Socket module, how to send integer

Question

I am reading in a value on the client side and want to send that to a server side so it can check if its prime. I'm getting an error because the server is expecting a string

server side

import socket

tcpsocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
tcpsocket.bind( ("0.0.0.0", 8000) ) 

tcpsocket.listen(2)
(client, (ip,port) ) = tcpsocket.accept()

print "received connection from %s" %ip
print " and port number %d" %port

client.send("Python is fun!") 

client side

import sys
import socket

tcpsocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 

num = int(raw_input("Enter number: "))

tcpsocket.connect( ('192.168.233.132', 8000) ) 
tcpsocket.send(num)

Error: must be string or buffer, not int.

How can I resolve this?

Answer 1

Never send raw data on a stream without defining an upper level protocol saying how to interpret the received bytes.

You can of course send integers in either binary or string format

• in string format, you should define an end of string marker, generally a space or a newline

  val = str(num) + sep # sep = ' ' or sep = `\n`
  tcpsocket.send(val)
  

  and client side:

  buf = ''
  while sep not in buf:
      buf += client.recv(8)
  num = int(buf)
  

• in binary format, you should define a precise encoding, struct module can help

  val = pack('!i', num)
  tcpsocket.send(val)
  

  and client side:

  buf = ''
  while len(buf) < 4:
      buf += client.recv(8)
  num = struct.unpack('!i', buf[:4])[0]
  

Those 2 methods allow you to realiably exchange data even across different architectures

Answer 2

tcpsocket.send(num) accept a string, link to the api, so don't convert the number you insert to int.

Answer 3

I found a super light way to send an integer by socket:

#server side:
num=123
# convert num to str, then encode to utf8 byte
tcpsocket.send(bytes(str(num), 'utf8'))

#client side
data = tcpsocket.recv(1024)
# decode to unicode string 
strings = str(data, 'utf8')
#get the num
num = int(strings)

equally use encode(), decode(), instead of bytes() and str():

#server side:
num=123
# convert num to str, then encode to utf8 byte
tcpsocket.send(str(num).encode('utf8'))

#client side
data = tcpsocket.recv(1024)
# decode to unicode string 
strings = data.decode('utf8')
#get the num
num = int(strings)

Answer 4

In Python 3.7.2

>>>i_num = 123
>>>b_num = i_num.to_bytes(2, 'little', signed=False)
>>>b_num
b'{\x00'
>>>reverted = int.from_bytes(b_num, 'little', signed=False)
>>>i_num == reverted
True