nghttpx: Define ~Config for automatic clean up with std::unique_ptr

Now config global is backed with std::unique_ptr.  configuration
swapping dance is now a bit cleaner, but YMMV.

src/shrpx.cc

@@ -2571,20 +2571,19 @@ void reload_config(WorkerProcess *wp) {
   // fork_worker_process and forked child process assumes new
   // configuration can be obtained from get_config().
 
-  auto old_config = replace_config(new_config.get());
+  auto old_config = replace_config(std::move(new_config));
 
   auto pid = fork_worker_process(ipc_fd, iaddrs);
 
   if (pid == -1) {
     LOG(ERROR) << "Failed to process new configuration";
+
+    new_config = replace_config(std::move(old_config));
     close_not_inherited_fd(new_config.get(), iaddrs);
-    replace_config(old_config);
+
     return;
   }
 
-  new_config.release();
-  delete_config(old_config);
-
   close_unused_inherited_addr(iaddrs);
 
   // Send last worker process a graceful shutdown notice

src/shrpx_config.cc

@@ -60,41 +60,35 @@
 namespace shrpx {
 
 namespace {
-Config *config = nullptr;
+std::unique_ptr<Config> config;
 } // namespace
 
 constexpr auto SHRPX_UNIX_PATH_PREFIX = StringRef::from_lit("unix:");
 
-const Config *get_config() { return config; }
+const Config *get_config() { return config.get(); }
 
-Config *mod_config() { return config; }
+Config *mod_config() { return config.get(); }
 
-Config *replace_config(Config *new_config) {
-  std::swap(config, new_config);
-  return new_config;
+std::unique_ptr<Config> replace_config(std::unique_ptr<Config> another) {
+  config.swap(another);
+  return another;
 }
 
-void create_config() { config = new Config(); }
+void create_config() { config = make_unique<Config>(); }
 
-void delete_config(Config *config) {
-  if (config == nullptr) {
-    return;
-  }
-
-  auto &http2conf = config->http2;
-
-  auto &upstreamconf = http2conf.upstream;
+Config::~Config() {
+  auto &upstreamconf = http2.upstream;
 
   nghttp2_option_del(upstreamconf.option);
   nghttp2_option_del(upstreamconf.alt_mode_option);
   nghttp2_session_callbacks_del(upstreamconf.callbacks);
 
-  auto &downstreamconf = http2conf.downstream;
+  auto &downstreamconf = http2.downstream;
 
   nghttp2_option_del(downstreamconf.option);
   nghttp2_session_callbacks_del(downstreamconf.callbacks);
 
-  auto &dumpconf = http2conf.upstream.debug.dump;
+  auto &dumpconf = http2.upstream.debug.dump;
 
   if (dumpconf.request_header) {
     fclose(dumpconf.request_header);
@@ -103,8 +97,6 @@ void delete_config(Config *config) {
   if (dumpconf.response_header) {
     fclose(dumpconf.response_header);
   }
-
-  delete config;
 }
 
 TicketKeys::~TicketKeys() {

src/shrpx_config.h

@@ -706,6 +706,8 @@ struct APIConfig {
 };
 
 struct Config {
+  ~Config();
+
   HttpProxy downstream_http_proxy;
   HttpConfig http;
   Http2Config http2;
@@ -734,9 +736,8 @@ const Config *get_config();
 Config *mod_config();
 // Replaces the current config with given |new_config|.  The old config is
 // returned.
-Config *replace_config(Config *new_config);
+std::unique_ptr<Config> replace_config(std::unique_ptr<Config> new_config);
 void create_config();
-void delete_config(Config *config);
 
 // generated by gennghttpxfun.py
 enum {