package org.postgresql;

import java.io.*;
import java.net.*;
import java.sql.*;
import java.util.*;
import java.security.*;
import org.postgresql.Field;
import org.postgresql.fastpath.*;
import org.postgresql.largeobject.*;
import org.postgresql.util.*;
import org.postgresql.core.*;

/**
 * $Id: Connection.java,v 1.34 2001/11/01 01:08:36 barry Exp $
 *
 * This abstract class is used by org.postgresql.Driver to open either the JDBC1 or
 * JDBC2 versions of the Connection class.
 *
 */
public abstract class Connection
{
	// This is the network stream associated with this connection
	public PG_Stream pg_stream;

	private String PG_HOST;
	private int PG_PORT;
	private String PG_USER;
	private String PG_PASSWORD;
	private String PG_DATABASE;
	private boolean PG_STATUS;
	private String compatible;

	/**
	 *	The encoding to use for this connection.
	 */
	private Encoding encoding = Encoding.defaultEncoding();

	private String dbVersionNumber;

	public boolean CONNECTION_OK = true;
	public boolean CONNECTION_BAD = false;

	public boolean autoCommit = true;
	public boolean readOnly = false;

	public Driver this_driver;
	private String this_url;
	private String cursor = null;	// The positioned update cursor name

	// These are new for v6.3, they determine the current protocol versions
	// supported by this version of the driver. They are defined in
	// src/include/libpq/pqcomm.h
	protected static final int PG_PROTOCOL_LATEST_MAJOR = 2;
	protected static final int PG_PROTOCOL_LATEST_MINOR = 0;
	private static final int SM_DATABASE	= 64;
	private static final int SM_USER	= 32;
	private static final int SM_OPTIONS = 64;
	private static final int SM_UNUSED	= 64;
	private static final int SM_TTY = 64;

	private static final int AUTH_REQ_OK = 0;
	private static final int AUTH_REQ_KRB4 = 1;
	private static final int AUTH_REQ_KRB5 = 2;
	private static final int AUTH_REQ_PASSWORD = 3;
	private static final int AUTH_REQ_CRYPT = 4;
        private static final int AUTH_REQ_MD5 = 5;

	// New for 6.3, salt value for crypt authorisation
	private String salt;

	// These are used to cache oids, PGTypes and SQLTypes
	private static Hashtable sqlTypeCache = new Hashtable();  // oid -> SQLType
	private static Hashtable pgTypeCache = new Hashtable();  // oid -> PGType
	private static Hashtable typeOidCache = new Hashtable();  //PGType -> oid

	// Now handle notices as warnings, so things like "show" now work
	public SQLWarning firstWarning = null;

	/**
	 * Cache of the current isolation level
	 */
	private int isolationLevel = java.sql.Connection.TRANSACTION_READ_COMMITTED;

	// The PID an cancellation key we get from the backend process
	public int pid;
	public int ckey;

	/**
	 * This is called by Class.forName() from within org.postgresql.Driver
	 */
	public Connection()
	{}

	/**
	 * This method actually opens the connection. It is called by Driver.
	 *
	 * @param host the hostname of the database back end
	 * @param port the port number of the postmaster process
	 * @param info a Properties[] thing of the user and password
	 * @param database the database to connect to
	 * @param u the URL of the connection
	 * @param d the Driver instantation of the connection
	 * @return a valid connection profile
	 * @exception SQLException if a database access error occurs
	 */
	protected void openConnection(String host, int port, Properties info, String database, String url, Driver d) throws SQLException
	{
		// Throw an exception if the user or password properties are missing
		// This occasionally occurs when the client uses the properties version
		// of getConnection(), and is a common question on the email lists
		if (info.getProperty("user") == null)
			throw new PSQLException("postgresql.con.user");

		this_driver = d;
		this_url = url;
		PG_DATABASE = database;
		PG_USER = info.getProperty("user");
                PG_PASSWORD = info.getProperty("password","");
		PG_PORT = port;
		PG_HOST = host;
		PG_STATUS = CONNECTION_BAD;
		if (info.getProperty("compatible") == null)
		{
			compatible = d.getMajorVersion() + "." + d.getMinorVersion();
		}
		else
		{
			compatible = info.getProperty("compatible");
		}

		// Now make the initial connection
		try
		{
			pg_stream = new PG_Stream(host, port);
		}
		catch (ConnectException cex)
		{
			// Added by Peter Mount <peter@retep.org.uk>
			// ConnectException is thrown when the connection cannot be made.
			// we trap this an return a more meaningful message for the end user
			throw new PSQLException ("postgresql.con.refused");
		}
		catch (IOException e)
		{
			throw new PSQLException ("postgresql.con.failed", e);
		}

