Question

socket from c program sends 3 numbers to a socket in python. code and output below:

python server code:

import SocketServer
import threading
import select
import sys

class TCPHandler(SocketServer.StreamRequestHandler):
    def handle(self):
        self.data = self.rfile.readline()
        print "%s wrote:" % self.client_address[0]
        print (self.data)
        self.request.send(str(long(self.data)+1000))
        cur_connex.append({'ip': self.client_address, 'range': [long(self.data), long(self.data)+10000]})

        for a in cur_connex:
            print("%s did %d - %d on thread %s" % (a['ip'], a['range'][0], a['range'][1], threading.current_thread().name))

        while True:
            select.select([self.rfile], [], [])
            self.data = self.request.recv(10) #also tried "self.data = self.rfile.readline().strip("\n")" and without "strip()"
            print self.data


if __name__ == "__main__":
    HOST, PORT = "", 50001
    cur_connex = []
    done_up_to = 0

    # Create the server, binding to localhost on port 50001
    server = SocketServer.TCPServer((HOST, PORT), TCPHandler)

    # Activate the server on new thread
    listen_thread = threading.Thread(target=server.serve_forever, name='listen_th')
    listen_thread.start()

c++ client code:

for(unsigned long long i; i < perfect_numbers.size(); i++)
{
    cout << "i is " << i << " writing " << perfect_numbers[i] << "\n";

    for(int j = 0; j < perfect_numbers[i].size(); j++)
    {
        cout << perfect_numbers[i][j] << "|";
    }

    if(write(sock, perfect_numbers[i].c_str(), sizeof(perfect_numbers[i].c_str())) == -1)
    {
        cerr << "\nwrite failed: " << strerror(errno) << "\n";
        return -1;
    }
}

if(close(sock) == -1)
{
    cerr << "close sock error: " << strerror(errno) << "\n";
    return -1;
}

cout << "exiting...\n";
return 1;

server output:

>>> 127.0.0.1 wrote:
12695

('127.0.0.1', 55624) did 12695 - 22695 on thread listen_th
28
496
8128

…and then continuous newlines

client output:

that took 1.26624 seconds
i is 0 writing 28

2|8|
|i is 1 writing 496

4|9|6|
|i is 2 writing 8128

8|1|2|8|
|exiting...

I assume that last bit of the C++ client program is enough. Also assuming it’s something in that while True loop in the server. New to both these languages, I know my coding isn’t good yet, be gentle…

Answer 1

---

^{this post handles a bit more than what OP was asking for, I apologize for this matter. If you are only interested in how to fix the pending newlines written at the server please jump to section “python“.}

---

both client/server

• You should add a delimiter between the numbers sent/received, there is nothing guaranteeing that each number will arrive individually. You may get two numbers in the same call to self.request.recv (...).

---

python

• print will append a newline ('\n') to every statement passed to it, unless you end the print statement with a comma.

• You should add a check to see if there really was any data to be read, if not there might have been an error or the connection has been closed.

  while True:
      select.select([self.rfile], [], [self.rfile])
      self.data = self.request.recv(10) 
      if self.data:
         print self.data
      else:
         # <close connection here>
  

---

c++

write(sock, perfect_numbers[i].c_str(), sizeof(perfect_numbers[i].c_str()))

• The above will always try to write sizeof(char*) characters to the socket sock, no matter if perfect_numbers[i] is one or a billion bytes of length.

  The third argument to write should be the number of bytes that you wish to be written, therefore you should use perfect_numbers[i].size (). ¹

---

¹ I assume that you’ve been confused when looking at examples such as:

 char buf[1024];

 ...

 write (sock, buf, sizeof (buf));