improve new code selecting connection target by bindaddr family

the code added in 6ecc398 was modified to

- better match the rest of codestyle
- don't print gratuitous warning if no matching addrinfo record was found
- always select outgoing socket type according to first addrinfo result,
  like in the past, rather than enforcing the af of bindaddr even if no
  matching record exists.
- only call bind() if the selected addrinfo record matches the bind addr

as a sideeffect of the latter, bind() will no longer be called when there's
no DNS record matching the address family of the bindaddr, which means the
connection will use the system default route for the target.
whether this aligns with user's expectations remain to be seen, but imo
it's preferable to make the connection work rather than enforcing that no
packet goes out on another interface than the one specified via bind addr.

Author: rofl0r

sockssrv.c

@@ -111,19 +111,12 @@ struct thread {
 static void dolog(const char* fmt, ...) { }
 #endif
 
-static int family_choose(struct addrinfo* remote, union sockaddr_union* bind_addr) {
-	int family = SOCKADDR_UNION_AF(bind_addr);
-	return family == AF_UNSPEC ? remote->ai_family : family;
-}
-
 static struct addrinfo* addr_choose(struct addrinfo* list, union sockaddr_union* bind_addr) {
-	int family = SOCKADDR_UNION_AF(bind_addr);
-	if(family == AF_UNSPEC) return list;
+	int af = SOCKADDR_UNION_AF(bind_addr);
+	if(af == AF_UNSPEC) return list;
 	struct addrinfo* p;
-	for(p=list;p;p=p->ai_next) {
-		if(p->ai_family == family) return p;
-	}
-	dprintf(2, "warning: address family mismatch\n");
+	for(p=list; p; p=p->ai_next)
+		if(p->ai_family == af) return p;
 	return list;
 }
 
@@ -162,8 +155,8 @@ static int connect_socks_target(unsigned char *buf, size_t n, struct client *cli
 	port = (buf[minlen-2] << 8) | buf[minlen-1];
 	/* there's no suitable errorcode in rfc1928 for dns lookup failure */
 	if(resolve(namebuf, port, &remote)) return -EC_GENERAL_FAILURE;
-	int family = family_choose(remote, &bind_addr);
-	int fd = socket(family, SOCK_STREAM, 0);
+	struct addrinfo* raddr = addr_choose(remote, &bind_addr);
+	int fd = socket(raddr->ai_family, SOCK_STREAM, 0);
 	if(fd == -1) {
 		eval_errno:
 		if(fd != -1) close(fd);
@@ -188,10 +181,10 @@ static int connect_socks_target(unsigned char *buf, size_t n, struct client *cli
 			return -EC_GENERAL_FAILURE;
 		}
 	}
-	if(SOCKADDR_UNION_AF(&bind_addr) != AF_UNSPEC && bindtoip(fd, &bind_addr) == -1)
+	if(SOCKADDR_UNION_AF(&bind_addr) == raddr->ai_family &&
+	   bindtoip(fd, &bind_addr) == -1)
 		goto eval_errno;
-	struct addrinfo* addr = addr_choose(remote, &bind_addr);
-	if(connect(fd, addr->ai_addr, addr->ai_addrlen) == -1)
+	if(connect(fd, raddr->ai_addr, raddr->ai_addrlen) == -1)
 		goto eval_errno;
 
 	freeaddrinfo(remote);