/*
 * discovery_broadcast.c - UDP broadcast peer discovery
 * 
 * Falls back to broadcast when mDNS unavailable.
 * Broadcasts a discovery packet on local subnet and waits for responses.
 * Works on any LAN without requiring Avahi.
 */

#include "../include/rootstream.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <ifaddrs.h>
#include <poll.h>

#define DISCOVERY_BROADCAST_PORT 5555
#define DISCOVERY_MAGIC "ROOTSTREAM_DISCOVER"

typedef struct {
    uint8_t magic[20];        /* "ROOTSTREAM_DISCOVER" */
    uint32_t version;         /* Protocol version */
    char hostname[256];       /* Sender hostname */
    uint16_t listen_port;     /* Port peer is listening on */
    char rootstream_code[32]; /* User's RootStream code */
} discovery_broadcast_packet_t;

/*
 * Get local IP address for broadcast
 */
static int get_local_ip(char *ip_buf, size_t ip_len, char *bcast_buf, size_t bcast_len) {
    struct ifaddrs *ifaddr, *ifa;
    int ret = -1;

    if (getifaddrs(&ifaddr) == -1) {
        perror("getifaddrs");
        return -1;
    }

    for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
        if (ifa->ifa_addr == NULL) continue;

        /* Skip loopback and non-IPv4 */
        if (ifa->ifa_addr->sa_family != AF_INET) continue;
        if (strcmp(ifa->ifa_name, "lo") == 0) continue;

        struct sockaddr_in *sin = (struct sockaddr_in *)ifa->ifa_addr;
        struct sockaddr_in *broadcast = (struct sockaddr_in *)ifa->ifa_broadaddr;

        inet_ntop(AF_INET, &sin->sin_addr, ip_buf, ip_len);
        if (broadcast) {
            inet_ntop(AF_INET, &broadcast->sin_addr, bcast_buf, bcast_len);
        } else {
            snprintf(bcast_buf, bcast_len, "255.255.255.255");
        }

        printf("✓ Using interface %s (%s, broadcast %s)\n", 
               ifa->ifa_name, ip_buf, bcast_buf);
        ret = 0;
        break;
    }

    freeifaddrs(ifaddr);
    return ret;
}

/*
 * Broadcast discovery query
 */
int discovery_broadcast_announce(rootstream_ctx_t *ctx) {
    if (!ctx) return -1;

    char local_ip[INET_ADDRSTRLEN];
    char broadcast_ip[INET_ADDRSTRLEN];

    if (get_local_ip(local_ip, sizeof(local_ip), 
                     broadcast_ip, sizeof(broadcast_ip)) < 0) {
        fprintf(stderr, "ERROR: Cannot determine local IP\n");
        return -1;
    }

    int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (sock < 0) {
        perror("socket");
        return -1;
    }

    /* Enable broadcast */
    int broadcast_flag = 1;
    if (setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &broadcast_flag, 
                   sizeof(broadcast_flag)) < 0) {
        perror("setsockopt SO_BROADCAST");
        close(sock);
        return -1;
    }

    /* Create announcement packet */
    discovery_broadcast_packet_t pkt;
    memcpy(pkt.magic, DISCOVERY_MAGIC, strlen(DISCOVERY_MAGIC));
    pkt.version = PROTOCOL_VERSION;
    gethostname(pkt.hostname, sizeof(pkt.hostname));
    pkt.listen_port = ctx->network.listen_port;
    strncpy(pkt.rootstream_code, ctx->rootstream_code, sizeof(pkt.rootstream_code) - 1);

    str...

</details>



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