content: /*
   * Copyright (c) 2010, 2021, Oracle and/or its affiliates.
   *
   * This program is free software; you can redistribute it and/or modify it under
   * the terms of the GNU General Public License, version 2.0, as published by the
   * Free Software Foundation.
   *
   * This program is also distributed with certain software (including but not
   * limited to OpenSSL) that is licensed under separate terms, as designated in a
   * particular file or component or in included license documentation. The
   * authors of MySQL hereby grant you an additional permission to link the
   * program and your derivative works with the separately licensed software that
   * they have included with MySQL.
   *
   * Without limiting anything contained in the foregoing, this file, which is
   * part of MySQL Connector/J, is also subject to the Universal FOSS Exception,
   * version 1.0, a copy of which can be found at
   * http://oss.oracle.com/licenses/universal-foss-exception.
   *
   * 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, version 2.0,
   * for more details.
   *
   * You should have received a copy of the GNU General Public License along with
   * this program; if not, write to the Free Software Foundation, Inc.,
   * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
   */
  
  package com.mysql.cj.jdbc.ha;
  
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.sql.SQLException;
  import java.util.concurrent.Executor;
  
  import com.mysql.cj.conf.ConnectionUrl;
  import com.mysql.cj.conf.PropertyKey;
  import com.mysql.cj.exceptions.CJCommunicationsException;
  import com.mysql.cj.exceptions.CJException;
  import com.mysql.cj.exceptions.MysqlErrorNumbers;
  import com.mysql.cj.jdbc.ConnectionImpl;
  import com.mysql.cj.jdbc.JdbcConnection;
  import com.mysql.cj.jdbc.JdbcPropertySetImpl;
  import com.mysql.cj.jdbc.exceptions.CommunicationsException;
  import com.mysql.cj.jdbc.exceptions.SQLError;
  import com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping;
  import com.mysql.cj.util.Util;
  
  /**
   * A proxy for a dynamic com.mysql.cj.jdbc.JdbcConnection implementation that provides failover features for list of hosts. Connection switching occurs on
   * communications related exceptions and/or user defined settings, namely when one of the conditions set in 'secondsBeforeRetrySource' or
   * 'queriesBeforeRetrySource' is met.
   */
  public class FailoverConnectionProxy extends MultiHostConnectionProxy {
      private static final String METHOD_SET_READ_ONLY = "setReadOnly";
      private static final String METHOD_SET_AUTO_COMMIT = "setAutoCommit";
      private static final String METHOD_COMMIT = "commit";
      private static final String METHOD_ROLLBACK = "rollback";
  
      private static final int NO_CONNECTION_INDEX = -1;
      private static final int DEFAULT_PRIMARY_HOST_INDEX = 0;
  
      private int secondsBeforeRetryPrimaryHost;
      private long queriesBeforeRetryPrimaryHost;
      private boolean failoverReadOnly;
      private int retriesAllDown;
  
      private int currentHostIndex = NO_CONNECTION_INDEX;
      private int primaryHostIndex = DEFAULT_PRIMARY_HOST_INDEX;
      private Boolean explicitlyReadOnly = null;
      private boolean explicitlyAutoCommit = true;
  
      private boolean enableFallBackToPrimaryHost = true;
      private long primaryHostFailTimeMillis = 0;
      private long queriesIssuedSinceFailover = 0;
  
      /**
       * Proxy class to intercept and deal with errors that may occur in any object bound to the current connection.
       * Additionally intercepts query executions and triggers an execution count on the outer class.
       */
      class FailoverJdbcInterfaceProxy extends JdbcInterfaceProxy {
          FailoverJdbcInterfaceProxy(Object toInvokeOn) {
              super(toInvokeOn);
          }
  
          @SuppressWarnings("synthetic-access")
          @Override
          public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
              String methodName = method.getName();
  
              boolean isExecute = methodName.startsWith("execute");
  
              if (FailoverConnectionProxy.this.connectedToSecondaryHost() && isExecute) {
                  FailoverConnectionProxy.this.incrementQueriesIssuedSinceFailover();
              }
  
