Accept abstract namespace paths for unix domain sockets

Accept paths starting with a null byte in create_unix_listener and
connect_unix_socket to allow creating abstract unix sockets. Fixes #781

src/anyio/_core/_sockets.py

@@ -683,16 +683,30 @@ async def setup_unix_local_socket(
     path_str: str | bytes | None
     if path is not None:
         path_str = os.fspath(path)
+        is_abstract = (
+            path_str.startswith(b"\0")
+            if isinstance(path_str, bytes)
+            else path_str.startswith("\0")
+        )
 
-        # Copied from pathlib...
-        try:
-            stat_result = os.stat(path)
-        except OSError as e:
-            if e.errno not in (errno.ENOENT, errno.ENOTDIR, errno.EBADF, errno.ELOOP):
-                raise
+        if is_abstract:
+            # Unix abstract namespace socket. No file backing so skip stat call
+            pass
         else:
-            if stat.S_ISSOCK(stat_result.st_mode):
-                os.unlink(path)
+            # Copied from pathlib...
+            try:
+                stat_result = os.stat(path)
+            except OSError as e:
+                if e.errno not in (
+                    errno.ENOENT,
+                    errno.ENOTDIR,
+                    errno.EBADF,
+                    errno.ELOOP,
+                ):
+                    raise
+            else:
+                if stat.S_ISSOCK(stat_result.st_mode):
+                    os.unlink(path)
     else:
         path_str = None
 

tests/test_sockets.py

@@ -735,12 +735,17 @@ async def test_bind_link_local(self) -> None:
     sys.platform == "win32", reason="UNIX sockets are not available on Windows"
 )
 class TestUNIXStream:
-    @pytest.fixture
-    def socket_path(self) -> Generator[Path, None, None]:
+    @pytest.fixture(params=["path", "abstract"])
+    def socket_path(
+        self, request: SubRequest, tmp_path_factory: TempPathFactory
+    ) -> Generator[Path, None, None]:
         # Use stdlib tempdir generation
         # Fixes `OSError: AF_UNIX path too long` from pytest generated temp_path
         with tempfile.TemporaryDirectory() as path:
-            yield Path(path) / "socket"
+            if request.param == "path":
+                yield Path(path) / "socket"
+            elif request.param == "abstract":
+                yield Path(f"\0{path}") / "socket"
 
     @pytest.fixture(params=[False, True], ids=["str", "path"])
     def socket_path_or_str(self, request: SubRequest, socket_path: Path) -> Path | str:
@@ -764,7 +769,15 @@ async def test_extra_attributes(
             assert (
                 stream.extra(SocketAttribute.local_address) == raw_socket.getsockname()
             )
-            assert stream.extra(SocketAttribute.remote_address) == str(socket_path)
+            remote_addr = stream.extra(SocketAttribute.remote_address)
+            if isinstance(remote_addr, str):
+                assert stream.extra(SocketAttribute.remote_address) == str(socket_path)
+            else:
+                assert isinstance(remote_addr, bytes)
+                assert stream.extra(SocketAttribute.remote_address) == bytes(
+                    socket_path
+                )
+
             pytest.raises(
                 TypedAttributeLookupError, stream.extra, SocketAttribute.local_port
             )
@@ -1031,8 +1044,12 @@ async def test_send_after_close(
             await stream.send(b"foo")
 
     async def test_cannot_connect(self, socket_path: Path) -> None:
-        with pytest.raises(FileNotFoundError):
-            await connect_unix(socket_path)
+        if str(socket_path).startswith("\0"):
+            with pytest.raises(ConnectionRefusedError):
+                await connect_unix(socket_path)
+        else:
+            with pytest.raises(FileNotFoundError):
+                await connect_unix(socket_path)
 
     async def test_connecting_using_bytes(
         self, server_sock: socket.socket, socket_path: Path
@@ -1057,12 +1074,17 @@ async def test_connecting_with_non_utf8(self, socket_path: Path) -> None:
     sys.platform == "win32", reason="UNIX sockets are not available on Windows"
 )
 class TestUNIXListener:
-    @pytest.fixture
-    def socket_path(self) -> Generator[Path, None, None]:
+    @pytest.fixture(params=["path", "abstract"])
+    def socket_path(
+        self, request: SubRequest, tmp_path_factory: TempPathFactory
+    ) -> Generator[Path, None, None]:
         # Use stdlib tempdir generation
         # Fixes `OSError: AF_UNIX path too long` from pytest generated temp_path
         with tempfile.TemporaryDirectory() as path:
-            yield Path(path) / "socket"
+            if request.param == "path":
+                yield Path(path) / "socket"
+            elif request.param == "abstract":
+                yield Path(f"\0{path}") / "socket"
 
     @pytest.fixture(params=[False, True], ids=["str", "path"])
     def socket_path_or_str(self, request: SubRequest, socket_path: Path) -> Path | str: