? ? ? ? 我將插件設計為兩種類型。一種是框架自身攜帶的插件，用于增強其基礎能力。一種是用戶自定義插件，用于完成業務。本文將分別介紹在peleus框架下，這兩種插件該怎么寫。（轉載請指明出于breaksoftware的csdn博客）

? ? ? ? 本文談下框架自身攜帶的插件怎么寫。我們以操作mysql為例。

? ? ? ? 第一步把mysqlclient開發環境給準備好。

Wget https://downloads.mysql.com/archives/get/file/mysql-connector-c-6.1.11-src.tar.gz .
tar -zxvf mysql-connector-c-6.1.11-src.tar.gz
cd mysql-connector-c-6.1.11-src
cmake -G "Unix Makefiles"
cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=/usr
make
sudo make install

? ? ? ? 由于實際安裝到系統中的頭文件不全，我們還要從https://github.com/mysql/mysql-server/blob/5.6/include/hash.h把hash.h文件放到/usr/include下。

? ? ? ? 因為mysql-connector-c是C語言編碼，為了統一peleus下語言棧，我們將其封裝成一個類

#include "mysql_connection.h"
#include <butil/logging.h>
#include <errmsg.h>
#include "mysql_error.h"namespace peleus {
namespace plugins {
namespace mysql_conns {using peleus::plugins::configure::mysql_connection;MysqlConnection::MysqlConnection() {_conn = NULL;
}MysqlConnection::~MysqlConnection() {_disconnect();
}void MysqlConnection::init(const mysql_connection& conf) {_conf.CopyFrom(conf);
}int MysqlConnection::mysql_real_query(const std::string& sql) {int ret = 0;if (!_conn) {ret = _reconnct();if (ret) {return ret;}}LOG(INFO) << "query sql:" << sql.c_str();const int max_retry = 2;for (auto i = 0; i < max_retry; i++) {ret = ::mysql_real_query(_conn, sql.c_str(), sql.length());if (0 == ret) {break;}else if (i < max_retry - 1){LOG(INFO) << "mysql connection is lost.retry " << i;int ret_re = _reconnct();if (ret_re) {LOG(WARNING) << "mysql connection is lost.retry error" << ret_re;return ret_re;}}else if (ret != CR_SERVER_LOST && ret != CR_SERVER_GONE_ERROR) {LOG(ERROR) << "query error:" << ret << " sql:" << sql.c_str();return ret;}}return ret;
}MYSQL_RES* MysqlConnection::mysql_store_result() {if (_conn) {return ::mysql_store_result(_conn);}else {return NULL;}
}int MysqlConnection::_reconnct() {if (_conn) {_disconnect();}return _connect();
}int MysqlConnection::_connect() {_conn = mysql_init(NULL);if (!_conn) {return CR_OUT_OF_MEMORY;}unsigned long time_out = _conf.read_timeout();unsigned long conn_out = _conf.conn_timeout();mysql_options(_conn, MYSQL_OPT_READ_TIMEOUT, (char*)&time_out);mysql_options(_conn, MYSQL_OPT_CONNECT_TIMEOUT, (char*)&conn_out);if (!mysql_real_connect(_conn,_conf.host().c_str(),_conf.user().c_str(),_conf.password().c_str(),_conf.dbname().c_str(),_conf.port(),NULL, 0)){_disconnect();return CR_SERVER_GONE_ERROR;}int ret = mysql_set_character_set(_conn, _conf.character_set().c_str());if (ret) {_disconnect();}return ret;
}void MysqlConnection::_disconnect() {if (_conn) {mysql_close(_conn);_conn = NULL;}
}}
}
}

