Add hostname resolving to dosguard (#1000)

Fixes #983.

Cassandra, ETL sorces and cache already support hostname resolving.

Also added config to show missing includes by clangd.

src/web/Resolver.cpp

@@ -0,0 +1,69 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2023, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "web/Resolver.h"
+
+#include <boost/asio/ip/address.hpp>
+
+#include <string>
+#include <string_view>
+#include <vector>
+
+namespace asio = boost::asio;
+
+namespace web {
+
+namespace {
+
+// Check if the hostname is an IP address or a subnet.
+bool
+isAddress(std::string_view hostname)
+{
+    boost::system::error_code ec;
+    asio::ip::make_address(hostname.data(), ec);
+    if (ec == boost::system::errc::success) {
+        return true;
+    }
+
+    asio::ip::make_network_v4(hostname.data(), ec);
+    if (ec == boost::system::errc::success) {
+        return true;
+    }
+
+    asio::ip::make_network_v6(hostname.data(), ec);
+    return ec == boost::system::errc::success;
+}
+
+}  // namespace
+
+std::vector<std::string>
+Resolver::resolve(std::string_view hostname, std::string_view service)
+{
+    if (isAddress(hostname)) {
+        return {std::string(hostname)};
+    }
+
+    std::vector<std::string> endpoints;
+    for (auto const& endpoint : resolver_.resolve(hostname, service)) {
+        endpoints.push_back(endpoint.endpoint().address().to_string());
+    }
+    return endpoints;
+}
+
+}  // namespace web