Merge pull request #2045 from xnoreq/master

Fix DNS timeouts

src/resolv.c

@@ -65,9 +65,15 @@
  * Implement DNS resolution interface using libc-ares
  */
 
+
+#define SS_NUM_IOS 6
+#define SS_INVALID_FD -1
+#define SS_TIMER_AFTER 1.0
+
 struct resolv_ctx {
-    struct ev_io io;
-    struct ev_timer tw;
+    struct ev_io ios[SS_NUM_IOS];
+    struct ev_timer timer;
+    ev_tstamp  last_tick;
 
     ares_channel channel;
     struct ares_options options;
@@ -90,7 +96,7 @@ struct resolv_query {
 
 extern int verbose;
 
-struct resolv_ctx default_ctx;
+static struct resolv_ctx default_ctx;
 static struct ev_loop *default_loop;
 
 enum {
@@ -101,7 +107,7 @@ enum {
 static int resolv_mode = MODE_IPV4_FIRST;
 
 static void resolv_sock_cb(struct ev_loop *, struct ev_io *, int);
-static void resolv_timeout_cb(struct ev_loop *, struct ev_timer *, int);
+static void resolv_timer_cb(struct ev_loop *, struct ev_timer *, int);
 static void resolv_sock_state_cb(void *, int, int, int);
 
 static void dns_query_v4_cb(void *, int, int, struct hostent *);
@@ -113,16 +119,12 @@ static struct sockaddr *choose_ipv4_first(struct resolv_query *);
 static struct sockaddr *choose_ipv6_first(struct resolv_query *);
 static struct sockaddr *choose_any(struct resolv_query *);
 
-static void reset_timer();
-
 /*
  * DNS UDP socket activity callback
  */
 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)
@@ -130,9 +132,9 @@ resolv_sock_cb(EV_P_ ev_io *w, int revents)
     if (revents & EV_WRITE)
         wfd = w->fd;
 
-    ares_process_fd(ctx->channel, rfd, wfd);
+    default_ctx.last_tick = ev_now(default_loop);
 
-    reset_timer();
+    ares_process_fd(default_ctx.channel, rfd, wfd);
 }
 
 int
@@ -181,8 +183,13 @@ resolv_init(struct ev_loop *loop, char *nameservers, int ipv6first)
         FATAL("failed to set nameservers");
     }
 
-    ev_init(&default_ctx.io, resolv_sock_cb);
-    ev_timer_init(&default_ctx.tw, resolv_timeout_cb, 0.0, 0.0);
+    for (int i = 0; i < SS_NUM_IOS; i++) {
+        ev_io_init(&default_ctx.ios[i], resolv_sock_cb, SS_INVALID_FD, 0);
+    }
+
+    default_ctx.last_tick = ev_now(default_loop);
+    ev_init(&default_ctx.timer, resolv_timer_cb);
+    resolv_timer_cb(default_loop, &default_ctx.timer, 0);
 
     return 0;
 }
@@ -190,6 +197,11 @@ resolv_init(struct ev_loop *loop, char *nameservers, int ipv6first)
 void
 resolv_shutdown(struct ev_loop *loop)
 {
+    ev_timer_stop(default_loop, &default_ctx.timer);
+    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);
 
@@ -220,8 +232,6 @@ resolv_start(const char *hostname, uint16_t port,
 
     ares_gethostbyname(default_ctx.channel, hostname, AF_INET, dns_query_v4_cb, query);
     ares_gethostbyname(default_ctx.channel, hostname, AF_INET6, dns_query_v6_cb, query);
-
-    reset_timer();
 }
 
 /*
@@ -427,30 +437,26 @@ all_requests_are_null(struct resolv_query *query)
 }
 
 /*
- *  DNS timeout callback
+ *  Timer callback
  */
 static void
-resolv_timeout_cb(struct ev_loop *loop, struct ev_timer *w, int revents)
+resolv_timer_cb(struct ev_loop *loop, struct ev_timer *w, int revents)
 {
-    struct resolv_ctx *ctx = cork_container_of(w, struct resolv_ctx, tw);
+    struct resolv_ctx *ctx = cork_container_of(w, struct resolv_ctx, timer);
 
-    ares_process_fd(ctx->channel, ARES_SOCKET_BAD, ARES_SOCKET_BAD);
+    ev_tstamp now = ev_now(default_loop);
+    ev_tstamp after = ctx->last_tick - now + SS_TIMER_AFTER;
 
-    reset_timer();
-}
+    if (after < 0.0) {
+        ctx->last_tick = now;
+        ares_process_fd(ctx->channel, ARES_SOCKET_BAD, ARES_SOCKET_BAD);
 
-static void
-reset_timer()
-{
-    struct timeval tvout;
-    struct timeval *tv = ares_timeout(default_ctx.channel, NULL, &tvout);
-    if (tv == NULL) {
-        return;
+        ev_timer_set(w, SS_TIMER_AFTER, 0.0);
+    } else {
+        ev_timer_set(w, after, 0.0);
     }
-    float repeat = tv->tv_sec + tv->tv_usec / 1000000. + 1e-9;
-    repeat = repeat < 1.f ? 1.f : repeat;
-    ev_timer_set(&default_ctx.tw, repeat, repeat);
-    ev_timer_again(default_loop, &default_ctx.tw);
+
+    ev_timer_start(loop, w);
 }
 
 /*
@@ -460,13 +466,35 @@ 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);
     }
 }