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srtla_rec.c
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srtla_rec.c
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/*
srtla - SRT transport proxy with link aggregation
Copyright (C) 2020-2021 BELABOX project
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <endian.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <errno.h>
#include "common.h"
#define MAX_CONNS_PER_GROUP 8
#define MAX_GROUPS 200
#define CLEANUP_PERIOD 3
#define GROUP_TIMEOUT 10
#define CONN_TIMEOUT 10
#define RECV_ACK_INT 10
typedef struct srtla_conn {
struct srtla_conn *next;
struct sockaddr addr;
time_t last_rcvd;
int recv_idx;
uint32_t recv_log[RECV_ACK_INT];
} conn_t;
typedef struct srtla_conn_group {
struct srtla_conn_group *next;
conn_t *conns;
time_t created_at;
int srt_sock;
struct sockaddr last_addr;
char id[SRTLA_ID_LEN];
} conn_group_t;
typedef struct {
uint32_t type;
uint32_t acks[RECV_ACK_INT];
} srtla_ack_pkt;
int srtla_sock;
struct sockaddr srt_addr;
const socklen_t addr_len = sizeof(struct sockaddr);
conn_group_t *groups = NULL;
int group_count = 0;
FILE *urandom;
/*
Async I/O support
*/
int socket_epoll;
int epoll_add(int fd, uint32_t events, void *userdata) {
struct epoll_event ev={0};
ev.events = events;
ev.data.ptr = userdata;
return epoll_ctl(socket_epoll, EPOLL_CTL_ADD, fd, &ev);
}
int epoll_rem(int fd) {
struct epoll_event ev; // non-NULL for Linux < 2.6.9, however unlikely it is
return epoll_ctl(socket_epoll, EPOLL_CTL_DEL, fd, &ev);
}
/*
Misc helper functions
*/
void print_help() {
fprintf(stderr,
"Syntax: srtla_rec [-v] SRTLA_LISTEN_PORT SRT_HOST SRT_PORT\n\n"
"-v Print the version and exit\n");
}
int const_time_cmp(const void *a, const void *b, int len) {
char diff = 0;
char *ca = (char *)a;
char *cb = (char *)b;
for (int i = 0; i < len; i++) {
diff |= *ca - *cb;
ca++;
cb++;
}
return diff ? -1 : 0;
}
int get_random(void *dest, size_t len) {
while (len) {
int ret = fread(dest, 1, len, urandom);
if (ret <= 0) return -1;
len -= ret;
}
return 0;
}
/*
Connection and group management functions
*/
conn_group_t *group_find_by_id(char *id) {
for (conn_group_t* g = groups; g != NULL; g = g->next) {
if (const_time_cmp(g->id, id, SRTLA_ID_LEN) == 0) {
return g;
}
}
return NULL;
}
int group_find_by_addr(struct sockaddr *addr, conn_group_t **rg, conn_t **rc) {
for (conn_group_t* g = groups; g != NULL; g = g->next) {
for (conn_t *c = g->conns; c != NULL; c = c->next) {
if (const_time_cmp(&(c->addr), addr, addr_len) == 0) {
*rg = g;
*rc = c;
return 1;
}
}
if (const_time_cmp(&g->last_addr, addr, addr_len) == 0) {
*rg = g;
*rc = NULL;
return 0;
}
}
return -1;
}
conn_group_t *group_create(char *sender_id, time_t ts) {
// Make sure the ID isn't a duplicate - very unlikely
char id[SRTLA_ID_LEN];
memcpy(&id, sender_id, SRTLA_ID_LEN/2);
do {
int ret = get_random(&id[SRTLA_ID_LEN/2], SRTLA_ID_LEN/2);
if (ret != 0) return NULL;
} while(group_find_by_id(id) != NULL);
// Allocate the new group
conn_group_t *g = malloc(sizeof(conn_group_t));
if (g == NULL) {
err("malloc() failed\n");
return NULL;
}
// And initialize it with the ID we've built above
memcpy(&g->id, id, SRTLA_ID_LEN);
g->conns = NULL;
g->srt_sock = -1;
g->created_at = ts;
