libbb: new option FEATURE_ETC_SERVICES: if off, /etc/services reads often avoided

In practice, "wget http://host.com/" always uses port 80.
People explicitly set non-standard ports via options or parameters
("telnet 1.2.3.4 567" or "telnet 1.2.3.4 ftp") instead of modifying
/etc/services.

function                                             old     new   delta
telnet_main                                         1466    1464      -2
rdate_main                                           215     198     -17
fakeidentd_main                                      269     252     -17
parse_url                                            459     392     -67
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-103)           Total: -103 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

6 files changed, 25 insertions, 7 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 646c58b..a605c7f 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -640,6 +640,11 @@ int setsockopt_bindtodevice(int fd, const char *iface) FAST_FUNC;
 int bb_getsockname(int sockfd, void *addr, socklen_t addrlen) FAST_FUNC;
 /* NB: returns port in host byte order */
 unsigned bb_lookup_port(const char *port, const char *protocol, unsigned default_port) FAST_FUNC;
+#if ENABLE_FEATURE_ETC_SERVICES
+# define bb_lookup_std_port(portstr, protocol, portnum) bb_lookup_port(portstr, protocol, portnum)
+#else
+# define bb_lookup_std_port(portstr, protocol, portnum) (portnum)
+#endif
 typedef struct len_and_sockaddr {
 	socklen_t len;
 	union {
diff --git a/libbb/Config.src b/libbb/Config.src
index fdf8bbb..16e1648 100644
--- a/libbb/Config.src
+++ b/libbb/Config.src
@@ -76,6 +76,18 @@ config FEATURE_ETC_NETWORKS
 	a rarely used feature which allows you to use names
 	instead of IP/mask pairs in route command.
 
+config FEATURE_ETC_SERVICES
+	bool "Consult /etc/services even for well-known ports"
+	default n
+	help
+	Look up e.g. "telnet" and "http" in /etc/services file
+	instead of assuming ports 23 and 80.
+	This is almost never necessary (everybody uses standard ports),
+	and it makes sense to avoid reading this file.
+	If you disable this option, in the cases where port is explicitly
+	specified as a service name (e.g. "telnet HOST PORTNAME"),
+	it will still be looked up in /etc/services.
+
 config FEATURE_EDITING
 	bool "Command line editing"
 	default y
diff --git a/networking/isrv_identd.c b/networking/isrv_identd.c
index 133d62a..0c33dde 100644
--- a/networking/isrv_identd.c
+++ b/networking/isrv_identd.c
@@ -159,7 +159,7 @@ int fakeidentd_main(int argc UNUSED_PARAM, char **argv)
 	fd = 0;
 	if (!(opt & OPT_inetdwait)) {
 		fd = create_and_bind_stream_or_die(bind_address,
-				bb_lookup_port("identd", "tcp", 113));
+				bb_lookup_std_port("identd", "tcp", 113));
 		xlisten(fd, 5);
 	}
 
diff --git a/networking/telnet.c b/networking/telnet.c
index 15d6a08..1e6be85 100644
--- a/networking/telnet.c
+++ b/networking/telnet.c
@@ -643,7 +643,8 @@ int telnet_main(int argc UNUSED_PARAM, char **argv)
 	if (!*argv)
 		bb_show_usage();
 	host = *argv++;
-	port = bb_lookup_port(*argv ? *argv++ : "telnet", "tcp", 23);
+	port = *argv ? bb_lookup_port(*argv++, "tcp", 23)
+		: bb_lookup_std_port("telnet", "tcp", 23);
 	if (*argv) /* extra params?? */
 		bb_show_usage();
 
diff --git a/networking/wget.c b/networking/wget.c
index 2650b53..b6c76e9 100644
--- a/networking/wget.c
+++ b/networking/wget.c
@@ -505,23 +505,23 @@ static void parse_url(const char *src_url, struct host_info *h)
 		*p = '\0';
 		h->host = p + 3;
 		if (strcmp(url, P_FTP) == 0) {
-			h->port = bb_lookup_port(P_FTP, "tcp", 21);
+			h->port = bb_lookup_std_port(P_FTP, "tcp", 21);
 		} else
 #if SSL_SUPPORTED
 # if ENABLE_FEATURE_WGET_HTTPS
 		if (strcmp(url, P_FTPS) == 0) {
-			h->port = bb_lookup_port(P_FTPS, "tcp", 990);
+			h->port = bb_lookup_std_port(P_FTPS, "tcp", 990);
 			h->protocol = P_FTPS;
 		} else
 # endif
 		if (strcmp(url, P_HTTPS) == 0) {
-			h->port = bb_lookup_port(P_HTTPS, "tcp", 443);
+			h->port = bb_lookup_std_port(P_HTTPS, "tcp", 443);
 			h->protocol = P_HTTPS;
 		} else
 #endif
 		if (strcmp(url, P_HTTP) == 0) {
  http:
-			h->port = bb_lookup_port(P_HTTP, "tcp", 80);
+			h->port = bb_lookup_std_port(P_HTTP, "tcp", 80);
 			h->protocol = P_HTTP;
 		} else {
 			*p = ':';
diff --git a/util-linux/rdate.c b/util-linux/rdate.c
index f27294e..5ec7952 100644
--- a/util-linux/rdate.c
+++ b/util-linux/rdate.c
@@ -45,7 +45,7 @@ static time_t askremotedate(const char *host)
 	alarm(10);
 	signal(SIGALRM, socket_timeout);
 
-	fd = create_and_connect_stream_or_die(host, bb_lookup_port("time", "tcp", 37));
+	fd = create_and_connect_stream_or_die(host, bb_lookup_std_port("time", "tcp", 37));
 
 	if (safe_read(fd, &nett, 4) != 4)    /* read time from server */
 		bb_error_msg_and_die("%s: %s", host, "short read");