CSE4303H3/server.cpp

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>

// open ssl
#include <openssl/conf.h>
#include <openssl/evp.h>
#include <openssl/err.h>

#include <errno.h>  // for perror()
#include <unistd.h> // for close()

#include <string>
#include <cstring>
#include <cstdlib> // for atoi()
#include <vector>

// load environment variables from .env file, and additional helper functions
#include "helper.h"

using std::string;
using std::vector;

int main(void)
{
    printf("Server starting...\n");
    load_env(".env");

    // Declare variables
    const char *server_ip = getenv("SERVER_IP");
    const int server_port = atoi(getenv("SERVER_PORT"));
    char client_message[2048];
    char server_message[2048];
    const char *custom_message_success = "Server: Hello from server, message authenticated!\n";
    const char *custom_message_failed = "Server: Hello from server, message failed authentication!\n";

    // debug
    printf("Server starting at IP: %s, Port: %d\n", server_ip, server_port);

    // Create socket
    const int server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket == -1)
    {
        perror("Failed to create socket");
        return 1;
    }

    // Bind to the set port and IP
    struct sockaddr_in server_addr;
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(server_port);
    inet_pton(AF_INET, server_ip, &server_addr.sin_addr);

    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1)
    {
        perror("Failed to bind socket");
        close(server_socket);
        return 1;
    }
    printf("Done with binding with IP: %s, Port: %d\n", server_ip, server_port);

    // Listen for clients:
    const char *client_ip = getenv("CLIENT_IP");
    if (listen(server_socket, 1) == -1)
    {
        perror("Failed to listen on socket");
        close(server_socket);
        return 1;
    }
    printf("Listening for incoming connections...\n");

    // Accept an incoming connection
    struct sockaddr_in client_addr;
    socklen_t client_addr_len = sizeof(client_addr);
    int client_socket = accept(server_socket, (struct sockaddr *)&client_addr, &client_addr_len);
    if (client_socket == -1)
    {
        perror("Failed to accept connection");
        close(server_socket);
        return 1;
    }
    printf("Client connected at IP: %s \n", client_ip);

    // clean exising buffer
    memset(client_message, 0, sizeof(client_message));

    // store message history, for HMAC calculation
    // msg on odd is msg, and on even is corresponding HMAC
    vector<string> message_history;

    // Receive client's message
    while (1)
    {
        // clean exising buffer
        memset(client_message, 0, sizeof(client_message));

        ssize_t n = recv(client_socket, client_message, sizeof(client_message), 0);
        if (n == 0)
            break;
        if (n < 0)
        {
            perror("recv");
            break;
        }

        if (strcmp((char *)client_message, "\\exit\n") == 0)
            break;

        printf("Msg from client: %s \n", byte_to_hex((unsigned char *)client_message, n));
        // store message history for HMAC calculation
        message_history.push_back(string((char *)client_message, n));

        // only respond after receiving both msg and HMAC
        if (message_history.size() % 2 == 1)
            continue;

        // check HMAC
        const string expected_hmac_str = message_history.back();
        unsigned char expected_hmac[20];
        memcpy(expected_hmac, expected_hmac_str.c_str(), 20);
        const string plaintext_str = message_history[message_history.size() - 2];
        char plaintext_cstr[2048];
        strcpy(plaintext_cstr, plaintext_str.c_str());
        printf("Plaintext: %s, string length: %d\n", byte_to_hex((unsigned char *)plaintext_cstr, strlen(plaintext_cstr)), strlen(plaintext_cstr));

        unsigned char calculated_hmac[20];
        memset(calculated_hmac, 0, sizeof(calculated_hmac));
        cal_hmac(calculated_hmac, plaintext_cstr);

        if (memcmp(expected_hmac, calculated_hmac, 20) != 0)
        {
            fprintf(stderr, "HMAC mismatch\n, expected: %s, calculated: %s\n", byte_to_hex(expected_hmac, 20), byte_to_hex(calculated_hmac, 20));
            memcpy(server_message, custom_message_failed, strlen(custom_message_failed));
            ;
        }
        else
        {
            memcpy(server_message, custom_message_success, strlen(custom_message_success));
            ;
        }
        // Respond to client
        // prepare server message

        size_t reply_len = strlen(server_message);
        if (send(client_socket, server_message, reply_len, 0) == -1)
        {
            perror("Send failed");
            break;
        }

        printf("Response sent to client: %s\n", server_message);
    }
    // Close the socket
    close(client_socket);
    close(server_socket);

    return 0;
}