campaignd: Add server id to server id request

[server_info] id= defines a free-form string that can be used to
identify the server instance independently from the campaignd version
used for it.

Meant for PR #5588, which requires an unchanging identification for
campaignd instances in lieu of game_config::wesnoth_version.

src/addon/client.cpp

@@ -50,6 +50,7 @@ addons_client::addons_client(const std::string& address)
 	, conn_(nullptr)
 	, last_error_()
 	, last_error_data_()
+	, server_id_()
 	, server_version_()
 	, server_capabilities_()
 	, server_url_()
@@ -82,6 +83,7 @@ void addons_client::connect()
 
 	if(!update_last_error(response_buf)) {
 		if(const auto& info = response_buf.child("server_id")) {
+			server_id_ = info["id"].str();
 			server_version_ = info["version"].str();
 
 			for(const auto& cap : utils::split(info["cap"].str())) {
@@ -96,14 +98,15 @@ void addons_client::connect()
 	}
 
 	if(server_version_.empty()) {
-		LOG_ADDONS << "Server version 1.15.7 or earlier\n";
 		// An educated guess
 		server_capabilities_ = { "auth:legacy" };
-	} else {
-		LOG_ADDONS << "Server version " << server_version_ << '\n';
 	}
 
-	LOG_ADDONS << "Server supports: " << utils::join(server_capabilities_, " ") << '\n';
+	const std::string version_desc = server_version_.empty() ? "<1.15.7 or earlier>" : server_version_;
+	const std::string id_desc = server_id_.empty() ? "<id not provided>" : server_id_;
+
+	LOG_ADDONS << "Server " << id_desc << " version " << version_desc
+			   << " supports: " << utils::join(server_capabilities_, " ") << '\n';
 }
 
 bool addons_client::request_addons_list(config& cfg)
@@ -599,6 +602,7 @@ void addons_client::clear_last_error()
 
 void addons_client::clear_server_info()
 {
+	server_id_.clear();
 	server_version_.clear();
 	server_capabilities_.clear();
 	server_url_.clear();

src/addon/client.hpp

@@ -216,6 +216,7 @@ private:
 	std::string last_error_;
 	std::string last_error_data_;
 
+	std::string server_id_;
 	std::string server_version_;
 	std::set<std::string> server_capabilities_;
 	std::string server_url_;

src/server/campaignd/server.cpp

@@ -271,6 +271,7 @@ server::server(const std::string& cfg_file, unsigned short port)
 	, strict_versions_(true)
 	, hooks_()
 	, handlers_()
+	, server_id_()
 	, feedback_url_format_()
 	, web_url_()
 	, license_notice_()
@@ -331,6 +332,7 @@ void server::load_config()
 	update_pack_lifespan_ = cfg_["update_pack_lifespan"].to_time_t(30 * 24 * 60 * 60);
 
 	if(const auto& svinfo_cfg = server_info()) {
+		server_id_ = svinfo_cfg["id"].str();
 		feedback_url_format_ = svinfo_cfg["feedback_url_format"].str();
 		web_url_ = svinfo_cfg["web_url"].str(default_web_url);
 		license_notice_ = svinfo_cfg["license_notice"].str(default_license_notice);
@@ -884,6 +886,7 @@ void server::handle_server_id(const server::request& req)
 
 	std::ostringstream ostr;
 	write(ostr, config{"server_id", config{
+		"id",					server_id_,
 		"cap",					utils::join(capabilities_),
 		"version",				game_config::revision,
 		"url",					web_url_,

src/server/campaignd/server.hpp

@@ -121,6 +121,8 @@ private:
 	std::map<std::string, std::string> hooks_;
 	request_handlers_table handlers_;
 
+	std::string server_id_;
+
 	std::string feedback_url_format_;
 
 	std::string web_url_;