def get_available_name(self, name, max_length=None):
"""
Returns a filename that's free on the target storage system, and
available for new content to be written to.
"""
dir_name, file_name = os.path.split(name)
file_root, file_ext = os.path.splitext(file_name)
# If the filename already exists, add an underscore and a random 7
# character alphanumeric string (before the file extension, if one
# exists) to the filename until the generated filename doesn't exist.
# Truncate original name if required, so the new filename does not
# exceed the max_length.
while self.exists(name) or (max_length and len(name) > max_length):
# file_ext includes the dot.
name = os.path.join(dir_name, "%s_%s%s" % (file_root, get_random_string(7), file_ext))
if max_length is None:
continue
# Truncate file_root if max_length exceeded.
truncation = len(name) - max_length
if truncation > 0:
file_root = file_root[:-truncation]
# Entire file_root was truncated in attempt to find an available filename.
if not file_root:
raise SuspiciousFileOperation(
'Storage can not find an available filename for "%s". '
'Please make sure that the corresponding file field '
'allows sufficient "max_length".' % name
)
name = os.path.join(dir_name, "%s_%s%s" % (file_root, get_random_string(7), file_ext))
return name
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