              Object result = super.invoke(proxy, method, args);
  
              if (FailoverConnectionProxy.this.explicitlyAutoCommit && isExecute && readyToFallBackToPrimaryHost()) {
                  // Fall back to primary host at transaction boundary
                  fallBackToPrimaryIfAvailable();
              }
  
              return result;
          }
      }
  
      public static JdbcConnection createProxyInstance(ConnectionUrl connectionUrl) throws SQLException {
          FailoverConnectionProxy connProxy = new FailoverConnectionProxy(connectionUrl);
  
          return (JdbcConnection) java.lang.reflect.Proxy.newProxyInstance(JdbcConnection.class.getClassLoader(), new Class<?>[] { JdbcConnection.class },
                  connProxy);
      }
  
      /**
       * Instantiates a new FailoverConnectionProxy for the given list of hosts and connection properties.
       * 
       * @param connectionUrl
       *            {@link ConnectionUrl} instance containing the lists of hosts available to switch on.
       * @throws SQLException
       *             if an error occurs
       */
      private FailoverConnectionProxy(ConnectionUrl connectionUrl) throws SQLException {
          super(connectionUrl);
  
          JdbcPropertySetImpl connProps = new JdbcPropertySetImpl();
          connProps.initializeProperties(connectionUrl.getConnectionArgumentsAsProperties());
  
          this.secondsBeforeRetryPrimaryHost = connProps.getIntegerProperty(PropertyKey.secondsBeforeRetrySource).getValue();
          this.queriesBeforeRetryPrimaryHost = connProps.getIntegerProperty(PropertyKey.queriesBeforeRetrySource).getValue();
          this.failoverReadOnly = connProps.getBooleanProperty(PropertyKey.failOverReadOnly).getValue();
          this.retriesAllDown = connProps.getIntegerProperty(PropertyKey.retriesAllDown).getValue();
  
          this.enableFallBackToPrimaryHost = this.secondsBeforeRetryPrimaryHost > 0 || this.queriesBeforeRetryPrimaryHost > 0;
  
          pickNewConnection();
  
          this.explicitlyAutoCommit = this.currentConnection.getAutoCommit();
      }
  
      /**
       * Gets locally bound instances of FailoverJdbcInterfaceProxy.
       * 
       */
      @Override
      JdbcInterfaceProxy getNewJdbcInterfaceProxy(Object toProxy) {
          return new FailoverJdbcInterfaceProxy(toProxy);
      }
  
      /*
       * Local implementation for the connection switch exception checker.
       */
      @Override
      boolean shouldExceptionTriggerConnectionSwitch(Throwable t) {
  
          String sqlState = null;
          if (t instanceof CommunicationsException || t instanceof CJCommunicationsException) {
              return true;
          } else if (t instanceof SQLException) {
              sqlState = ((SQLException) t).getSQLState();
          } else if (t instanceof CJException) {
              sqlState = ((CJException) t).getSQLState();
          }
  
          if (sqlState != null) {
              if (sqlState.startsWith("08")) {
                  // connection error
                  return true;
              }
          }
  
          return false;
      }
  
      /**
       * Checks if current connection is to a source host.
       */
      @Override
      boolean isSourceConnection() {
          return connectedToPrimaryHost();
      }
  
      /*
       * Local implementation for the new connection picker.
       */
      @Override
      synchronized void pickNewConnection() throws SQLException {
          if (this.isClosed && this.closedExplicitly) {
              return;
          }
  
          if (!isConnected() || readyToFallBackToPrimaryHost()) {
              try {
                  connectTo(this.primaryHostIndex);
              } catch (SQLException e) {
                  resetAutoFallBackCounters();
                  failOver(this.primaryHostIndex);
              }
          } else {
              failOver();
          }
      }
  
