Struct.calcsize (fmt): This is used to calculate the size of the structure described in the FMT format.įormat strings consists of one or more format characters, and the description of these format characters is described with reference to Python Manual as follows:įirst pack the parameters 1, 2, 3, 1, 2, 3 before the packaging of the Python data type, and then become the C structure of the binary string, and the string type of Python is displayed is' \ X01. Returns a tuple (TUPLE) obtained by unpacking data, even if only one data will be solved by Len (String) must be equal to CalcSize (FMT), which involves a CalcSize function. For example, Pack is packaged, then you can unpack it with unpack. Finally returns a wrapped stringĪs the name suggestion, unpacking. The packaged parameters must be strictly compliant with FMT. The values of parameters such as V1, V2 are packaged, and the method of packaging is specified by FMT. Generally entered channel sources of binary stream.ĭuring the conversion process, a format string is mainly used to specify the method and format of the transformation, and the main methods are described below: ![]() The struct in Python is mainly used to process the C structure data, first converted to a string type of Python, and then converted to Python's structured type, such as a tuple. To implement the client's download function, first we have a TFTP server, can download TFTP32 server software from the Internet We wrote the code implementation of the TFTP client. Print ' Has been successfully downloaded! ! ! ' break elif cmd = 5: # Whether is an error response print " error num:%d "% currentPackNum # If the received data is less than 516, it is considered an error. # Whether the package number is equal to the last time if p_num 1 = currentPackNum: If cmd = 3: # Is it a packet? # If you receive data for the first time, then create a file. # print recvAddr # for test # print len(recvData) # for testĬmdTuple = struct.unpack( " !HH ", recvData) RecvData,recvAddr = udpSocket.recvfrom(1024 ) # Send download file request data to the specified server Ip = sys.argv # Acquire parameters outside the program # Create a UDP socketĬmd_buf = struct.pack( " !H8sb5sb ",1, " test.jpg ",0, " octet " ,0) Import struct # Structural module import sys The format of the TFTP packet is as follows: In order to mark the data has been sent, it is specified that when the data received by the client is less than 516 (2 byte operation code 2 bytes of the serial number 512 byte data), the server is finished. In order to let the server know that the client has received the packet that has just been sent, when the client receives a packet You need to send confirmation information to the server, that is, send it, such a package is an ACK (answer package) Indicates the function of this packet (called an opcode), and in front of the serial numberīecause the Packet of the UDP is not safe, that is, if the sender is successful, it cannot be determined, so it is specified in the TFTP protocol. In order to distinguish whether the service is sent is the file content or the wrong prompt information, it has used 2 bytes. Placed in front of 512 byte data, the serial number starts from 1īecause the file may not exist from the server from the server, then the server will send an error message. If the total size of the file is large (such as 3M), the server is sent multiple times, and each time you read 512 bytes of data from the file.īecause the number of times the transmission is likely to be many, in order to sort the received data, it will send multiple data of the data, and the sequence number is used to store the sequence number. ![]() ![]() When the server finds the current file, open the file, send the data in the file to the client through the TFTP protocol. If you approve this request, use a new, temporary port for data transfer. When the client sends a "Download" request (ie, read request), you need to send to the server's 69 port. Is a protocol used in the TCP / IP protocol to make simple file transfer between clients and servers TFTP (Trivial File Transfer Protocol, Simple File Transfer Protocol)
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