Pass callback to get provider options to provider_v26 constructor

Passing a callback allows constructing the options string using
config service after loading the provider but before initializing
the provider.

Author: temeo

include/wsrep/provider.hpp

@@ -29,6 +29,7 @@
 
 #include <cstring>
 
+#include <functional>
 #include <memory>
 #include <string>
 #include <vector>
@@ -514,10 +515,9 @@ namespace wsrep
         static std::unique_ptr<provider> make_provider(
             wsrep::server_state&,
             const std::string& provider_spec,
-            const std::string& provider_options,
+            const std::function<std::string()>& provider_options_cb,
             const wsrep::provider::services& services
             = wsrep::provider::services());
-
     protected:
         wsrep::server_state& server_state_;
     };

include/wsrep/server_state.hpp

@@ -283,6 +283,24 @@ namespace wsrep
          */
         enum wsrep::provider::status send_pending_rollback_events();
 
+        /**
+         * Load WSRep provider.
+         *
+         * @param provider WSRep provider library to be loaded.
+         * @param provider_options_cb Callback to get provider options.
+         *                            The function to be called must be
+         *                            idempotent.
+         * @param services Application defined services passed to
+         *                 the provider.
+         *
+         * @return Zero on success, non-zero on error.
+         */
+        int load_provider(const std::string& provider,
+                          const std::function<std::string()>& provider_options_cb,
+                          const wsrep::provider::services& services
+                          = wsrep::provider::services());
+
+
         /**
          * Load WSRep provider.
          *
@@ -293,11 +311,18 @@ namespace wsrep
          *                 the provider.
          *
          * @return Zero on success, non-zero on error.
+         *
+         * @note Provided for backward compatibility.
          */
         int load_provider(const std::string& provider,
                           const std::string& provider_options,
                           const wsrep::provider::services& services
-                          = wsrep::provider::services());
+                          = wsrep::provider::services())
+        {
+            return load_provider(provider,
+                                [provider_options]() { return provider_options; },
+                                services);
+        }
 
         using provider_factory_func =
             std::function<decltype(wsrep::provider::make_provider)>;

src/provider.cpp

@@ -29,27 +29,27 @@
 std::unique_ptr<wsrep::provider> wsrep::provider::make_provider(
     wsrep::server_state& server_state,
     const std::string& provider_spec,
-    const std::string& provider_options,
+    const std::function<std::string()>& provider_options_cb,
     const wsrep::provider::services& services)
 {
     try
     {
         return std::unique_ptr<wsrep::provider>(new wsrep::wsrep_provider_v26(
-            server_state, provider_options, provider_spec, services));
+            server_state, provider_spec, provider_options_cb, services));
     }
     catch (const wsrep::runtime_error& e)
     {
         wsrep::log_error() << "Failed to create a new provider '"
                            << provider_spec << "'"
-                           << " with options '" << provider_options
+                           << " with options '" << provider_options_cb()
                            << "': " << e.what();
     }
     catch (...)
     {
         wsrep::log_error() << "Caught unknown exception when trying to "
                            << "create a new provider '"
                            << provider_spec << "'"
-                           << " with options '" << provider_options;
+                           << " with options '" << provider_options_cb();
     }
     return 0;
 }

src/server_state.cpp

@@ -499,13 +499,14 @@ static int apply_toi(wsrep::provider& provider,
 //////////////////////////////////////////////////////////////////////////////
 
 int wsrep::server_state::load_provider(
-    const std::string& provider_spec, const std::string& provider_options,
+    const std::string& provider_spec,
+    const std::function<std::string()>& provider_options_cb,
     const wsrep::provider::services& services)
 {
     wsrep::log_info() << "Loading provider " << provider_spec
                       << " initial position: " << initial_position_;
     provider_
-        = provider_factory_(*this, provider_spec, provider_options, services);
+        = provider_factory_(*this, provider_spec, provider_options_cb, services);
     return (provider_ ? 0 : 1);
 }
 

src/wsrep_provider_v26.cpp

@@ -742,8 +742,8 @@ void wsrep::wsrep_provider_v26::deinit_services()
 
 wsrep::wsrep_provider_v26::wsrep_provider_v26(
     wsrep::server_state& server_state,
-    const std::string& provider_options,
     const std::string& provider_spec,
+    const std::function<std::string()>& provider_options_cb,
     const wsrep::provider::services& services)
     : provider(server_state)
     , wsrep_()
@@ -763,6 +763,7 @@ wsrep::wsrep_provider_v26::wsrep_provider_v26(
     init_args.node_address = server_state_.address().c_str();
     init_args.node_incoming = server_state_.incoming_address().c_str();
     init_args.data_dir = server_state_.working_dir().c_str();
+    const auto& provider_options = provider_options_cb();
     init_args.options = provider_options.c_str();
     init_args.proto_ver = server_state.max_protocol_version();
     init_args.state_id = &state_id;

src/wsrep_provider_v26.hpp

@@ -33,7 +33,7 @@ namespace wsrep
         void init_services(const wsrep::provider::services& services);
         void deinit_services();
         wsrep_provider_v26(wsrep::server_state&, const std::string&,
-                           const std::string&,
+                           const std::function<std::string()>&,
                            const wsrep::provider::services& services);
         ~wsrep_provider_v26() WSREP_OVERRIDE;
         enum wsrep::provider::status