      /**
       * Creates a new connection instance for host pointed out by the given host index.
       * 
       * @param hostIndex
       *            The host index in the global hosts list.
       * @return
       *         The new connection instance.
       * @throws SQLException
       *             if an error occurs
       */
      synchronized ConnectionImpl createConnectionForHostIndex(int hostIndex) throws SQLException {
          return createConnectionForHost(this.hostsList.get(hostIndex));
      }
  
      /**
       * Connects this dynamic failover connection proxy to the host pointed out by the given host index.
       * 
       * @param hostIndex
       *            The host index in the global hosts list.
       * @throws SQLException
       *             if an error occurs
       */
      private synchronized void connectTo(int hostIndex) throws SQLException {
          try {
              switchCurrentConnectionTo(hostIndex, createConnectionForHostIndex(hostIndex));
          } catch (SQLException e) {
              if (this.currentConnection != null) {
                  StringBuilder msg = new StringBuilder("Connection to ").append(isPrimaryHostIndex(hostIndex) ? "primary" : "secondary").append(" host '")
                          .append(this.hostsList.get(hostIndex)).append("' failed");
                  try {
                      this.currentConnection.getSession().getLog().logWarn(msg.toString(), e);
                  } catch (CJException ex) {
                      throw SQLExceptionsMapping.translateException(e, this.currentConnection.getExceptionInterceptor());
                  }
              }
              throw e;
          }
      }
  
      /**
       * Replaces the previous underlying connection by the connection given. State from previous connection, if any, is synchronized with the new one.
       * 
       * @param hostIndex
       *            The host index in the global hosts list that matches the given connection.
       * @param connection
       *            The connection instance to switch to.
       * @throws SQLException
       *             if an error occurs
       */
      private synchronized void switchCurrentConnectionTo(int hostIndex, JdbcConnection connection) throws SQLException {
          invalidateCurrentConnection();
  
          boolean readOnly;
          if (isPrimaryHostIndex(hostIndex)) {
              readOnly = this.explicitlyReadOnly == null ? false : this.explicitlyReadOnly;
          } else if (this.failoverReadOnly) {
              readOnly = true;
          } else if (this.explicitlyReadOnly != null) {
              readOnly = this.explicitlyReadOnly;
          } else if (this.currentConnection != null) {
              readOnly = this.currentConnection.isReadOnly();
          } else {
              readOnly = false;
          }
          syncSessionState(this.currentConnection, connection, readOnly);
          this.currentConnection = connection;
          this.currentHostIndex = hostIndex;
      }
  
      /**
       * Initiates a default failover procedure starting at the current connection host index.
       * 
       * @throws SQLException
       *             if an error occurs
       */
      private synchronized void failOver() throws SQLException {
          failOver(this.currentHostIndex);
      }
  
      /**
       * Initiates a default failover procedure starting at the given host index.
       * This process tries to connect, sequentially, to the next host in the list. The primary host may or may not be excluded from the connection attempts.
       * 
       * @param failedHostIdx
       *            The host index where to start from. First connection attempt will be the next one.
       * @throws SQLException
       *             if an error occurs
       */
      private synchronized void failOver(int failedHostIdx) throws SQLException {
          int prevHostIndex = this.currentHostIndex;
          int nextHostIndex = nextHost(failedHostIdx, false);
          int firstHostIndexTried = nextHostIndex;
  
          SQLException lastExceptionCaught = null;
          int attempts = 0;
          boolean gotConnection = false;
          boolean firstConnOrPassedByPrimaryHost = prevHostIndex == NO_CONNECTION_INDEX || isPrimaryHostIndex(prevHostIndex);
          do {
              try {
                  firstConnOrPassedByPrimaryHost = firstConnOrPassedByPrimaryHost || isPrimaryHostIndex(nextHostIndex);
  
                  connectTo(nextHostIndex);
  
                  if (firstConnOrPassedByPrimaryHost && connectedToSecondaryHost()) {
                      resetAutoFallBackCounters();
                  }
                  gotConnection = true;
  
