Swift API 参数约束

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在看Dev Guide的时候，有一些关于请求参数的约束内容，但分布的比较零散。今天早上整理了一下，并做了验证，现在PO出来。

1）account、object、container的自定义元数据约束

每次请求：自定义的X-Account/Object/Container-Meta-*的条目数量 <= 90 个；
每次请求：自定义的X-Account/Object/Container-Meta-*的每个value，经过UTF-8的URL-Encoded之后的字节 <= 256（一个汉字算3个字节）；
每次请求：自定义的X-Account/Object/Container-Meta-*的所有<key + value>，经过UTF-8的URL-Encoded之后的字节 <= 4096（一个汉字算3个字节）；
X-Account/Object/Container-Meta-*的总量目前没发现限制。虽然官方文档上说，Object和Container的元数据最多是90个，但是经实测发现，只是每次请求最多90个，总量并没有限制。至少，现在还未发现。

2）Container名称约束

不能包含'/'字符：结尾可以添加'/'，会被自动忽略，且不计入总长度；
经过UTF-8的URL-Encoded之后的字节 <= 256。虽然官方文档上说，是经过URL编码之后的长度不能大于256，但经实测发现，这个长度其实是UTF-8字节，URL-Encoded之后，一个汉字（%xx%xx%xx）算3个字节。

3）Object名称约束

不能包含保留字符。官方文档上如是说，但没说哪些是保留字符，源码里也没找到 -。-；
经过UTF-8的URL-Encoded之后的字节 <= 1024。虽然官方文档上说，是经过URL编码之后的长度不能大于1024，但经实测发现，这个长度其实是UTF-8字节，URL-Encoded之后，一个汉字（%xx%xx%xx）算3个字节。

4）参数（marker、endMarker、prefix）约束

　　URL-Encoded的

5）Request Line

　　Request Line <= 8192字节。这个完全就是URL-Encoded之后的长度，一个汉字（%xx%xx%xx）算9个字节。

以下为源码constraints.py。

约束值的定义：

#: Max file size allowed for objects
MAX_FILE_SIZE = constraints_conf_int('max_file_size', 5368709122)  # 5 * 1024 * 1024 * 1024 + 2
#: Max length of the name of a key for metadata
MAX_META_NAME_LENGTH = constraints_conf_int('max_meta_name_length', 128)
#: Max length of the value of a key for metadata
MAX_META_VALUE_LENGTH = constraints_conf_int('max_meta_value_length', 256)
#: Max number of metadata items
MAX_META_COUNT = constraints_conf_int('max_meta_count', 90)
#: Max overall size of metadata
MAX_META_OVERALL_SIZE = constraints_conf_int('max_meta_overall_size', 4096)
#: Max object name length
MAX_OBJECT_NAME_LENGTH = constraints_conf_int('max_object_name_length', 1024)
#: Max object list length of a get request for a container
CONTAINER_LISTING_LIMIT = constraints_conf_int('container_listing_limit', 10000)
#: Max container list length of a get request for an account
ACCOUNT_LISTING_LIMIT = constraints_conf_int('account_listing_limit', 10000)
#: Max account name length
MAX_ACCOUNT_NAME_LENGTH = constraints_conf_int('max_account_name_length', 256)
#: Max container name length
MAX_CONTAINER_NAME_LENGTH = constraints_conf_int('max_container_name_length', 256)


#: Query string format= values to their corresponding content-type values
FORMAT2CONTENT_TYPE = {'plain': 'text/plain', 'json': 'application/json', 'xml': 'application/xml'}

判断元数据是否合法：

def check_metadata(req, target_type):
    """
    Check metadata sent in the request headers.

    :param req: request object
    :param target_type: str: one of: object, container, or account: indicates
                        which type the target storage for the metadata is
    :raises HTTPBadRequest: bad metadata
    """
    prefix = 'x-%s-meta-' % target_type.lower()
    meta_count = 0
    meta_size = 0
    for key, value in req.headers.iteritems():
        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')
        meta_count += 1
        meta_size += len(key) + len(value)
        if len(key) > MAX_META_NAME_LENGTH:
            return HTTPBadRequest(
                body='Metadata name too long; max %d' % MAX_META_NAME_LENGTH,
                request=req, content_type='text/plain')
        elif len(value) > MAX_META_VALUE_LENGTH:
            return HTTPBadRequest(
                body='Metadata value too long; max %d' % MAX_META_VALUE_LENGTH,
                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

判断创建对象的数据是否合法：

def check_object_creation(req, object_name):
    """
    Check to ensure that everything is alright about an object to be created.

    :param req: HTTP request object
    :param object_name: name of object to be created
    :raises HTTPRequestEntityTooLarge: the object is too large
    :raises HTTPLengthRequered: missing content-length header and not
                                a chunked request
    :raises HTTPBadRequest: missing or bad content-type header, or
                            bad metadata
    """
    if req.content_length and req.content_length > MAX_FILE_SIZE:
        return HTTPRequestEntityTooLarge(body='Your request is too large.',
                                         request=req,
                                         content_type='text/plain')
    if req.content_length is None and \
            req.headers.get('transfer-encoding') != 'chunked':
        return HTTPLengthRequired(request=req)
    if 'X-Copy-From' in req.headers and req.content_length:
        return HTTPBadRequest(body='Copy requests require a zero byte body',
                              request=req, content_type='text/plain')
    if len(object_name) > MAX_OBJECT_NAME_LENGTH:
        return HTTPBadRequest(body='Object name length of %d longer than %d' %
                              (len(object_name), MAX_OBJECT_NAME_LENGTH),
                              request=req, content_type='text/plain')
    if 'Content-Type' not in req.headers:
        return HTTPBadRequest(request=req, content_type='text/plain',
                              body='No content type')
    if not check_utf8(req.headers['Content-Type']):
        return HTTPBadRequest(request=req, body='Invalid Content-Type',
                              content_type='text/plain')
    if 'x-object-manifest' in req.headers:
        value = req.headers['x-object-manifest']
        container = prefix = None
        try:
            container, prefix = value.split('/', 1)
        except ValueError:
            pass
        if not container or not prefix or '?' in value or '&' in value or \
                prefix[0] == '/':
            return HTTPBadRequest(
                request=req,
                body='X-Object-Manifest must in the format container/prefix')
    return check_metadata(req, 'object')