From e3e2b36ecf6a1340f1dc2542233bafe0862447fa Mon Sep 17 00:00:00 2001
From: Curtis McEnroe <june@causal.agency>
Date: Sun, 16 Sep 2018 13:00:49 -0400
Subject: Race parallel connects

---
 irc.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 57 insertions(+), 22 deletions(-)

(limited to 'irc.c')

diff --git a/irc.c b/irc.c
index 6754e16..0bd8ca6 100644
--- a/irc.c
+++ b/irc.c
@@ -15,9 +15,11 @@
  */
 
 #include <err.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <netdb.h>
 #include <netinet/in.h>
+#include <poll.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -29,6 +31,60 @@
 
 #include "chat.h"
 
+static int connectRace(const char *host, const char *port) {
+	int error;
+	struct addrinfo *head;
+	struct addrinfo hints = {
+		.ai_family = AF_UNSPEC,
+		.ai_socktype = SOCK_STREAM,
+		.ai_protocol = IPPROTO_TCP,
+	};
+	error = getaddrinfo(host, port, &hints, &head);
+	if (error) errx(EX_NOHOST, "getaddrinfo: %s", gai_strerror(error));
+
+	nfds_t len = 0;
+	enum { SocksLen = 16 };
+	struct pollfd socks[SocksLen];
+	for (struct addrinfo *ai = head; ai; ai = ai->ai_next) {
+		if (len == SocksLen) break;
+
+		socks[len].events = POLLOUT;
+		socks[len].fd = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
+		if (socks[len].fd < 0) err(EX_OSERR, "socket");
+
+		error = fcntl(socks[len].fd, F_SETFL, O_NONBLOCK);
+		if (error) err(EX_OSERR, "fcntl");
+
+		error = connect(socks[len].fd, ai->ai_addr, ai->ai_addrlen);
+		if (error && errno != EINPROGRESS && errno != EINTR) {
+			close(socks[len].fd);
+			continue;
+		}
+
+		len++;
+	}
+	if (!len) err(EX_UNAVAILABLE, "connect");
+	freeaddrinfo(head);
+
+	int ready = poll(socks, len, -1);
+	if (ready < 0) err(EX_IOERR, "poll");
+
+	int sock = -1;
+	for (nfds_t i = 0; i < len; ++i) {
+		if ((socks[i].revents & POLLOUT) && sock < 0) {
+			sock = socks[i].fd;
+		} else {
+			close(socks[i].fd);
+		}
+	}
+	if (sock < 0) errx(EX_UNAVAILABLE, "no socket became writable");
+
+	error = fcntl(sock, F_SETFL, 0);
+	if (error) err(EX_IOERR, "fcntl");
+
+	return sock;
+}
+
 static struct tls *client;
 
 static void webirc(const char *pass) {
@@ -59,28 +115,7 @@ int ircConnect(
 	if (error) errx(EX_SOFTWARE, "tls_configure");
 	tls_config_free(config);
 
-	struct addrinfo *head;
-	struct addrinfo hints = {
-		.ai_family = AF_UNSPEC,
-		.ai_socktype = SOCK_STREAM,
-		.ai_protocol = IPPROTO_TCP,
-	};
-	error = getaddrinfo(host, port, &hints, &head);
-	if (error) errx(EX_NOHOST, "getaddrinfo: %s", gai_strerror(error));
-
-	int sock = -1;
-	for (struct addrinfo *ai = head; ai; ai = ai->ai_next) {
-		sock = socket(ai->ai_family, ai->ai_socktype, ai->ai_protocol);
-		if (sock < 0) err(EX_OSERR, "socket");
-
-		error = connect(sock, ai->ai_addr, ai->ai_addrlen);
-		if (!error) break;
-
-		close(sock);
-		sock = -1;
-	}
-	if (sock < 0) err(EX_UNAVAILABLE, "connect");
-	freeaddrinfo(head);
+	int sock = connectRace(host, port);
 
 	error = fcntl(sock, F_SETFD, FD_CLOEXEC);
 	if (error) err(EX_IOERR, "fcntl");
-- 
cgit 1.4.1