Use SetUnixFileMode for chmod

[kasperk81]

To stay compatible with the behavior described in the .NET specs:

• https://github.com/dotnet/designs/blob/main/accepted/2021/workloads/workload-installation.md#setting-unix-file-permissions
• https://github.com/dotnet/templating/blob/0756f9688a803dcb64f966180d7b61922d76576e/docs/Post-Action-Registry.md#change-file-permissions

these specs effectively define the permission string as whatever chmod accepts which makes the format somewhat vague and underspecified.

To accommodate this, I added chmod-style permission parsing based on POSIX spec e.g. cases handled in: https://github.com/landley/toybox/blob/c9c0d42aae50b80cda27bd6131f315e57513be47/lib/lib.c#L950. This is used as a fallback when parsing user-provided System.IO.UnixFileMode enum names fails: https://learn.microsoft.com/en-us/dotnet/api/system.io.unixfilemode#fields

As a result, the following formats are supported.

Existing data/UnixFilePermissions.xml (unchanged)

<FileList>
  <File Path="data/Darwin/mono" Permission="755" />
  <File Path="data/Darwin/dotnet" Permission="+x" />
</FileList>

New (enum-based permissions)

<FileList>
  <File Path="data/Darwin/mono" Permission="UserWrite|OtherRead" />
</FileList>

This preserves backward compatibility while also allowing explicit permissions using the UnixFileMode enum.

[KalleOlaviNiemitalo]

Does this support o+r-w? In chmod, that is the same as o+r,o-w.

[kasperk81]

Does this support o+r-w? In chmod, that is the same as o+r,o-w.

yes it does same as POSIX/toybox implementation

[KalleOlaviNiemitalo]

Really? It seems to me there aren't enough nested loops.

[KalleOlaviNiemitalo]

It seems to execute o+r-w as o+r,-w rather than o+r,o-w.

1. Initializes int i = 0 and enters the while (i < argument.Length) loop on line 84.
2. Parses u/g/o/a, finds o.
3. Sets op = '+'.
4. Enters the “Parse permissions” loop while (i < argument.Length && argument[i] != ',' && "+-=".IndexOf(argument[i]) == -1).
5. Recognises 'r' and sets permMask.
6. Reaches '-' and exits the “Parse permissions” loop.
7. Applies the + operation and the 'r' permission to o.
8. Loops back to line 84 while (i < argument.Length).
9. Tries to parse u/g/o/a but doesn’t find any, thus defaults to u = g = o = true!
10. Sets op = '-'.
11. Enters the “Parse permissions” loop.
12. Recognises 'w' and sets permMask.
13. Reaches argument.Length and exits the “Parse permissions” loop.
14. Applies the - operation and the w permission to ugo rather than only to o!

[kasperk81]

@KalleOlaviNiemitalo thanks! after the fix, tested with:

Console.WriteLine("o+r-w -> " + ChmodHelper.Parse("o+r-w", UnixFileMode.UserWrite | UnixFileMode.GroupWrite));
Console.WriteLine("u+x,g-w -> " + ChmodHelper.Parse("u+x,g-w", UnixFileMode.UserWrite | UnixFileMode.GroupWrite));
Console.WriteLine("a=r -> " + ChmodHelper.Parse("a=r", 0));
Console.WriteLine("g=u -> " + ChmodHelper.Parse("g=u", UnixFileMode.UserRead | UnixFileMode.UserWrite));
Console.WriteLine("u+s,g+s,o+t -> " + ChmodHelper.Parse("u+s,g+s,o+t", 0));
Console.WriteLine("u+rwx,g-r,o-r -> " + ChmodHelper.Parse("u+rwx,g-r,o-r", UnixFileMode.UserWrite | UnixFileMode.GroupWrite | UnixFileMode.OtherRead));
Console.WriteLine("o+x,u-g -> " + ChmodHelper.Parse("o+x,u-g", UnixFileMode.UserRead | UnixFileMode.GroupRead));

o+r-w -> OtherRead, GroupWrite, UserWrite
u+x,g-w -> UserExecute, UserWrite
a=r -> OtherRead, GroupRead, UserRead
g=u -> GroupWrite, GroupRead, UserWrite, UserRead
u+s,g+s,o+t -> StickyBit, SetGroup, SetUser
u+rwx,g-r,o-r -> GroupWrite, UserExecute, UserWrite, UserRead
o+x,u-g -> OtherExecute, GroupRead

[kasperk81]

@tmds, @akoeplinger ptal

[akoeplinger]

@kasperk81 I'm not sure adding all this parsing logic is a good idea. For the UnixFilePermissions.xml we can just support the numerical formats and use SetUnixFileMode, but for the templating case I'd just leave it as is