Open PDF from Google Drive in ASP.NET Core

17 Nov 20258 minutes to read

Follow these steps to load a PDF from Google Drive using the server-backed PDF Viewer.

Step 1: Set up Google Drive API

You must set up a project in the Google Developers Console and enable the Google Drive API. Obtain the necessary credentials to access the API. For more information, view the official link.

Step 2: Create a PDF Viewer sample in ASP.NET Core

Follow instructions provided in the Syncfusion^® PDF Viewer 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.Auth.OAuth2;
using Google.Apis.Services;
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 OnPostLoad() method to load the PDF files from Google drive.

public async Task<IActionResult> OnPostLoadAsync([FromBody] jsonObjects responseData)
{
    PdfRenderer pdfviewer = new PdfRenderer(_cache);
    MemoryStream stream = new MemoryStream();
    var jsonObject = JsonConverterstring(responseData);
    object jsonResult = new object();
    if (jsonObject != null && jsonObject.ContainsKey("document"))
    {
        if (bool.Parse(jsonObject["isFileName"]))
        {
            string objectName = jsonObject["document"];

            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 Google Drive API service.
            var service = new DriveService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = applicationName,
            });

            //This object is used to construct a request to list files from Google Drive.
            FilesResource.ListRequest listRequest = service.Files.List();
            listRequest.Q = "mimeType='application/pdf' and '" + folderId + "' in parents and trashed=false";
            listRequest.Fields = "files(id, name)";
            var files = await listRequest.ExecuteAsync();

            // Process the list of files (you can use 'files' to retrieve the list of files)
            string fileIdToDownload = null;
            foreach (var file in files.Files)
            {
                string fileId = file.Id;
                string fileName = file.Name;
                if (fileName == objectName)
                {
                    // Save the matching fileId
                    fileIdToDownload = fileId;
                    break;
                }
            }
            string fileIds = fileIdToDownload;
            var request = service.Files.Get(fileIds);
            await request.DownloadAsync(stream);
            stream.Position = 0;
        }
        else
        {
            byte[] bytes = Convert.FromBase64String(jsonObject["document"]);
            stream = new MemoryStream(bytes);
        }
    }
    jsonResult = pdfviewer.Load(stream, jsonObject);
    return Content(JsonConvert.SerializeObject(jsonResult));
}

1. Open the appsettings.json file in your web service project, 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 Your Google Drive Folder ID, Your Application name, and Your Path to the OAuth 2.0 Client IDs json file with your actual Google drive folder ID , Your name for your application and the path for the JSON file.

NOTE

The FolderId part is the unique identifier for the folder. For example, if your folder URL is: https://drive.google.com/drive/folders/abc123xyz456, then the folder ID is abc123xyz456.

Step 4: Configure the PDF Viewer component

Set the serviceUrl to your web service endpoint (replace the localhost URL with your server URL). Set documentPath to the PDF file name to load from Google Drive. Ensure the document name exists in your Drive 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

The Google.Apis.Drive.v3 NuGet package must be installed in your application to use the previous code example.

View sample in GitHub