltermaxavg, maximum average size of an index occurrence in the header spam filter */
+static const unsigned int DEFAULT_HEADER_SPAM_FILTER_MAX_AVG = 10;
+
 /** Maximum number of headers to announce when relaying blocks with headers message.*/
 static const unsigned int MAX_BLOCKS_TO_ANNOUNCE = 8;