download file from google drive using asp.net - asp.net

Question

I am trying download file from google drive using the code below:
public static Boolean downloadFile(string downloadurl, string _saveTo)
{
if (!String.IsNullOrEmpty(downloadurl))
{
try
{
var x = service.HttpClient.GetByteArrayAsync(downloadurl);
byte[] arrBytes = x.Result;
System.IO.File.WriteAllBytes(_saveTo, arrBytes);
return true;
}
catch (Exception e)
{
Console.WriteLine("An error occurred: " + e.Message);
return false;
}
}
else
{
// The file doesn't have any content stored on Drive.
return false;
}
}
On debugging the above code throwing exception as below:
?service.HttpClient.GetByteArrayAsync(downloadurl)
Id = 10, Status = WaitingForActivation, Method = "{null}", Result = "{Not yet computed}"
AsyncState: null
CancellationPending: false
CreationOptions: None
Exception: null
Id: 10
Result: null
Status: WaitingForActivation
I am trying to do it from my Service account created using Google API Console.
and the exception detail is as follows:
System.NullReferenceException was caught
HResult=-2147467261
Message=Object reference not set to an instance of an object.
Source=System.Net.Http
StackTrace:
at System.Net.Http.Headers.HttpRequestHeaders.AddHeaders(HttpHeaders sourceHeaders)
at System.Net.Http.HttpClient.PrepareRequestMessage(HttpRequestMessage request)
at System.Net.Http.HttpClient.SendAsync(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationToken cancellationToken)
at System.Net.Http.HttpClient.GetAsync(Uri requestUri, HttpCompletionOption completionOption, CancellationToken cancellationToken)
at System.Net.Http.HttpClient.GetContentAsync[T](Uri requestUri, HttpCompletionOption completionOption, T defaultValue, Func`2 readAs)
at System.Net.Http.HttpClient.GetByteArrayAsync(Uri requestUri)
at System.Net.Http.HttpClient.GetByteArrayAsync(String requestUri)

Answer 1

You can try this.
link
using Google.Apis.Authentication;
using Google.Apis.Drive.v2;
using Google.Apis.Drive.v2.Data;
using System.Net;
public class MyClass {
public static System.IO.Stream DownloadFile(
IAuthenticator authenticator, File file) {
if (!String.IsNullOrEmpty(file.DownloadUrl)) {
try {
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(
new Uri(file.DownloadUrl));
authenticator.ApplyAuthenticationToRequest(request);
HttpWebResponse response = (HttpWebResponse) request.GetResponse();
if (response.StatusCode == HttpStatusCode.OK) {
return response.GetResponseStream();
} else {
Console.WriteLine(
"An error occurred: " + response.StatusDescription);
return null;
}
} catch (Exception e) {
Console.WriteLine("An error occurred: " + e.Message);
return null;
}
} else {
// The file doesn't have any content stored on Drive.
return null;
}
}
}

Answer 2

Code using the Google .net client library
Service account:
string[] scopes = new string[] {DriveService.Scope.Drive}; // Full access
var keyFilePath = #"c:\file.p12" ; // Downloaded from https://console.developers.google.com
var serviceAccountEmail = "xx#developer.gserviceaccount.com"; // found https://console.developers.google.com
//loading the Key file
var certificate = new X509Certificate2(keyFilePath, "notasecret", X509KeyStorageFlags.Exportable);
var credential = new ServiceAccountCredential( new ServiceAccountCredential.Initializer(serviceAccountEmail) {
Scopes = scopes}.FromCertificate(certificate));
create drive service
var service = new DriveService(new BaseClientService.Initializer() {HttpClientInitializer = credential,
ApplicationName = "Drive API Sample",});
You can use files.list to list all of the files on drive.
FilesResource.ListRequest request = service.Files.List();
request.Q = "trashed=false";
title = 'hello'
FileList files = request.Execute();
loop though the items returned find the file you want it is a file resource you can pass it to the following method to down load your file
/// <summary>
/// Download a file
/// Documentation: https://developers.google.com/drive/v2/reference/files/get
/// </summary>
/// <param name="_service">a Valid authenticated DriveService</param>
/// <param name="_fileResource">File resource of the file to download</param>
/// <param name="_saveTo">location of where to save the file including the file name to save it as.</param>
/// <returns></returns>
public static Boolean downloadFile(DriveService _service, File _fileResource, string _saveTo)
{
if (!String.IsNullOrEmpty(_fileResource.DownloadUrl))
{
try
{
var x = _service.HttpClient.GetByteArrayAsync(_fileResource.DownloadUrl );
byte[] arrBytes = x.Result;
System.IO.File.WriteAllBytes(_saveTo, arrBytes);
return true;
}
catch (Exception e)
{
Console.WriteLine("An error occurred: " + e.Message);
return false;
}
}
else
{
// The file doesn't have any content stored on Drive.
return false;
}
}
code ripped from Google drive authentication C#