Issue: The DownloadFileAsync method will throw an OutOfMemoryExceptio…

…n if the file is too large (#342)

* DownloadFileWithouBufferingAsync method added to avoid buffering of the recording file stream

* cancellation token added

* Apply PR comments

---------

Co-authored-by: P. Gritsenko <pavel.gritsenko@lanit-tercom.com>

Source/ZoomNet/Resources/CloudRecordings.cs

@@ -4,10 +4,12 @@
 using System.IO;
 using System.Linq;
 using System.Net.Http;
+using System.Net.Http.Headers;
 using System.Text.Json.Nodes;
 using System.Threading;
 using System.Threading.Tasks;
 using ZoomNet.Models;
+using ZoomNet.Utilities;
 
 namespace ZoomNet.Resources
 {
@@ -356,20 +358,44 @@ public Task RejectRegistrantsAsync(long meetingId, IEnumerable<string> registran
 			return UpdateRegistrantsStatusAsync(meetingId, registrantIds, "deny", cancellationToken);
 		}
 
-		/// <summary>
-		/// Download the recording file.
-		/// </summary>
-		/// <param name="downloadUrl">The URL of the recording file to download.</param>
-		/// <param name="cancellationToken">Cancellation token.</param>
-		/// <returns>
-		/// The <see cref="Stream"/> containing the file.
-		/// </returns>
-		public Task<Stream> DownloadFileAsync(string downloadUrl, CancellationToken cancellationToken = default)
+		/// <inheritdoc/>
+		public async Task<Stream> DownloadFileAsync(string downloadUrl, CancellationToken cancellationToken = default)
 		{
-			return _client
+			/*
+			 * PLEASE NOTE:
+			 *
+			 * The HttpRequestMessage in this method is dispatched with its completion option set to "ResponseHeadersRead".
+			 * This ensures the content of the response is streamed rather than buffered in memory.
+			 * This is important in cases where the downloaded file is quite large.
+			 * In this scenario, we don't want the entirety of the file to be buffered in a MemoryStream because
+			 * it could lead to "out of memory" exceptions if the file is large enough.
+			 * See https://github.com/Jericho/ZoomNet/pull/342 for a discussion on this topic.
+			 *
+			 * Forthermore, as of this writing, the FluentHttp library does not allow us to stream the content of responses
+			 * which means that the code in this method cannot be simplified like so:
+			 return _client
 				.GetAsync(downloadUrl)
 				.WithCancellationToken(cancellationToken)
 				.AsStream();
+			 *
+			 * The downside of not using the FluentHttp library to dispatch the request is that we lose automatic retries,
+			 * error handling, logging, etc.
+			 */
+
+			using (var request = new HttpRequestMessage(HttpMethod.Get, downloadUrl))
+			{
+				var tokenHandler = _client.Filters.OfType<ITokenHandler>().SingleOrDefault();
+				if (tokenHandler != null)
+				{
+					request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", tokenHandler.Token);
+				}
+
+				var response = await _client.BaseClient.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken).ConfigureAwait(false);
+
+				response.EnsureSuccessStatusCode();
+
+				return await response.Content.ReadAsStreamAsync();
+			}
 		}
 
 		private Task UpdateRegistrantsStatusAsync(long meetingId, IEnumerable<string> registrantIds, string status, CancellationToken cancellationToken = default)