              } catch (SQLException e) {
                  lastExceptionCaught = e;
  
                  if (shouldExceptionTriggerConnectionSwitch(e)) {
                      int newNextHostIndex = nextHost(nextHostIndex, attempts > 0);
  
                      if (newNextHostIndex == firstHostIndexTried && newNextHostIndex == (newNextHostIndex = nextHost(nextHostIndex, true))) { // Full turn
                          attempts++;
  
                          try {
                              Thread.sleep(250);
                          } catch (InterruptedException ie) {
                          }
                      }
  
                      nextHostIndex = newNextHostIndex;
  
                  } else {
                      throw e;
                  }
              }
          } while (attempts < this.retriesAllDown && !gotConnection);
  
          if (!gotConnection) {
              throw lastExceptionCaught;
          }
      }
  
      /**
       * Falls back to primary host or keep current connection if primary not available.
       */
      synchronized void fallBackToPrimaryIfAvailable() {
          JdbcConnection connection = null;
          try {
              connection = createConnectionForHostIndex(this.primaryHostIndex);
              switchCurrentConnectionTo(this.primaryHostIndex, connection);
          } catch (SQLException e1) {
              if (connection != null) {
                  try {
                      connection.close();
                  } catch (SQLException e2) {
                  }
              }
              // Keep current connection and reset counters
              resetAutoFallBackCounters();
          }
      }
  
      /**
       * Gets the next host on the hosts list. Uses a round-robin algorithm to find the next element, but it may skip the index for the primary host.
       * General rules to include the primary host are:
       * - not currently connected to any host.
       * - primary host is vouched (usually because connection to all secondary hosts has failed).
       * - conditions to fall back to primary host are met (or they are disabled).
       * 
       * @param currHostIdx
       *            Current host index.
       * @param vouchForPrimaryHost
       *            Allows to return the primary host index even if the usual required conditions aren't met.
       * @return next host index
       */
      private int nextHost(int currHostIdx, boolean vouchForPrimaryHost) {
          int nextHostIdx = (currHostIdx + 1) % this.hostsList.size();
          if (isPrimaryHostIndex(nextHostIdx) && isConnected() && !vouchForPrimaryHost && this.enableFallBackToPrimaryHost && !readyToFallBackToPrimaryHost()) {
              // Skip primary host, assume this.hostList.size() >= 2
              nextHostIdx = nextHost(nextHostIdx, vouchForPrimaryHost);
          }
          return nextHostIdx;
      }
  
      /**
       * Increments counter for query executions.
       */
      synchronized void incrementQueriesIssuedSinceFailover() {
          this.queriesIssuedSinceFailover++;
      }
  
      /**
       * Checks if at least one of the required conditions to fall back to primary host is met, which is determined by the properties 'queriesBeforeRetrySource'
       * and 'secondsBeforeRetrySource'.
       * 
       * @return true if ready
       */
      synchronized boolean readyToFallBackToPrimaryHost() {
          return this.enableFallBackToPrimaryHost && connectedToSecondaryHost() && (secondsBeforeRetryPrimaryHostIsMet() || queriesBeforeRetryPrimaryHostIsMet());
      }
  
      /**
       * Checks if there is a underlying connection for this proxy.
       * 
       * @return true if there is a connection
       */
      synchronized boolean isConnected() {
          return this.currentHostIndex != NO_CONNECTION_INDEX;
      }
  
      /**
       * Checks if the given host index points to the primary host.
       * 
       * @param hostIndex
       *            The host index in the global hosts list.
       * @return true if so
       */
      synchronized boolean isPrimaryHostIndex(int hostIndex) {
          return hostIndex == this.primaryHostIndex;
      }
  
      /**
       * Checks if this proxy is using the primary host in the underlying connection.
       * 
       * @return true if so
       */
      synchronized boolean connectedToPrimaryHost() {
          return isPrimaryHostIndex(this.currentHostIndex);
      }
  
