SetCreationTime on Mac

[hamarb123]

Description

The method System.IO.File.SetCreationTime[Utc](string, DateTime) does not work correctly on mac, but the System.IO.File.GetCreationTime[Utc](string, DateTime) does.
The following code snippet creates different results on mac and windows:

using System.IO;

static class Program
{
  static void Main()
  {
    string filePath = @"/path/to/file"; //change to appropriate path where file doesn't exist
    File.Create(filePath);
    FileInfo fi = new FileInfo(filePath);
    fi.LastAccessTimeUtc = new DateTime(2020, 1, 2);
    fi.LastWriteTimeUtc = new DateTime(2020, 1, 3);
    fi.CreationTimeUtc = new DateTime(2020, 1, 1);
    fi.Refresh();
    Console.WriteLine(fi.LastAccessTimeUtc.ToString()); //expect 2/1/2020 12:00:00 am
    Console.WriteLine(fi.LastWriteTimeUtc.ToString()); //expect 3/1/2020 12:00:00 am, get 1/1/2020 12:00:00 am on Mac
    Console.WriteLine(fi.CreationTimeUtc.ToString()); //expect 1/1/2020 12:00:00 am
  }
}

I believe that this method contains the implementation for Unix platforms, but I think that Mac should have a different implementation for this function to Unix as there is an actual way to do this on Mac.

Swift code to change date:

let filePath = "/path/to/file"
let date = NSDate()
let fileAttributes = [FileAttributeKey.creationDate: date]
FileManager.default.setAttributes(fileAttributes, ofItemAtPath: filePath)

This code, in theory, sets the creation date of the file; there must be a way to implement this in C# on the Mac version, it is also probably a good idea to implement the other methods (last write and access dates) like this, as it seems that setting the last write date changes the creation date sometimes (see this).

Configuration

I tested the code on macOS Catalina (x64) and Windows 10 (x64). It is specific to unix platforms.

Regression?

I do not know.

Other information

A workaround could be to set the creation date, and then set the modification date back again. This will work sometimes, but not always.

[Dotnet-GitSync-Bot]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[danmoseley]

We'd certainly like to make it work if there's an API. Can you figure out what API we could call? I assume there's something lower level.

[hamarb123]

We'd certainly like to make it work if there's an API. Can you figure out what API we could call? I assume there's something lower level.

@danmosemsft It took me a while, but I have figured out working C# code that does what it should:

using System;
using System.Runtime.InteropServices;

namespace dotnet_runtime_39132_poc
{
	class Program
	{
		internal const string libobjc = "/usr/lib/libobjc.dylib";

		[DllImport(libobjc)]
		private static extern IntPtr objc_getClass(string className);

		[DllImport(libobjc)]
		private static extern IntPtr sel_registerName(string str);

		[DllImport(libobjc)]
		private static extern IntPtr objc_msgSend(IntPtr basePtr, IntPtr selector);

		[DllImport(libobjc)]
		private static extern IntPtr objc_msgSend(IntPtr basePtr, IntPtr selector, double secondsSince);

		[DllImport(libobjc)]
		private static extern IntPtr objc_msgSend(IntPtr basePtr, IntPtr selector, [MarshalAs(UnmanagedType.LPUTF8Str)] string arg1);

		[DllImport(libobjc)]
		private static extern IntPtr objc_msgSend(IntPtr basePtr, IntPtr selector, IntPtr arg1, IntPtr arg2);

		[DllImport(libobjc)]
		private static extern sbyte objc_msgSend(IntPtr basePtr, IntPtr selector, IntPtr arg1, IntPtr arg2, IntPtr arg3);

		static void Main(string[] args)
		{
			SetTime("/Users/Hamish/Desktop/test file", true, new DateTime(2020, 1, 1, 10, 0, 57));
			SetTime("/Users/Hamish/Desktop/test file", false, new DateTime(2020, 1, 2, 10, 0, 57));
		}

		static IntPtr NSDate;
		static IntPtr NSDictionary;
		static IntPtr NSFileManager;
		static IntPtr NSString;
		static IntPtr alloc;
		static IntPtr init;
		static IntPtr initWithUTF8String_;
		static IntPtr initWithTimeIntervalSince1970_;
		static IntPtr dictionaryWithObject_forKey_;
		static IntPtr defaultManager;
		static IntPtr setAttributes_ofItemAtPath_error_;
		static IntPtr release;
		static IntPtr NSFileCreationDate;
		static IntPtr NSFileModificationDate;
		static IntPtr _NSFileManager;

		static Program()
		{
			NSDate = objc_getClass("NSDate");
			NSDictionary = objc_getClass("NSDictionary");
			NSFileManager = objc_getClass("NSFileManager");
			NSString = objc_getClass("NSString");

			alloc = sel_registerName("alloc");
			init = sel_registerName("init");
			initWithUTF8String_ = sel_registerName("initWithUTF8String:");
			initWithTimeIntervalSince1970_ = sel_registerName("initWithTimeIntervalSince1970:");
			dictionaryWithObject_forKey_ = sel_registerName("dictionaryWithObject:forKey:");
			defaultManager = sel_registerName("defaultManager");
			setAttributes_ofItemAtPath_error_ = sel_registerName("setAttributes:ofItemAtPath:error:");
			release = sel_registerName("release");

			NSFileCreationDate = objc_msgSend(NSString, alloc);
			NSFileCreationDate = objc_msgSend(NSFileCreationDate, initWithUTF8String_, "NSFileCreationDate");

			NSFileModificationDate = objc_msgSend(NSString, alloc);
			NSFileModificationDate = objc_msgSend(NSFileModificationDate, initWithUTF8String_, "NSFileModificationDate");

			_NSFileManager = objc_msgSend(NSFileManager, defaultManager);
		}

		static void SetTime(string path, bool isModificationDate, DateTime time)
		{
			var date = objc_msgSend(NSDate, alloc);
			date = objc_msgSend(date, initWithTimeIntervalSince1970_, (time.ToUniversalTime() - DateTime.UnixEpoch).TotalSeconds);
			var fileAttributes = objc_msgSend(NSDictionary, dictionaryWithObject_forKey_, date, isModificationDate ? NSFileModificationDate : NSFileCreationDate);
			var native_filePath = objc_msgSend(NSString, alloc);
			native_filePath = objc_msgSend(native_filePath, initWithUTF8String_, path);
			var retV = objc_msgSend(_NSFileManager, setAttributes_ofItemAtPath_error_, fileAttributes, native_filePath, IntPtr.Zero);
			objc_msgSend(date, release);
			objc_msgSend(fileAttributes, release);
			objc_msgSend(native_filePath, release);
		}
	}
}

This code can set the creation date, and the modification date.
There is one caveat: if you set the modification date to before the creation date it will change the creation date to the new modification date, which differs in behaviour to Windows. This could easily happen when you are copying file (the modification date stays, but the creation date changes to the current date). So I recommend that we check the creation date when changing the modification date, and changing the creation date back afterwards if it was after the new modification date, which would look something like this:

var creationDate = File.GetCreationTimeUtc(path);
SetTime(path, true, newModDateUtc);
if (newModDateUtc < creationDate) SetTime(path, false, creationDate);

Would this be an acceptable way to implement this? If so I'll create a PR with the necessary changes (I'll need to know how to make this code Mac only w/o using #ifs if that's required).

[danmoseley]

Area owners for IO should answer whether they'd accept a PR. (@carlossanlop @jozkee)

Most IO stuff is done with glibc calls - but we do have some libobjc use elsewhere: https://github.com/dotnet/runtime/blob/master/src/libraries/Common/src/Interop/OSX/Interop.libobjc.cs

https://github.com/dotnet/runtime/blob/master/src/libraries/System.IO.FileSystem/src/System/IO/FileStatus.Unix.cs would have to be split into ...OSX.cs and OtherUnix.cs and System.IO.FileSystem.dll looks like it only has a Unix configuration today, it would need to have an OSX configuration broken out.

[hamarb123]

@carlossanlop @jozkee, would you guys accept a PR for this?

[jozkee]

FWIW: This also fails on linux distros, I tried it on WSL and got the reported error so maybe we don't have to split the file and perhaps there is an unified way to solve the problem for Unix (Linux and OSX).

[hamarb123]

FWIW: This also fails on linux distros, I tried it on WSL and got the reported error so maybe we don't have to split the file and perhaps there is an unified way to solve the problem for Unix (Linux and OSX).

@jozkee I do not believe that there is an easy way to do it on all Unix systems. It says that there is no API to update the CreationTime on Unix systems here, and it says that Linux does not even store it, so I think that we should either have it as a known issue on Linux (and document it, as it took me quite a while to debug my code when it was undocumented), or throw a PlatformNotSupportedException when trying to set the creation date on Linux platforms.

[hamarb123]

But there could be an API that I do not know about.

[danmoseley]

From what I have read recently and in the past, there is not really a way to do this on Linux. And that is why the Apple way is not using a POSIX API at all.

[jozkee]

It says that there is no API to update the CreationTime on Unix systems here

Ah, I didn't see that part.

OK, in that case I think is good that we could fix this for Mac, @hamarb123 a PR for it would be very welcome.

[hamarb123]

@jozkee what TFMs should I break it up into? The current csproj file has:

<TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;$(NetCoreAppCurrent)-Unix;$(NetCoreAppCurrent)-Browser</TargetFrameworks>