Improve SFTP performance on medium-high latency connections

- Increases maxPendingReads from 10 to 100
- Increases socket send/receive buffer to 10 SSH packets (320K)

Author: Pedro Fonseca

src/Renci.SshNet/Connection/ConnectorBase.cs

@@ -42,7 +42,7 @@ protected Socket SocketConnect(string host, int port, TimeSpan timeout)
             {
                 SocketAbstraction.Connect(socket, ep, timeout);
 
-                const int socketBufferSize = 2 * Session.MaximumSshPacketSize;
+                const int socketBufferSize = 10 * Session.MaximumSshPacketSize;
                 socket.SendBufferSize = socketBufferSize;
                 socket.ReceiveBufferSize = socketBufferSize;
                 return socket;

src/Renci.SshNet/ServiceFactory.cs

@@ -112,7 +112,7 @@ from s in serverAlgorithms
 
         public ISftpFileReader CreateSftpFileReader(string fileName, ISftpSession sftpSession, uint bufferSize)
         {
-            const int defaultMaxPendingReads = 3;
+            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
@@ -132,7 +132,7 @@ public ISftpFileReader CreateSftpFileReader(string fileName, ISftpSession sftpSe
             {
                 var fileAttributes = sftpSession.EndLStat(statAsyncResult);
                 fileSize = fileAttributes.Size;
-                maxPendingReads = Math.Min(10, (int) Math.Ceiling((double) fileAttributes.Size / chunkSize) + 1);
+                maxPendingReads = Math.Min(100, (int) Math.Ceiling((double)(fileSize - (long)offset) / chunkSize) + 1);
             }
             catch (SshException ex)
             {