PostgreSQL Synchronization Tool

/* npq - A C# libpq wrapper
 * 
 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the "License").  You may not use this file except
 * in compliance with the License.
 *
 * You can obtain a copy of the license at
 * http://www.opensource.org/licenses/cddl1.php.
 * See the License for the specific language governing
 * permissions and limitations under the License.
 *
 * Copyright 2009 by martin.faust@e56.de
 */
using System;

namespace npq {
		
	/// <summary>
	/// A large object wrapper
	/// </summary>
	public class LargeObject {
		PostgreSQL psql;
		int fd;
		
		/// <summary>
		/// Constructor
		/// </summary>
		public LargeObject(PostgreSQL _psql) {
			psql = _psql;
			fd = -1;
		}
		
		/// <summary>
		/// Deletes a large object
		/// </summary>
		public void Delete(int oid) {
			if (PG.lo_unlink(psql.conn, oid) < 0)
				throw new PostgreSQLException(PG.PQerrorMessage(psql.conn));
		}
		
		/// <summary>
		/// Exports a large object to a local file
		/// </summary>
		public void Export(int oid, string filename) {
			if (PG.lo_export(psql.conn, oid, filename) < 0)
				throw new PostgreSQLException(PG.PQerrorMessage(psql.conn));
		}

		/// <summary>
		/// Imports a local file into a large object and returns its id
		/// </summary>
		public int  Import(int oid, string filename) {
			int id = PG.lo_import(psql.conn, filename);
			if (id < 0)
				throw new PostgreSQLException(PG.PQerrorMessage(psql.conn));
			
			return id;
		}

		/// <summary>
		/// Create a new large object and returns the object id
		/// </summary>
		public int Create() {
			psql.StartTransaction();
			int oid = PG.lo_creat(psql.conn, PG.INV_READ|PG.INV_WRITE);	
			psql.ComitTransaction();
			return oid;
		}
		
		/// <summary>
		/// Opens a large object for reading/writing
		/// </summary>
		public void Open(int id) {
			psql.StartTransaction();
			fd = PG.lo_open(psql.conn, id, PG.INV_READ|PG.INV_WRITE);
			if (fd < 0) {
				psql.RollbackTransaction();
				throw new PostgreSQLException(PG.PQerrorMessage(psql.conn));
			}
		}
		
		/// <summary>
		/// Closes a large object
		/// </summary>
		public void Close() {
			if (fd < 0)
				return;
			PG.lo_close(psql.conn, fd);
			psql.ComitTransaction();
			fd = -1;
		}
		
		/// <summary>
		/// Write data to the large object
		/// </summary>
		public int Write(byte[] data, int length) {
			return PG.lo_write(psql.conn, fd, data, length);
		}
		
		/// <summary>
		/// Reads data from the large object
		/// </summary>
		public int Read(byte[] data, int length) {
			return PG.lo_read(psql.conn, fd, data, length);
		}
		
		/// <summary>
		/// The size of the large object
		/// </summary>
		public int Size() {
			return PG.lo_length(psql.conn, fd);
		}
	}
}