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NpgsqlLargeObjectManager.cs
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#region License
// The PostgreSQL License
//
// Copyright (C) 2015 The Npgsql Development Team
//
// Permission to use, copy, modify, and distribute this software and its
// documentation for any purpose, without fee, and without a written
// agreement is hereby granted, provided that the above copyright notice
// and this paragraph and the following two paragraphs appear in all copies.
//
// IN NO EVENT SHALL THE NPGSQL DEVELOPMENT TEAM BE LIABLE TO ANY PARTY
// FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
// INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
// DOCUMENTATION, EVEN IF THE NPGSQL DEVELOPMENT TEAM HAS BEEN ADVISED OF
// THE POSSIBILITY OF SUCH DAMAGE.
//
// THE NPGSQL DEVELOPMENT TEAM SPECIFICALLY DISCLAIMS ANY WARRANTIES,
// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
// ON AN "AS IS" BASIS, AND THE NPGSQL DEVELOPMENT TEAM HAS NO OBLIGATIONS
// TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
#endregion
using Npgsql.FrontendMessages;
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Text;
using AsyncRewriter;
namespace Npgsql
{
/// <summary>
/// Large object manager. This class can be used to store very large files in a PostgreSQL database.
/// </summary>
public partial class NpgsqlLargeObjectManager
{
const int INV_WRITE = 0x00020000;
const int INV_READ = 0x00040000;
internal readonly NpgsqlConnection _connection;
/// <summary>
/// The largest chunk size (in bytes) read and write operations will read/write each roundtrip to the network. Default 4 MB.
/// </summary>
public int MaxTransferBlockSize { get; set; }
/// <summary>
/// Creates an NpgsqlLargeObjectManager for this connection. The connection must be opened to perform remote operations.
/// </summary>
/// <param name="connection"></param>
public NpgsqlLargeObjectManager(NpgsqlConnection connection)
{
_connection = connection;
MaxTransferBlockSize = 4 * 1024 * 1024; // 4MB
}
/// <summary>
/// Execute a function
/// </summary>
/// <param name="function"></param>
/// <param name="arguments"></param>
/// <returns></returns>
[RewriteAsync]
internal T ExecuteFunction<T>(string function, params object[] arguments)
{
using (var command = new NpgsqlCommand(function, _connection))
{
command.CommandType = CommandType.StoredProcedure;
command.CommandText = function;
foreach (var argument in arguments)
{
command.Parameters.Add(new NpgsqlParameter() { Value = argument });
}
return (T)command.ExecuteScalar();
}
}
/// <summary>
/// Execute a function that returns a byte array
/// </summary>
/// <returns></returns>
[RewriteAsync]
internal int ExecuteFunctionGetBytes(string function, byte[] buffer, int offset, int len, params object[] arguments)
{
using (var command = new NpgsqlCommand(function, _connection))
{
command.CommandType = CommandType.StoredProcedure;
foreach (var argument in arguments)
{
command.Parameters.Add(new NpgsqlParameter() { Value = argument });
}
using (var reader = command.ExecuteReader(System.Data.CommandBehavior.SequentialAccess))
{
reader.Read();
return (int)reader.GetBytes(0, 0, buffer, offset, len);
}
}
}
/// <summary>
/// Create an empty large object in the database. If an oid is specified but is already in use, an NpgsqlException will be thrown.
/// </summary>
/// <param name="preferredOid">A preferred oid, or specify 0 if one should be automatically assigned</param>
/// <returns>The oid for the large object created</returns>
/// <exception cref="NpgsqlException">If an oid is already in use</exception>
[RewriteAsync]
public uint Create(uint preferredOid = 0)
{
return ExecuteFunction<uint>("lo_create", (int)preferredOid);
}
/// <summary>
/// Opens a large object on the backend, returning a stream controlling this remote object.
/// A transaction snapshot is taken by the backend when the object is opened with only read permissions.
/// When reading from this object, the contents reflects the time when the snapshot was taken.
/// Note that this method, as well as operations on the stream must be wrapped inside a transaction.
/// </summary>
/// <param name="oid">Oid of the object</param>
/// <returns>An NpgsqlLargeObjectStream</returns>
[RewriteAsync]
public NpgsqlLargeObjectStream OpenRead(uint oid)
{
var fd = ExecuteFunction<int>("lo_open", (int)oid, INV_READ);
return new NpgsqlLargeObjectStream(this, oid, fd, false);
}
/// <summary>
/// Opens a large object on the backend, returning a stream controlling this remote object.
/// Note that this method, as well as operations on the stream must be wrapped inside a transaction.
/// </summary>
/// <param name="oid">Oid of the object</param>
/// <returns>An NpgsqlLargeObjectStream</returns>
[RewriteAsync]
public NpgsqlLargeObjectStream OpenReadWrite(uint oid)
{
var fd = ExecuteFunction<int>("lo_open", (int)oid, INV_READ | INV_WRITE);
return new NpgsqlLargeObjectStream(this, oid, fd, true);
}
/// <summary>
/// Deletes a large object on the backend.
/// </summary>
/// <param name="oid">Oid of the object to delete</param>
[RewriteAsync]
public void Unlink(uint oid)
{
ExecuteFunction<object>("lo_unlink", (int)oid);
}
/// <summary>
/// Exports a large object stored in the database to a file on the backend. This requires superuser permissions.
/// </summary>
/// <param name="oid">Oid of the object to export</param>
/// <param name="path">Path to write the file on the backend</param>
[RewriteAsync]
public void ExportRemote(uint oid, string path)
{
ExecuteFunction<object>("lo_export", (int)oid, path);
}
/// <summary>
/// Imports a large object to be stored as a large object in the database from a file stored on the backend. This requires superuser permissions.
/// </summary>
/// <param name="path">Path to read the file on the backend</param>
/// <param name="oid">A preferred oid, or specify 0 if one should be automatically assigned</param>
[RewriteAsync]
public void ImportRemote(string path, uint oid = 0)
{
ExecuteFunction<object>("lo_import", path, (int)oid);
}
/// <summary>
/// Since PostgreSQL 9.3, large objects larger than 2GB can be handled, up to 4TB.
/// This property returns true whether the PostgreSQL version is >= 9.3.
/// </summary>
public bool Has64BitSupport => _connection.PostgreSqlVersion >= new Version(9, 3);
/*
internal enum Function : uint
{
lo_open = 952,
lo_close = 953,
loread = 954,
lowrite = 955,
lo_lseek = 956,
lo_lseek64 = 3170, // Since PostgreSQL 9.3
lo_creat = 957,
lo_create = 715,
lo_tell = 958,
lo_tell64 = 3171, // Since PostgreSQL 9.3
lo_truncate = 1004,
lo_truncate64 = 3172, // Since PostgreSQL 9.3
// These four are available since PostgreSQL 9.4
lo_from_bytea = 3457,
lo_get = 3458,
lo_get_fragment = 3459,
lo_put = 3460,
lo_unlink = 964,
lo_import = 764,
lo_import_with_oid = 767,
lo_export = 765,
}
*/
}
}