		// Now we need to construct and send a startup packet
		try
		{
			// Ver 6.3 code
			pg_stream.SendInteger(4 + 4 + SM_DATABASE + SM_USER + SM_OPTIONS + SM_UNUSED + SM_TTY, 4);
			pg_stream.SendInteger(PG_PROTOCOL_LATEST_MAJOR, 2);
			pg_stream.SendInteger(PG_PROTOCOL_LATEST_MINOR, 2);
			pg_stream.Send(database.getBytes(), SM_DATABASE);

			// This last send includes the unused fields
			pg_stream.Send(PG_USER.getBytes(), SM_USER + SM_OPTIONS + SM_UNUSED + SM_TTY);

			// now flush the startup packets to the backend
			pg_stream.flush();

			// Now get the response from the backend, either an error message
			// or an authentication request
			int areq = -1; // must have a value here
			do
			{
				int beresp = pg_stream.ReceiveChar();
				switch (beresp)
				{
				case 'E':
					// An error occured, so pass the error message to the
					// user.
					//
					// The most common one to be thrown here is:
					// "User authentication failed"
					//
					throw new SQLException(pg_stream.ReceiveString(encoding));

				case 'R':
					// Get the type of request
					areq = pg_stream.ReceiveIntegerR(4);

					// Get the crypt password salt if there is one
					if (areq == AUTH_REQ_CRYPT)
					{
						byte[] rst = new byte[2];
						rst[0] = (byte)pg_stream.ReceiveChar();
						rst[1] = (byte)pg_stream.ReceiveChar();
						salt = new String(rst, 0, 2);
						DriverManager.println("Crypt salt=" + salt);
					}

					// Or get the md5 password salt if there is one
					if (areq == AUTH_REQ_MD5)
					{
						byte[] rst = new byte[4];
						rst[0] = (byte)pg_stream.ReceiveChar();
						rst[1] = (byte)pg_stream.ReceiveChar();
						rst[2] = (byte)pg_stream.ReceiveChar();
						rst[3] = (byte)pg_stream.ReceiveChar();
						salt = new String(rst, 0, 4);
						DriverManager.println("MD5 salt=" + salt);
					}

					// now send the auth packet
					switch (areq)
					{
					case AUTH_REQ_OK:
					    break;
						
					case AUTH_REQ_KRB4:
						DriverManager.println("postgresql: KRB4");
						throw new PSQLException("postgresql.con.kerb4");

					case AUTH_REQ_KRB5:
						DriverManager.println("postgresql: KRB5");
						throw new PSQLException("postgresql.con.kerb5");

					case AUTH_REQ_PASSWORD:
						DriverManager.println("postgresql: PASSWORD");
						pg_stream.SendInteger(5 + PG_PASSWORD.length(), 4);
						pg_stream.Send(PG_PASSWORD.getBytes());
						pg_stream.SendInteger(0, 1);
						pg_stream.flush();
						break;

					case AUTH_REQ_CRYPT:
						DriverManager.println("postgresql: CRYPT");
						String crypted = UnixCrypt.crypt(salt, PG_PASSWORD);
						pg_stream.SendInteger(5 + crypted.length(), 4);
						pg_stream.Send(crypted.getBytes());
						pg_stream.SendInteger(0, 1);
						pg_stream.flush();
						break;

					case AUTH_REQ_MD5:
					        try {
						    MessageDigest md = MessageDigest.getInstance("MD5");
						    byte[] temp_digest, pass_digest;
						    byte[] hex_digest = new byte[35];

						    DriverManager.println("postgresql: MD5");

						    md.update(PG_PASSWORD.getBytes());
						    md.update(PG_USER.getBytes());
						    temp_digest = md.digest();

						    bytesToHex(temp_digest, hex_digest, 0);
						    md.update(hex_digest, 0, 32);
						    md.update(salt.getBytes());
						    pass_digest = md.digest();

						    bytesToHex(pass_digest, hex_digest, 3);
						    hex_digest[0] = 'm'; hex_digest[1] = 'd'; hex_digest[2] = '5';

						    pg_stream.SendInteger(5 + hex_digest.length, 4);
						    pg_stream.Send(hex_digest);
						    pg_stream.SendInteger(0, 1);
						    pg_stream.flush();
						} catch (Exception e) {
						    ; // "MessageDigest failure; " + e
						}
						break;

					default:
						throw new PSQLException("postgresql.con.auth", new Integer(areq));
					}
					break;

				default:
					throw new PSQLException("postgresql.con.authfail");
				}
			}
			while (areq != AUTH_REQ_OK);

		}
		catch (IOException e)
		{
			throw new PSQLException("postgresql.con.failed", e);
		}


