Socket communication by C language and Python

C

This is a sample program for socket communication in C language. Here, for the experiment, I am trying to connect from the client to the loopback address 127.0.0.1 so that I can do it on one computer. I referred to a website, but I forgot where it is, so I can't mention it, This is a beginner's memorandum.

Source code

sserver

sserver.c

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
 
int main() {
    int sockfd;
    int client_sockfd;
    struct sockaddr_in addr;
 
    socklen_t len = sizeof( struct sockaddr_in );
    struct sockaddr_in from_addr;
 
    char buf[1024];
 
    //Receive buffer initialization
    memset( buf, 0, sizeof( buf ) );
 
    //Socket generation
    if( ( sockfd = socket( AF_INET, SOCK_STREAM, 0 ) ) < 0 ) {
        perror( "socket" );
    }
 
    //Stand-by IP / port number setting
    addr.sin_family = AF_INET;
    addr.sin_port = htons( 1234 );
    addr.sin_addr.s_addr = INADDR_ANY;
 
    //bind
    if( bind( sockfd, (struct sockaddr *)&addr, sizeof( addr ) ) < 0 ) {
        perror( "bind" );
    }
 
    printf("waiting for client's connection..\n");
    //Waiting for reception
    if( listen( sockfd, SOMAXCONN ) < 0 ) {
        perror( "listen" );
    }
 
    //Waiting for a connect request from a client
    if( ( client_sockfd = accept( sockfd, (struct sockaddr *)&from_addr, &len ) ) < 0 ) {
        perror( "accept" );
    }
 
    //Receive
    int rsize;
    while( 1 ) {
        rsize = recv( client_sockfd, buf, sizeof( buf ), 0 );
 
        if ( rsize == 0 ) {
            break;
        } else if ( rsize == -1 ) {
            perror( "recv" );
        } else {
            printf( "receive:%s\n", buf );
            sleep( 1 );
 
            //response
            printf( "send:%s\n", buf );
            write( client_sockfd, buf, rsize );
        }
    }
 
    //Socket closed
    close( client_sockfd );
    close( sockfd );
 
    return 0;
}

sclient

sclient.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
 
int main() {
    int sockfd;
    struct sockaddr_in addr;
 
    //Socket generation
    if( (sockfd = socket( AF_INET, SOCK_STREAM, 0) ) < 0 ) {
        perror( "socket" );
    }
 
    //Destination address / port number setting
    addr.sin_family = AF_INET;
    addr.sin_port = htons( 1234 );
    addr.sin_addr.s_addr = inet_addr( "127.0.0.1" );
 
    //Server connection
    connect( sockfd, (struct sockaddr *)&addr, sizeof( struct sockaddr_in ) );
 
    //Data transmission
    char send_str[10];
    char receive_str[10];
    for ( int i = 0; i < 8; i++ ){
        sprintf( send_str, "%d", i );
        printf( "send:%d\n", i );
        if( send( sockfd, send_str, 10, 0 ) < 0 ) {
            perror( "send" );
        } else {
            recv( sockfd, receive_str, 10, 0 );
            printf( "receive:%s\n", receive_str );
        }
        sleep( 1 );
    }
 
    //Socket closed
    close( sockfd );
 
    return 0;
}

compile

Compile with cc sserver.c -o ss for the server and cc sclient.c -o sc for the client.

Experiment

First, launch sserver. Then launch sclient from another terminal. Then, 8 data will be sent from sclient, the data will be displayed, and the process will end.

Experiment result server side

$ ./ss
waiting for client's connection..
receive:0
send:0
receive:1
send:1
receive:2
send:2
receive:3
send:3
receive:4
send:4
receive:5
send:5
receive:6
send:6
receive:7
send:7

Experimental results Client side

$ ./sc
send:0
receive:0
send:1
receive:1
send:2
receive:2
send:3
receive:3
send:4
receive:4
send:5
receive:5
send:6
receive:6
send:7
receive:7

Python3

I also wrote it in Python. This works the same as the C version. Compared to C, you can write much more clearly. Reference Qiita: [Communication processing by Python] Encode to binary with .encode () and decode to string with .decode (). When encoding utf-8, use .encode ('utf-8').

sserver.py

#!/usr/bin/python3
import socket

host = "127.0.0.1"
port = 1234

serversock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
serversock.bind((host,port)) #Bind by specifying IP and PORT
serversock.listen(10) #Listen for a connection (specify the maximum number of queues)

print('Waiting for connections...')
clientsock, client_address = serversock.accept() #Store data when connected

for i in range ( 8 ):
    rcvmsg = clientsock.recv(1024).decode()
    print('Received : %s' % (rcvmsg))
    s_msg = str(i)
    print('Send : %s' % s_msg)
    clientsock.sendall(s_msg.encode())
clientsock.close()

sclient.py

#!/usr/bin/python3
import socket

host = "127.0.0.1"
port = 1234

client = socket.socket(socket.AF_INET, socket.SOCK_STREAM) #Create an object

client.connect((host, port)) #Now connect to the server

for i in range(8):
  message = str(i)
  print('Send : %s' % message)
  client.send(message.encode()) #Send data
  response = client.recv(4096) #Receive should be a power of 2 (not too large)
  print('Received: %s' % response.decode())