Buffer size when receiving data through a socket?

John Salerno johnjsal at NOSPAMgmail.com
Tue Jun 17 02:21:35 CEST 2008


I wrote some pretty basic socket programming again, but I'm still confused about what's happening with the buffer_size variable. Here are the server and client programs:

--------------

from socket import *

host = ''
port = 51567
address = (host, port)
buffer_size = 1024

server_socket = socket(AF_INET, SOCK_STREAM)
server_socket.bind(address)
server_socket.listen(5)

while True:
    print 'waiting for connection...'
    client_socket, client_address = server_socket.accept()
    print '...connected from:', client_address

    while True:
        data = client_socket.recv(buffer_size)
        if not data:
            break
        client_socket.send('%s %s' % ('You typed:', data))

    client_socket.close()

server_socket.close()

------------

from socket import *

host = 'localhost'
port = 51567
address = (host, port)
buffer_size = 1024

client_socket = socket(AF_INET, SOCK_STREAM)
client_socket.connect(address)

while True:
    data = raw_input('> ')
    if not data:
        break
    client_socket.send(data)
    data = client_socket.recv(buffer_size)
    if not data:
        break
    print data

client_socket.close()

---------------

I tried changing buffer_size to 10 and I got this output:

john at john-laptop:~$ python myclient.py 
> hello
You typed:
> something
 hello
> this is a long string
You typed:
> why doesn't this work right
 something
> 
john at john-laptop:~$ 

My first question is, isn't buffer_size the number of bytes being sent at one time? If so, why doesn't 'hello' get printed after the server returns the data to the client? Isn't 'hello' just 5 bytes?

Secondly, how is it working that once I type in a new string (e.g. 'something') and then the server returns data to the client, it prints the *previous* string, (i.e. 'hello')? Wouldn't the data variable get overwritten with the value, or is the value being stored somewhere else at this point?

Thanks!



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