		// As of protocol version 2.0, we should now receive the cancellation key and the pid
		int beresp = pg_stream.ReceiveChar();
		switch (beresp)
		{
		case 'K':
			pid = pg_stream.ReceiveInteger(4);
			ckey = pg_stream.ReceiveInteger(4);
			break;
		case 'E':
		case 'N':
			throw new SQLException(pg_stream.ReceiveString(encoding));
		default:
			throw new PSQLException("postgresql.con.setup");
		}

		// Expect ReadyForQuery packet
		beresp = pg_stream.ReceiveChar();
		switch (beresp)
		{
		case 'Z':
			break;
		case 'E':
		case 'N':
			throw new SQLException(pg_stream.ReceiveString(encoding));
		default:
			throw new PSQLException("postgresql.con.setup");
		}

		firstWarning = null;

		// "pg_encoding_to_char(1)" will return 'EUC_JP' for a backend compiled with multibyte,
		// otherwise it's hardcoded to 'SQL_ASCII'.
		// If the backend doesn't know about multibyte we can't assume anything about the encoding
		// used, so we denote this with 'UNKNOWN'.
		//Note: begining with 7.2 we should be using pg_client_encoding() which
		//is new in 7.2.  However it isn't easy to conditionally call this new
		//function, since we don't yet have the information as to what server
		//version we are talking to.  Thus we will continue to call
		//getdatabaseencoding() until we drop support for 7.1 and older versions
		//or until someone comes up with a conditional way to run one or
		//the other function depending on server version that doesn't require
		//two round trips to the server per connection

		final String encodingQuery =
			"case when pg_encoding_to_char(1) = 'SQL_ASCII' then 'UNKNOWN' else getdatabaseencoding() end";

		// Set datestyle and fetch db encoding in a single call, to avoid making
		// more than one round trip to the backend during connection startup.

		java.sql.ResultSet resultSet =
			ExecSQL("set datestyle to 'ISO'; select version(), " + encodingQuery + ";");

		if (! resultSet.next())
		{
			throw new PSQLException("postgresql.con.failed", "failed getting backend encoding");
		}
		String version = resultSet.getString(1);
		dbVersionNumber = extractVersionNumber(version);

		String dbEncoding = resultSet.getString(2);
		encoding = Encoding.getEncoding(dbEncoding, info.getProperty("charSet"));

		// Initialise object handling
		initObjectTypes();

		// Mark the connection as ok, and cleanup
		firstWarning = null;
		PG_STATUS = CONNECTION_OK;
	}

        private static void bytesToHex(byte[] bytes, byte[] hex, int offset)
        {
	        final char lookup[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
					'a', 'b', 'c', 'd', 'e', 'f' };

		int i, c, j, pos = offset;

		for (i = 0; i < 16; i++) {
		    c = bytes[i] & 0xFF; j = c >> 4;
		    hex[pos++] = (byte) lookup[j];
		    j = (c & 0xF);
		    hex[pos++] = (byte) lookup[j];
		}
        }

	// These methods used to be in the main Connection implementation. As they
	// are common to all implementations (JDBC1 or 2), they are placed here.
	// This should make it easy to maintain the two specifications.

	/**
	 * This adds a warning to the warning chain.
	 * @param msg message to add
	 */
	public void addWarning(String msg)
	{
		DriverManager.println(msg);

		// Add the warning to the chain
		if (firstWarning != null)
			firstWarning.setNextWarning(new SQLWarning(msg));
		else
			firstWarning = new SQLWarning(msg);

		// Now check for some specific messages

		// This is obsolete in 6.5, but I've left it in here so if we need to use this
		// technique again, we'll know where to place it.
		//
		// This is generated by the SQL "show datestyle"
		//if(msg.startsWith("NOTICE:") && msg.indexOf("DateStyle")>0) {
		//// 13 is the length off "DateStyle is "
		//msg = msg.substring(msg.indexOf("DateStyle is ")+13);
		//
		//for(int i=0;i<dateStyles.length;i+=2)
		//if(msg.startsWith(dateStyles[i]))
		//currentDateStyle=i+1; // this is the index of the format
		//}
	}

	/**
	 * Send a query to the backend.  Returns one of the ResultSet
	 * objects.
	 *
	 * <B>Note:</B> there does not seem to be any method currently
	 * in existance to return the update count.
	 *
	 * @param sql the SQL statement to be executed
	 * @return a ResultSet holding the results
	 * @exception SQLException if a database error occurs
	 */
	public java.sql.ResultSet ExecSQL(String sql) throws SQLException
	{
		return ExecSQL(sql, null);
	}

