Swift API 参数约束
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')
其实我在测试的过程中发现，swift已经相当健壮了，会对违反以上所描述的所有约束的情况进行错误处理：拒绝请求，返回响应的错误码、错误原因说明。因此，我们本打算在SDK层再进行一次约束的想法就没那么重要了，反而会增加复杂度、降低SDK效率。因此，只添加业务层约束就OK，例如：
- X-Account/Object/Container-Meta-*中的'*'即key值，ISO-8859-1字符集，即英文字母、-、_、空格等简单字符；
- 用户不能直接创建、访问、删除后缀为"_segments"的Container；
- 用户不能直接创建、访问、删除后缀为"_versions"的Container。
