The Prisoner\'s Dilemma: The prisoner\'s dilemma is a standard example of a game

Question

The Prisoner's Dilemma: The prisoner's dilemma is a standard example of a game analyzed in game theory that shows why two completely "rational" individuals might not cooperate, even if it appears that it is in their best interests to do so.1 It is presented as follows: "Two members of a criminal gang are arrested and imprisoned. Each prisoner is in solitary confinement with no means of communicating with the other. The prosecutors lack sufficient evidence to convict the pair on the principal charge. They hope to get both sentenced to a year in prison on a lesser charge. Simultaneously, the prosecutors offer each prisoner a bargain. Each prisoner is given the opportunity either to: betray the other by testifying that the other committed the crime, or to cooperate with the other by remaining silent. The offer is: . If A and B each betray the other, each of them serves 2 years in prison .If A betrays B but B remains silent, A will be set free and B will serve 3 years in prison (and vice versa) If A and B both remain silent, both will only serve 1 year in prison (on the lesser charge)"1

Explanation / Answer

Server:

#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/wait.h>
#include <time.h>
#define PORT 50009
int main(int argc, char const *argv[])
{
    int server_fd, new_socket, valread;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[1024] = {0};
    char *hello = "Hello from server";
    char recv1[20];
    char recv2[20];
    char *resp1 = "B";
    char *resp2 = "S";
    pid_t pid;

   
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0)
    {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

   
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,&opt, sizeof(opt)))
    {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons( PORT );

  
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address))<0)
    {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }
    if (listen(server_fd, 3) < 0)
    {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    while (1){
       //printf("Waiting for connection,,, ");
       if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen))<0)
       {
           perror("accept");
           exit(EXIT_FAILURE);
       }
       pid = fork();
       if (pid < 0){
           perror("Error in fork ");
           return 0;
       }
       if (pid == 0){
          close(server_fd);
          valread = read( new_socket , buffer, 20);
          printf("Received %s ",buffer );
          //sleep(10);
          if (rand() % 2 == 0){
             send(new_socket , resp1 , strlen(resp1) , 0 );
             printf("Sent:%s ",resp1);
          }
          else {
             send(new_socket , resp2 , strlen(resp2) , 0 );
             printf("Sent:%s ",resp2);
          }
          valread = read( new_socket , buffer, 20);
          printf("Received %s ",buffer );
          //sleep(10);
          if (rand() % 2 == 0){
             send(new_socket , resp1 , strlen(resp1) , 0 );
             printf("Sent:%s ",resp1);
          }
          else {
             send(new_socket , resp2 , strlen(resp2) , 0 );
             printf("Sent:%s ",resp2);
          }
          //printf("Hello message sent ");
          close(new_socket);
          return;
       }
       else {
        close(new_socket);
       }
    }
    return 0;
}

Client:

#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
//#define PORT 50009

int main(int argc, char const *argv[])
{
    struct sockaddr_in address;
    int sock = 0, valread;
    struct sockaddr_in serv_addr;
    char *hello = "Hello from client";
    char msg[20];
    char buffer[1024] = {0};
    int port;
    char resp1[20];
    char resp2[20];
    port = atoi(argv[2]);
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
    {
        printf(" Socket creation error ");
        return -1;
    }
    memset(&serv_addr, '0', sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(port);

   
    if(inet_pton(AF_INET, argv[1], &serv_addr.sin_addr)<=0)
    {
        printf(" Invalid address/ Address not supported ");
        return -1;
    }
    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
    {
        printf(" Connection Failed ");
        return -1;
    }
    printf(" Enter input for prisoner B:");
    scanf("%s",msg);
   
    send(sock , msg , strlen(msg) , 0 );
    printf("Sent:%s ",msg);
    valread = read( sock , resp1, 20);
    printf("Recived:%c ",resp1[0]);
    printf(" Enter input for prisoner A:");
    scanf("%s",msg);

    send(sock , msg , strlen(msg) , 0 );
    printf("Sent:%s ",msg);
    valread = read( sock , resp2,20);
    printf("Recived:%c %c ",resp1[0], resp2[0]);
    if (resp1[0] == 'B' && resp2[0] == 'B'){
       printf("2 years imprisonment for prisoner A and B ");
    }
    else if (resp1[0] == 'S' && resp2[0] == 'B'){
       printf("B is free and 3 years for A ");
    }
    else if (resp1[0] == 'B' && resp2[0] == 'S'){
       printf("A is free and 3 years for B ");
    }
    else if (resp1[0] == 'S' && resp2[0] == 'S'){
       printf("1 year for A and B ");
    }

    printf("%s ",buffer );
    return 0;
}

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