Fixed: Don't rollback file move if destination already exists

(cherry picked from commit f05405fe1ce4c78a8c75e27920c863c5b83686bd)
(cherry picked from commit 8ab040f612ee04dac4813a08cdeaddd446a64dc9)

src/NzbDrone.Common.Test/DiskTests/DiskTransferServiceFixture.cs

@@ -351,6 +351,26 @@ public void should_rollback_move_on_partial_if_source_remains()
                 .Verify(v => v.DeleteFile(_targetPath), Times.Once());
         }
 
+        [Test]
+        public void should_not_rollback_move_on_partial_if_destination_already_exists()
+        {
+            Mocker.GetMock<IDiskProvider>()
+                .Setup(v => v.MoveFile(_sourcePath, _targetPath, false))
+                .Callback(() =>
+                {
+                    WithExistingFile(_targetPath, true, 900);
+                });
+
+            Mocker.GetMock<IDiskProvider>()
+                .Setup(v => v.MoveFile(_sourcePath, _targetPath, false))
+                .Throws(new FileAlreadyExistsException("File already exists", _targetPath));
+
+            Assert.Throws<FileAlreadyExistsException>(() => Subject.TransferFile(_sourcePath, _targetPath, TransferMode.Move));
+
+            Mocker.GetMock<IDiskProvider>()
+                .Verify(v => v.DeleteFile(_targetPath), Times.Never());
+        }
+
         [Test]
         public void should_log_error_if_rollback_partialmove_fails()
         {

src/NzbDrone.Common/Disk/DiskProviderBase.cs

@@ -264,6 +264,11 @@ public void MoveFolder(string source, string destination, bool overwrite = false
 
         protected virtual void MoveFileInternal(string source, string destination)
         {
+            if (File.Exists(destination))
+            {
+                throw new FileAlreadyExistsException("File already exists", destination);
+            }
+
             File.Move(source, destination);
         }
 

src/NzbDrone.Common/Disk/DiskTransferService.cs

@@ -500,9 +500,13 @@ private void TryMoveFileVerified(string sourcePath, string targetPath, long orig
                     throw new IOException(string.Format("File move incomplete, data loss may have occurred. [{0}] was {1} bytes long instead of the expected {2}.", targetPath, targetSize, originalSize));
                 }
             }
-            catch
+            catch (Exception ex)
             {
-                RollbackPartialMove(sourcePath, targetPath);
+                if (ex is not FileAlreadyExistsException)
+                {
+                    RollbackPartialMove(sourcePath, targetPath);
+                }
+
                 throw;
             }
         }

src/NzbDrone.Common/Disk/FileAlreadyExistsException.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace NzbDrone.Common.Disk
+{
+    public class FileAlreadyExistsException : Exception
+    {
+        public string Filename { get; set; }
+
+        public FileAlreadyExistsException(string message, string filename)
+            : base(message)
+        {
+            Filename = filename;
+        }
+    }
+}