g->next = groups;
groups = g;
return g;
}
int group_destroy(conn_group_t *g, conn_group_t **prev_link) {
if (g == NULL) return -1;
for (conn_t *c = g->conns; c != NULL;) {
conn_t *next = c->next;
free(c);
c = next;
}
if (g->srt_sock > 0) {
epoll_rem(g->srt_sock);
close(g->srt_sock);
}
if (prev_link != NULL) {
// The caller passed us a pointer to the linked list pointer to this group
*prev_link = g->next;
} else {
// Search and unlink
for (conn_group_t **it = &groups; (*it) != NULL; it = &((*it)->next)) {
if (*it == g) {
*it = g->next;
break;
}
} // for
} // prev_link == NULL
free(g);
/* Must ensure statements updating group_count on the creation and
destruction code paths match up so we don't drift */
group_count--;
return 0;
}
int group_count_conns(conn_group_t *g) {
int count = 0;
for (conn_t *c = g->conns; c != NULL; c = c->next) {
count++;
}
return count;
}
int group_reg(struct sockaddr *addr, char *in_buf, time_t ts) {
if (group_count >= MAX_GROUPS) {
err("%s:%d: group count is %d, rejecting group registration\n",
print_addr(addr), port_no(addr), group_count);
goto err;
}
// If this remote address is already registered, abort
conn_group_t *g = NULL;
conn_t *c;
int ret = group_find_by_addr(addr, &g, &c);
if (ret != -1) goto err;
// Allocate the group
char *id = in_buf + 2;
g = group_create(id, ts);
if (g == NULL) goto err;
/* Record the address used to register the group
It won't be allowed to register another group while this one is active */
g->last_addr = *addr;
// Build a REG2 packet
char out_buf[SRTLA_TYPE_REG2_LEN];
uint16_t header = htobe16(SRTLA_TYPE_REG2);
memcpy(out_buf, &header, sizeof(header));
memcpy(out_buf + sizeof(header), g->id, SRTLA_ID_LEN);
// Send the REG2 packet
ret = sendto(srtla_sock, &out_buf, sizeof(out_buf), 0, addr, addr_len);
if (ret != sizeof(out_buf)) goto err_destroy;
info("%s:%d: group %p registered\n", print_addr(addr), port_no(addr), g);
// Only count the group after everything else succeeded
group_count++;
return 0;
err_destroy:
groups = g->next;
free(g);
err:
err("%s:%d: group registration failed\n", print_addr(addr), port_no(addr));
header = htobe16(SRTLA_TYPE_REG_ERR);
sendto(srtla_sock, &header, sizeof(header), 0, addr, addr_len);
return -1;
}
int conn_reg(struct sockaddr *addr, char *in_buf, time_t ts) {
conn_group_t *g, *tmp;
conn_t *c;
char *id = in_buf + 2;
g = group_find_by_id(id);
if (g == NULL) {
uint16_t header = htobe16(SRTLA_TYPE_REG_NGP);
sendto(srtla_sock, &header, sizeof(header), 0, addr, addr_len);
goto err_early;
}
/* If the connection is already registered, we'll allow it to register
again to the same group, but not to a new one */
int ret = group_find_by_addr(addr, &tmp, &c);
if (ret != -1 && tmp != g) goto err;
/* If the connection is already registered to the group, we can
just skip ahead to sending the SRTLA_REG3 */
if (ret != 1) {
int conn_count = group_count_conns(g);
if (conn_count >= MAX_CONNS_PER_GROUP) goto err;
c = malloc(sizeof(conn_t));
if (c == NULL) {
err("malloc() failed\n");
goto err;
}
c->addr = *addr;
c->recv_idx = 0;
c->last_rcvd = ts;
c->next = g->conns;
g->conns = c;
}
uint16_t header = htobe16(SRTLA_TYPE_REG3);
ret = sendto(srtla_sock, &header, sizeof(header), 0, addr, addr_len);
