Adjust remote_only argument to only apply to copying plain files

This commit adjusts the behavior of the "remote_only" argument in
SFTPClient copy() and mcopy() to only raise an error when attempting
to copy a plain file on a system which doesn't support remote copy.
Other operations during the copy such as creating directories and
symlinks and setting attributes will always be allowed.

When an error handler is set, it will be called once for each plain
file copy which is attempted when remote_only is set and the server
doesn't support remote copy. The exceptions will include the source
and destination pathname, to allow other forms of copy to be
performed.

asyncssh/sftp.py

@@ -3759,7 +3759,8 @@ async def _copy(self, srcfs: _SFTPFSProtocol, dstfs: _SFTPFSProtocol,
                     preserve: bool, recurse: bool, follow_symlinks: bool,
                     block_size: int, max_requests: int,
                     progress_handler: SFTPProgressHandler,
-                    error_handler: SFTPErrorHandler) -> None:
+                    error_handler: SFTPErrorHandler,
+                    remote_only: bool) -> None:
         """Copy a file, directory, or symbolic link"""
 
         try:
@@ -3795,7 +3796,8 @@ async def _copy(self, srcfs: _SFTPFSProtocol, dstfs: _SFTPFSProtocol,
                     await self._copy(srcfs, dstfs, srcfile, dstfile,
                                      srcname.attrs, preserve, recurse,
                                      follow_symlinks, block_size, max_requests,
-                                     progress_handler, error_handler)
+                                     progress_handler, error_handler,
+                                     remote_only)
 
                 self.logger.info('  Finished copy of directory %s to %s',
                                  srcpath, dstpath)
@@ -3810,6 +3812,9 @@ async def _copy(self, srcfs: _SFTPFSProtocol, dstfs: _SFTPFSProtocol,
             else:
                 self.logger.info('  Copying file %s to %s', srcpath, dstpath)
 
+                if remote_only and not self.supports_remote_copy:
+                    raise SFTPOpUnsupported('Remote copy not supported')
+
                 await _SFTPFileCopier(block_size, max_requests, 0,
                                       srcattrs.size or 0, srcfs, dstfs,
                                       srcpath, dstpath, progress_handler).run()
@@ -3846,7 +3851,8 @@ async def _begin_copy(self, srcfs: _SFTPFSProtocol, dstfs: _SFTPFSProtocol,
                           recurse: bool, follow_symlinks: bool,
                           block_size: int, max_requests: int,
                           progress_handler: SFTPProgressHandler,
-                          error_handler: SFTPErrorHandler) -> None:
+                          error_handler: SFTPErrorHandler,
+                          remote_only: bool = False) -> None:
         """Begin a new file upload, download, or copy"""
 
         if block_size <= 0:
@@ -3903,7 +3909,8 @@ async def _begin_copy(self, srcfs: _SFTPFSProtocol, dstfs: _SFTPFSProtocol,
 
             await self._copy(srcfs, dstfs, srcfile, dstfile, srcname.attrs,
                              preserve, recurse, follow_symlinks, block_size,
-                             max_requests, progress_handler, error_handler)
+                             max_requests, progress_handler, error_handler,
+                             remote_only)
 
     async def get(self, remotepaths: _SFTPPaths,
                   localpath: Optional[_SFTPPath] = None, *,
@@ -4222,13 +4229,10 @@ async def copy(self, srcpaths: _SFTPPaths,
 
         """
 
-        if remote_only and not self.supports_remote_copy:
-            raise SFTPOpUnsupported('Remote copy not supported')
-
         await self._begin_copy(self, self, srcpaths, dstpath, 'remote copy',
                                False, preserve, recurse, follow_symlinks,
                                block_size, max_requests, progress_handler,
-                               error_handler)
+                               error_handler, remote_only)
 
     async def mget(self, remotepaths: _SFTPPaths,
                    localpath: Optional[_SFTPPath] = None, *,
@@ -4295,13 +4299,10 @@ async def mcopy(self, srcpaths: _SFTPPaths,
 
         """
 
-        if remote_only and not self.supports_remote_copy:
-            raise SFTPOpUnsupported('Remote copy not supported')
-
         await self._begin_copy(self, self, srcpaths, dstpath, 'remote mcopy',
                                True, preserve, recurse, follow_symlinks,
                                block_size, max_requests, progress_handler,
-                               error_handler)
+                               error_handler, remote_only)
 
     async def remote_copy(self, src: _SFTPClientFileOrPath,
                           dst: _SFTPClientFileOrPath, src_offset: int = 0,

tests/test_sftp.py

@@ -777,9 +777,14 @@ async def _test_copy_remote_only(self, sftp):
 
             for method in ('copy', 'mcopy'):
                 with self.subTest(method=method):
-                    with self.assertRaises(SFTPOpUnsupported):
-                        await getattr(sftp, method)('src', 'dst',
-                                                    remote_only=True)
+                    try:
+                        self._create_file('src')
+
+                        with self.assertRaises(SFTPOpUnsupported):
+                            await getattr(sftp, method)('src', 'dst',
+                                                        remote_only=True)
+                    finally:
+                        remove('src')
 
         with patch('asyncssh.sftp.SFTPServerHandler._extensions', []):
             # pylint: disable=no-value-for-parameter