	/**
	 * Send a query to the backend.  Returns one of the ResultSet
	 * objects.
	 *
	 * <B>Note:</B> there does not seem to be any method currently
	 * in existance to return the update count.
	 *
	 * @param sql the SQL statement to be executed
	 * @param stat The Statement associated with this query (may be null)
	 * @return a ResultSet holding the results
	 * @exception SQLException if a database error occurs
	 */
	public java.sql.ResultSet ExecSQL(String sql, java.sql.Statement stat) throws SQLException
	{
		return new QueryExecutor(sql, stat, pg_stream, this).execute();
	}

	/**
	 * In SQL, a result table can be retrieved through a cursor that
	 * is named.  The current row of a result can be updated or deleted
	 * using a positioned update/delete statement that references the
	 * cursor name.
	 *
	 * We support one cursor per connection.
	 *
	 * setCursorName sets the cursor name.
	 *
	 * @param cursor the cursor name
	 * @exception SQLException if a database access error occurs
	 */
	public void setCursorName(String cursor) throws SQLException
	{
		this.cursor = cursor;
	}

	/**
	 * getCursorName gets the cursor name.
	 *
	 * @return the current cursor name
	 * @exception SQLException if a database access error occurs
	 */
	public String getCursorName() throws SQLException
	{
		return cursor;
	}

	/**
	 * We are required to bring back certain information by
	 * the DatabaseMetaData class.	These functions do that.
	 *
	 * Method getURL() brings back the URL (good job we saved it)
	 *
	 * @return the url
	 * @exception SQLException just in case...
	 */
	public String getURL() throws SQLException
	{
		return this_url;
	}

	/**
	 * Method getUserName() brings back the User Name (again, we
	 * saved it)
	 *
	 * @return the user name
	 * @exception SQLException just in case...
	 */
	public String getUserName() throws SQLException
	{
		return PG_USER;
	}

	/**
	 * Get the character encoding to use for this connection.
	 */
	public Encoding getEncoding() throws SQLException
	{
		return encoding;
	}

	/**
	 * This returns the Fastpath API for the current connection.
	 *
	 * <p><b>NOTE:</b> This is not part of JDBC, but allows access to
	 * functions on the org.postgresql backend itself.
	 *
	 * <p>It is primarily used by the LargeObject API
	 *
	 * <p>The best way to use this is as follows:
	 *
	 * <p><pre>
	 * import org.postgresql.fastpath.*;
	 * ...
	 * Fastpath fp = ((org.postgresql.Connection)myconn).getFastpathAPI();
	 * </pre>
	 *
	 * <p>where myconn is an open Connection to org.postgresql.
	 *
	 * @return Fastpath object allowing access to functions on the org.postgresql
	 * backend.
	 * @exception SQLException by Fastpath when initialising for first time
	 */
	public Fastpath getFastpathAPI() throws SQLException
	{
		if (fastpath == null)
			fastpath = new Fastpath(this, pg_stream);
		return fastpath;
	}

	// This holds a reference to the Fastpath API if already open
	private Fastpath fastpath = null;

	/**
	 * This returns the LargeObject API for the current connection.
	 *
	 * <p><b>NOTE:</b> This is not part of JDBC, but allows access to
	 * functions on the org.postgresql backend itself.
	 *
	 * <p>The best way to use this is as follows:
	 *
	 * <p><pre>
	 * import org.postgresql.largeobject.*;
	 * ...
	 * LargeObjectManager lo = ((org.postgresql.Connection)myconn).getLargeObjectAPI();
	 * </pre>
	 *
	 * <p>where myconn is an open Connection to org.postgresql.
	 *
	 * @return LargeObject object that implements the API
	 * @exception SQLException by LargeObject when initialising for first time
	 */
	public LargeObjectManager getLargeObjectAPI() throws SQLException
	{
		if (largeobject == null)
			largeobject = new LargeObjectManager(this);
		return largeobject;
	}

	// This holds a reference to the LargeObject API if already open
	private LargeObjectManager largeobject = null;

	/**
	 * This method is used internally to return an object based around
	 * org.postgresql's more unique data types.
	 *
	 * <p>It uses an internal Hashtable to get the handling class. If the
	 * type is not supported, then an instance of org.postgresql.util.PGobject
	 * is returned.
	 *
	 * You can use the getValue() or setValue() methods to handle the returned
	 * object. Custom objects can have their own methods.
	 *
	 * In 6.4, this is extended to use the org.postgresql.util.Serialize class to
	 * allow the Serialization of Java Objects into the database without using
	 * Blobs. Refer to that class for details on how this new feature works.
	 *
	 * @return PGobject for this type, and set to value
	 * @exception SQLException if value is not correct for this type
	 * @see org.postgresql.util.Serialize
	 */
	public Object getObject(String type, String value) throws SQLException
	{
		try
		{
			Object o = objectTypes.get(type);

