battleship/client.c

/**
 * @file client.c
 * @author Tobias Eidelpes <e01527193@student.tuwien.ac.at>
 * @date 2018-03-21
 *
 * @brief Client for OSUE exercise 1B `Battleship'.
 */

#include "common.h"

/**
 * @details Constant which holds the port number to connect to.
 */
static const char *port = DEFAULT_PORT;

/**
 * @details Struct which holds info for the socket.
 */
static struct addrinfo *ai = NULL;

/**
 * @details Global variable for the hostname to connect to.
 */
static char *hostname = NULL;

/**
 * @details Global variable for the socket file descriptor (easy cleanup).
 */
static int sockfd = -1;

/**
 * @details Global variable for the program name for error messages.
 */
static char* pname;

/**
 * @details Global variable for tracking where we have already fired a shot.
 */
static int field[MAP_SIZE][MAP_SIZE];

/**
 * @details Global variable for the x coordinate.
 */
static uint8_t x;

/**
 * @details Global variable for the y coordinate.
 */
static uint8_t y;

/**
 * @details Variable which get set on signal received.
 */
volatile sig_atomic_t quit = 0;

/**
 * @details Signal handler.
 * @param signal The number of the received signal.
 * @return Function has no return value.
 */
static void handle_signal(int signal)
{
        quit = 1;
}

/**
 * @details Prints the program usage.
 * @param void Function takes no arguments.
 * @return Always non-zero.
 */
static void usage(void)
{
        fprintf(stderr, "[%s] Usage:\n\tSYNOPSIS\n\t\t [-h HOSTNAME] [-p PORT]\n\tEXAMPLE\n\tclient -h localhost -p 1280\n", pname);
        exit(EXIT_FAILURE);
}

/**
 * @details Sets even parity for the supplied message.
 * @param msg The encoded coordinates in 2 bytes.
 * @return Returns the message with even parity set.
 */
static uint16_t setParity(uint16_t msg)
{
        uint16_t v = msg;
        v &= 0x7FF;
        uint8_t parity = 0;

        while (v) {
                parity = !parity;
                v = v & (v - 1);
        }

        if (parity)
                msg += 0x8000;

        return msg;
}

/**
 * @details Parses the commandline arguments.
 * @param argc Count of commandline arguments.
 * @param argv Array of commandline arguments.
 * @return Function has no return value.
 */
static void parse(int argc, char *argv[])
{
        if (argc == 1) {
                hostname = NULL;
                port = "1280";
        } else {
                int opt_index = 0;
                while ((opt_index = getopt(argc, argv, "h:p:")) != -1) {
                        switch (opt_index) {
                        case 'h':
                                hostname = optarg;
                                break;
                        case 'p':
                                port = optarg;
                                break;
                        case '?':
                                usage();
                        default:
                                assert(0);
                        }
                }
        }
}

/**
 * @details Function for convenient cleanup of resources.
 * @param void Function takes no arguments.
 * @return 0 on success. Non-zero on failure.
 */
static int cleanup(void)
{
        if (close(sockfd) < 0) {
		perror(pname);
		return 1;	
	}
	
        free(ai);

	return 0;
}

/**
 * @details Calls target mode by testing adjacent fields.
 * @param void Function takes no arguments.
 * @return Function has no return value.
 */
static void markSunk(void)
{
        // check north
        for (int i = y; i >= 0; i--) {
                if (field[x][i] == 2)
                        field[x][i] = 3;
                else
                        break;
        }

        // check south
        for (int i = y; i < MAP_SIZE; i++) {
                if (field[x][i] == 2)
                        field[x][i] = 3;
                else
                        break;
        }

        // check east
        for (int i = x; i >= 0; i--) {
                if (field[i][y] == 2)
                        field[i][y] = 3;
                else
                        break;
        }

        // check west
        for (int i = x; i < MAP_SIZE; i++) {
                if (field[i][y] == 2)
                        field[i][y] = 3;
                else
                        break;
        }
}

/**
 * @details Function checks the north tile and sets x and y if not already hit.
 * @param void Function takes no arguments.
 * @return 1 if field north not hit. 0 otherwise.
 */
static int checkNorth(void)
{
        int j = y - 1;

        for (; j >= 0; --j) {
                if (field[x][j] == 0) {
                        y = j;
                        return 1;
                } else {
                        return 0;
                }
        }

        return 0;
}

/**
 * @details Function checks the south tile and sets x and y if not already hit.
 * @param void Function takes no arguments.
 * @return 1 if field north not hit. 0 otherwise.
 */
static int checkSouth(void)
{
        int j = y + 1;

        for (; j < MAP_SIZE; ++j) {
                if (field[x][j] == 0) {
                        y = j;
                        return 1;
                } else {
                        return 0;
                }
        }