      /**
       * Checks if this proxy is using a secondary host in the underlying connection.
       * 
       * @return true if so
       */
      synchronized boolean connectedToSecondaryHost() {
          return this.currentHostIndex >= 0 && !isPrimaryHostIndex(this.currentHostIndex);
      }
  
      /**
       * Checks the condition set by the property 'secondsBeforeRetrySource'.
       * 
       * @return value
       */
      private synchronized boolean secondsBeforeRetryPrimaryHostIsMet() {
          return this.secondsBeforeRetryPrimaryHost > 0 && Util.secondsSinceMillis(this.primaryHostFailTimeMillis) >= this.secondsBeforeRetryPrimaryHost;
      }
  
      /**
       * Checks the condition set by the property 'queriesBeforeRetrySource'.
       * 
       * @return value
       */
      private synchronized boolean queriesBeforeRetryPrimaryHostIsMet() {
          return this.queriesBeforeRetryPrimaryHost > 0 && this.queriesIssuedSinceFailover >= this.queriesBeforeRetryPrimaryHost;
      }
  
      /**
       * Resets auto-fall back counters.
       */
      private synchronized void resetAutoFallBackCounters() {
          this.primaryHostFailTimeMillis = System.currentTimeMillis();
          this.queriesIssuedSinceFailover = 0;
      }
  
      /**
       * Closes current connection.
       * 
       * @throws SQLException
       *             if an error occurs
       */
      @Override
      synchronized void doClose() throws SQLException {
          this.currentConnection.close();
      }
  
      /**
       * Aborts current connection.
       * 
       * @throws SQLException
       *             if an error occurs
       */
      @Override
      synchronized void doAbortInternal() throws SQLException {
          this.currentConnection.abortInternal();
      }
  
      /**
       * Aborts current connection using the given executor.
       * 
       * @throws SQLException
       *             if an error occurs
       */
      @Override
      synchronized void doAbort(Executor executor) throws SQLException {
          this.currentConnection.abort(executor);
      }
  
      /*
       * Local method invocation handling for this proxy.
       * This is the continuation of MultiHostConnectionProxy#invoke(Object, Method, Object[]).
       */
      @Override
      public Object invokeMore(Object proxy, Method method, Object[] args) throws Throwable {
          String methodName = method.getName();
  
          if (METHOD_SET_READ_ONLY.equals(methodName)) {
              this.explicitlyReadOnly = (Boolean) args[0];
              if (this.failoverReadOnly && connectedToSecondaryHost()) {
                  return null;
              }
          }
  
          if (this.isClosed && !allowedOnClosedConnection(method)) {
              if (this.autoReconnect && !this.closedExplicitly) {
                  this.currentHostIndex = NO_CONNECTION_INDEX; // Act as if this is the first connection but let it sync with the previous one.
                  pickNewConnection();
                  this.isClosed = false;
                  this.closedReason = null;
              } else {
                  String reason = "No operations allowed after connection closed.";
                  if (this.closedReason != null) {
                      reason += ("  " + this.closedReason);
                  }
                  throw SQLError.createSQLException(reason, MysqlErrorNumbers.SQL_STATE_CONNECTION_NOT_OPEN, null /* no access to a interceptor here... */);
              }
          }
  
          Object result = null;
  
          try {
              result = method.invoke(this.thisAsConnection, args);
              result = proxyIfReturnTypeIsJdbcInterface(method.getReturnType(), result);
          } catch (InvocationTargetException e) {
              dealWithInvocationException(e);
          }
  
          if (METHOD_SET_AUTO_COMMIT.equals(methodName)) {
              this.explicitlyAutoCommit = (Boolean) args[0];
          }
  
          if ((this.explicitlyAutoCommit || METHOD_COMMIT.equals(methodName) || METHOD_ROLLBACK.equals(methodName)) && readyToFallBackToPrimaryHost()) {
              // Fall back to primary host at transaction boundary
              fallBackToPrimaryIfAvailable();
          }
  
          return result;
      }
  }
  