limit total length of user agent comments

Reworked-By: Wladimir J. van der Laan <laanwj@gmail.com>

src/net.h

@@ -49,6 +49,8 @@ static const unsigned int MAX_INV_SZ = 50000;
 static const unsigned int MAX_ADDR_TO_SEND = 1000;
 /** Maximum length of incoming protocol messages (no message over 2 MiB is currently acceptable). */
 static const unsigned int MAX_PROTOCOL_MESSAGE_LENGTH = 2 * 1024 * 1024;
+/** Maximum length of strSubVer in `version` message */
+static const unsigned int MAX_SUBVERSION_LENGTH = 256;
 /** -listen default */
 static const bool DEFAULT_LISTEN = true;
 /** The maximum number of entries in mapAskFor */
@@ -156,6 +158,9 @@ extern CCriticalSection cs_vAddedNodes;
 extern NodeId nLastNodeId;
 extern CCriticalSection cs_nLastNodeId;
 
+/** Subversion as sent to the P2P network in `version` messages */
+extern std::string strSubVersion;
+
 struct LocalServiceInfo {
     int nScore;
     int nPort;