How to Upload Large Files to SharePoint Using Microsoft Graph SDK in C# (Step-by-Step)

Uploading large files to SharePoint can be tricky, but Microsoft Graph SDK’s upload sessions make it reliable by splitting files into manageable chunks. Here’s how to do it in C#—no jargon, just clear steps!

What is an Upload Session?

An upload session lets you:

1. Upload large files (e.g., >4MB) in smaller chunks.

2. Resume uploads if the connection drops.

3. Avoid timeouts common with single-request uploads.

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Step 1: Set Up Prerequisites

1. Install NuGet Packages:

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   Install-Package Microsoft.Graph  
   Install-Package Microsoft.Graph.Core  

2. Azure App Registration:

   • Register your app in Azure AD.

   • Grant Sites.ReadWrite.All (Application permissions).

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Step 2: Authenticate with Microsoft Graph

Use the ClientSecretCredential to authenticate your app:

csharp

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using Microsoft.Graph;  
using Azure.Identity;  

var tenantId = "YOUR_TENANT_ID";  
var clientId = "YOUR_CLIENT_ID";  
var clientSecret = "YOUR_CLIENT_SECRET";  

var credential = new ClientSecretCredential(tenantId, clientId, clientSecret);  
var graphClient = new GraphServiceClient(credential);  

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Step 3: Create the Upload Session

Specify the SharePoint file path (replace placeholders):

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var siteId = "your-site-id";     // SharePoint site ID  
var driveId = "your-drive-id";   // Document library ID  
var fileName = "largefile.zip";  // File name  
var folderPath = "Shared%20Documents"; // URL-encoded folder path  

// Request upload session  
var uploadSession = await graphClient.Sites[siteId]  
    .Drives[driveId]  
    .Root  
    .ItemWithPath($"{folderPath}/{fileName}")  
    .CreateUploadSession()  
    .Request()  
    .PostAsync();  

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Step 4: Upload the File in Chunks

Use LargeFileUploadTask to handle chunking automatically:

csharp

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using var fileStream = File.OpenRead("C:/path/to/largefile.zip");  

// Max chunk size (default: 320 KB)  
var maxChunkSize = 320 * 1024;  

var uploadTask = new LargeFileUploadTask<DriveItem>(  
    uploadSession,  
    fileStream,  
    maxChunkSize  
);  

// Upload all chunks  
var uploadResult = await uploadTask.UploadAsync();  

if (uploadResult.UploadSucceeded)  
{  
    Console.WriteLine("File uploaded!");  
}  

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Key Details Explained

• Site/Drive IDs:

  • Find them in SharePoint URL: https://contoso.sharepoint.com/sites/{site-id}/_layouts/15/...

  • Use the Graph API to list sites/drives if unsure.

• Chunk Size:

  • Smaller chunks = more requests but better reliability.

  • Max supported chunk size: 60 MiB.

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Handling Errors

Wrap the upload in a try-catch block:

csharp

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try  
{  
    var uploadResult = await uploadTask.UploadAsync();  
}  
catch (ServiceException ex)  
{  
    Console.WriteLine($"Error: {ex.Message}");  
}  

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Full Example

csharp

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using Microsoft.Graph;  
using Azure.Identity;  
using System;  
using System.IO;  
using System.Threading.Tasks;  

class Program  
{  
    static async Task Main()  
    {  
        var tenantId = "YOUR_TENANT_ID";  
        var clientId = "YOUR_CLIENT_ID";  
        var clientSecret = "YOUR_CLIENT_SECRET";  

        var credential = new ClientSecretCredential(tenantId, clientId, clientSecret);  
        var graphClient = new GraphServiceClient(credential);  

        var siteId = "contoso.sharepoint.com,abc123";  
        var driveId = "b!12345";  
        var fileName = "project-backup.zip";  
        var folderPath = "Shared%20Documents/Backups";  

        try  
        {  
            // Create session  
            var uploadSession = await graphClient.Sites[siteId]  
                .Drives[driveId]  
                .Root  
                .ItemWithPath($"{folderPath}/{fileName}")  
                .CreateUploadSession()  
                .Request()  
                .PostAsync();  

            // Upload file  
            using var fileStream = File.OpenRead("C:/backups/project-backup.zip");  
            var uploadTask = new LargeFileUploadTask<DriveItem>(uploadSession, fileStream);  

            var result = await uploadTask.UploadAsync();  
            Console.WriteLine(result.UploadSucceeded ? "Success!" : "Failed.");  
        }  
        catch (Exception ex)  
        {  
            Console.WriteLine($"Error: {ex.Message}");  
        }  
    }  
}  

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Troubleshooting Tips

1. Permissions: Ensure your app has Sites.ReadWrite.All in Azure AD.

2. Path Encoding: Use %20 for spaces in folder paths.

3. Session Expiry: Upload sessions expire after 24 hours.

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By following these steps, you can reliably upload massive files to SharePoint without timeouts or headaches. Happy uploading! 🚀