			// If o is null, then the type is unknown, so check to see if type
			// is an actual table name. If it does, see if a Class is known that
			// can handle it
			if (o == null)
			{
				Serialize ser = new Serialize(this, type);
				objectTypes.put(type, ser);
				return ser.fetch(Integer.parseInt(value));
			}

			// If o is not null, and it is a String, then its a class name that
			// extends PGobject.
			//
			// This is used to implement the org.postgresql unique types (like lseg,
			// point, etc).
			if (o instanceof String)
			{
				// 6.3 style extending PG_Object
				PGobject obj = null;
				obj = (PGobject)(Class.forName((String)o).newInstance());
				obj.setType(type);
				obj.setValue(value);
				return (Object)obj;
			}
			else
			{
				// If it's an object, it should be an instance of our Serialize class
				// If so, then call it's fetch method.
				if (o instanceof Serialize)
					return ((Serialize)o).fetch(Integer.parseInt(value));
			}
		}
		catch (SQLException sx)
		{
			// rethrow the exception. Done because we capture any others next
			sx.fillInStackTrace();
			throw sx;
		}
		catch (Exception ex)
		{
			throw new PSQLException("postgresql.con.creobj", type, ex);
		}

		// should never be reached
		return null;
	}

	/**
	 * This stores an object into the database.
	 * @param o Object to store
	 * @return OID of the new rectord
	 * @exception SQLException if value is not correct for this type
	 * @see org.postgresql.util.Serialize
	 */
	public int putObject(Object o) throws SQLException
	{
		try
		{
			String type = o.getClass().getName();
			Object x = objectTypes.get(type);

			// If x is null, then the type is unknown, so check to see if type
			// is an actual table name. If it does, see if a Class is known that
			// can handle it
			if (x == null)
			{
				Serialize ser = new Serialize(this, type);
				objectTypes.put(type, ser);
				return ser.store(o);
			}

			// If it's an object, it should be an instance of our Serialize class
			// If so, then call it's fetch method.
			if (x instanceof Serialize)
				return ((Serialize)x).store(o);

			// Thow an exception because the type is unknown
			throw new PSQLException("postgresql.con.strobj");

		}
		catch (SQLException sx)
		{
			// rethrow the exception. Done because we capture any others next
			sx.fillInStackTrace();
			throw sx;
		}
		catch (Exception ex)
		{
			throw new PSQLException("postgresql.con.strobjex", ex);
		}
	}

	/**
	 * This allows client code to add a handler for one of org.postgresql's
	 * more unique data types.
	 *
	 * <p><b>NOTE:</b> This is not part of JDBC, but an extension.
	 *
	 * <p>The best way to use this is as follows:
	 *
	 * <p><pre>
	 * ...
	 * ((org.postgresql.Connection)myconn).addDataType("mytype","my.class.name");
	 * ...
	 * </pre>
	 *
	 * <p>where myconn is an open Connection to org.postgresql.
	 *
	 * <p>The handling class must extend org.postgresql.util.PGobject
	 *
	 * @see org.postgresql.util.PGobject
	 */
	public void addDataType(String type, String name)
	{
		objectTypes.put(type, name);
	}

	// This holds the available types
	private Hashtable objectTypes = new Hashtable();

	// This array contains the types that are supported as standard.
	//
	// The first entry is the types name on the database, the second
	// the full class name of the handling class.
	//
	private static final String defaultObjectTypes[][] = {
				{"box", "org.postgresql.geometric.PGbox"},
				{"circle", "org.postgresql.geometric.PGcircle"},
				{"line", "org.postgresql.geometric.PGline"},
				{"lseg", "org.postgresql.geometric.PGlseg"},
				{"path", "org.postgresql.geometric.PGpath"},
				{"point", "org.postgresql.geometric.PGpoint"},
				{"polygon", "org.postgresql.geometric.PGpolygon"},
				{"money", "org.postgresql.util.PGmoney"}
			};

	// This initialises the objectTypes hashtable
	private void initObjectTypes()
	{
		for (int i = 0;i < defaultObjectTypes.length;i++)
			objectTypes.put(defaultObjectTypes[i][0], defaultObjectTypes[i][1]);
	}

	// These are required by other common classes
	public abstract java.sql.Statement createStatement() throws SQLException;

	/**
	 * This returns a resultset. It must be overridden, so that the correct
	 * version (from jdbc1 or jdbc2) are returned.
	 */
	public abstract java.sql.ResultSet getResultSet(org.postgresql.Connection conn, java.sql.Statement stat, Field[] fields, Vector tuples, String status, int updateCount, int insertOID, boolean binaryCursor) throws SQLException;

