def check_metadata(req, target_type):
    """
    Check metadata sent in the request headers.  This should only check
    that the metadata in the request given is valid.  Checks against
    account/container overall metadata should be forwarded on to its
    respective server to be checked.

    :param req: request object
    :param target_type: str: one of: object, container, or account: indicates
                        which type the target storage for the metadata is
    :returns: HTTPBadRequest with bad metadata otherwise None
    """
    target_type = target_type.lower()
    prefix = 'x-%s-meta-' % target_type
    meta_count = 0
    meta_size = 0
    for key, value in req.headers.items():
        if (isinstance(value, six.string_types)
           and len(value) > MAX_HEADER_SIZE):

            return HTTPBadRequest(body='Header value too long: %s' %
                                  key[:MAX_META_NAME_LENGTH],
                                  request=req, content_type='text/plain')
        if not key.lower().startswith(prefix):
            continue
        key = key[len(prefix):]
        if not key:
            return HTTPBadRequest(body='Metadata name cannot be empty',
                                  request=req, content_type='text/plain')
        bad_key = not check_utf8(key)
        bad_value = value and not check_utf8(value)
        if target_type in ('account', 'container') and (bad_key or bad_value):
            return HTTPBadRequest(body='Metadata must be valid UTF-8',
                                  request=req, content_type='text/plain')
        meta_count += 1
        meta_size += len(key) + len(value)
        if len(key) > MAX_META_NAME_LENGTH:
            return HTTPBadRequest(
                body='Metadata name too long: %s%s' % (prefix, key),
                request=req, content_type='text/plain')
        elif len(value) > MAX_META_VALUE_LENGTH:
            return HTTPBadRequest(
                body='Metadata value longer than %d: %s%s' % (
                    MAX_META_VALUE_LENGTH, prefix, key),
                request=req, content_type='text/plain')
        elif meta_count > MAX_META_COUNT:
            return HTTPBadRequest(
                body='Too many metadata items; max %d' % MAX_META_COUNT,
                request=req, content_type='text/plain')
        elif meta_size > MAX_META_OVERALL_SIZE:
            return HTTPBadRequest(
                body='Total metadata too large; max %d'
                % MAX_META_OVERALL_SIZE,
                request=req, content_type='text/plain')
    return None
dataset/ETHPy150Open openstack/swift/swift/common/constraints.py/check_metadata/original