// Server side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define PORT 8008
#define RECIEVE_BUFFER_SIZE 1024
const char* responseMessage = "Hello from server";

// Driver code
int main() {

        //Create a UDP socket
        //int socket(int domain, int type, int protocol);
        //Domain is the place where the data goes. AF_BLUETOOTH, AF_INET6, AF_UNIX is local communication between different programs
        //Type is the type of connection, so connection based (TCP), connectionless (UDP) or somewhere in between or beyond
        //Protocol is an enum or flags that give some more options specific to that type. For SOCK_STREAM, you can force it to use SCTP instead of TCP. For SOCK_RAW, it can give you control over the ip frame, and even the ethernet frame.
        //So this function makes a file descriptor to an IPV4 UDP 'connection' with no options.
        int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
        // Creating socket file descriptor
        if ( sockfd < 0) {
                perror("socket creation failed");
                exit(EXIT_FAILURE);
        }


        struct sockaddr_in serverAddress;
        memset(&serverAddress, 0, sizeof(serverAddress));

        // Filling server information
        serverAddress.sin_family = AF_INET; // IPv4
        serverAddress.sin_addr.s_addr = INADDR_ANY;
        serverAddress.sin_port = htons(PORT);

        // Bind the socket with the server address
        if(bind(sockfd, (const struct sockaddr*)&serverAddress, sizeof(serverAddress))){        //Bind returns 0 if succeeded, or -1 if failed. -1 is still true.
                perror("bind failed");
                exit(EXIT_FAILURE);
        }

        struct sockaddr_in clientAddress; unsigned int clientAddressSize = sizeof(clientAddress);
        memset(&clientAddress, 0, clientAddressSize);

        char buffer[RECIEVE_BUFFER_SIZE];
        int bytesRecieved = recvfrom(sockfd, (char*)buffer, RECIEVE_BUFFER_SIZE, MSG_WAITALL, (struct sockaddr*) &clientAddress, &clientAddressSize); //sets clientAddress to the client's address and the new size
        buffer[bytesRecieved] = '\0';
        printf("Client : %s\n", buffer);

        sendto(sockfd, (const char*)responseMessage, strlen(responseMessage), MSG_CONFIRM, (const struct sockaddr*) &clientAddress, clientAddressSize);
        printf("Hello message sent.\n");

        return 0;
}

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
  pid_t pid; /* could be int */
  int i;
  pid = fork();
  printf("PID=%d\n", pid);
  if (pid > 0) {
    /* parent */
    for (i = 0; i < 10; i++)
      printf("\t\t\tPARENT %d\n", i);
  } else {
    /* child */
    for (i = 0; i < 10; i++)
      printf("CHILD %d\n", i);
  }
  return 0;
}

// compile: gcc socketTCPServer.c -o socketTCPServer.out
// usage  : ./socketTCPServer.out port
// Server

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>

int main(int argc, char *argv[]){
        int listenfd = 0, connfd = 0, cli_size, portno;

        struct sockaddr_in serv_addr, cli_addr;

        char sendBuff[1025];

        if((listenfd = socket(AF_INET, SOCK_STREAM, 0)) == -1){
                printf("socket error\n");
                exit(EXIT_FAILURE);
        }

        memset(&serv_addr, '0', sizeof(serv_addr));
        memset(sendBuff, '0', sizeof(sendBuff));

        serv_addr.sin_family = AF_INET;
        serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
        portno = atoi(argv[1]);
        serv_addr.sin_port = htons(portno);

        const int on = 1;
        setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));

        if(bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1){
                printf("bind error\n");
                exit(EXIT_FAILURE);
        }


        if(listen(listenfd, 5) == -1){
                printf("listen error\n");
                exit(EXIT_FAILURE);
        }

        while(1){
                cli_size = sizeof(cli_addr);
                if((connfd = accept(listenfd, (struct sockaddr*)&cli_addr, &cli_size)) == -1){
                        printf("accept error\n");
                        exit(EXIT_FAILURE);
                }

                strcpy(sendBuff, "Server Message: SUCCESS\n");
                write(connfd, sendBuff, strlen(sendBuff));

                close(connfd);
                sleep(1);
        }
        return 0;
}

// Server side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define PORT 8008
#define RECIEVE_BUFFER_SIZE 1024

// Driver code
int main() {

        //Create a UDP socket
        //int socket(int domain, int type, int protocol);
        //Domain is the place where the data goes. AF_BLUETOOTH, AF_INET6, AF_UNIX is local communication between different programs
        //Type is the type of connection, so connection based (TCP), connectionless (UDP) or somewhere in between or beyond
        //Protocol is an enum or flags that give some more options specific to that type. For SOCK_STREAM, you can force it to use SCTP instead of TCP. For SOCK_RAW, it can give you control over the ip frame, and even the ethernet frame.
        //So this function makes a file descriptor to an IPV4 UDP 'connection' with no options.
        int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
        // Creating socket file descriptor
        if ( sockfd < 0) {
                perror("socket creation failed");
                exit(EXIT_FAILURE);
        }


        struct sockaddr_in serverAddress;
        memset(&serverAddress, 0, sizeof(serverAddress));

        // Filling server information
        serverAddress.sin_family = AF_INET; // IPv4
        serverAddress.sin_addr.s_addr = INADDR_ANY;
        serverAddress.sin_port = htons(PORT);

        // Bind the socket with the server address
        if(bind(sockfd, (const struct sockaddr*)&serverAddress, sizeof(serverAddress))){        //Bind returns 0 if succeeded, or -1 if failed. -1 is still true.
                perror("bind failed");
                exit(EXIT_FAILURE);
        }

        struct sockaddr_in clientAddress; unsigned int clientAddressSize = sizeof(clientAddress);
        memset(&clientAddress, 0, clientAddressSize);

        char buffer[RECIEVE_BUFFER_SIZE];
        while(1){
                int bytesRecieved = recvfrom(sockfd, (char*)buffer, RECIEVE_BUFFER_SIZE, MSG_WAITALL, (struct sockaddr*) &clientAddress, &clientAddressSize); //sets clientAddress to the client's address and the new size
                buffer[bytesRecieved] = '\0';
                //printf("Client : %s\n", buffer);

                //The client might be like PINGUIN or something, but this is to ensure PING\n\r also gets accepted
                if(bytesRecieved >= 4 && (strncmp("PING", buffer, 4) == 0)){
                        const char* responseMessage = "PONG";
                        sendto(sockfd, (const char*)responseMessage, strlen(responseMessage), MSG_CONFIRM, (const struct sockaddr*) &clientAddress, clientAddressSize);
                        //printf("Hello message sent.\n");
                }else{
                        printf("Server bytes recieved: %d\nServer message recieved: %s", bytesRecieved, buffer);
                }
        }

        return 0;
}

#include <stdio.h>
#include <unistd.h>

int main() {
  char * cmd[] = {
    "who",
    "ls",
    "date"
  };
  int i;
  printf("0=who 1=ls 2=date : ");
  scanf("%d", & i);
  execlp(cmd[i], cmd[i], (char * ) 0);
  printf("execlp failed\n");
  return 0;
}

#include <stdio.h>
#include <assert.h>
#include <signal.h>

void myHandler(int iSig) {
  printf("In myHandler with argument %d\n", iSig);
}
int main() {
  void( * pfRet)(int) = signal(SIGINT, myHandler);
  assert(pfRet != SIG_ERR);
  printf("Entering an infinite loop\n");
  while (1) {
    printf(".");
  }
  return 0; // use CTRL+\ to exit
}