namedstruct 是一个解析二进制结构体的专用库，它不仅可以解析简单的 C 结构体，还可以支持变长结构体、可扩展的结构体之类复杂的情况。它被用来在 VLCP 中解析 OpenFlow（SDN 专用的二进制协议）。
使用这个库，你会发现，即便是像 OpenFlow 这样复杂的协议，实际上只需要将对应的 C 程序的头文件（比如openflow.h）按照相应的规则进行修改，添加一些简单的参数说明结构体之间的关系，就可以用一行代码将它完整解析出来，或者用一行代码生成出相应的结构体。
可以使用pip安装：
pip install nstruct
###### BASIC STRUCT ##### from namedstruct import * mytype = nstruct((uint16, 'myshort'), # unsigned short int (uint8, 'mybyte'), # unsigned char (uint8,), # a padding byte of unsigned char (char[5], 'mystr'), # a 16-byte bytes string (uint8,), (uint16[5], 'myarray'), # name = 'mytype', padding = 1) # Create an object obj0 = mytype() # Access a field s = obj0.myshort obj0.myshort = 12 # Create an object with the specified fields initialized obj1 = mytype(myshort = 2, mystr = b'123', myarray = [1,2,3,4,5]) # Unpack an object from stream, return the object and bytes size used obj2,size = mytype.parse(b'\x00\x02\x01\x00123\x00\x00\x00\x00\x01\x00\x02\x00\x03\x00\x04\x00\x05') # Unpack an object from packed bytes obj3 = mytype.create(b'\x00\x02\x01\x00123\x00\x00\x00\x00\x01\x00\x02\x00\x03\x00\x04\x00\x05') # Estimate the struct size size = len(obj0) # Estimate the struct size excludes automatic padding bytes size2 = obj0._realsize() # Pack the object b = obj0._tobytes() b2 = mytype.tobytes(obj0) # Use the type in other structs mytype2 = nstruct((mytype, 'mydata'), (mytype[4], 'mystructarray'), name = 'mytype2', padding = 1) obj4 = mytype2() obj4.mydata.myshort = 12 obj4.mystructarray[0].mybyte = 7 b3 = obj4._tobytes() ###### VARIABLE LENGTH TYPES ##### my_unsize_struct = nstruct((uint16, 'length'), (raw, 'data'), padding = 1, name = 'my_unsize_struct') """ >>> my_unsize_struct.create(b'\x00\x07abcde').data b'abcde' >>> my_unsize_struct.parse(b'\x00\x07abcde')[0].data b'' """ my_size_struct = nstruct((uint16, 'length'), (raw, 'data'), padding = 1, name = 'my_size_struct', prepack = packrealsize('length'), size = lambda x: x.length) """ packrealsize('length') is equivalent to: def _packsize(x): x.length = x._realsize() """ """ >>> my_unsize_struct(data = b'abcde')._tobytes() b'\x00\x07abcde' >>> my_unsize_struct.parse(b'\x00\x07abcde')[0].data b'abcde' """ ##### EXTENDING ##### my_base = nstruct((uint16, 'length'), (uint8, 'type'), (uint8, 'basedata'), name = 'my_base', size = lambda x: x.length, prepack = packrealsize('length'), padding = 4) my_child1 = nstruct((uint16, 'data1'), (uint8, 'data2'), name = 'my_child1', base = my_base, criteria = lambda x: x.type == 1, init = packvalue(1, 'type')) my_child2 = nstruct((uint32, 'data3'), name = 'my_child2', base = my_base, criteria = lambda x: x.type == 2, init = packvalue(2, 'type')) """ Fields and most base class options are inherited, e.g. size, prepack, padding >>> my_child1(basedata = 1, data1 = 2, data2 = 3)._tobytes() b'\x00\x07\x01\x01\x00\x02\x03\x00' >>> my_child2(basedata = 1, data3 = 4)._tobytes() b'\x00\x08\x02\x01\x00\x00\x00\x04' """ # Fields in child classes are automatically parsed when the type is determined obj1, _ = my_base.parse(b'\x00\x07\x01\x01\x00\x02\x03\x00') """ >>> obj1.basedata 1 >>> obj1.data1 2 >>> obj1.data2 3 >>> obj1._gettype() my_child1 """ # Base type can be used in fields or arrays of other structs my_base_array = nstruct((uint16, 'total_len'), (my_base[0], 'array'), name = 'my_base_array', padding = 1, size = lambda x: x.total_len, prepack = packrealsize('total_len')) obj2 = my_base_array() obj2.array.append(my_child1(data1 = 1, data2 = 2, basedata = 3)) obj2.array.append(my_child2(data3 = 4, basedata = 5)) """ >>> obj2._tobytes() b'\x00\x12\x00\x07\x01\x03\x00\x01\x02\x00\x00\x08\x02\x05\x00\x00\x00\x04' """ obj3, _ = my_base_array.parse(b'\x00\x12\x00\x07\x01\x03\x00\x01\x02\x00\x00\x08\x02\x05\x00\x00\x00\x04') """ >>> obj3.array[0].data2 2 """
