+ * Resolve IPv4/IPv6 address and create a ready-to-use active or passive socket.
+ *
+ * \param l3type The layer-3 type (\p AF_INET, \p AF_INET6, \p AF_UNSPEC).
+ * \param l4type The layer-4 type (\p IPPROTO_xxx).
+ * \param passive Whether this is a passive (1) or active (0) socket.
+ * \param host Remote or local hostname or IPv/6 address string.
+ * \param port_number Decimal port number.
+ *
+ * This creates a ready-made IPv4/v6 socket structure after looking up the
+ * necessary parameters. The interpretation of \a host depends on the value of
+ * \a passive:
+ * - on a passive socket host is interpreted as an interface IPv4/6 address
+ * (can be left NULL);
+ * - on an active socket, \a host is the peer DNS name or IPv4/6 address
+ * to connect to;
+ * - \a port_number is in either case the numeric port number (not service
+ * string).
+ *
+ * Furthermore, bind(2) is called on passive sockets, and connect(2) on active
+ * sockets. The algorithm tries all possible address combinations until it
+ * succeeds.
+ *
+ * \return This function returns 1 on success and \a -E_ADDRESS_LOOKUP when no
+ * matching connection could be set up (with details in the error log).
+ *
+ * \sa ipv6(7), getaddrinfo(3), bind(2), connect(2).
+ */
+int makesock(unsigned l3type, unsigned l4type, int passive,
+ const char *host, unsigned short port_number)
+{
+ struct addrinfo *local = NULL, *src,
+ *remote = NULL, *dst, hints;
+ int rc, on = 1, sockfd = -1,
+ socktype = sock_type(l4type);
+ char port[6]; /* port number has at most 5 digits */
+
+ sprintf(port, "%u", port_number);
+ /* Set up address hint structure */
+ memset(&hints, 0, sizeof(hints));
+ hints.ai_family = l3type;
+ hints.ai_socktype = socktype;
+ /*
+ * getaddrinfo does not support SOCK_DCCP, so for the sake of lookup
+ * (and only then) pretend to be UDP.
+ */
+ if (l4type == IPPROTO_DCCP)
+ hints.ai_socktype = SOCK_DGRAM;
+
+ /* only use addresses available on the host */
+ hints.ai_flags = AI_ADDRCONFIG;
+ if (l3type == AF_INET6)
+ /* use v4-mapped-v6 if no v6 addresses found */
+ hints.ai_flags |= AI_V4MAPPED | AI_ALL;
+
+ if (passive && host == NULL)
+ hints.ai_flags |= AI_PASSIVE;
+
+ /* Obtain local/remote address information */
+ if ((rc = getaddrinfo(host, port, &hints, passive ? &local : &remote))) {
+ PARA_ERROR_LOG("can not resolve %s address %s#%s: %s.\n",
+ layer4_name(l4type),
+ host? host : (passive? "[loopback]" : "[localhost]"),
+ port, gai_strerror(rc));
+ return -E_ADDRESS_LOOKUP;
+ }
+
+ /* Iterate over all src/dst combination, exhausting dst first */
+ for (src = local, dst = remote; src != NULL || dst != NULL; /* no op */ ) {
+ if (src && dst && src->ai_family == AF_INET
+ && dst->ai_family == AF_INET6)
+ goto get_next_dst; /* v4 -> v6 is not possible */
+
+ sockfd = socket(src ? src->ai_family : dst->ai_family,
+ socktype, l4type);
+ if (sockfd < 0)
+ goto get_next_dst;
+
+ /*
+ * Set those options that need to be set before establishing
+ * the connection. Reuse the address on passive (listening)
+ * sockets to avoid failure on restart.
+ */
+ if (passive && setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR,
+ &on, sizeof(on)) == -1) {
+ PARA_ERROR_LOG("can not set SO_REUSEADDR: %s\n",
+ strerror(errno));
+ return -ERRNO_TO_PARA_ERROR(errno);
+ }
+
+ if (src) {
+ if (bind(sockfd, src->ai_addr, src->ai_addrlen) < 0) {
+ close(sockfd);
+ goto get_next_src;
+ }
+ if (!dst) /* bind-only completed successfully */
+ break;
+ }
+
+ if (dst && connect(sockfd, dst->ai_addr, dst->ai_addrlen) == 0)
+ break; /* connection completed successfully */
+ close(sockfd);
+get_next_dst:
+ if (dst && (dst = dst->ai_next))
+ continue;
+get_next_src:
+ if (src && (src = src->ai_next)) /* restart inner loop */
+ dst = remote;
+ }
+ if (local)
+ freeaddrinfo(local);
+ if (remote)
+ freeaddrinfo(remote);
+
+ if (src == NULL && dst == NULL) {
+ PARA_ERROR_LOG("can not create %s socket %s#%s.\n",
+ layer4_name(l4type), host? host : (passive?
+ "[loopback]" : "[localhost]"), port);
+ return -ERRNO_TO_PARA_ERROR(errno);
+ }
+ return sockfd;
+}
+
+/**
+ * Create a passive / listening socket.
+ *
+ * \param l3type The network-layer type (\p AF_xxx).
+ * \param l4type The transport-layer type (\p IPPROTO_xxx).
+ * \param port The decimal port number to listen on.