if (ret != sizeof(header)) goto err_destroy;
info("%s:%d (group %p): connection registration\n", print_addr(addr), port_no(addr), g);
// If it all worked, mark this peer as the most recently active one
g->last_addr = *addr;
return 0;
err_destroy:
g->conns = c->next;
free(c);
err:
header = htobe16(SRTLA_TYPE_REG_ERR);
sendto(srtla_sock, &header, sizeof(header), 0, addr, addr_len);
err_early:
err("%s:%d: connection registration for group %p failed\n",
print_addr(addr), port_no(addr), g);
return -1;
}
/*
The main network event handlers
Resource limits:
* connections per group MAX_CONNS_PER_GROUP
* total groups MAX_GROUPS
*/
void handle_srt_data(conn_group_t *g) {
char buf[MTU];
if (g == NULL) return;
int n = recv(g->srt_sock, &buf, MTU, 0);
if (n < SRT_MIN_LEN) {
err("Group %p: failed to read the SRT sock, terminating the group\n", g);
group_destroy(g, NULL);
return;
}
// ACK
if (is_srt_ack(buf, n)) {
// Broadcast SRT ACKs over all connections for timely delivery
for (conn_t *c = g->conns; c != NULL; c = c->next) {
int ret = sendto(srtla_sock, &buf, n, 0, &c->addr, addr_len);
if (ret != n) {
err("%s:%d (group %p): failed to send the SRT ack\n",
print_addr(&c->addr), port_no(&c->addr), g);
}
}
} else {
// send other packets over the most recently used SRTLA connection
int ret = sendto(srtla_sock, &buf, n, 0, &g->last_addr, addr_len);
if (ret != n) {
err("%s:%d (group %p): failed to send the SRT packet\n",
print_addr(&g->last_addr), port_no(&g->last_addr), g);
}
}
}
void register_packet(conn_group_t *g, conn_t *c, int32_t sn) {
// store the sequence numbers in BE, as they're transmitted over the network
c->recv_log[c->recv_idx++] = htobe32(sn);
if (c->recv_idx == RECV_ACK_INT) {
srtla_ack_pkt ack;
ack.type = htobe32(SRTLA_TYPE_ACK << 16);
memcpy(&ack.acks, &c->recv_log, sizeof(c->recv_log));
int ret = sendto(srtla_sock, &ack, sizeof(ack), 0, &c->addr, addr_len);
if (ret != sizeof(ack)) {
err("%s:%d (group %p): failed to send the srtla ack\n",
print_addr(&c->addr), port_no(&c->addr), g);
}
c->recv_idx = 0;
}
}
void handle_srtla_data(time_t ts) {
char buf[MTU];
int ret;
// Get the packet
struct sockaddr srtla_addr;
socklen_t len = addr_len;
int n = recvfrom(srtla_sock, &buf, MTU, 0, &srtla_addr, &len);
if (n < 0) {
err("Failed to read a srtla packet\n");
return;
}
// Handle srtla registration packets
if (is_srtla_reg1(buf, n)) {
group_reg(&srtla_addr, buf, ts);
return;
}
if (is_srtla_reg2(buf, n)) {
conn_reg(&srtla_addr, buf, ts);
return;
}
// Check that the peer is a member of a connection group, discard otherwise
conn_t *c;
conn_group_t *g;
ret = group_find_by_addr(&srtla_addr, &g, &c);
if (ret != 1) return;
// Update the connection's use timestamp
c->last_rcvd = ts;
// Resend SRTLA keep-alive packets to the sender
if (is_srtla_keepalive(buf, n)) {
int ret = sendto(srtla_sock, &buf, n, 0, &srtla_addr, addr_len);
if (ret != n) {
err("%s:%d (group %p): failed to send the srtla keepalive\n",
print_addr(&srtla_addr), port_no(&srtla_addr), g);
}
return;
}
// Check that the packet is large enough to be an SRT packet, discard otherwise
if (n < SRT_MIN_LEN) return;
// Record the most recently active peer
g->last_addr = srtla_addr;
// Keep track of the received data packets to send SRTLA ACKs
int32_t sn = get_srt_sn(buf, n);
