The minor extension made to the MySQL connector

Also added the utility class to handle simple query cases.

src/mysql/CMakeLists.txt

@@ -5,6 +5,7 @@ target_sources(mysql PRIVATE
     LocalInfile.cc
     MySqlConfig.cc
     MySqlConnection.cc
+    MySqlUtils.cc
     RowBuffer.cc
     SchemaFactory.cc
 )

src/mysql/MySqlConnection.cc

@@ -188,6 +188,19 @@ bool MySqlConnection::selectDb(std::string const& dbName) {
     return true;
 }
 
+std::vector<std::string> MySqlConnection::getColumnNames() const {
+    assert(_mysql);
+    assert(_mysql_res);
+    std::vector<std::string> names;
+    if (0 != mysql_field_count(_mysql)) {
+        auto fields = mysql_fetch_fields(_mysql_res);
+        for (unsigned int i = 0; i < mysql_num_fields(_mysql_res); i++) {
+            names.push_back(std::string(fields[i].name));
+        }
+    }
+    return names;
+}
+
 ////////////////////////////////////////////////////////////////////////
 // MySqlConnection
 // private:

src/mysql/MySqlConnection.h

@@ -33,6 +33,7 @@
 #include <memory>
 #include <mutex>
 #include <string>
+#include <vector>
 
 // Third-party headers
 #include "boost/utility.hpp"
@@ -80,6 +81,7 @@ class MySqlConnection : boost::noncopyable {
         assert(_mysql);
         return mysql_field_count(_mysql);
     }
+    std::vector<std::string> getColumnNames() const;
     unsigned int getErrno() const {
         assert(_mysql);
         return mysql_errno(_mysql);

src/mysql/MySqlUtils.cc

@@ -0,0 +1,95 @@
+// -*- LSST-C++ -*-
+/*
+ * LSST Data Management System
+ *
+ * This product includes software developed by the
+ * LSST Project (http://www.lsst.org/).
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the LSST License Statement and
+ * the GNU General Public License along with this program.  If not,
+ * see <http://www.lsstcorp.org/LegalNotices/>.
+ */
+
+// Class header
+#include "mysql/MySqlUtils.h"
+
+// System headers
+#include <string>
+
+// Third party headers
+#include <mysql/mysql.h>
+#include <mysql/mysqld_error.h>
+#include <mysql/errmsg.h>
+
+// Qserv headers
+#include "mysql/MySqlConfig.h"
+#include "mysql/MySqlConnection.h"
+
+using namespace std;
+using json = nlohmann::json;
+
+namespace {
+
+string errInfo(lsst::qserv::mysql::MySqlConnection const& conn) {
+    return "errno: " + to_string(conn.getErrno()) + ", error: " + conn.getError();
+}
+
+}  // anonymous namespace
+
+namespace lsst::qserv::mysql {
+
+json MySqlUtils::processList(MySqlConfig const& config, bool full) {
+    string const context = "MySqlUtils::" + string(__func__);
+    string const query = "SHOW" + string(full ? " FULL" : "") + " PROCESSLIST";
+
+    MySqlConnection conn(config);
+    if (!conn.connect()) {
+        string const err = context + " failed to connect to the worker database, " + ::errInfo(conn);
+        throw MySqlQueryError(err);
+    }
+    if (!conn.queryUnbuffered(query)) {
+        string const err = "failed to execute the query: '" + query + "', " + ::errInfo(conn);
+        throw MySqlQueryError(err);
+    }
+    json result;
+    result["queries"] = json::object({{"columns", json::array()}, {"rows", json::array()}});
+    int const numFields = conn.getResultFieldCount();
+    if (numFields > 0) {
+        result["queries"]["columns"] = conn.getColumnNames();
+        auto& rows = result["queries"]["rows"];
+        MYSQL_RES* mysqlResult = conn.getResult();
+        while (true) {
+            MYSQL_ROW mysqlRow = mysql_fetch_row(mysqlResult);
+            if (!mysqlRow) {
+                if (0 == conn.getErrno()) {
+                    // End of iteration if no specific error was reported.
+                    break;
+                }
+                string const err =
+                        context + " failed to fetch next row for query: '" + query + "', " + ::errInfo(conn);
+                throw MySqlQueryError(err);
+            }
+            size_t const* lengths = mysql_fetch_lengths(mysqlResult);
+            json row = json::array();
+            for (int i = 0; i < numFields; i++) {
+                // Report the empty string for SQL NULL.
+                auto const length = lengths[i];
+                row.push_back(length == 0 ? string() : string(mysqlRow[i], length));
+            }
+            rows.push_back(row);
+        }
+    }
+    return result;
+}
+
+}  // namespace lsst::qserv::mysql

src/mysql/MySqlUtils.h

@@ -0,0 +1,71 @@
+// -*- LSST-C++ -*-
+/*
+ * LSST Data Management System
+ *
+ * This product includes software developed by the
+ * LSST Project (http://www.lsst.org/).
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the LSST License Statement and
+ * the GNU General Public License along with this program.  If not,
+ * see <http://www.lsstcorp.org/LegalNotices/>.
+ */
+#ifndef LSST_QSERV_MYSQL_MYSQLUTILS_H
+#define LSST_QSERV_MYSQL_MYSQLUTILS_H
+
+// System headers
+#include <stdexcept>
+
+// Third-party headers
+#include "nlohmann/json.hpp"
+
+/// Forward declarations.
+namespace lsst::qserv::mysql {
+class MySqlConfig;
+}  // namespace lsst::qserv::mysql
+
+/// This header declarations.
+namespace lsst::qserv::mysql {
+
+/**
+ * Class MySqlQueryError represents exceptions to be throw on specific errors
+ * detected when attempting to execute the queries.
+ */
+class MySqlQueryError : public std::runtime_error {
+    using std::runtime_error::runtime_error;
+};
+
+/**
+ * Class MySqlUtils is the utility class providing a collection of useful queries reporting
+ * small result sets.
+ * @note Each tool of the collection does its own connection handling (opening/etc.).
+ */
+class MySqlUtils {
+public:
+    /**
+     * Report info on the on-going queries using 'SHOW [FULL] PROCESSLIST'.
+     * @param A scope of the operaton depends on the user credentials privided
+     *   in the configuration object. Normally, a subset of queries which belong
+     *   to the specified user will be reported.
+     * @param config Configuration parameters of the MySQL connector.
+     * @param full The optional modifier which (if set) allows seeing the full text
+     *   of the queries.
+     * @return A collection of queries encoded as the JSON object. Please, see the code
+     *   for further details on the schema of the object.
+     * @throws MySqlQueryError on errors detected during query execution/processing.
+     */
+    static nlohmann::json processList(MySqlConfig const& config, bool full = false);
+};
+
+}  // namespace lsst::qserv::mysql
+
+#endif  // LSST_QSERV_MYSQL_MYSQLUTILS_H