? ? ? ??MysqlConnection類主要對外提供連接和查詢數據庫的功能，并支持斷開重連功能。這是針對一個連接的，我們需要連接池來提高連接的使用率。

MysqlConnectionPool::MysqlConnectionPool() {
}MysqlConnectionPool::~MysqlConnectionPool() {for (auto it = _unused.begin(); it != _unused.end(); it++) {if (*it) {delete *it;*it = NULL;}}
}void MysqlConnectionPool::init(const peleus::plugins::configure::mysql_connection_pool& conf) {_conf.CopyFrom(conf);int size = _conf.size();if (size < 0) {_use_pool = false;return;}_use_pool = true;pthread_mutex_init(&_mutex, NULL);pthread_mutex_lock(&_mutex);for (int i = 0; i< size; i++) {MysqlConnection* conn = new MysqlConnection();conn->init(_conf.conn_info());_unused.push_back(conn);}pthread_mutex_unlock(&_mutex);
}int MysqlConnectionPool::query(const std::string& sql, MysqlSession& session) {if (_use_pool) {return query_from_pool(sql, session);}return query_once(sql, session);
}void MysqlConnectionPool::recovery(MysqlConnection* conn) {if (_use_pool) {pthread_mutex_lock(&_mutex);_unused.push_back(conn);pthread_mutex_unlock(&_mutex);}
}int MysqlConnectionPool::query_once(const std::string& sql, MysqlSession& session) {MysqlConnection conn;conn.init(_conf.conn_info());int ret = conn.mysql_real_query(sql);session._res = conn.mysql_store_result();return ret;
}int MysqlConnectionPool::query_from_pool(const std::string& sql, MysqlSession& session) {MysqlConnection* conn = NULL;pthread_mutex_lock(&_mutex);if (!_unused.empty()) {conn = _unused.back();_unused.pop_back();}pthread_mutex_unlock(&_mutex);if (!conn) {LOG(ERROR) << "need more connection";return LACK_CONNECTION;}int ret = conn->mysql_real_query(sql);session._res = conn->mysql_store_result();session._conn = conn;session._conn_pool = this;return ret;
}

? ? ? ??MysqlConnectionPool將空閑連接放在_unused中。當需要做查詢操作時，便從_unused中取出一個連接使用。但是連接池里的連接不能交由用戶管理，于是需要暴露query_from_pool方法，將連接隱藏起來。

? ? ? ? 由于業務可能需要連接多個數據庫，所以需要做一個針對多個數據庫的連接管理器

MysqlConns::MysqlConns() {
}MysqlConns::~MysqlConns() {for (auto it = _conns.begin(); it != _conns.end(); it++) {if (it->second) {delete it->second;it->second = NULL;}}
}void MysqlConns::init(const char* conf_floder_path) {TraversalCallback traversal_floder = [this](const char* path) {this->init(path);};TraversalCallback traversal_file = [this](const char* path) {this->init_from_file(path);};TraversalFloder traversal;traversal.set_callback(traversal_floder, traversal_file, __FILE__);traversal.init(conf_floder_path);
}void MysqlConns::init_from_file(const char* conf_path) {mysql_connection_pool config;bool suc = peleus::utils::file2conf(conf_path, config);if (!suc) {LOG(ERROR) << "init " << conf_path << " error";return;}const std::string& conn_name = config.name();MysqlConnectionPool* conn_pool = init_conn_pool(config);if (!conn_pool) {LOG(ERROR) << "init mysql connection pool error:" << conn_name;return;}_conns[conn_name] = conn_pool;
}MysqlConnectionPool* MysqlConns::init_conn_pool(const mysql_connection_pool& conf) {MysqlConnectionPool* conn_pool = new MysqlConnectionPool();conn_pool->init(conf);return conn_pool;
}int MysqlConns::query(const std::string& conn_name,const std::string& sql,MysqlSession& session)
{auto it = _conns.find(conn_name);if (it == _conns.end()) {LOG(ERROR) << "cant find mysql connection:" << conn_name.c_str();return NO_CONNECTION;}if (!it->second) {LOG(ERROR) << "mysql connection pool is null";return NULL_CONNECTION;}return it->second->query(sql, session);
}