if (sn >= 0) {
register_packet(g, c, sn);
}
// Open a connection to the SRT server for the group
if (g->srt_sock < 0) {
int sock = socket(AF_INET, SOCK_DGRAM, 0);
if (sock < 0) {
err("Group %p: failed to create an SRT socket\n", g);
group_destroy(g, NULL);
return;
}
g->srt_sock = sock;
int ret = connect(sock, &srt_addr, addr_len);
if (ret != 0) {
err("Group %p: failed to connect() the SRT socket\n", g);
group_destroy(g, NULL);
return;
}
ret = epoll_add(sock, EPOLLIN, g);
if (ret != 0) {
err("Group %p: failed to add the SRT socket to the epoll\n", g);
group_destroy(g, NULL);
return;
}
}
ret = send(g->srt_sock, &buf, n, 0);
if (ret != n) {
err("Group %p: failed to forward the srtla packet, terminating the group\n", g);
group_destroy(g, NULL);
}
}
/*
Freeing resources
Groups:
* new groups with no connection: created_at < (ts - G_TIMEOUT)
* other groups: when all connections have timed out
Connections:
* GC last_rcvd < (ts - CONN_TIMEOUT)
*/
void connection_cleanup(time_t ts) {
static time_t last_ran = 0;
if ((last_ran + CLEANUP_PERIOD) > ts) return;
last_ran = ts;
if (groups == NULL) return;
int total_groups = 0, total_conns = 0, removed_groups = 0, removed_conns = 0;
debug("Started a cleanup run\n");
conn_group_t *next_g = NULL;
conn_group_t **prev_g = &groups;
for (conn_group_t *g = groups; g != NULL; g = next_g) {
total_groups++;
next_g = g->next;
conn_t *next_c = NULL;
conn_t **prev_c = &g->conns;
for (conn_t *c = g->conns; c != NULL; c = next_c) {
total_conns++;
next_c = c->next;
if ((c->last_rcvd + CONN_TIMEOUT) < ts) {
removed_conns++;
info("%s:%d (group %p): connection removed (timed out)\n",
print_addr(&c->addr), port_no(&c->addr), g);
*prev_c = next_c;
free(c);
continue;
}
prev_c = &c->next;
}
if (g->conns == NULL && (g->created_at + GROUP_TIMEOUT) < ts) {
removed_groups++;
info("Group %p: removed (no connections)\n", g);
group_destroy(g, prev_g);
continue;
}
prev_g = &g->next;
}
debug("Clean up run ended. Counted %d groups and %d connections. "
"Removed %d groups and %d connections\n",
total_groups, total_conns, removed_groups, removed_conns);
}
/*
SRT is connection-oriented and it won't reply to our packets at this point
unless we start a handshake, so we do that for each resolved address
Returns: -1 when an error has been encountered
0 when the address was resolved but SRT appears unreachable
1 when the address was resolved and SRT appears reachable
*/
int resolve_srt_addr(char *host, char *port) {
// Let's set up an SRT handshake induction packet
srt_handshake_t hs_packet = {0};
hs_packet.header.type = htobe16(SRT_TYPE_HANDSHAKE);
hs_packet.version = htobe32(4);
hs_packet.ext_field = htobe16(2);
hs_packet.handshake_type = htobe32(1);
struct addrinfo hints;
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_DGRAM;
struct addrinfo *srt_addrs;
int ret = getaddrinfo(host, port, &hints, &srt_addrs);
if (ret != 0) {
fprintf(stderr, "Failed to resolve the address %s:%s\n", host, port);
return -1;
}
int tmp_sock = socket(AF_INET, SOCK_DGRAM, 0);
if (tmp_sock < 0) {
perror("failed to create a UDP socket");
return -1;
}
struct timeval to = { .tv_sec = 1, .tv_usec = 0};
ret = setsockopt(tmp_sock, SOL_SOCKET, SO_RCVTIMEO, &to, sizeof(to));
if (ret != 0) {
