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@chrisdlees
Forked from yasirkula/FileDownloader.cs
Created January 31, 2022 11:19
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C# Download Public File From Google Drive™ (works for large files as well)
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.Net;
using System.Text;
/* EXAMPLE USAGE
FileDownloader fileDownloader = new FileDownloader();
// This callback is triggered for DownloadFileAsync only
fileDownloader.DownloadProgressChanged += ( sender, e ) => Console.WriteLine( "Progress changed " + e.BytesReceived + " " + e.TotalBytesToReceive );
// This callback is triggered for both DownloadFile and DownloadFileAsync
fileDownloader.DownloadFileCompleted += ( sender, e ) => Console.WriteLine( "Download completed" );
fileDownloader.DownloadFileAsync( "https://INSERT_DOWNLOAD_LINK_HERE", @"C:\downloadedFile.txt" );
*/
public class FileDownloader : IDisposable
{
private const string GOOGLE_DRIVE_DOMAIN = "drive.google.com";
private const string GOOGLE_DRIVE_DOMAIN2 = "https://drive.google.com";
// In the worst case, it is necessary to send 3 download requests to the Drive address
// 1. an NID cookie is returned instead of a download_warning cookie
// 2. download_warning cookie returned
// 3. the actual file is downloaded
private const int GOOGLE_DRIVE_MAX_DOWNLOAD_ATTEMPT = 3;
public delegate void DownloadProgressChangedEventHandler( object sender, DownloadProgress progress );
// Custom download progress reporting (needed for Google Drive)
public class DownloadProgress
{
public long BytesReceived, TotalBytesToReceive;
public object UserState;
public int ProgressPercentage
{
get
{
if( TotalBytesToReceive > 0L )
return (int) ( ( (double) BytesReceived / TotalBytesToReceive ) * 100 );
return 0;
}
}
}
// Web client that preserves cookies (needed for Google Drive)
private class CookieAwareWebClient : WebClient
{
private class CookieContainer
{
private readonly Dictionary<string, string> cookies = new Dictionary<string, string>();
public string this[Uri address]
{
get
{
string cookie;
if( cookies.TryGetValue( address.Host, out cookie ) )
return cookie;
return null;
}
set
{
cookies[address.Host] = value;
}
}
}
private readonly CookieContainer cookies = new CookieContainer();
public DownloadProgress ContentRangeTarget;
protected override WebRequest GetWebRequest( Uri address )
{
WebRequest request = base.GetWebRequest( address );
if( request is HttpWebRequest )
{
string cookie = cookies[address];
if( cookie != null )
( (HttpWebRequest) request ).Headers.Set( "cookie", cookie );
if( ContentRangeTarget != null )
( (HttpWebRequest) request ).AddRange( 0 );
}
return request;
}
protected override WebResponse GetWebResponse( WebRequest request, IAsyncResult result )
{
return ProcessResponse( base.GetWebResponse( request, result ) );
}
protected override WebResponse GetWebResponse( WebRequest request )
{
return ProcessResponse( base.GetWebResponse( request ) );
}
private WebResponse ProcessResponse( WebResponse response )
{
string[] cookies = response.Headers.GetValues( "Set-Cookie" );
if( cookies != null && cookies.Length > 0 )
{
int length = 0;
for( int i = 0; i < cookies.Length; i++ )
length += cookies[i].Length;
StringBuilder cookie = new StringBuilder( length );
for( int i = 0; i < cookies.Length; i++ )
cookie.Append( cookies[i] );
this.cookies[response.ResponseUri] = cookie.ToString();
}
if( ContentRangeTarget != null )
{
string[] rangeLengthHeader = response.Headers.GetValues( "Content-Range" );
if( rangeLengthHeader != null && rangeLengthHeader.Length > 0 )
{
int splitIndex = rangeLengthHeader[0].LastIndexOf( '/' );
if( splitIndex >= 0 && splitIndex < rangeLengthHeader[0].Length - 1 )
{
long length;
if( long.TryParse( rangeLengthHeader[0].Substring( splitIndex + 1 ), out length ) )
ContentRangeTarget.TotalBytesToReceive = length;
}
}
}
return response;
}
}
private readonly CookieAwareWebClient webClient;
private readonly DownloadProgress downloadProgress;
private Uri downloadAddress;
private string downloadPath;
private bool asyncDownload;
private object userToken;
private bool downloadingDriveFile;
private int driveDownloadAttempt;
public event DownloadProgressChangedEventHandler DownloadProgressChanged;
public event AsyncCompletedEventHandler DownloadFileCompleted;
public FileDownloader()
{
webClient = new CookieAwareWebClient();
webClient.DownloadProgressChanged += DownloadProgressChangedCallback;
webClient.DownloadFileCompleted += DownloadFileCompletedCallback;
