content: /*
   * Copyright 1999-2012 Alibaba Group.
   *  
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *  
   *      http://www.apache.org/licenses/LICENSE-2.0
   *  
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.alibaba.cobar.server.handler;
  
  import java.nio.ByteBuffer;
  import java.util.Set;
  
  import com.alibaba.cobar.config.ErrorCode;
  import com.alibaba.cobar.net.handler.FrontendPrivileges;
  import com.alibaba.cobar.net.mysql.OkPacket;
  import com.alibaba.cobar.server.ServerConnection;
  
  /**
   * @author xianmao.hexm
   */
  public final class UseHandler {
  
      public static void handle(String sql, ServerConnection c, int offset) {
          String schema = sql.substring(offset).trim();
          int length = schema.length();
          if (length > 0) {
              if (schema.charAt(0) == '`' && schema.charAt(length - 1) == '`') {
                  schema = schema.substring(1, length - 1);
              }
          }
  
          // 表示当前连接已经指定了schema
          if (c.getSchema() != null) {
              if (c.getSchema().equals(schema)) {
                  ByteBuffer buffer = c.allocate();
                  c.write(c.writeToBuffer(OkPacket.OK, buffer));
              } else {
                  c.writeErrMessage(ErrorCode.ER_DBACCESS_DENIED_ERROR, "Not allowed to change the database!");
              }
              return;
          }
  
          // 检查schema的有效性
          FrontendPrivileges privileges = c.getPrivileges();
          if (schema == null || !privileges.schemaExists(schema)) {
              c.writeErrMessage(ErrorCode.ER_BAD_DB_ERROR, "Unknown database '" + schema + "'");
              return;
          }
          String user = c.getUser();
          if (!privileges.userExists(user, c.getHost())) {
              c.writeErrMessage(ErrorCode.ER_ACCESS_DENIED_ERROR, "Access denied for user '" + c.getUser() + "'");
              return;
          }
          Set<String> schemas = privileges.getUserSchemas(user);
          if (schemas == null || schemas.size() == 0 || schemas.contains(schema)) {
              c.setSchema(schema);
              ByteBuffer buffer = c.allocate();
              c.write(c.writeToBuffer(OkPacket.OK, buffer));
          } else {
              String msg = "Access denied for user '" + c.getUser() + "' to database '" + schema + "'";
              c.writeErrMessage(ErrorCode.ER_DBACCESS_DENIED_ERROR, msg);
          }
      }
  
  }
  