Computer Networking Homework 1

client.c

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

#define BUFFER_SIZE 512
#define SERVER_PORT 3000

int main(int argc, char **argv)
{
    int socket_fd;
    struct sockaddr_in *server_addr;
    char *buf = (char *)malloc(sizeof(char) * BUFFER_SIZE);
    
    printf("Please input the server ip address:");
    scanf(" %s", buf);
    printf("Connecting the server from %s\n", buf);

    socket_fd = socket(AF_INET, SOCK_STREAM, 0); if (socket_fd == -1) printf("Creating socket arises error.\n");

    server_addr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in));
    
    inet_aton(buf, &server_addr->sin_addr);
    server_addr->sin_family        = AF_INET;
    server_addr->sin_port          = htons(SERVER_PORT);
    
    if (connect(socket_fd,  (struct sockaddr *)server_addr, sizeof(struct sockaddr)) != -1)
    {
        printf("Connect successfully.\n");
        do 
        {
            printf("Please input the two floating number(a,b): ");
            while(1)
            {
                float a, b;
                if (scanf(" %f,%f", &a, &b) == 2) 
                {
                    sprintf(buf, "%f,%f", a, b);
                    send(socket_fd, buf, strlen(buf), 0);
                    break;
                }
                else 
                {
                    // Clean up the input stream.
                    scanf(" %s", buf);
                }
                printf("Please input a floating number again(a,b): ");
            }

            printf("Please input operator such as +, -, *, /: ");
            while(1)
            {
                if (scanf(" %s", buf) && (strcmp(buf, "+") == 0
                                      || strcmp(buf, "-") == 0
                                      || strcmp(buf, "*") == 0
                                      || strcmp(buf, "/") == 0))
                {
                    send(socket_fd, buf, strlen(buf), 0);
                    break;
                }
                printf("Please input operator such as +, -, *, / again: ");
            }
            printf("Wait for result from server......\n");
            if (recv(socket_fd, buf, BUFFER_SIZE, 0)) printf("%s\n", buf);
            printf("Do you want to continue(Y/N): ");
            scanf(" %s", buf);
        } while (strcmp("Y", buf) == 0 || strcmp("y", buf) == 0);
    }
    else 
    {
        printf("Your ip address is wrong.\n");
        return 1;
    }

    close(socket_fd);

    return 0;
}

server.c

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

#define BUFFER_SIZE 512
#define PORT 3000
#define BACKLOG 5 // How many pending connections queue will hold.

float calculate(float a, float b, char operator, int *flag)
{
    float result = 0;
    switch (operator) 
    {
        case '+':
            result = a + b;
            break;
        case '-':
            result = a - b;
            break;
        case '*':
            result = a * b;
            break;
        case '/':
            if (b != 0.0) result = a / b;
            else *flag = 1;
            break;
    }

    return (float)((int)(result * 100 + 0.5) / 100.0);
}

int main(int argc, char **argv) 
{
    int socket_fd;
    int bind_state;
    struct sockaddr_in *my_addr;

    my_addr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in));
    // Create socket file descriptor. 
    // SOCK_STREAM: Create a TCP connection.
    // AF_INET: ipv4
    socket_fd = socket(AF_INET, SOCK_STREAM, 0);

    if (socket_fd == -1) printf("Creating socket arises error.\n");

    // Some information about server.
    my_addr->sin_family      = AF_INET; 
    my_addr->sin_port        = htons(PORT);
    // INADDR_ANY: Automatically set your ip address of local machine.
    my_addr->sin_addr.s_addr = INADDR_ANY;
    // or use my_addr.sin_addr.s_addr = inet_aton(IP);
    bind_state = bind(socket_fd, (struct sockaddr *)my_addr, sizeof(struct sockaddr));
    if (bind_state == -1) 
    {
        printf("Binding error.\n");
        return -1;
    }

    // Server listening.
    listen(socket_fd, BACKLOG);
    
    // Some information about client.
    int accepted_socket_fd;
    struct sockaddr_in *client_addr;
    int sin_size = sizeof(struct sockaddr_in);

    client_addr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in));
    accepted_socket_fd = accept(socket_fd, (struct sockaddr *)client_addr, &sin_size);
    
    if (accepted_socket_fd != -1) 
    {

        printf("New connection.\n");
        char *buf = (char *)malloc(sizeof(char) * BUFFER_SIZE);
        char operator;
        float a, b, result;

        int flag = 0; // The flag catch divide-by-zero.
        while(1) 
        { 
            printf("Wait for data.\n");
            if (accepted_socket_fd == -1) break;

            if (recv(accepted_socket_fd, buf, BUFFER_SIZE, 0)) 
            {
                printf("Receive %s from client\n", buf);
                sscanf(buf, "%f,%f", &a, &b);
                a = (float)((int)(a * 100 + 0.5) / 100.0);
                b = (float)((int)(b * 100 + 0.5) / 100.0);

                if (recv(accepted_socket_fd, buf, BUFFER_SIZE, 0)) 
                {
                    sscanf(buf, "%c\n", &operator);
                    result = calculate(a, b, operator, &flag);
                }

                if (flag)
                {
                    flag = 0;
                    sprintf(buf, "You cannot divide by zero.\n");
                    send(accepted_socket_fd, buf, strlen(buf), 0);
                }
                else
                {
                    printf("%.2f %c %.2f = %.2f\n", a, operator, b, result);
                    sprintf(buf, "%.2f %c %.2f = %.2f", a, operator, b, result);
                    send(accepted_socket_fd, buf, strlen(buf), 0);
                }
            }
            else 
            {
                // Close the client connection.
                close(accepted_socket_fd);
                break;
            }
        }
    }
    close(socket_fd);

    return 0;
}