	/**
	 * In some cases, it is desirable to immediately release a Connection's
	 * database and JDBC resources instead of waiting for them to be
	 * automatically released (cant think why off the top of my head)
	 *
	 * <B>Note:</B> A Connection is automatically closed when it is
	 * garbage collected.  Certain fatal errors also result in a closed
	 * connection.
	 *
	 * @exception SQLException if a database access error occurs
	 */
	public void close() throws SQLException
	{
		if (pg_stream != null)
		{
			try
			{
				pg_stream.SendChar('X');
				pg_stream.flush();
				pg_stream.close();
			}
			catch (IOException e)
			{}
			pg_stream = null;
		}
	}

	/**
	 * A driver may convert the JDBC sql grammar into its system's
	 * native SQL grammar prior to sending it; nativeSQL returns the
	 * native form of the statement that the driver would have sent.
	 *
	 * @param sql a SQL statement that may contain one or more '?'
	 *	parameter placeholders
	 * @return the native form of this statement
	 * @exception SQLException if a database access error occurs
	 */
	public String nativeSQL(String sql) throws SQLException
	{
		return sql;
	}

	/**
	 * The first warning reported by calls on this Connection is
	 * returned.
	 *
	 * <B>Note:</B> Sebsequent warnings will be changed to this
	 * SQLWarning
	 *
	 * @return the first SQLWarning or null
	 * @exception SQLException if a database access error occurs
	 */
	public SQLWarning getWarnings() throws SQLException
	{
		return firstWarning;
	}

	/**
	 * After this call, getWarnings returns null until a new warning
	 * is reported for this connection.
	 *
	 * @exception SQLException if a database access error occurs
	 */
	public void clearWarnings() throws SQLException
	{
		firstWarning = null;
	}


	/**
	 * You can put a connection in read-only mode as a hunt to enable
	 * database optimizations
	 *
	 * <B>Note:</B> setReadOnly cannot be called while in the middle
	 * of a transaction
	 *
	 * @param readOnly - true enables read-only mode; false disables it
	 * @exception SQLException if a database access error occurs
	 */
	public void setReadOnly(boolean readOnly) throws SQLException
	{
		this.readOnly = readOnly;
	}

	/**
	 * Tests to see if the connection is in Read Only Mode.  Note that
	 * we cannot really put the database in read only mode, but we pretend
	 * we can by returning the value of the readOnly flag
	 *
	 * @return true if the connection is read only
	 * @exception SQLException if a database access error occurs
	 */
	public boolean isReadOnly() throws SQLException
	{
		return readOnly;
	}

	/**
	 * If a connection is in auto-commit mode, than all its SQL
	 * statements will be executed and committed as individual
	 * transactions.  Otherwise, its SQL statements are grouped
	 * into transactions that are terminated by either commit()
	 * or rollback().  By default, new connections are in auto-
	 * commit mode.  The commit occurs when the statement completes
	 * or the next execute occurs, whichever comes first.  In the
	 * case of statements returning a ResultSet, the statement
	 * completes when the last row of the ResultSet has been retrieved
	 * or the ResultSet has been closed.  In advanced cases, a single
	 * statement may return multiple results as well as output parameter
	 * values.	Here the commit occurs when all results and output param
	 * values have been retrieved.
	 *
	 * @param autoCommit - true enables auto-commit; false disables it
	 * @exception SQLException if a database access error occurs
	 */
	public void setAutoCommit(boolean autoCommit) throws SQLException
	{
		if (this.autoCommit == autoCommit)
			return ;
		if (autoCommit)
			ExecSQL("end");
		else
		{
			if (haveMinimumServerVersion("7.1"))
			{
				ExecSQL("begin;" + getIsolationLevelSQL());
			}
			else
			{
				ExecSQL("begin");
				ExecSQL(getIsolationLevelSQL());
			}
		}
		this.autoCommit = autoCommit;
	}

	/**
	 * gets the current auto-commit state
	 *
	 * @return Current state of the auto-commit mode
	 * @exception SQLException (why?)
	 * @see setAutoCommit
	 */
	public boolean getAutoCommit() throws SQLException
	{
		return this.autoCommit;
	}

	/**
	 * The method commit() makes all changes made since the previous
	 * commit/rollback permanent and releases any database locks currently
	 * held by the Connection.	This method should only be used when
	 * auto-commit has been disabled.  (If autoCommit == true, then we
	 * just return anyhow)
	 *
	 * @exception SQLException if a database access error occurs
	 * @see setAutoCommit
	 */
	public void commit() throws SQLException
	{
		if (autoCommit)
			return ;
		if (haveMinimumServerVersion("7.1"))
		{
			ExecSQL("commit;begin;" + getIsolationLevelSQL());
		}
		else
		{
			ExecSQL("commit");
			ExecSQL("begin");
			ExecSQL(getIsolationLevelSQL());
		}
	}

