http: Restrict maximum size of request line + headers

Prevent memory exhaustion by sending lots of data.
Also add a test to `httpbasics.py`.

Closes #6425

qa/rpc-tests/httpbasics.py

@@ -97,5 +97,19 @@ class HTTPBasicsTest (BitcoinTestFramework):
         assert_equal('"error":null' in out1, True)
         assert_equal(conn.sock!=None, True) #connection must be closed because bitcoind should use keep-alive by default
 
+        # Check excessive request size
+        conn = httplib.HTTPConnection(urlNode2.hostname, urlNode2.port)
+        conn.connect()
+        conn.request('GET', '/' + ('x'*1000), '', headers)
+        out1 = conn.getresponse()
+        assert_equal(out1.status, httplib.NOT_FOUND)
+
+        conn = httplib.HTTPConnection(urlNode2.hostname, urlNode2.port)
+        conn.connect()
+        conn.request('GET', '/' + ('x'*10000), '', headers)
+        out1 = conn.getresponse()
+        assert_equal(out1.status, httplib.BAD_REQUEST)
+
+
 if __name__ == '__main__':
     HTTPBasicsTest ().main ()

src/httpserver.cpp

@@ -38,6 +38,9 @@
 #include <boost/foreach.hpp>
 #include <boost/scoped_ptr.hpp>
 
+/** Maximum size of http request (request line + headers) */
+static const size_t MAX_HEADERS_SIZE = 8192;
+
 /** HTTP request work item */
 class HTTPWorkItem : public HTTPClosure
 {
@@ -414,6 +417,7 @@ bool InitHTTPServer()
     }
 
     evhttp_set_timeout(http, GetArg("-rpcservertimeout", DEFAULT_HTTP_SERVER_TIMEOUT));
+    evhttp_set_max_headers_size(http, MAX_HEADERS_SIZE);
     evhttp_set_max_body_size(http, MAX_SIZE);
     evhttp_set_gencb(http, http_request_cb, NULL);