Build the read-ahead mechanism into SftpFileStream

Author: Rob-Hague

src/Renci.SshNet/Common/Extensions.cs

@@ -3,6 +3,7 @@
 using System.Globalization;
 #if !NET
 using System.IO;
+using System.Threading.Tasks;
 #endif
 using System.Net;
 using System.Net.Sockets;
@@ -409,6 +410,29 @@ internal static void ReadExactly(this Stream stream, byte[] buffer, int offset,
                 totalRead += read;
             }
         }
+
+        internal static Task<T> WaitAsync<T>(this Task<T> task, CancellationToken cancellationToken)
+        {
+            if (task.IsCompleted || !cancellationToken.CanBeCanceled)
+            {
+                return task;
+            }
+
+            return WaitCore();
+
+            async Task<T> WaitCore()
+            {
+                TaskCompletionSource<T> tcs = new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+                using var reg = cancellationToken.Register(
+                    () => tcs.TrySetCanceled(cancellationToken),
+                    useSynchronizationContext: false);
+
+                var completedTask = await Task.WhenAny(task, tcs.Task).ConfigureAwait(false);
+
+                return await completedTask.ConfigureAwait(false);
+            }
+        }
 #endif
     }
 }

src/Renci.SshNet/IServiceFactory.cs

@@ -83,18 +83,6 @@ internal partial interface IServiceFactory
         /// <exception cref="SshConnectionException">No key exchange algorithm is supported by both client and server.</exception>
         IKeyExchange CreateKeyExchange(IDictionary<string, Func<IKeyExchange>> clientAlgorithms, string[] serverAlgorithms);
 
-        /// <summary>
-        /// Creates an <see cref="ISftpFileReader"/> for the specified file and with the specified
-        /// buffer size.
-        /// </summary>
-        /// <param name="fileName">The file to read.</param>
-        /// <param name="sftpSession">The SFTP session to use.</param>
-        /// <param name="bufferSize">The size of buffer.</param>
-        /// <returns>
-        /// An <see cref="ISftpFileReader"/>.
-        /// </returns>
-        ISftpFileReader CreateSftpFileReader(string fileName, ISftpSession sftpSession, uint bufferSize);
-
         /// <summary>
         /// Creates a new <see cref="ISftpResponseFactory"/> instance.
         /// </summary>

src/Renci.SshNet/ServiceFactory.cs

@@ -4,8 +4,6 @@
 using System.Net.Sockets;
 using System.Text;
 
-using Microsoft.Extensions.Logging;
-
 using Renci.SshNet.Common;
 using Renci.SshNet.Connection;
 using Renci.SshNet.Messages.Transport;
@@ -118,51 +116,6 @@ public INetConfSession CreateNetConfSession(ISession session, int operationTimeo
             return new NetConfSession(session, operationTimeout);
         }
 
-        /// <summary>
-        /// Creates an <see cref="ISftpFileReader"/> for the specified file and with the specified
-        /// buffer size.
-        /// </summary>
-        /// <param name="fileName">The file to read.</param>
-        /// <param name="sftpSession">The SFTP session to use.</param>
-        /// <param name="bufferSize">The size of buffer.</param>
-        /// <returns>
-        /// An <see cref="ISftpFileReader"/>.
-        /// </returns>
-        public ISftpFileReader CreateSftpFileReader(string fileName, ISftpSession sftpSession, uint bufferSize)
-        {
-            const int defaultMaxPendingReads = 10;
-
-            // Issue #292: Avoid overlapping SSH_FXP_OPEN and SSH_FXP_LSTAT requests for the same file as this
-            // causes a performance degradation on Sun SSH
-            var openAsyncResult = sftpSession.BeginOpen(fileName, Flags.Read, callback: null, state: null);
-            var handle = sftpSession.EndOpen(openAsyncResult);
-
-            var statAsyncResult = sftpSession.BeginLStat(fileName, callback: null, state: null);
-
-            long? fileSize;
-            int maxPendingReads;
-
-            var chunkSize = sftpSession.CalculateOptimalReadLength(bufferSize);
-
-            // fallback to a default maximum of pending reads when remote server does not allow us to obtain
-            // the attributes of the file
-            try
-            {
-                var fileAttributes = sftpSession.EndLStat(statAsyncResult);
-                fileSize = fileAttributes.Size;
-                maxPendingReads = Math.Min(100, (int)Math.Ceiling((double)fileAttributes.Size / chunkSize) + 1);
-            }
-            catch (SshException ex)
-            {
-                fileSize = null;
-                maxPendingReads = defaultMaxPendingReads;
-
-                sftpSession.SessionLoggerFactory.CreateLogger<ServiceFactory>().LogInformation(ex, "Failed to obtain size of file. Allowing maximum {MaxPendingReads} pending reads", maxPendingReads);
-            }
-
-            return sftpSession.CreateFileReader(handle, sftpSession, chunkSize, maxPendingReads, fileSize);
-        }
-
         /// <summary>
         /// Creates a new <see cref="ISftpResponseFactory"/> instance.
         /// </summary>

src/Renci.SshNet/Sftp/ISftpFileReader.cs

@@ -71,7 +71,7 @@ internal interface ISftpSession : ISubsystemSession
         /// <returns>
         /// The file attributes.
         /// </returns>
-        SftpFileAttributes RequestFStat(byte[] handle, bool nullOnError);
+        SftpFileAttributes RequestFStat(byte[] handle, bool nullOnError = false);
 
         /// <summary>
         /// Asynchronously performs a <c>SSH_FXP_FSTAT</c> request.
@@ -522,19 +522,5 @@ void RequestWrite(byte[] handle,
         /// Currently, we do not take the remote window size into account.
         /// </remarks>
         uint CalculateOptimalWriteLength(uint bufferSize, byte[] handle);
-
-        /// <summary>
-        /// Creates an <see cref="ISftpFileReader"/> for reading the content of the file represented by a given <paramref name="handle"/>.
-        /// </summary>
-        /// <param name="handle">The handle of the file to read.</param>
-        /// <param name="sftpSession">The SFTP session.</param>
-        /// <param name="chunkSize">The maximum number of bytes to read with each chunk.</param>
-        /// <param name="maxPendingReads">The maximum number of pending reads.</param>
-        /// <param name="fileSize">The size of the file or <see langword="null"/> when the size could not be determined.</param>
-        /// <returns>
-        /// An <see cref="ISftpFileReader"/> for reading the content of the file represented by the
-        /// specified <paramref name="handle"/>.
-        /// </returns>
-        ISftpFileReader CreateFileReader(byte[] handle, ISftpSession sftpSession, uint chunkSize, int maxPendingReads, long? fileSize);
     }
 }