add a FileDescriptor type

It serves two main purposes. For one thing, it allows telling bare
integers and file descriptors apart on a typing level similar to a
NewType. For another it adds common methods to a file descriptor and
enables closing it via a context manager.

1 files changed, 16 insertions, 16 deletions

diff --git a/linuxnamespaces/atlocation.py b/linuxnamespaces/atlocation.py
index 8da5982..8a38650 100644
--- a/linuxnamespaces/atlocation.py
+++ b/linuxnamespaces/atlocation.py
@@ -9,15 +9,16 @@ code for doing so.
 
 import enum
 import errno
-import fcntl
 import os
 import os.path
 import pathlib
 import stat
 import typing
 
+from .filedescriptor import FileDescriptor
 
-AT_FDCWD = -100
+
+AT_FDCWD = FileDescriptor(-100)
 
 
 PathConvertible = typing.Union[str, os.PathLike]
@@ -51,7 +52,7 @@ class AtLocation:
     management.
     """
 
-    fd: int
+    fd: FileDescriptor
     location: PathConvertible
     flags: AtFlags
 
@@ -63,10 +64,10 @@ class AtLocation:
     ) -> "AtLocation":
         """The argument thing can be many different thing. If it is an
         AtLocation, it is copied and all other arguments must be unset. If it
-        is an integer, it is considered to be a file descriptor and the
-        location must be unset if flags contains AT_EMPTY_PATH. flags are used
-        as is except that AT_EMPTY_PATH is automatically added when given a
-        file descriptor and no location.
+        is an integer (e.g. FileDescriptor), it is considered to be a file
+        descriptor and the location must be unset if flags contains
+        AT_EMPTY_PATH. flags are used as is except that AT_EMPTY_PATH is
+        automatically added when given a file descriptor and no location.
         """
         if isinstance(thing, AtLocation):
             if location is not None or flags != AtFlags.NONE:
@@ -78,7 +79,10 @@ class AtLocation:
         if isinstance(thing, int):
             if thing < 0 and thing != AT_FDCWD:
                 raise ValueError("fd cannot be negative")
-            obj.fd = thing
+            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
@@ -100,7 +104,7 @@ class AtLocation:
     def close(self) -> None:
         """Close the underlying file descriptor."""
         if self.fd >= 0:
-            os.close(self.fd)
+            self.fd.close()
             self.fd = AT_FDCWD
 
     def as_emptypath(self, inheritable: bool = True) -> "AtLocation":
@@ -109,11 +113,7 @@ class AtLocation:
         all cases, the caller is responsible for closing the result object.
         """
         if self.flags & AtFlags.AT_EMPTY_PATH:
-            newfd = fcntl.fcntl(
-                self.fd,
-                fcntl.F_DUPFD if inheritable else fcntl.F_DUPFD_CLOEXEC,
-                0,
-            )
+            newfd = self.fd.dup(inheritable=inheritable)
             return AtLocation(newfd, flags=self.flags)
         return AtLocation(
             self.open(flags=os.O_PATH | (0 if inheritable else os.O_CLOEXEC))
@@ -175,7 +175,7 @@ class AtLocation:
     def __truediv__(self, name: "AtLocationLike") -> "AtLocation":
         return self.joinpath(name)
 
-    def fileno(self) -> int:
+    def fileno(self) -> FileDescriptor:
         """Return the underlying file descriptor if this is an AT_EMPTY_PATH
         location and raise a ValueError otherwise.
         """
@@ -186,7 +186,7 @@ class AtLocation:
         return self.fd
 
     @property
-    def fd_or_none(self) -> int | None:
+    def fd_or_none(self) -> FileDescriptor | None:
         """A variant of the fd attribute that replaces AT_FDCWD with None."""
         return None if self.fd == AT_FDCWD else self.fd