From c0201f722bba6c424dc840f9f8edfc5c37ab9b7b Mon Sep 17 00:00:00 2001
From: Marius Thesing <marius.thesing@gmail.com>
Date: Sat, 29 Mar 2025 11:43:26 +0100
Subject: [PATCH] lock SendData to fix random connection failures

---
 src/Renci.SshNet/Channels/Channel.cs          | 24 +++++++++++--------
 .../SftpClientTest.Upload.cs                  |  5 ----
 2 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/src/Renci.SshNet/Channels/Channel.cs b/src/Renci.SshNet/Channels/Channel.cs
index 4c3569cef..d009c3370 100644
--- a/src/Renci.SshNet/Channels/Channel.cs
+++ b/src/Renci.SshNet/Channels/Channel.cs
@@ -17,6 +17,7 @@ internal abstract class Channel : IChannel
     {
         private readonly Lock _serverWindowSizeLock = new Lock();
         private readonly Lock _messagingLock = new Lock();
+        private readonly Lock _sendDataLock = new Lock();
         private readonly uint _initialWindowSize;
         private readonly ISession _session;
         private readonly ILogger _logger;
@@ -340,19 +341,22 @@ public void SendData(byte[] data, int offset, int size)
                 return;
             }
 
-            var totalBytesToSend = size;
-            while (totalBytesToSend > 0)
+            lock (_sendDataLock)
             {
-                var sizeOfCurrentMessage = GetDataLengthThatCanBeSentInMessage(totalBytesToSend);
+                var totalBytesToSend = size;
+                while (totalBytesToSend > 0)
+                {
+                    var sizeOfCurrentMessage = GetDataLengthThatCanBeSentInMessage(totalBytesToSend);
 
-                var channelDataMessage = new ChannelDataMessage(RemoteChannelNumber,
-                                                                data,
-                                                                offset,
-                                                                sizeOfCurrentMessage);
-                _session.SendMessage(channelDataMessage);
+                    var channelDataMessage = new ChannelDataMessage(RemoteChannelNumber,
+                                                                    data,
+                                                                    offset,
+                                                                    sizeOfCurrentMessage);
+                    _session.SendMessage(channelDataMessage);
 
-                totalBytesToSend -= sizeOfCurrentMessage;
-                offset += sizeOfCurrentMessage;
+                    totalBytesToSend -= sizeOfCurrentMessage;
+                    offset += sizeOfCurrentMessage;
+                }
             }
         }
 
diff --git a/test/Renci.SshNet.IntegrationTests/OldIntegrationTests/SftpClientTest.Upload.cs b/test/Renci.SshNet.IntegrationTests/OldIntegrationTests/SftpClientTest.Upload.cs
index c48c53211..e5cd91400 100644
--- a/test/Renci.SshNet.IntegrationTests/OldIntegrationTests/SftpClientTest.Upload.cs
+++ b/test/Renci.SshNet.IntegrationTests/OldIntegrationTests/SftpClientTest.Upload.cs
@@ -77,11 +77,6 @@ public void Test_Sftp_Upload_Forbidden()
         [TestCategory("Sftp")]
         public void Test_Sftp_Multiple_Async_Upload_And_Download_10Files_5MB_Each()
         {
-            if (Environment.GetEnvironmentVariable("CI") == "true")
-            {
-                Assert.Inconclusive("Skipping because of failures in CI, see #1253");
-            }
-
             var maxFiles = 10;
             var maxSize = 5;