您可以在python中压缩字节并将其发送吗？

Question

I am writing a TCP python script, and I need the first 4 bytes to be the size of the file.

I got the size of the file by doing

SIZE_OF_FILE = os.path.getsize(infile.name)

The size is 392399 bytes.

When I do

s.send(str(SIZE_OF_FILE).encode("utf-8"))

it sends the file, and then on my server I have

fileSize = conn.recv(4).decode('utf-8')

This should read the first 4 bytes, and extract the file size information, but it returns 3923 instead of the 392399.

as the file size... what happened? "392399" should be able to fit into 4 bytes.

We are suppose to be using big endian.

Answer 1

This is because str(SIZE_OF_FILE) typesets the number using decimal notation - that is, you get the string "392399" , which is 6 characters (and 6 bytes in UTF-8). If you send only the first 4, you are sending "3923" .

What you probably want to do is use something like struct.pack to create a bytestring containing the binary representation of the number.

s.send(struct.pack(format_string, SIZE_OF_FILE))

Answer 2

You are sending the size as a string ( "392399" ), which is 6 ASCII characters and therefore 6 bytes. You want to send it as a raw integer; use struct.pack to do that:

s.send(struct.pack(">i", SIZE_OF_FILE))

To recieve:

fileSize = struct.unpack(">i", conn.recv(4))[0]

The > makes it big-endian. To make it little-endian, use < instead. i is the type; in this case, a 4-byte integer. The linked documentation has a list of types, in case you want to use another one.