Implement mono logic to not set owner/group with chown

New: Allow Owner or Group to be left blank to not set it when changing owner (mono only)
Closes #1220

src/NzbDrone.Mono/DiskProvider.cs

@@ -18,6 +18,10 @@ namespace NzbDrone.Mono
         private readonly IProcMountProvider _procMountProvider;
         private readonly ISymbolicLinkResolver _symLinkResolver;
 
+        // Mono supports sending -1 for a uint to indicate that the owner or group should not be set
+        // `unchecked((uint)-1)` and `uint.MaxValue` are the same thing.
+        private const uint UNCHANGED_ID = uint.MaxValue;
+
         public DiskProvider(IProcMountProvider procMountProvider, ISymbolicLinkResolver symLinkResolver)
         {
             _procMountProvider = procMountProvider;
@@ -75,50 +79,77 @@ namespace NzbDrone.Mono
 
         public override void SetPermissions(string path, string mask, string user, string group)
         {
-            Logger.Debug("Setting permissions: {0} on {1}", mask, path);
+            SetPermissions(path, mask);
+            SetOwner(path, user, group);
+        }
 
-            var filePermissions = NativeConvert.FromOctalPermissionString(mask);
+        public override System.Collections.Generic.List<IMount> GetMounts()
+        {
+            return base.GetMounts()
+                       .Concat(_procMountProvider.GetMounts())
+                       .DistinctBy(v => v.RootDirectory)
+                       .ToList();
+        }
 
-            if (Syscall.chmod(path, filePermissions) < 0)
+        public override long? GetTotalSize(string path)
         {
-                var error = Stdlib.GetLastError();
+            Ensure.That(path, () => path).IsValidPath();
 
-                throw new LinuxPermissionsException("Error setting file permissions: " + error);
-            }
+            try
+            {
+                var mount = GetMount(path);
 
-            if (string.IsNullOrWhiteSpace(user) || string.IsNullOrWhiteSpace(group))
+                if (mount == null) return null;
+
+                return mount.TotalSize;
+            }
+            catch (InvalidOperationException e)
             {
-                Logger.Debug("User or Group for chown not configured, skipping chown.");
-                return;
+                Logger.Error(e, "Couldn't get total space for " + path);
             }
 
-            uint userId;
-            uint groupId;
+            return null;
+        }
 
-            if (!uint.TryParse(user, out userId))
+        public override bool TryCreateHardLink(string source, string destination)
         {
-                var u = Syscall.getpwnam(user);
-
-                if (u == null)
+            try
             {
-                    throw new LinuxPermissionsException("Unknown user: {0}", user);
+                UnixFileSystemInfo.GetFileSystemEntry(source).CreateLink(destination);
+                return true;
+            }
+            catch (Exception ex)
+            {
+                Logger.Debug(ex, string.Format("Hardlink '{0}' to '{1}' failed.", source, destination));
+                return false;
             }
-
-                userId = u.pw_uid;
         }
 
-            if (!uint.TryParse(group, out groupId))
+        private void SetPermissions(string path, string mask)
         {
-                var g = Syscall.getgrnam(group);
+            Logger.Debug("Setting permissions: {0} on {1}", mask, path);
 
-                if (g == null)
+            var filePermissions = NativeConvert.FromOctalPermissionString(mask);
+
+            if (Syscall.chmod(path, filePermissions) < 0)
             {
-                    throw new LinuxPermissionsException("Unknown group: {0}", group);
+                var error = Stdlib.GetLastError();
+
+                throw new LinuxPermissionsException("Error setting file permissions: " + error);
+            }
         }
 
-                groupId = g.gr_gid;
+        private void SetOwner(string path, string user, string group)
+        {
+            if (string.IsNullOrWhiteSpace(user) && string.IsNullOrWhiteSpace(group))
+            {
+                Logger.Debug("User and Group for chown not configured, skipping chown.");
+                return;
             }
 
+            var userId = GetUserId(user);
+            var groupId = GetGroupId(group);
+
             if (Syscall.chown(path, userId, groupId) < 0)
             {
                 var error = Stdlib.GetLastError();
@@ -127,46 +158,54 @@ namespace NzbDrone.Mono
             }
         }
 
-        public override System.Collections.Generic.List<IMount> GetMounts()
+        private uint GetUserId(string user)
         {
-            return base.GetMounts()
-                       .Concat(_procMountProvider.GetMounts())
-                       .DistinctBy(v => v.RootDirectory)
-                       .ToList();
+            if (user.IsNullOrWhiteSpace())
+            {
+                return UNCHANGED_ID;
             }
 
-        public override long? GetTotalSize(string path)
-        {
-            Ensure.That(path, () => path).IsValidPath();
+            uint userId;
 
-            try
+            if (uint.TryParse(user, out userId))
             {
-                var mount = GetMount(path);
+                return userId;
+            }
 
-                if (mount == null) return null;
+            var u = Syscall.getpwnam(user);
 
-                return mount.TotalSize;
-            }
-            catch (InvalidOperationException e)
+            if (u == null)
             {
-                Logger.Error(e, "Couldn't get total space for " + path);
+                throw new LinuxPermissionsException("Unknown user: {0}", user);
             }
 
-            return null;
+            return u.pw_uid;
         }
 
-        public override bool TryCreateHardLink(string source, string destination)
+        private uint GetGroupId(string group)
         {
-            try
+            if (group.IsNullOrWhiteSpace())
             {
-                UnixFileSystemInfo.GetFileSystemEntry(source).CreateLink(destination);
-                return true;
+                return UNCHANGED_ID;
             }
-            catch (Exception ex)
+
+            uint groupId;
+
+            if (uint.TryParse(group, out groupId))
             {
-                Logger.Debug(ex, string.Format("Hardlink '{0}' to '{1}' failed.", source, destination));
-                return false;
+                return groupId;
+            }
+
+            var g = Syscall.getgrnam(group);
+
+            if (g == null)
+            {
+                throw new LinuxPermissionsException("Unknown group: {0}", group);
             }
+
+            return g.gr_gid;
+
+            
         }
     }
 }