How to resume older file version download in SharePoint online if interrupted/failed in between?

Question

While downloading large file older version in document library, if due any error (like network failure for second) if download (read() ) is failed or interrupted. In such scenario want to resume the download from that offset....

How to resume older file version download in SharePoint online if interrupted/failed in between?

Sample code to download older version of file is as below. Here changing offset does not work and file download starts from beginning.

           static void Main(string[] args)  
           {  
                string sitrUrl = "https://mysite.sharepoint.com/sites/test-site1";  
                //var fileURL = sitrUrl+ "/_vti_history/512/Shared Documents/txtDoc.txt";  
      
                using (var context = new ClientContext(sitrUrl))  
                {  
                      
                    context.Credentials = new SharePointOnlineCredentials("user1@xvz.com", StringToSecureString("password"));  
      
                    var targetSite = new Uri(context.Url);  
                    var webRequest = context.WebRequestExecutorFactory.CreateWebRequestExecutor(context, fileURL);  
      
                    String authenticationCookie = ((SharePointOnlineCredentials)context.Credentials).GetAuthenticationCookie(targetSite);  
                    webRequest.WebRequest.CookieContainer = new CookieContainer();  
                    webRequest.WebRequest.CookieContainer.Add(new Cookie("SPOIDCRL", authenticationCookie.TrimStart("SPOIDCRL=".ToCharArray()), String.Empty, targetSite.Authority));  
      
                    webRequest.Execute();  
      
                    var m_stream = webRequest.GetResponseStream();  
      
                    int offset = 0;  
                    int count = 25;  
      
                    while (true)  
                    {  
                        byte[] buffer = new byte[256];  
                        int bytesRead = m_stream.Read(buffer, offset, count);  
                        offset += bytesRead;  
                        //System.Console.WriteLine("offset:" + offset + ", bytesRead:" + bytesRead);  
                        //System.Console.WriteLine(Encoding.Default.GetString(buffer));  
                        if (bytesRead == 0)  
                            break;  
                    }  
                }  
            }  

@Tong Zhang_MSFT

@RaytheonXie_MSFT

Answer 1

Hi @Mahesh Surkar ,

According to my research and testing, please try to use the following code to download file with resume support:

var buffer = new byte[4096];  
int bytesRead;  
  
while ((bytesRead = responseStream.Read(buffer, 0, buffer.Length)) > 0)  
{  
       totalBytesRead += bytesRead;  
       RequestContentLength += bytesRead;  
       localFileStream.Write(buffer, 0, bytesRead);  
}  

And here is a document about C# download file with resume, you can refer to the code in this document: C# download file with resume

Hope it can help you. Thanks for your understanding.

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Answer 2

did you find a way to keep your cookie container up to date with legacy authentication disabled ?