? ? ? ? 至此，我們將mysql最基礎的操作部分給封裝完畢。現在開始寫插件

class MysqlVisitorService :public peleus::plugins::MysqlVisitorService,public peleus::entrance::Entrance
{
public:explicit MysqlVisitorService(const char* name);public:virtual void query(::google::protobuf::RpcController* controller,const ::peleus::plugins::MysqlVisitorServiceRequest* request,::peleus::plugins::MysqlVisitorServiceResponse* response,::google::protobuf::Closure* done) override;
public:virtual void on_init(const char* conf_path) final;virtual void reset() final;
private:void parse_res(MYSQL_RES* res,::peleus::plugins::MysqlVisitorServiceResponse* response);void parse_session(peleus::plugins::mysql_conns::MysqlSession& session,::peleus::plugins::MysqlVisitorServiceResponse* response);
};

? ? ? ??MysqlVisitorService將作為內部服務的一個業務邏輯存在，同時它也是一個入口，所以繼承于Entrance接口。MysqlVisitorService是protobuf產生的接口類

syntax="proto2";
option cc_generic_services = true;package peleus.plugins;message MysqlVisitorServiceRequest {required string conn_name = 1;required string command = 2;
};message MysqlVisitorRow {repeated string column = 1;
};message MysqlVisitorServiceResponse {required bool suc = 1;repeated MysqlVisitorRow rows = 2;
};service MysqlVisitorService {rpc query(MysqlVisitorServiceRequest) returns (MysqlVisitorServiceResponse);
};

? ? ? ??MysqlVisitorService的業務代碼就是query，其會調用MysqlConns類的方法去查詢結果，然后解析和封裝返回

MysqlVisitorService::MysqlVisitorService(const char* name) :peleus::entrance::Entrance(name) {
}void MysqlVisitorService::query(::google::protobuf::RpcController* controller,const ::peleus::plugins::MysqlVisitorServiceRequest* request,::peleus::plugins::MysqlVisitorServiceResponse* response,::google::protobuf::Closure* done)
{ClosureGuard done_guard(done);const std::string& conn_name = request->conn_name();const std::string& command = request->command();MysqlSession session;int ret = MysqlConns::get_mutable_instance().query(conn_name, command, session);parse_session(session, response);response->set_suc(0 == ret ? true : false);
}void MysqlVisitorService::parse_session(MysqlSession& session,::peleus::plugins::MysqlVisitorServiceResponse* response)
{MYSQL_RES* res = session._res;if (!res) {return;}int row_size = mysql_num_rows(res);for (int i = 0; i < row_size; i++) {parse_res(res, response);}
}void MysqlVisitorService::parse_res(MYSQL_RES* res,::peleus::plugins::MysqlVisitorServiceResponse* response)
{MysqlVisitorRow* row = response->add_rows();MYSQL_ROW res_row = mysql_fetch_row(res);if (!row) {LOG(ERROR) << "add_rows return null";return;}int field_size = mysql_num_fields(res);for (int i = 0; i < field_size; i++) {row->add_column(std::string(res_row[i]));}
}

? ? ? ? 最后在插件啟動代碼中加入注冊方法就行了

extern "C" {bool plugins_main(const char*);
};#define USE(x, y)   \if (item_conf.name() == x) {    \y::get_mutable_instance().init(item_conf.conf_path().c_str());    \}#define REG(x, y, z)    \if (item_conf.name() == x) {   \return register_class<y>(z);    \}bool load_moudle(const plugin_conf& item_conf) {if (!item_conf.on()) {return true;}REG("mysql_visitor_service", MysqlVisitorService, "MysqlVisitorService");return true;
}bool plugins_main(const char* conf_path) {plugins_conf config;bool suc = file2conf(conf_path, config);if (!suc) {LOG(ERROR) << "conv config error:" << conf_path;return false;}size_t size = config.conf_size();for (size_t i = 0; i < size; i++) {const plugin_conf& item_conf = config.conf(i);if (!load_moudle(item_conf)) {break;}}return true;
}

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