Add support for proxying through an external command.

Proxy type "exec" can be used to have an external script or binary set
up an outgoing connection. Standard input and output will be used to
exchange data with the external command. The variables REMOTEADDRESS and
REMOTEPORT are set to the intended destination address and port.

src/net_socket.c

@@ -294,13 +294,62 @@ void retry_outgoing(outgoing_t *outgoing) {
 void finish_connecting(connection_t *c) {
 	ifdebug(CONNECTIONS) logger(LOG_INFO, "Connected to %s (%s)", c->name, c->hostname);
 
-	configure_tcp(c);
+	if(proxytype != PROXY_EXEC)
+		configure_tcp(c);
 
 	c->last_ping_time = now;
 
 	send_id(c);
 }
 
+static void do_outgoing_pipe(connection_t *c, char *command) {
+#ifndef HAVE_MINGW
+	int fd[2];
+
+	if(socketpair(AF_UNIX, SOCK_STREAM, 0, fd)) {
+		logger(LOG_ERR, "Could not create socketpair: %s\n", strerror(errno));
+		return;
+	}
+
+	if(fork()) {
+		c->socket = fd[0];
+		close(fd[1]);
+		logger(LOG_DEBUG, "Using proxy %s", command);
+		return;
+	}
+
+	close(0);
+	close(1);
+	close(fd[0]);
+	dup2(fd[1], 0);
+	dup2(fd[1], 1);
+	close(fd[1]);
+
+	// Other filedescriptors should be closed automatically by CLOEXEC
+
+	char *host = NULL;
+	char *port = NULL;
+
+	sockaddr2str(&c->address, &host, &port);
+	setenv("REMOTEADDRESS", host, true);
+	setenv("REMOTEPORT", port, true);
+	setenv("NODE", c->name, true);
+	setenv("NAME", myself->name, true);
+	if(netname)
+		setenv("NETNAME", netname, true);
+
+	int result = system(command);
+	if(result < 0)
+		logger(LOG_ERR, "Could not execute %s: %s\n", command, strerror(errno));
+	else if(result)
+		logger(LOG_ERR, "%s exited with non-zero status %d", command, result);
+	exit(result);
+#else
+	logger(LOG_ERR, "Proxy type exec not supported on this platform!");
+	return false;
+#endif
+}
+
 void do_outgoing_connection(connection_t *c) {
 	char *address, *port, *space;
 	struct addrinfo *proxyai;
@@ -361,7 +410,10 @@ begin:
 
 	if(!proxytype) {
 		c->socket = socket(c->address.sa.sa_family, SOCK_STREAM, IPPROTO_TCP);
-	} else {
+		configure_tcp(c);
+	} if(proxytype == PROXY_EXEC) {
+		do_outgoing_pipe(c, proxyhost);
+	}  else {
 		proxyai = str2addrinfo(proxyhost, proxyport, SOCK_STREAM);
 		if(!proxyai)
 			goto begin;
@@ -378,22 +430,22 @@ begin:
 	fcntl(c->socket, F_SETFD, FD_CLOEXEC);
 #endif
 
+	if(proxytype != PROXY_EXEC) {
 #if defined(SOL_IPV6) && defined(IPV6_V6ONLY)
-	int option = 1;
-	if(c->address.sa.sa_family == AF_INET6)
-		setsockopt(c->socket, SOL_IPV6, IPV6_V6ONLY, (void *)&option, sizeof option);
+		int option = 1;
+		if(c->address.sa.sa_family == AF_INET6)
+			setsockopt(c->socket, SOL_IPV6, IPV6_V6ONLY, (void *)&option, sizeof option);
 #endif
 
-	bind_to_interface(c->socket);
-
-	/* Optimize TCP settings */
-
-//	configure_tcp(c);
+		bind_to_interface(c->socket);
+	}
 
 	/* Connect */
 
 	if(!proxytype) {
 		result = connect(c->socket, &c->address.sa, SALEN(c->address.sa));
+	} else if(proxytype == PROXY_EXEC) {
+		result = 0;
 	} else {
 		result = connect(c->socket, proxyai->ai_addr, proxyai->ai_addrlen);
 		freeaddrinfo(proxyai);

src/netutl.c

@@ -83,8 +83,10 @@ void sockaddr2str(const sockaddr_t *sa, char **addrstr, char **portstr) {
 	int err;
 
 	if(sa->sa.sa_family == AF_UNKNOWN) {
-		*addrstr = xstrdup(sa->unknown.address);
-		*portstr = xstrdup(sa->unknown.port);
+		if(addrstr)
+			*addrstr = xstrdup(sa->unknown.address);
+		if(portstr)
+			*portstr = xstrdup(sa->unknown.port);
 		return;
 	}
 

src/protocol_auth.c

@@ -117,6 +117,8 @@ static bool send_proxyrequest(connection_t *c) {
 		case PROXY_SOCKS4A:
 			logger(LOG_ERR, "Proxy type not implemented yet");
 			return false;
+		case PROXY_EXEC:
+			return true;
 		default:
 			logger(LOG_ERR, "Unknown proxy type");
 			return false;