receiver.c

#include "crc16.h"
#include "bitvec.h"
#include "manchester.h"
#include "netutil.h"

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

#define PORT 5050 // Port number for receiver

void receiver_start()
{

    int listenfd = socket(AF_INET, SOCK_STREAM, 0);
    if (listenfd < 0)
    {
        perror("socket");
        exit(1);
    }

    int opt = 1; // Reuse address option
    setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));

    struct sockaddr_in addr = {0};
    addr.sin_family = AF_INET;
    addr.sin_port = htons(PORT);
    addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);

    if (bind(listenfd, (struct sockaddr *)&addr, sizeof(addr)) < 0)
    {
        perror("bind");
        exit(1);
    }
    listen(listenfd, 1);

    printf("[Receiver] Listening on port %d\n", PORT);

    int c = accept(listenfd, NULL, NULL);
    printf("[Receiver] Connected.\n");

    while (1)
    {
        uint32_t netlen;
        if (recv_all(c, &netlen, sizeof(netlen)) <= 0)
            break;

        size_t nbytes = ntohl(netlen);
        if (nbytes == 0)
        {
            printf("[Receiver] End of transmission.\n");
            break;
        }

        uint8_t *buf = malloc(nbytes); // Buffer for received frame
        recv_all(c, buf, nbytes);

        /* ---- UNPACK BITS ---- */
        bitvec enc_bits;
        unpack_bits(buf, nbytes, &enc_bits);

        /* ---- MANCHESTER DECODE ---- */
        bitvec dec_bits;
        if (manchester_decode_bits(&enc_bits, &dec_bits) != 0)
        {
            printf("[Receiver] Manchester decode failure\n\n");
            free(buf);
            bitvec_free(&enc_bits);
            continue;
        }

        /* ---- VERIFY FRAME HAS CRC ---- */
        if (dec_bits.len < 16)
        {
            printf("[Receiver] Too short (corrupt)\n\n");
            free(buf);
            bitvec_free(&enc_bits);
            bitvec_free(&dec_bits);
            continue;
        }

        size_t payload_bits = dec_bits.len - 16;
        size_t payload_bytes = (payload_bits + 7) / 8;

        /* ---- EXTRACT PAYLOAD BYTES ---- */
        uint8_t *payload = calloc(payload_bytes + 1, 1); // +1 for safe printing
        for (size_t i = 0; i < payload_bits; ++i)
        {
            if (dec_bits.buf[i])
                payload[i / 8] |= (1 << (7 - (i % 8)));
        }
        payload[payload_bytes] = '\0';

        /* ---- EXTRACT RECEIVED CRC ---- */
        uint16_t recv_crc = 0;
        for (int i = 0; i < 16; ++i)
        {
            recv_crc = (recv_crc << 1) | dec_bits.buf[payload_bits + i];
        }

        /* ---- COMPUTE LOCAL CRC ---- */
        uint16_t calc_crc = crc16_ccitt(payload, payload_bytes);

        /* ---- DISPLAY RESULTS ---- */
        printf("\n==============================================\n");
        printf(" RECEIVED FRAME\n");
        printf("==============================================\n");

        printf("Payload (%zu bytes):\n", payload_bytes);
        printf("  \"%s\"\n", payload);

        printf("\nCRC Check:\n");
        printf("  Received CRC : 0x%04X\n", recv_crc);
        printf("  Calculated CRC: 0x%04X\n", calc_crc);

        if (recv_crc == calc_crc)
            printf("  --> CRC STATUS: PASS (Message Correct)\n");
        else
            printf("  --> CRC STATUS: FAIL (Message Corrupted!)\n");

        printf("==============================================\n\n");

        /* ---- CLEAN UP ---- */
        free(payload);
        free(buf);
        bitvec_free(&enc_bits);
        bitvec_free(&dec_bits);
    }

    close(c);
    close(listenfd);
    return;
}

int main() {
    receiver_start();
    return 0;
}