Harmonize socket address families: ipv4 vs ipv6

If `-b bindaddr` is used, then created sockets must be of the same address family as `bindaddr` (otherwise, calls to `bind()` will fail).

This patch harmonizes the address family across the calls to `socket()`, `bind()`, and `connect()`.

Prior to this patch, `microsocks` would use the first `addrinfo` record returned by `getaddrinfo()`.  On systems with both IPv4 and IPv6, sometimes the address family of the first record would be a mismatch with `bindaddr`, resulting in an error.

This patch may fix issue rofl0r#30.  (And issue rofl0r#40?)

sockssrv.c

@@ -111,6 +111,22 @@ 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;
+ 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");
+ return list;
+}
+
 static int connect_socks_target(unsigned char *buf, size_t n, struct client *client) {
  if(n < 5) return -EC_GENERAL_FAILURE;
  if(buf[0] != 5) return -EC_GENERAL_FAILURE;
@@ -146,7 +162,8 @@ 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 fd = socket(remote->ai_addr->sa_family, SOCK_STREAM, 0);
+ int family = family_choose(remote, &bind_addr);
+ int fd = socket(family, SOCK_STREAM, 0);
  if(fd == -1) {
  eval_errno:
  if(fd != -1) close(fd);
@@ -173,7 +190,8 @@ static int connect_socks_target(unsigned char *buf, size_t n, struct client *cli
  }
  if(SOCKADDR_UNION_AF(&bind_addr) != AF_UNSPEC && bindtoip(fd, &bind_addr) == -1)
  goto eval_errno;
- if(connect(fd, remote->ai_addr, remote->ai_addrlen) == -1)
+ struct addrinfo* addr = addr_choose(remote, &bind_addr);
+ if(connect(fd, addr->ai_addr, addr->ai_addrlen) == -1)
  goto eval_errno;
 
  freeaddrinfo(remote);