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FtpWebRequest.ContentOffset Property

Gets or sets a byte offset into the file being downloaded by this request.

Namespace:  System.Net
Assembly:  System (in System.dll)

public long ContentOffset { get; set; }

Property Value

Type: System.Int64
An Int64 instance that specifies the file offset, in bytes. The default value is zero.

ExceptionCondition
InvalidOperationException

A new value was specified for this property for a request that is already in progress.

ArgumentOutOfRangeException

The value specified for this property is less than zero.

Set the ContentOffset property when downloading a file from an FTP server. This offset indicates the position in the server's file that marks the start of the data to be downloaded. The offset is specified as the number of bytes from the start of the file; the offset of the first byte is zero.

Setting ContentOffset causes the FtpWebRequest to send a restart (REST) command to the server. This command is ignored by most FTP server implementations if you are uploading data to the server.

Changing ContentOffset after calling the GetRequestStream, BeginGetRequestStream, GetResponse, or BeginGetResponse method causes an InvalidOperationException exception.

The following code example demonstrates downloading part of a file from a server and appending the downloaded data to a local file.

public static bool RestartDownloadFromServer(string fileName, Uri serverUri, long offset)
{
    // The serverUri parameter should use the ftp:// scheme. 
    // It identifies the server file that is to be downloaded 
    // Example: ftp://contoso.com/someFile.txt. 

    // The fileName parameter identifies the local file. 
    //The serverUri parameter identifies the remote file. 
    // The offset parameter specifies where in the server file to start reading data. 

    if (serverUri.Scheme != Uri.UriSchemeFtp)
    {
        return false;
    }
    // Get the object used to communicate with the server.
    FtpWebRequest request = (FtpWebRequest)WebRequest.Create(serverUri);
    request.Method = WebRequestMethods.Ftp.DownloadFile;
    request.ContentOffset = offset;
    FtpWebResponse response = null;
    try 
    {
        response = (FtpWebResponse) request.GetResponse();
    }
    catch (WebException e)
    {
        Console.WriteLine (e.Status);
        Console.WriteLine (e.Message);
        return false;
    }
    // Get the data stream from the response.
    Stream newFile = response.GetResponseStream();
    // Use a StreamReader to simplify reading the response data.
    StreamReader reader  = new StreamReader(newFile);
    string newFileData = reader.ReadToEnd();
    // Append the response data to the local file 
    // using a StreamWriter.
    StreamWriter writer = File.AppendText(fileName);
    writer.Write(newFileData);
    // Display the status description. 

    // Cleanup.
    writer.Close();
    reader.Close();
    response.Close();
    Console.WriteLine("Download restart - status: {0}",response.StatusDescription);
    return true;
}
    // NOT Working - throws a protocolError - 350 Restarting at 8. for args shown in Main.
public:
    static bool DownloadPartialFileFromServer(String* /*fileName*/, Uri* serverUri, long offset)
    {
        // The serverUri parameter should use the ftp:// scheme.
        // It identifies the server file that is to be appended.
        // Example: ftp://contoso.com/someFile.txt.
        // 
        // The fileName parameter identifies the local file
        //
        // The offset parameter specifies where in the server file to start reading data.

        if (serverUri->Scheme != Uri::UriSchemeFtp)
        {
            return false;
        }
        // Get the object used to communicate with the server.
        FtpWebRequest* request = dynamic_cast<FtpWebRequest*>(WebRequest::Create(serverUri));
        request->Method = FtpMethods::DownloadFile;
        request->ContentOffset = offset;
        FtpWebResponse* response = 0;
        try 
        {
            response = dynamic_cast<FtpWebResponse*> (request->GetResponse());
        }
        catch (WebException* e)
        {
            Console::WriteLine (e->Status);
            Console::WriteLine (e->Message);

            return false;

        }
        Stream* newFile = response->GetResponseStream();

        StreamReader* sr = new StreamReader(newFile);
        // Display downloaded data.
        String* newFileData = sr->ReadToEnd();
        // string fileString = System.Text.Encoding.UTF8.GetString(newFileData);
        Console::WriteLine(sr);
        Console::WriteLine(S"Download partial file - status: {0}",response->StatusDescription);
        response->Close();  
        return true;
    }

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

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