copyfile update=True ignores files per mtime

When update=True (regardless of the value of overwrite) then files are
only copied if the destination file does not exist or its modification
time is less than the source. Ie files are only overwritten when the
source file is considered newer than the destination.

fs/errors.py

@@ -187,6 +187,11 @@ class DestinationExistsError(ResourceError):
     default_message = "Destination exists: %(path)s"
 
 
+class DestinationNotOlderError(ResourceError):
+    """Exception raised when a target destination is not older than a source."""
+    default_message = "Destination not older: %(path)s"
+
+
 class DirectoryNotEmptyError(ResourceError):
     """Exception raised when a directory to be removed is not empty."""
     default_message = "Directory is not empty: %(path)s"

fs/utils.py

@@ -24,18 +24,24 @@
 
 from fs.mountfs import MountFS
 from fs.path import pathjoin
-from fs.errors import DestinationExistsError, RemoveRootError
+from fs.errors import DestinationNotOlderError, DestinationExistsError, \
+                      RemoveRootError, ResourceNotFoundError, \
+                      ResourceInvalidError, ParentDirectoryMissingError
 from fs.base import FS
 
 
-def copyfile(src_fs, src_path, dst_fs, dst_path, overwrite=True, chunk_size=64*1024):
+def copyfile(src_fs, src_path, dst_fs, dst_path, overwrite=True, update=False,
+             chunk_size=64*1024):
     """Copy a file from one filesystem to another. Will use system copyfile, if both files have a syspath.
-    Otherwise file will be copied a chunk at a time.
+    Otherwise file will be copied a chunk at a time. In the case where ``overwrite`` is False and
+    ``update`` is True, the behaviour of ``update`` takes precedence.
 
     :param src_fs: Source filesystem object
     :param src_path: -- Source path
     :param dst_fs: Destination filesystem object
     :param dst_path: Destination filesystem object
+    :param overwrite: Write to destination files even if they already exist
+    :param update: Write to destination files only if the source is newer
     :param chunk_size: Size of chunks to move if system copyfile is not available (default 64K)
 
     """
@@ -48,8 +54,18 @@ def copyfile(src_fs, src_path, dst_fs, dst_path, overwrite=True, chunk_size=64*1
     src_syspath = src_fs.getsyspath(src_path, allow_none=True)
     dst_syspath = dst_fs.getsyspath(dst_path, allow_none=True)
 
-    if not overwrite and dst_fs.exists(dst_path):
-        raise DestinationExistsError(dst_path)
+    if update:
+        try:
+            src_mtime = src_fs.getinfokeys(dst_path, "modified_time")["modified_time"]
+            dst_mtime = dst_fs.getinfokeys(dst_path, "modified_time")["modified_time"]
+            if src_mtime <= dst_mtime:
+                raise DestinationNotOlderError(dst_path)
+        except (KeyError, ParentDirectoryMissingError, ResourceNotFoundError,
+                ResourceInvalidError), e:
+            pass
+    elif not overwrite:
+        if dst_fs.exists(dst_path):
+            raise DestinationExistsError(dst_path)
 
     # System copy if there are two sys paths
     if src_syspath is not None and dst_syspath is not None: