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Fix DNS timeouts

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C-ares creates up to two sockets per nameserver. With up to three nameservers
in resolv.conf this makes a max of six active sockets.
Having only one ev_io watcher resulted in closing watchers that were
still active, needlessly resulting in DNS timeouts.
This commit is contained in:
xnor
2018-05-08 21:16:28 +00:00
parent 380cb81234
commit a5db5ef71f
1 changed files with 43 additions and 12 deletions
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src/resolv.c
+43 -12
View File
@@ -65,8 +65,12 @@
* Implement DNS resolution interface using libc-ares
*/
#define SS_NUM_IOS 6
#define SS_INVALID_FD -1
struct resolv_ctx {
struct ev_io io;
struct ev_io ios[SS_NUM_IOS];
struct ev_timer tw;
ares_channel channel;
@@ -90,7 +94,7 @@ struct resolv_query {
extern int verbose;
struct resolv_ctx default_ctx;
static struct resolv_ctx default_ctx;
static struct ev_loop *default_loop;
enum {
@@ -121,8 +125,6 @@ static void reset_timer();
static void
resolv_sock_cb(EV_P_ ev_io *w, int revents)
{
struct resolv_ctx *ctx = (struct resolv_ctx *)w;
ares_socket_t rfd = ARES_SOCKET_BAD, wfd = ARES_SOCKET_BAD;
if (revents & EV_READ)
@@ -130,7 +132,7 @@ resolv_sock_cb(EV_P_ ev_io *w, int revents)
if (revents & EV_WRITE)
wfd = w->fd;
ares_process_fd(ctx->channel, rfd, wfd);
ares_process_fd(default_ctx.channel, rfd, wfd);
reset_timer();
}
@@ -181,7 +183,9 @@ resolv_init(struct ev_loop *loop, char *nameservers, int ipv6first)
FATAL("failed to set nameservers");
}
ev_init(&default_ctx.io, resolv_sock_cb);
for (int i = 0; i < SS_NUM_IOS; i++) {
ev_io_init(&default_ctx.ios[i], resolv_sock_cb, SS_INVALID_FD, 0);
}
ev_timer_init(&default_ctx.tw, resolv_timeout_cb, 0.0, 0.0);
return 0;
@@ -190,6 +194,11 @@ resolv_init(struct ev_loop *loop, char *nameservers, int ipv6first)
void
resolv_shutdown(struct ev_loop *loop)
{
ev_timer_stop(default_loop, &default_ctx.tw);
for (int i = 0; i < SS_NUM_IOS; i++) {
ev_io_stop(default_loop, &default_ctx.ios[i]);
}
ares_cancel(default_ctx.channel);
ares_destroy(default_ctx.channel);
@@ -460,13 +469,35 @@ static void
resolv_sock_state_cb(void *data, int s, int read, int write)
{
struct resolv_ctx *ctx = (struct resolv_ctx *)data;
int events = (read ? EV_READ : 0) | (write ? EV_WRITE : 0);
if (read || write) {
ev_io_stop(default_loop, &ctx->io);
ev_io_set(&ctx->io, s, (read ? EV_READ : 0) | (write ? EV_WRITE : 0));
ev_io_start(default_loop, &ctx->io);
int i = 0, ffi = -1;
for (; i < SS_NUM_IOS; i++) {
if (ctx->ios[i].fd == s) {
break;
}
if (ffi < 0 && ctx->ios[i].fd == SS_INVALID_FD) {
// first free index
ffi = i;
}
}
if (i < SS_NUM_IOS) {
ev_io_stop(default_loop, &ctx->ios[i]);
} else if (ffi > -1) {
i = ffi;
} else {
ev_io_stop(default_loop, &ctx->io);
ev_io_set(&ctx->io, -1, 0);
LOGE("failed to find free I/O watcher slot for DNS query");
// last resort: stop io and re-use slot, will cause timeout
i = 0;
ev_io_stop(default_loop, &ctx->ios[i]);
}
if (events) {
ev_io_set(&ctx->ios[i], s, events);
ev_io_start(default_loop, &ctx->ios[i]);
} else {
ev_io_set(&ctx->ios[i], SS_INVALID_FD, 0);
}
}