SSDP msearch 구현 - C언어

SSDP msearch 구현

알아둘 사항

• msearch 패킷을 날리기 위해 multicast join 할 필요는 없음

동작 방식

• SSDP M-SEARCH 패킷을 multicast 주소인 239.255.255.250:1900 으로 송신
• M-SEARCH 패킷에 명시된 제한시간 (MX header field) 만큼 response 수신

socket programming

• IPv4
• datagram socket
• select (multiplex)

Linux 환경 + C 언어

함수 설명

• tick_milli() - time milliseconds
• create_ssdp_sender() - socket_sender_t 생성 및 socket 생성
• release_ssdp_sender() - socket_sender_t 제거
• send_msearch() - msearch 패킷 전송
• pending_ssdp_sender() - msearch 응답 기다림
• receive_ssdp_response() - 패킷 수신

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <ifaddrs.h>
#include <netdb.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <net/if.h>

static const char * SSDP_HOST = "239.255.255.250";
static const int SSDP_PORT = 1900;

static unsigned long tick_milli(void) {
struct timeval tv;
if (gettimeofday(&tv, NULL) != 0) {
return 0;
}
return (tv.tv_sec * 1000) + (tv.tv_usec / 1000);
}

typedef void (*__ssdp_handler_cb)(struct sockaddr *, const char *);

/* ssdp sender */
typedef struct _ssdp_sender_t
{
    int sock;
fd_set read_fds;
__ssdp_handler_cb handler;
} ssdp_sender_t;

static ssdp_sender_t * create_ssdp_sender(void) {
ssdp_sender_t * sender = (ssdp_sender_t*)malloc(sizeof(ssdp_sender_t));
memset(sender, 0, sizeof(ssdp_sender_t));
sender->sock = socket(AF_INET, SOCK_DGRAM, 0);
assert(sender->sock >= 0);
FD_ZERO(&(sender->read_fds));
FD_SET(sender->sock, &(sender->read_fds));
return sender;
}

static void release_ssdp_sender(ssdp_sender_t * sender) {
close(sender->sock);
free(sender);
}

static void send_msearch(ssdp_sender_t * sender, const char * type, int mx)
{
static const char * SSDP_FMT =
"M-SEARCH * HTTP/1.1\r\n"
"Host: %s:%d\r\n"
"ST: %s\r\n"
"MX: %d\r\n"
"MAN: %s\r\n"
"User-Agent: UPnP/1.0 Sample/1.0 Linux/1.0\r\n"
"\r\n";

struct sockaddr_in addr;
socklen_t addr_len = sizeof(addr);

char buffer[4096] = {0,};
snprintf(buffer, sizeof(buffer), SSDP_FMT,
SSDP_HOST, SSDP_PORT, type, mx, "\"ssdp:discover\"");

memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr(SSDP_HOST);
addr.sin_port = htons(SSDP_PORT);

sendto(sender->sock, buffer, strlen(buffer), 0, (struct sockaddr *)&addr, addr_len);
}

static int pending_ssdp_sender(ssdp_sender_t * sender, unsigned long wait_milli) {
fd_set fds = sender->read_fds;
struct timeval timeout;
timeout.tv_sec = wait_milli / 1000;
timeout.tv_usec = (wait_milli % 1000) * 1000;
return select(sender->sock + 1, &fds, NULL, NULL, &timeout);
}

static void receive_ssdp_response(ssdp_sender_t * sender) {
char buffer[4096] = {0,};
struct sockaddr_in addr = {0,};
socklen_t addr_len = sizeof(addr);
int len = recvfrom(sender->sock, buffer, sizeof(buffer), 0, (struct sockaddr *)&addr, &addr_len);
assert(len > 0);
printf("[RECV]\n");
printf("%s", buffer);
if (sender->handler) {
sender->handler((struct sockaddr *)&addr, buffer);
}
}

int main(int argc, char *argv[])
{
int count = 0;
int mx = 5;
unsigned long tick;
ssdp_sender_t * sender = create_ssdp_sender();
send_msearch(sender, "upnp:rootdevice", mx);
tick = tick_milli();
while (tick_milli() - tick < mx * 1000) {
if (pending_ssdp_sender(sender, 10) > 0) {
count++;
receive_ssdp_response(sender);
}
}
release_ssdp_sender(sender);
printf("count := %d\n", count);
printf("[DONE]\n");
    
    return 0;
}