expand use of FileDescriptor and add FileDescriptorLike type alias

When accepting file descriptors, non-int objects with a fileno method
are now generally accepted. When returning a file descriptor, a
FileDescriptor instance is now returned.

1 files changed, 12 insertions, 9 deletions

diff --git a/linuxnamespaces/atlocation.py b/linuxnamespaces/atlocation.py
index 0003c35..d30e88f 100644
--- a/linuxnamespaces/atlocation.py
+++ b/linuxnamespaces/atlocation.py
@@ -15,7 +15,7 @@ import pathlib
 import stat
 import typing
 
-from .filedescriptor import FileDescriptor
+from .filedescriptor import FileDescriptor, FileDescriptorLike, HasFileno
 
 
 AT_FDCWD = FileDescriptor(-100)
@@ -58,7 +58,7 @@ class AtLocation:
 
     def __new__(
         cls,
-        thing: typing.Union["AtLocation", int, PathConvertible],
+        thing: typing.Union["AtLocation", FileDescriptorLike, PathConvertible],
         location: PathConvertible | None = None,
         flags: AtFlags = AtFlags.NONE,
     ) -> "AtLocation":
@@ -76,13 +76,14 @@ class AtLocation:
                 )
             return thing  # Don't copy.
         obj = super(AtLocation, cls).__new__(cls)
-        if isinstance(thing, int):
+        if not isinstance(thing, FileDescriptor):
+            if isinstance(thing, int) or isinstance(thing, HasFileno):
+                thing = FileDescriptor(thing)
+        if isinstance(thing, FileDescriptor):
             if thing < 0 and thing != AT_FDCWD:
                 raise ValueError("fd cannot be negative")
             if isinstance(thing, FileDescriptor):
                 obj.fd = thing
-            else:
-                obj.fd = FileDescriptor(thing)
             if location is None:
                 obj.location = ""
                 obj.flags = flags | AtFlags.AT_EMPTY_PATH
@@ -148,7 +149,7 @@ class AtLocation:
         them with a slash as separator. The returned AtLocation borrows its fd
         if any.
         """
-        if isinstance(other, int):
+        if isinstance(other, int) or isinstance(other, HasFileno):
             # A an fd is considered an absolute AT_EMPTY_PATH path.
             return AtLocation(other)
         non_empty_flags = self.flags & ~AtFlags.AT_EMPTY_PATH
@@ -422,7 +423,7 @@ class AtLocation:
         assert self.location
         os.mknod(self.location, mode, device, dir_fd=self.fd_or_none)
 
-    def open(self, flags: int, mode: int = 0o777) -> int:
+    def open(self, flags: int, mode: int = 0o777) -> FileDescriptor:
         """Wrapper for os.open supplying path and dir_fd."""
         if self.flags == AtFlags.AT_SYMLINK_NOFOLLOW:
             flags |= os.O_NOFOLLOW
@@ -431,7 +432,9 @@ class AtLocation:
                 "opening an AtLocation only supports flag AT_SYMLINK_NOFOLLOW"
             )
         assert self.location
-        return os.open(self.location, flags, mode, dir_fd=self.fd_or_none)
+        return FileDescriptor(
+            os.open(self.location, flags, mode, dir_fd=self.fd_or_none)
+        )
 
     def readlink(self) -> str:
         """Wrapper for os.readlink supplying path and dir_fd."""
@@ -595,4 +598,4 @@ class AtLocation:
         return f"{cn}({self.fd}, flags={self.flags!r})"
 
 
-AtLocationLike = typing.Union[AtLocation, int, PathConvertible]
+AtLocationLike = typing.Union[AtLocation, FileDescriptorLike, PathConvertible]