perror("failed to set a socket timeout");
return -1;
}
int found = -1;
for (struct addrinfo *addr = srt_addrs; addr != NULL && found == -1; addr = addr->ai_next) {
info("Trying to connect to SRT at %s:%s... ", print_addr(addr->ai_addr), port);
/* We're not printing this at all log levels, but a
flush won't hurt if we didn't print anything */
fflush(stderr);
ret = connect(tmp_sock, addr->ai_addr, addr->ai_addrlen);
if (ret == 0) {
ret = send(tmp_sock, &hs_packet, sizeof(hs_packet), 0);
if (ret == sizeof(hs_packet)) {
char buf[MTU];
ret = recv(tmp_sock, &buf, MTU, 0);
if (ret == sizeof(hs_packet)) {
info("success\n");
srt_addr = *addr->ai_addr;
found = 1;
}
} // ret == sizeof(buf)
} // ret == 0
if (found == -1) {
info("error\n");
}
}
close(tmp_sock);
if (found == -1) {
srt_addr = *srt_addrs->ai_addr;
fprintf(stderr, "WARNING: Failed to confirm that a SRT server is reachable at any address\n"
"Proceeding with the first address %s\n", print_addr(&srt_addr));
found = 0;
}
freeaddrinfo(srt_addrs);
return found;
}
#define ARG_LISTEN_PORT (argv[1])
#define ARG_SRT_HOST (argv[2])
#define ARG_SRT_PORT (argv[3])
int main(int argc, char **argv) {
// Command line argument parsing
if (argc == 2 && strcmp(argv[1], "-v") == 0) {
printf(VERSION "\n");
exit(0);
}
if (argc != 4) exit_help();
struct sockaddr_in listen_addr;
int srtla_port = parse_port(ARG_LISTEN_PORT);
if (srtla_port < 0) exit_help();
// Try to detect if the SRT server is reachable.
int ret = resolve_srt_addr(ARG_SRT_HOST, ARG_SRT_PORT);
if (ret < 0) {
exit(EXIT_FAILURE);
}
// urandom is used to generate random ids
urandom = fopen("/dev/urandom", "rb");
if (urandom == NULL) {
perror("failed to open urandom\n");
exit(EXIT_FAILURE);
}
// We use epoll for event-driven network I/O
socket_epoll = epoll_create(1000); // the number is ignored since Linux 2.6.8
if (socket_epoll < 0) {
perror("epoll creation failed\n");
exit(EXIT_FAILURE);
}
// Set up the listener socket for incoming SRT connections
listen_addr.sin_family = AF_INET;
listen_addr.sin_addr.s_addr = INADDR_ANY;
listen_addr.sin_port = htons(srtla_port);
srtla_sock = socket(AF_INET, SOCK_DGRAM, 0);
if (srtla_sock < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
ret = bind(srtla_sock, (const struct sockaddr *)&listen_addr, addr_len);
if (ret < 0) {
perror("bind failed");
exit(EXIT_FAILURE);
}
ret = epoll_add(srtla_sock, EPOLLIN, NULL);
if (ret != 0) {
perror("failed to add the srtla sock to the epoll\n");
exit(EXIT_FAILURE);
}
info("srtla_rec is now running\n");
while(1) {
#define MAX_EPOLL_EVENTS 10
struct epoll_event events[MAX_EPOLL_EVENTS];
int eventcnt = epoll_wait(socket_epoll, events, MAX_EPOLL_EVENTS, 1000);
time_t ts = 0;
int ret = get_seconds(&ts);
if (ret != 0) {
err("Failed to get the timestamp\n");
}
int group_cnt;
for (int i = 0; i < eventcnt; i++) {
group_cnt = group_count;
if (events[i].data.ptr == NULL) {
handle_srtla_data(ts);
} else {
handle_srt_data((conn_group_t*)events[i].data.ptr);
}
/* If we've removed a group due to a socket error, then we might have
pending events already waiting for us in events[], and now pointing
to freed() memory. Get an updated list from epoll_wait() */
if (group_count < group_cnt) break;
} // for
connection_cleanup(ts);
} // while(1);
}