locator: added a production_snitch_base implementation

- Implements the non-trivial versions of get_rack() and get_datacenter().
     Performs a lookup in a following order:
        1) Searches in a gossiper::endpoint_state_map.
        2) Searches in a SystemTable.
        3) If not found in any of the above returns a default value.

Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>

New in v2:
   - Introduce db::system_keyspace::endpoint_dc_rack.
   - Kill trim() and split().
   - Added missing copyright and license statements.
   - _my_rack and _my_dc are not optional anymore.
   - Added a promiss that has to be set when snitch is stopped.

locator/production_snitch_base.hh

@@ -0,0 +1,102 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Modified by Cloudius Systems.
+ * Copyright 2015 Cloudius Systems.
+ */
+
+#pragma once
+
+#include <unordered_map>
+#include <utility>
+#include <experimental/optional>
+
+#include "gms/endpoint_state.hh"
+#include "gms/gossiper.hh"
+#include "utils/fb_utilities.hh"
+#include "db/system_keyspace.hh"
+#include "core/sstring.hh"
+#include "snitch_base.hh"
+
+namespace locator {
+
+class production_snitch_base : public snitch_base {
+public:
+    // map of inet address to (datacenter, rack) pair
+    typedef std::unordered_map<inet_address, db::system_keyspace::endpoint_dc_rack> addr2dc_rack_map;
+
+    static constexpr const char* default_dc   = "UNKNOWN_DC";
+    static constexpr const char* default_rack = "UNKNOWN_RACK";
+
+    virtual sstring get_rack(inet_address endpoint) {
+        if (endpoint == utils::fb_utilities::get_broadcast_address()) {
+            return _my_rack;
+        }
+
+        return get_endpoint_info(endpoint,
+                                 gms::application_state::RACK,
+                                 default_rack);
+    }
+
+    virtual sstring get_datacenter(inet_address endpoint) {
+        if (endpoint == utils::fb_utilities::get_broadcast_address()) {
+            return _my_dc;
+        }
+
+        return get_endpoint_info(endpoint,
+                                 gms::application_state::DC,
+                                 default_dc);
+    }
+
+private:
+    sstring get_endpoint_info(inet_address endpoint, gms::application_state key,
+                              const sstring& default_val) {
+        gms::gossiper& local_gossiper = gms::get_local_gossiper();
+        auto state = local_gossiper.get_endpoint_state_for_endpoint(endpoint);
+
+        // First, look in the gossiper::endpoint_state_map...
+        if (state) {
+            auto ep_state = state->get_application_state(key);
+            if (ep_state) {
+                return ep_state->value;
+            }
+        }
+
+        // ...if not found - look in the SystemTable...
+        if (!_saved_endpoints) {
+            _saved_endpoints = db::system_keyspace::load_dc_rack_info();
+        }
+
+        auto it = _saved_endpoints->find(endpoint);
+
+        if (it != _saved_endpoints->end()) {
+            if (key == gms::application_state::RACK) {
+                return it->second.rack;
+            } else { // gms::application_state::DC
+                return it->second.dc;
+            }
+        }
+
+        // ...if still not found - return a default value
+        return default_val;
+    }
+
+protected:
+    promise<> _snitch_is_stopped;
+    std::experimental::optional<addr2dc_rack_map> _saved_endpoints;
+};
+} // namespace locator