downloadProgress = new DownloadProgress();
}
public void DownloadFile( string address, string fileName )
{
DownloadFile( address, fileName, false, null );
}
public void DownloadFileAsync( string address, string fileName, object userToken = null )
{
DownloadFile( address, fileName, true, userToken );
}
private void DownloadFile( string address, string fileName, bool asyncDownload, object userToken )
{
downloadingDriveFile = address.StartsWith( GOOGLE_DRIVE_DOMAIN ) || address.StartsWith( GOOGLE_DRIVE_DOMAIN2 );
if( downloadingDriveFile )
{
address = GetGoogleDriveDownloadAddress( address );
driveDownloadAttempt = 1;
webClient.ContentRangeTarget = downloadProgress;
}
else
webClient.ContentRangeTarget = null;
downloadAddress = new Uri( address );
downloadPath = fileName;
downloadProgress.TotalBytesToReceive = -1L;
downloadProgress.UserState = userToken;
this.asyncDownload = asyncDownload;
this.userToken = userToken;
DownloadFileInternal();
}
private void DownloadFileInternal()
{
if( !asyncDownload )
{
webClient.DownloadFile( downloadAddress, downloadPath );
// This callback isn't triggered for synchronous downloads, manually trigger it
DownloadFileCompletedCallback( webClient, new AsyncCompletedEventArgs( null, false, null ) );
}
else if( userToken == null )
webClient.DownloadFileAsync( downloadAddress, downloadPath );
else
webClient.DownloadFileAsync( downloadAddress, downloadPath, userToken );
}
private void DownloadProgressChangedCallback( object sender, DownloadProgressChangedEventArgs e )
{
if( DownloadProgressChanged != null )
{
downloadProgress.BytesReceived = e.BytesReceived;
if( e.TotalBytesToReceive > 0L )
downloadProgress.TotalBytesToReceive = e.TotalBytesToReceive;
DownloadProgressChanged( this, downloadProgress );
}
}
private void DownloadFileCompletedCallback( object sender, AsyncCompletedEventArgs e )
{
if( !downloadingDriveFile )
{
if( DownloadFileCompleted != null )
DownloadFileCompleted( this, e );
}
else
{
if( driveDownloadAttempt < GOOGLE_DRIVE_MAX_DOWNLOAD_ATTEMPT && !ProcessDriveDownload() )
{
// Try downloading the Drive file again
driveDownloadAttempt++;
DownloadFileInternal();
}
else if( DownloadFileCompleted != null )
DownloadFileCompleted( this, e );
}
}
// Downloading large files from Google Drive prompts a warning screen and requires manual confirmation
// Consider that case and try to confirm the download automatically if warning prompt occurs
// Returns true, if no more download requests are necessary
private bool ProcessDriveDownload()
{
FileInfo downloadedFile = new FileInfo( downloadPath );
if( downloadedFile == null )
return true;
// Confirmation page is around 50KB, shouldn't be larger than 60KB
if( downloadedFile.Length > 60000L )
return true;
// Downloaded file might be the confirmation page, check it
string content;
using( var reader = downloadedFile.OpenText() )
{
// Confirmation page starts with <!DOCTYPE html>, which can be preceeded by a newline
char[] header = new char[20];
int readCount = reader.ReadBlock( header, 0, 20 );
if( readCount < 20 || !( new string( header ).Contains( "<!DOCTYPE html>" ) ) )
return true;
content = reader.ReadToEnd();
}
int linkIndex = content.LastIndexOf( "href=\"/uc?" );
if( linkIndex < 0 )
return true;
linkIndex += 6;
int linkEnd = content.IndexOf( '"', linkIndex );
if( linkEnd < 0 )
return true;
downloadAddress = new Uri( "https://drive.google.com" + content.Substring( linkIndex, linkEnd - linkIndex ).Replace( "&amp;", "&" ) );
return false;
}
// Handles the following formats (links can be preceeded by https://):
// - drive.google.com/open?id=FILEID
// - drive.google.com/file/d/FILEID/view?usp=sharing
// - drive.google.com/uc?id=FILEID&export=download
private string GetGoogleDriveDownloadAddress( string address )
{
int index = address.IndexOf( "id=" );
int closingIndex;
if( index > 0 )
{
index += 3;
closingIndex = address.IndexOf( '&', index );
if( closingIndex < 0 )
closingIndex = address.Length;
}
else
{
index = address.IndexOf( "file/d/" );
if( index < 0 ) // address is not in any of the supported forms
return string.Empty;
index += 7;
closingIndex = address.IndexOf( '/', index );
if( closingIndex < 0 )
{
closingIndex = address.IndexOf( '?', index );
if( closingIndex < 0 )
closingIndex = address.Length;
}
}
return string.Concat( "https://drive.google.com/uc?id=", address.Substring( index, closingIndex - index ), "&export=download" );
}
public void Dispose()
{
webClient.Dispose();
}
}
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