Save PDF files to Google Drive

28 Feb 20265 minutes to read

Follow the steps below to save a PDF file to Google Drive using the ASP.NET Core PDF Viewer with a server-backed web service.

Step 1: Set up the Google Drive API

Create a project in the Google Cloud Console and enable the Google Drive API. Obtain the necessary credentials to access the API. For more information, see the official guide

Step 2: Create an ASP.NET Core PDF Viewer sample

Follow the instructions in this Getting Started guide to create a simple PDF Viewer sample in ASP.NET Core.

Step 3: Modify the Index.cshtml.cs file in the project

1. Import the required namespaces at the top of the file:

using System.IO;
using Google.Apis.Drive.v3;
using Google.Apis.Util.Store;

1. Add the following private fields and constructor parameters to the Index.cshtml.cs class. In the constructor, assign the values from the configuration to the corresponding fields.

string[] Scopes = { DriveService.Scope.Drive };
private IConfiguration _configuration;
public readonly string folderId;
private readonly string applicationName;
public readonly string credentialPath;

public IndexModel(Microsoft.AspNetCore.Hosting.IHostingEnvironment hostingEnvironment, IMemoryCache cache, IConfiguration configuration)
{
    _hostingEnvironment = hostingEnvironment;
    _cache = cache;
    _configuration = configuration;
    folderId = _configuration.GetValue<string>("FolderId");
    credentialPath = _configuration.GetValue<string>("CredentialPath");
    applicationName = _configuration.GetValue<string>("ApplicationName");
}

1. Modify the OnPostDownloadAsync() method to save the downloaded PDF files to the Google Drive folder.

public async Task<IActionResult> OnPostDownloadAsync([FromBody] jsonObjects responseData)
{
    PdfRenderer pdfviewer = new PdfRenderer(_cache);
    var jsonObject = JsonConverterstring(responseData);
    string documentBase = pdfviewer.GetDocumentAsBase64(jsonObject);
    byte[] documentBytes = Convert.FromBase64String(documentBase.Split(",")[1]);
    string documentId = jsonObject["documentId"];
    string result = Path.GetFileNameWithoutExtension(documentId);
    string fileName = result + "_downloaded.pdf";

    UserCredential credential;

    using (var memStream = new FileStream(credentialPath, FileMode.Open, FileAccess.Read))
    {
        string credPath = "token.json";
        credential = await GoogleWebAuthorizationBroker.AuthorizeAsync(
            GoogleClientSecrets.Load(memStream).Secrets,
            Scopes,
            "user",
            CancellationToken.None,
            new FileDataStore(credPath, true));
    }

    // Create the Drive API service.
    var service = new DriveService(new BaseClientService.Initializer()
    {
        HttpClientInitializer = credential,
        ApplicationName = applicationName,
    });
    var fileMetadata = new Google.Apis.Drive.v3.Data.File()
    {
        Name = fileName,
        Parents = new List<string> { folderId }
    };
    FilesResource.CreateMediaUpload request;
    using (var stream = new MemoryStream(documentBytes))
    {
        request = service.Files.Create(fileMetadata, stream, "application/pdf");
        request.Fields = "id";
        object value = await request.UploadAsync();
    }
    return Content(documentBase);
}

1. Open the appsettings.json file in the project and add the following lines below the existing “AllowedHosts” configuration.

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "FolderId": "Your Google Drive Folder ID",
  "CredentialPath": "Your Path to the OAuth 2.0 Client IDs json file",
  "ApplicationName": "Your Application name"
}

NOTE

Replace the placeholders with the actual Google Drive folder ID, application name, and the path to the OAuth 2.0 Client IDs JSON file. The folder ID is the unique identifier in the folder URL. For example, in https://drive.google.com/drive/folders/abc123xyz456, the ID is abc123xyz456.

Step 4: Set the PDF Viewer properties in the ASP.NET Core PDF Viewer component

Set the documentPath property of the PDF Viewer component to the desired PDF file name that you wish to load from Google Drive. Ensure that the document exists in the target folder.

@page "{handler?}"
@model IndexModel
@{
    ViewData["Title"] = "Home page";
}

<div class="text-center">
    <ejs-pdfviewer id="pdfviewer" style="height:600px" serviceUrl="/Index" documentPath="PDF_Succinctly.pdf">
    </ejs-pdfviewer>
</div>

NOTE

Install the Google.Apis.Drive.v3 NuGet package in the application to use the previous code example.

View sample in GitHub