        return 0;
}

/**
 * @details Function checks the eastern tile and sets x and y if not already hit.
 * @param void Function takes no arguments.
 * @return 1 if field north not hit. 0 otherwise.
 */
static int checkEast(void)
{
        int i = x - 1;

        for (; i >= 0; --i) {
                if (field[i][y] == 0) {
                        x = i;
                        return 1;
                } else {
                        return 0;
                }
        }

        return 0;
}

/**
 * @details Function checks the western tile and sets x and y if not already hit.
 * @param void Function takes no arguments.
 * @return 1 if field north not hit. 0 otherwise.
 */
static int checkWest(void)
{
        int i = x + 1;

        for (; i < MAP_SIZE; ++i) {
                if (field[i][y] == 0) {
                        x = i;
                        return 1;
                } else {
                        return 0;
                }
        }

        return 0;
}

/**
 * @details Searches for a tile not already hit and calls adjacent hit functions
 *          when a ship has been hit but not sunk.
 * @param void Functions takes no arguments.
 * @return Function has no return value.
 */
static void searchHit(void)
{
        for (int j = 0; j < MAP_SIZE; j++) {
                for (int i = 0; i < MAP_SIZE; i++) {
                        if (field[i][j] == 2) {
                                x = i;
                                y = j;
                                if (checkNorth()) {
                                        return;
                                }
                                if (checkSouth()) {
                                        return;
                                }
                                if (checkEast()) {
                                        return;
                                }
                                if (checkWest()) {
                                        return;
                                }
                        }
                }
        }

        x = rand() % 10;
        y = rand() % 10;

        while(field[x][y] != 0) {
                x = rand() % 10;
                y = rand() % 10;
        }
}

/**
 * @details Reads x and y and contructs the encoded message in 2 bytes. Then
 *          sends the bytes on by one to the server and waits for response. Marks
 *          the tile hit accordingly.
 * @param void Function takes no arguments.
 * @return Function has no return value.
 */
static void makeHit(void)
{
        uint8_t buffer[1];
        uint8_t status;
        uint8_t hit;
        uint16_t msg;

        msg = x;
        msg <<= 6;
        msg += y;
        msg = setParity(msg);
        uint16_t v = msg;
        v &= 0x00FF;
        buffer[0] = v;
        send(sockfd, buffer, 1, 0);

        v = msg;
        v &= 0xFF00;
        v >>= 8;
        buffer[0] = v;
        send(sockfd, buffer, 1, 0);

        recv(sockfd, buffer, 1, 0);

        status = buffer[0];
        status &= 0x0C;
        hit = buffer[0];
        hit &= 0x03;

        switch (status) {
        case 2:
                fprintf(stderr, "[%s] Parity error\n", pname);
                cleanup();
                exit(2);
        case 3:
                fprintf(stderr, "[%s] Invalid coordinate\n", pname);
                cleanup();
                exit(3);
        default:
                break;
        }

        if (status == 1 && (hit == 0 || hit == 1 || hit == 2)) {
                fprintf(stdout, "[%s] Game lost\n", pname);
                cleanup();
                exit(EXIT_SUCCESS);
        } else if (status == 1 && hit == 3) {
                fprintf(stdout, "[%s] I win :)\n", pname);
                cleanup();
                exit(EXIT_SUCCESS);
        }

        if (hit == 0)
                field[x][y] = 1;
        if (hit == 1)
                field[x][y] = 2;
        if (hit == 2)
                markSunk();
}

/**
 * The main entry point of the program.
 * @deails Sets up signal handler. Parses the commandline arguments. Connects to
 *         the server and starts the game.
 * @param argc Count of commandline arguments.
 * @param argv Array of commandline arguments.
 * @return 0 on success. Non-zero on failure.
 */
int main(int argc, char *argv[])
{
        struct sigaction sa;
        memset(&sa, 0, sizeof(sa));
        sa.sa_handler = handle_signal;
        sigaction(SIGINT, &sa, NULL);
        sigaction(SIGTERM, &sa, NULL);

        pname = argv[0];

        parse(argc, argv);

        struct addrinfo hints;
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = AF_INET;
        hints.ai_socktype = SOCK_STREAM;
        hints.ai_flags = AI_PASSIVE;

        int res = getaddrinfo(hostname, port, &hints, &ai);
        if (res < 0) {
                fprintf(stderr, "[%s] ERROR: Failed to get address info: %s\n", pname, gai_strerror(res));
                exit(EXIT_FAILURE);
        }

        sockfd = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
        if (sockfd < 0) {
                perror(pname);
                exit(EXIT_FAILURE);
        }
        if (connect(sockfd, ai->ai_addr, ai->ai_addrlen) < 0) {
                close(sockfd);
                perror(pname);
                exit(EXIT_FAILURE);
        }

        srand(time(NULL));

        while(quit == 0) {
                searchHit();
                makeHit();
        }

        cleanup();
        exit(EXIT_SUCCESS);
}