swift object metadata

gistfile1.txt

Read from filesystem extended attributes (through diskfile.py) for a HEAD request

Written to filesystem extended attributes (through diskfile.py) as part of a POST request

To set custom object metadata - https://prosuncsedu.wordpress.com/2015/12/09/set-metadata-on-openstack-swift-objects/


swift/obj/server.py
=====================

    def HEAD(self, request):
        """Handle HTTP HEAD requests for the Swift Object Server."""
        device, partition, account, container, obj, policy = \
            get_name_and_placement(request, 5, 5, True)
        try:
            disk_file = self.get_diskfile(
                device, partition, account, container, obj,
                policy=policy)
        except DiskFileDeviceUnavailable:
            return HTTPInsufficientStorage(drive=device, request=request)
        try:
            metadata = disk_file.read_metadata()
        except DiskFileXattrNotSupported:
            return HTTPInsufficientStorage(drive=device, request=request)
        except (DiskFileNotExist, DiskFileQuarantined) as e:
            headers = {}
            if hasattr(e, 'timestamp'):
                headers['X-Backend-Timestamp'] = e.timestamp.internal
            return HTTPNotFound(request=request, headers=headers,
                                conditional_response=True)


    def POST(self, request):
        """Handle HTTP POST requests for the Swift Object Server."""
        device, partition, account, container, obj, policy = \
            get_name_and_placement(request, 5, 5, True)
        req_timestamp = valid_timestamp(request)
        new_delete_at = int(request.headers.get('X-Delete-At') or 0)
        if new_delete_at and new_delete_at < time.time():
            return HTTPBadRequest(body='X-Delete-At in past', request=request,
                                  content_type='text/plain')

        ...

        try:
            disk_file.write_metadata(metadata)
        except (DiskFileXattrNotSupported, DiskFileNoSpace):
            return HTTPInsufficientStorage(drive=device, request=request)


swift/obj/diskfile.py
=====================

METADATA_KEY = 'user.swift.metadata'


read_metadata - Helper function to read the pickled metadata from an object file.

def read_metadata(fd):
    """
    Helper function to read the pickled metadata from an object file.

    :param fd: file descriptor or filename to load the metadata from

    :returns: dictionary of metadata
    """
    metadata = b''
    key = 0
    try:
        while True:
            metadata += xattr.getxattr(fd, '%s%s' % (METADATA_KEY,
                                                     (key or '')))
            key += 1
    except (IOError, OSError) as e:
        for err in 'ENOTSUP', 'EOPNOTSUPP':
            if hasattr(errno, err) and e.errno == getattr(errno, err):
                msg = "Filesystem at %s does not support xattr" % \
                      _get_filename(fd)
                logging.exception(msg)
                raise DiskFileXattrNotSupported(e)
        if e.errno == errno.ENOENT:
            raise DiskFileNotExist()
        # TODO: we might want to re-raise errors that don't denote a missing
        # xattr here.  Seems to be ENODATA on linux and ENOATTR on BSD/OSX.
    return pickle.loads(metadata)


def write_metadata(fd, metadata, xattr_size=65536):
    """
    Helper function to write pickled metadata for an object file.

    :param fd: file descriptor or filename to write the metadata
    :param metadata: metadata to write
    """
    metastr = pickle.dumps(metadata, PICKLE_PROTOCOL)
    key = 0
    while metastr:
        try:
            xattr.setxattr(fd, '%s%s' % (METADATA_KEY, key or ''),
                           metastr[:xattr_size])
            metastr = metastr[xattr_size:]
            key += 1
        except IOError as e:
            for err in 'ENOTSUP', 'EOPNOTSUPP':
                if hasattr(errno, err) and e.errno == getattr(errno, err):
                    msg = "Filesystem at %s does not support xattr" % \
                          _get_filename(fd)
                    logging.exception(msg)
                    raise DiskFileXattrNotSupported(e)
            if e.errno in (errno.ENOSPC, errno.EDQUOT):
                msg = "No space left on device for %s" % _get_filename(fd)
                logging.exception(msg)
                raise DiskFileNoSpace()
            raise