	/**
	 * The method rollback() drops all changes made since the previous
	 * commit/rollback and releases any database locks currently held by
	 * the Connection.
	 *
	 * @exception SQLException if a database access error occurs
	 * @see commit
	 */
	public void rollback() throws SQLException
	{
		if (autoCommit)
			return ;
		if (haveMinimumServerVersion("7.1"))
		{
			ExecSQL("rollback; begin;" + getIsolationLevelSQL());
		}
		else
		{
			ExecSQL("rollback");
			ExecSQL("begin");
			ExecSQL(getIsolationLevelSQL());
		}
	}

	/**
	 * Get this Connection's current transaction isolation mode.
	 *
	 * @return the current TRANSACTION_* mode value
	 * @exception SQLException if a database access error occurs
	 */
	public int getTransactionIsolation() throws SQLException
	{
		clearWarnings();
		ExecSQL("show xactisolevel");

		SQLWarning warning = getWarnings();
		if (warning != null)
		{
			String message = warning.getMessage();
			clearWarnings();
			if (message.indexOf("READ COMMITTED") != -1)
				return java.sql.Connection.TRANSACTION_READ_COMMITTED;
			else if (message.indexOf("READ UNCOMMITTED") != -1)
				return java.sql.Connection.TRANSACTION_READ_UNCOMMITTED;
			else if (message.indexOf("REPEATABLE READ") != -1)
				return java.sql.Connection.TRANSACTION_REPEATABLE_READ;
			else if (message.indexOf("SERIALIZABLE") != -1)
				return java.sql.Connection.TRANSACTION_SERIALIZABLE;
		}
		return java.sql.Connection.TRANSACTION_READ_COMMITTED;
	}

	/**
	 * You can call this method to try to change the transaction
	 * isolation level using one of the TRANSACTION_* values.
	 *
	 * <B>Note:</B> setTransactionIsolation cannot be called while
	 * in the middle of a transaction
	 *
	 * @param level one of the TRANSACTION_* isolation values with
	 *	the exception of TRANSACTION_NONE; some databases may
	 *	not support other values
	 * @exception SQLException if a database access error occurs
	 * @see java.sql.DatabaseMetaData#supportsTransactionIsolationLevel
	 */
	public void setTransactionIsolation(int level) throws SQLException
	{
		//In 7.1 and later versions of the server it is possible using
		//the "set session" command to set this once for all future txns
		//however in 7.0 and prior versions it is necessary to set it in
		//each transaction, thus adding complexity below.
		//When we decide to drop support for servers older than 7.1
		//this can be simplified
		isolationLevel = level;
		String isolationLevelSQL;

		if (!haveMinimumServerVersion("7.1"))
		{
			isolationLevelSQL = getIsolationLevelSQL();
		}
		else
		{
			isolationLevelSQL = "SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL ";
			switch (isolationLevel)
			{
			case java.sql.Connection.TRANSACTION_READ_COMMITTED:
				isolationLevelSQL += "READ COMMITTED";
				break;
			case java.sql.Connection.TRANSACTION_SERIALIZABLE:
				isolationLevelSQL += "SERIALIZABLE";
				break;
			default:
				throw new PSQLException("postgresql.con.isolevel",
										new Integer(isolationLevel));
			}
		}
		ExecSQL(isolationLevelSQL);
	}

	/**
	 * Helper method used by setTransactionIsolation(), commit(), rollback()
	 * and setAutoCommit(). This returns the SQL string needed to
	 * set the isolation level for a transaction.  In 7.1 and later it
	 * is possible to set a default isolation level that applies to all
	 * future transactions, this method is only necesary for 7.0 and older
	 * servers, and should be removed when support for these older
	 * servers are dropped
	 */
	protected String getIsolationLevelSQL() throws SQLException
	{
		//7.1 and higher servers have a default specified so
		//no additional SQL is required to set the isolation level
		if (haveMinimumServerVersion("7.1"))
		{
			return "";
		}
		StringBuffer sb = new StringBuffer("SET TRANSACTION ISOLATION LEVEL");

		switch (isolationLevel)
		{
		case java.sql.Connection.TRANSACTION_READ_COMMITTED:
			sb.append(" READ COMMITTED");
			break;

		case java.sql.Connection.TRANSACTION_SERIALIZABLE:
			sb.append(" SERIALIZABLE");
			break;

		default:
			throw new PSQLException("postgresql.con.isolevel", new Integer(isolationLevel));
		}
		return sb.toString();
	}

	/**
	 * A sub-space of this Connection's database may be selected by
	 * setting a catalog name.	If the driver does not support catalogs,
	 * it will silently ignore this request
	 *
	 * @exception SQLException if a database access error occurs
	 */
	public void setCatalog(String catalog) throws SQLException
	{
		//no-op
	}

	/**
	 * Return the connections current catalog name, or null if no
	 * catalog name is set, or we dont support catalogs.
	 *
	 * @return the current catalog name or null
	 * @exception SQLException if a database access error occurs
	 */
	public String getCatalog() throws SQLException
	{
		return PG_DATABASE;
	}

	/**
	 * Overides finalize(). If called, it closes the connection.
	 *
	 * This was done at the request of Rachel Greenham
	 * <rachel@enlarion.demon.co.uk> who hit a problem where multiple
	 * clients didn't close the connection, and once a fortnight enough
	 * clients were open to kill the org.postgres server.
	 */
	public void finalize() throws Throwable
	{
		close();
	}

	private static String extractVersionNumber(String fullVersionString)
	{
		StringTokenizer versionParts = new StringTokenizer(fullVersionString);
		versionParts.nextToken(); /* "PostgreSQL" */
		return versionParts.nextToken(); /* "X.Y.Z" */
	}

	/**
	 * Get server version number
	 */
	public String getDBVersionNumber()
	{
		return dbVersionNumber;
	}

	public boolean haveMinimumServerVersion(String ver) throws SQLException
	{
		return (getDBVersionNumber().compareTo(ver) >= 0);
	}

	/**
	 * This method returns true if the compatible level set in the connection
	 * (which can be passed into the connection or specified in the URL)
	 * is at least the value passed to this method.  This is used to toggle
	 * between different functionality as it changes across different releases
	 * of the jdbc driver code.  The values here are versions of the jdbc client
	 * and not server versions.  For example in 7.1 get/setBytes worked on
	 * LargeObject values, in 7.2 these methods were changed to work on bytea
	 * values.	This change in functionality could be disabled by setting the
	 * "compatible" level to be 7.1, in which case the driver will revert to
	 * the 7.1 functionality.
	 */
	public boolean haveMinimumCompatibleVersion(String ver) throws SQLException
	{
		return (compatible.compareTo(ver) >= 0);
	}


	/**
	 * This returns the java.sql.Types type for a PG type oid
	 *
	 * @param oid PostgreSQL type oid
	 * @return the java.sql.Types type
	 * @exception SQLException if a database access error occurs
	 */
	public int getSQLType(int oid) throws SQLException
	{
		Integer sqlType = (Integer)typeOidCache.get(new Integer(oid));

		// it's not in the cache, so perform a query, and add the result to the cache
		if (sqlType == null)
		{
			ResultSet result = (org.postgresql.ResultSet)ExecSQL("select typname from pg_type where oid = " + oid);
			if (result.getColumnCount() != 1 || result.getTupleCount() != 1)
				throw new PSQLException("postgresql.unexpected");
			result.next();
			String pgType = result.getString(1);
			Integer iOid = new Integer(oid);
			sqlType = new Integer(getSQLType(result.getString(1)));
			sqlTypeCache.put(iOid, sqlType);
			pgTypeCache.put(iOid, pgType);
			result.close();
		}

		return sqlType.intValue();
	}

	/**
	 * This returns the java.sql.Types type for a PG type
	 *
	 * @param pgTypeName PostgreSQL type name
	 * @return the java.sql.Types type
	 */
	public abstract int getSQLType(String pgTypeName);

	/**
	 * This returns the oid for a given PG data type
	 * @param typeName PostgreSQL type name
	 * @return PostgreSQL oid value for a field of this type
	 */
	public int getOID(String typeName) throws SQLException
	{
		int oid = -1;
		if (typeName != null)
		{
			Integer oidValue = (Integer) typeOidCache.get(typeName);
			if (oidValue != null)
			{
				oid = oidValue.intValue();
			}
			else
			{
				// it's not in the cache, so perform a query, and add the result to the cache
				ResultSet result = (org.postgresql.ResultSet)ExecSQL("select oid from pg_type where typname='"
								   + typeName + "'");
				if (result.getColumnCount() != 1 || result.getTupleCount() != 1)
					throw new PSQLException("postgresql.unexpected");
				result.next();
				oid = Integer.parseInt(result.getString(1));
				typeOidCache.put(typeName, new Integer(oid));
				result.close();
			}
		}
		return oid;
	}

	/**
	 * We also need to get the PG type name as returned by the back end.
	 *
	 * @return the String representation of the type of this field
	 * @exception SQLException if a database access error occurs
	 */
	public String getPGType(int oid) throws SQLException
	{
		String pgType = (String) pgTypeCache.get(new Integer(oid));
		if (pgType == null)
		{
			getSQLType(oid);
			pgType = (String) pgTypeCache.get(new Integer(oid));
		}
		return pgType;
	}

}