public async Task DownloadAsync(Uri address, string directory, string fileName, CancellationToken cancellationToken)
{
cancellationToken.ThrowIfCancellationRequested();
DownloadContext downloadContext = new DownloadContext();
if (!_uriContexts.TryAdd(address, downloadContext))
{
throw new ApplicationException("The url is downloading.");
}
try {
using (cancellationToken.Register(CancelAsync))
using (Stream responseStream = await OpenReadTaskAsync(address).ConfigureAwait(false)) {
HttpWebResponse response = _uriContexts[address].Response;
if (fileName.IsNullOrEmpty())
{
fileName = response.GetContentDispositionFileName() ??
Path.GetFileName(response.ResponseUri.AbsolutePath) ??
throw new ArgumentException("fileName");
}
string fullPath = Path.Combine(directory, fileName);
FileMode fileMode = FileMode.Create;
FileInfo file = new FileInfo(fullPath);
if (file.Exists)
{
FileExistsContext fileExistsContext = new FileExistsContext(response.ResponseUri, fullPath)
{
FileExistsHandling = _defaultFileExistsHandling,
};
FileExists?.Invoke(this, new EventArgs <FileExistsContext>(fileExistsContext));
switch (fileExistsContext.FileExistsHandling)
{
case FileExistsHandling.Ignore:
return;
case FileExistsHandling.Resume:
if (file.Length >= response.ContentLength)
{
return;
}
fileMode = FileMode.OpenOrCreate;
downloadContext.CurrentFileLength = file.Length;
break;
case FileExistsHandling.Rename:
do
{
string newFileName = "{0} - New{1}".FormatWith(
Path.GetFileNameWithoutExtension(fullPath), Path.GetExtension(fullPath));
fullPath = Path.Combine(directory, newFileName);
file = new FileInfo(fullPath);
} while (file.Exists);
break;
}
}
using (FileStream fileStream = new FileStream(fullPath, fileMode)) {
if (downloadContext.CurrentFileLength > 0 && downloadContext.Response.IsRangeSupported())
{
fileStream.Seek(downloadContext.CurrentFileLength, SeekOrigin.Begin);
}
await responseStream.CopyToAsync(fileStream).ConfigureAwait(false);
await fileStream.FlushAsync().ConfigureAwait(false);
}
}
}
finally {
_uriContexts.TryRemove(address, out DownloadContext value);
}
}
