Connect to local interfaces for localhost

If connecting to localhost fails, try connecting to all local addresses.
This works around ssb-server binding to a local address and not a loopback address.

sbotc.1

@@ -78,7 +78,9 @@ Connect to server over IPv6 only.
 Capability key for secret-handshake. Default is SSB's capability key,
 .Li 1KHLiKZvAvjbY1ziZEHMXawbCEIM6qwjCDm3VYRan/s= .
 .It Fl s Ar host
-The hostname to connect to. Default is localhost.
+The hostname to connect to. Default is localhost. If set to localhost and connection to localhost fails,
+.Nm
+may attempt to connect to other local interface addresses.
 .It Fl p Ar port
 The port to connect to. Default is 8008.
 .It Fl u Ar socket_path

sbotc.c

@@ -13,6 +13,7 @@
 #include <err.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <ifaddrs.h>
 #include <limits.h>
 #include <netdb.h>
 #include <netinet/in.h>
@@ -24,6 +25,7 @@
 #include <sys/select.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
+#include <sys/types.h>
 #include <sys/un.h>
 #include <termios.h>
 #include <unistd.h>
@@ -119,6 +121,41 @@ static void usage() {
 	exit(EXIT_FAILURE);
 }
 
+static int connect_localhost(const char *port, enum ip_family ip_family) {
+	int rc, family, fd, err;
+	struct ifaddrs *ifaddr, *ifa;
+	rc = getifaddrs(&ifaddr);
+	if (rc < 0) return -1;
+	int port_n = htons(atoi(port));
+
+	for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
+		if (ifa->ifa_addr == NULL) continue;
+		family = ifa->ifa_addr->sa_family;
+		socklen_t addrlen;
+		if (family == AF_INET) {
+			if (ip_family != ip_family_ipv4 && ip_family != ip_family_any) continue;
+			addrlen = sizeof(struct sockaddr_in);
+			struct sockaddr_in *addr = (struct sockaddr_in *)ifa->ifa_addr;
+			addr->sin_port = port_n;
+		} else if (family == AF_INET6) {
+			if (ip_family != ip_family_ipv6 && ip_family != ip_family_any) continue;
+			addrlen = sizeof(struct sockaddr_in6);
+			struct sockaddr_in6 *addr = (struct sockaddr_in6 *)ifa->ifa_addr;
+			addr->sin6_port = port_n;
+		} else continue;
+		fd = socket(family, SOCK_STREAM, IPPROTO_TCP);
+		if (fd < 0) continue;
+		if (connect(fd, ifa->ifa_addr, addrlen) == 0) break;
+		err = errno;
+		close(fd);
+		errno = err;
+	}
+	if (ifa == NULL) fd = -1;
+
+	freeifaddrs(ifaddr);
+	return fd;
+}
+
 static int tcp_connect(const char *host, const char *port, enum ip_family ip_family) {
 	struct addrinfo hints;
 	struct addrinfo *result, *rp;
@@ -144,6 +181,11 @@ static int tcp_connect(const char *host, const char *port, enum ip_family ip_fam
 	if (rp == NULL) fd = -1;
 
 	freeaddrinfo(result);
+
+	if (fd == -1 && errno == ECONNREFUSED && (host == NULL || !strcmp(host, "localhost"))) {
+		return connect_localhost(port, ip_family);
+	}
+
 	return fd;
 }